--- jsr166/src/jsr166y/ForkJoinPool.java 2009/07/22 01:36:51 1.13
+++ jsr166/src/jsr166y/ForkJoinPool.java 2012/01/28 04:32:25 1.117
@@ -1,61 +1,124 @@
/*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
- * http://creativecommons.org/licenses/publicdomain
+ * http://creativecommons.org/publicdomain/zero/1.0/
*/
package jsr166y;
-import java.util.*;
-import java.util.concurrent.*;
-import java.util.concurrent.locks.*;
-import java.util.concurrent.atomic.*;
-import sun.misc.Unsafe;
-import java.lang.reflect.*;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Random;
+import java.util.concurrent.AbstractExecutorService;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
+import java.util.concurrent.RejectedExecutionException;
+import java.util.concurrent.RunnableFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.locks.ReentrantLock;
+import java.util.concurrent.locks.Condition;
/**
- * An {@link ExecutorService} for running {@link ForkJoinTask}s. A
- * ForkJoinPool provides the entry point for submissions from
- * non-ForkJoinTasks, as well as management and monitoring operations.
- * Normally a single ForkJoinPool is used for a large number of
- * submitted tasks. Otherwise, use would not usually outweigh the
- * construction and bookkeeping overhead of creating a large set of
- * threads.
+ * An {@link ExecutorService} for running {@link ForkJoinTask}s.
+ * A {@code ForkJoinPool} provides the entry point for submissions
+ * from non-{@code ForkJoinTask} clients, as well as management and
+ * monitoring operations.
*
- * ForkJoinPools differ from other kinds of Executors mainly in
- * that they provide work-stealing: all threads in the pool
- * attempt to find and execute subtasks created by other active tasks
- * (eventually blocking if none exist). This makes them efficient when
- * most tasks spawn other subtasks (as do most ForkJoinTasks), as well
- * as the mixed execution of some plain Runnable- or Callable- based
- * activities along with ForkJoinTasks. When setting
- * {@code setAsyncMode}, a ForkJoinPools may also be appropriate for
- * use with fine-grained tasks that are never joined. Otherwise, other
- * ExecutorService implementations are typically more appropriate
- * choices.
+ *
A {@code ForkJoinPool} differs from other kinds of {@link
+ * ExecutorService} mainly by virtue of employing
+ * work-stealing: all threads in the pool attempt to find and
+ * execute tasks submitted to the pool and/or created by other active
+ * tasks (eventually blocking waiting for work if none exist). This
+ * enables efficient processing when most tasks spawn other subtasks
+ * (as do most {@code ForkJoinTask}s), as well as when many small
+ * tasks are submitted to the pool from external clients. Especially
+ * when setting asyncMode to true in constructors, {@code
+ * ForkJoinPool}s may also be appropriate for use with event-style
+ * tasks that are never joined.
*
- *
A ForkJoinPool may be constructed with a given parallelism level
- * (target pool size), which it attempts to maintain by dynamically
- * adding, suspending, or resuming threads, even if some tasks are
- * waiting to join others. However, no such adjustments are performed
- * in the face of blocked IO or other unmanaged synchronization. The
- * nested {@code ManagedBlocker} interface enables extension of
- * the kinds of synchronization accommodated. The target parallelism
- * level may also be changed dynamically ({@code setParallelism})
- * and thread construction can be limited using methods
- * {@code setMaximumPoolSize} and/or
- * {@code setMaintainsParallelism}.
+ *
A {@code ForkJoinPool} is constructed with a given target
+ * parallelism level; by default, equal to the number of available
+ * processors. The pool attempts to maintain enough active (or
+ * available) threads by dynamically adding, suspending, or resuming
+ * internal worker threads, even if some tasks are stalled waiting to
+ * join others. However, no such adjustments are guaranteed in the
+ * face of blocked IO or other unmanaged synchronization. The nested
+ * {@link ManagedBlocker} interface enables extension of the kinds of
+ * synchronization accommodated.
*
*
In addition to execution and lifecycle control methods, this
* class provides status check methods (for example
- * {@code getStealCount}) that are intended to aid in developing,
+ * {@link #getStealCount}) that are intended to aid in developing,
* tuning, and monitoring fork/join applications. Also, method
- * {@code toString} returns indications of pool state in a
+ * {@link #toString} returns indications of pool state in a
* convenient form for informal monitoring.
*
+ *
As is the case with other ExecutorServices, there are three
+ * main task execution methods summarized in the following table.
+ * These are designed to be used primarily by clients not already
+ * engaged in fork/join computations in the current pool. The main
+ * forms of these methods accept instances of {@code ForkJoinTask},
+ * but overloaded forms also allow mixed execution of plain {@code
+ * Runnable}- or {@code Callable}- based activities as well. However,
+ * tasks that are already executing in a pool should normally instead
+ * use the within-computation forms listed in the table unless using
+ * async event-style tasks that are not usually joined, in which case
+ * there is little difference among choice of methods.
+ *
+ *
+ *
+ * |
+ * Call from non-fork/join clients |
+ * Call from within fork/join computations |
+ *
+ *
+ * | Arrange async execution |
+ * {@link #execute(ForkJoinTask)} |
+ * {@link ForkJoinTask#fork} |
+ *
+ *
+ * | Await and obtain result |
+ * {@link #invoke(ForkJoinTask)} |
+ * {@link ForkJoinTask#invoke} |
+ *
+ *
+ * | Arrange exec and obtain Future |
+ * {@link #submit(ForkJoinTask)} |
+ * {@link ForkJoinTask#fork} (ForkJoinTasks are Futures) |
+ *
+ *
+ *
+ * Sample Usage. Normally a single {@code ForkJoinPool} is
+ * used for all parallel task execution in a program or subsystem.
+ * Otherwise, use would not usually outweigh the construction and
+ * bookkeeping overhead of creating a large set of threads. For
+ * example, a common pool could be used for the {@code SortTasks}
+ * illustrated in {@link RecursiveAction}. Because {@code
+ * ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
+ * daemon} mode, there is typically no need to explicitly {@link
+ * #shutdown} such a pool upon program exit.
+ *
+ *
{@code
+ * static final ForkJoinPool mainPool = new ForkJoinPool();
+ * ...
+ * public void sort(long[] array) {
+ * mainPool.invoke(new SortTask(array, 0, array.length));
+ * }}
+ *
* Implementation notes: This implementation restricts the
* maximum number of running threads to 32767. Attempts to create
- * pools with greater than the maximum result in
- * IllegalArgumentExceptions.
+ * pools with greater than the maximum number result in
+ * {@code IllegalArgumentException}.
+ *
+ *
This implementation rejects submitted tasks (that is, by throwing
+ * {@link RejectedExecutionException}) only when the pool is shut down
+ * or internal resources have been exhausted.
*
* @since 1.7
* @author Doug Lea
@@ -63,44 +126,353 @@ import java.lang.reflect.*;
public class ForkJoinPool extends AbstractExecutorService {
/*
- * See the extended comments interspersed below for design,
- * rationale, and walkthroughs.
- */
-
- /** Mask for packing and unpacking shorts */
- private static final int shortMask = 0xffff;
-
- /** Max pool size -- must be a power of two minus 1 */
- private static final int MAX_THREADS = 0x7FFF;
-
- /**
- * Factory for creating new ForkJoinWorkerThreads. A
- * ForkJoinWorkerThreadFactory must be defined and used for
- * ForkJoinWorkerThread subclasses that extend base functionality
- * or initialize threads with different contexts.
+ * Implementation Overview
+ *
+ * This class and its nested classes provide the main
+ * functionality and control for a set of worker threads:
+ * Submissions from non-FJ threads enter into submission queues.
+ * Workers take these tasks and typically split them into subtasks
+ * that may be stolen by other workers. Preference rules give
+ * first priority to processing tasks from their own queues (LIFO
+ * or FIFO, depending on mode), then to randomized FIFO steals of
+ * tasks in other queues.
+ *
+ * WorkQueues
+ * ==========
+ *
+ * Most operations occur within work-stealing queues (in nested
+ * class WorkQueue). These are special forms of Deques that
+ * support only three of the four possible end-operations -- push,
+ * pop, and poll (aka steal), under the further constraints that
+ * push and pop are called only from the owning thread (or, as
+ * extended here, under a lock), while poll may be called from
+ * other threads. (If you are unfamiliar with them, you probably
+ * want to read Herlihy and Shavit's book "The Art of
+ * Multiprocessor programming", chapter 16 describing these in
+ * more detail before proceeding.) The main work-stealing queue
+ * design is roughly similar to those in the papers "Dynamic
+ * Circular Work-Stealing Deque" by Chase and Lev, SPAA 2005
+ * (http://research.sun.com/scalable/pubs/index.html) and
+ * "Idempotent work stealing" by Michael, Saraswat, and Vechev,
+ * PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186).
+ * The main differences ultimately stem from GC requirements that
+ * we null out taken slots as soon as we can, to maintain as small
+ * a footprint as possible even in programs generating huge
+ * numbers of tasks. To accomplish this, we shift the CAS
+ * arbitrating pop vs poll (steal) from being on the indices
+ * ("base" and "top") to the slots themselves. So, both a
+ * successful pop and poll mainly entail a CAS of a slot from
+ * non-null to null. Because we rely on CASes of references, we
+ * do not need tag bits on base or top. They are simple ints as
+ * used in any circular array-based queue (see for example
+ * ArrayDeque). Updates to the indices must still be ordered in a
+ * way that guarantees that top == base means the queue is empty,
+ * but otherwise may err on the side of possibly making the queue
+ * appear nonempty when a push, pop, or poll have not fully
+ * committed. Note that this means that the poll operation,
+ * considered individually, is not wait-free. One thief cannot
+ * successfully continue until another in-progress one (or, if
+ * previously empty, a push) completes. However, in the
+ * aggregate, we ensure at least probabilistic non-blockingness.
+ * If an attempted steal fails, a thief always chooses a different
+ * random victim target to try next. So, in order for one thief to
+ * progress, it suffices for any in-progress poll or new push on
+ * any empty queue to complete.
+ *
+ * This approach also enables support of a user mode in which local
+ * task processing is in FIFO, not LIFO order, simply by using
+ * poll rather than pop. This can be useful in message-passing
+ * frameworks in which tasks are never joined. However neither
+ * mode considers affinities, loads, cache localities, etc, so
+ * rarely provide the best possible performance on a given
+ * machine, but portably provide good throughput by averaging over
+ * these factors. (Further, even if we did try to use such
+ * information, we do not usually have a basis for exploiting it.
+ * For example, some sets of tasks profit from cache affinities,
+ * but others are harmed by cache pollution effects.)
+ *
+ * WorkQueues are also used in a similar way for tasks submitted
+ * to the pool. We cannot mix these tasks in the same queues used
+ * for work-stealing (this would contaminate lifo/fifo
+ * processing). Instead, we loosely associate submission queues
+ * with submitting threads, using a form of hashing. The
+ * ThreadLocal Submitter class contains a value initially used as
+ * a hash code for choosing existing queues, but may be randomly
+ * repositioned upon contention with other submitters. In
+ * essence, submitters act like workers except that they never
+ * take tasks, and they are multiplexed on to a finite number of
+ * shared work queues. However, classes are set up so that future
+ * extensions could allow submitters to optionally help perform
+ * tasks as well. Pool submissions from internal workers are also
+ * allowed, but use randomized rather than thread-hashed queue
+ * indices to avoid imbalance. Insertion of tasks in shared mode
+ * requires a lock (mainly to protect in the case of resizing) but
+ * we use only a simple spinlock (using bits in field runState),
+ * because submitters encountering a busy queue try or create
+ * others so never block.
+ *
+ * Management
+ * ==========
+ *
+ * The main throughput advantages of work-stealing stem from
+ * decentralized control -- workers mostly take tasks from
+ * themselves or each other. We cannot negate this in the
+ * implementation of other management responsibilities. The main
+ * tactic for avoiding bottlenecks is packing nearly all
+ * essentially atomic control state into two volatile variables
+ * that are by far most often read (not written) as status and
+ * consistency checks.
+ *
+ * Field "ctl" contains 64 bits holding all the information needed
+ * to atomically decide to add, inactivate, enqueue (on an event
+ * queue), dequeue, and/or re-activate workers. To enable this
+ * packing, we restrict maximum parallelism to (1<<15)-1 (which is
+ * far in excess of normal operating range) to allow ids, counts,
+ * and their negations (used for thresholding) to fit into 16bit
+ * fields.
+ *
+ * Field "runState" contains 32 bits needed to register and
+ * deregister WorkQueues, as well as to enable shutdown. It is
+ * only modified under a lock (normally briefly held, but
+ * occasionally protecting allocations and resizings) but even
+ * when locked remains available to check consistency.
+ *
+ * Recording WorkQueues. WorkQueues are recorded in the
+ * "workQueues" array that is created upon pool construction and
+ * expanded if necessary. Updates to the array while recording
+ * new workers and unrecording terminated ones are protected from
+ * each other by a lock but the array is otherwise concurrently
+ * readable, and accessed directly. To simplify index-based
+ * operations, the array size is always a power of two, and all
+ * readers must tolerate null slots. Shared (submission) queues
+ * are at even indices, worker queues at odd indices. Grouping
+ * them together in this way simplifies and speeds up task
+ * scanning. To avoid flailing during start-up, the array is
+ * presized to hold twice #parallelism workers (which is unlikely
+ * to need further resizing during execution). But to avoid
+ * dealing with so many null slots, variable runState includes a
+ * mask for the nearest power of two that contains all current
+ * workers. All worker thread creation is on-demand, triggered by
+ * task submissions, replacement of terminated workers, and/or
+ * compensation for blocked workers. However, all other support
+ * code is set up to work with other policies. To ensure that we
+ * do not hold on to worker references that would prevent GC, ALL
+ * accesses to workQueues are via indices into the workQueues
+ * array (which is one source of some of the messy code
+ * constructions here). In essence, the workQueues array serves as
+ * a weak reference mechanism. Thus for example the wait queue
+ * field of ctl stores indices, not references. Access to the
+ * workQueues in associated methods (for example signalWork) must
+ * both index-check and null-check the IDs. All such accesses
+ * ignore bad IDs by returning out early from what they are doing,
+ * since this can only be associated with termination, in which
+ * case it is OK to give up.
+ *
+ * All uses of the workQueues array check that it is non-null
+ * (even if previously non-null). This allows nulling during
+ * termination, which is currently not necessary, but remains an
+ * option for resource-revocation-based shutdown schemes. It also
+ * helps reduce JIT issuance of uncommon-trap code, which tends to
+ * unnecessarily complicate control flow in some methods.
+ *
+ * Event Queuing. Unlike HPC work-stealing frameworks, we cannot
+ * let workers spin indefinitely scanning for tasks when none can
+ * be found immediately, and we cannot start/resume workers unless
+ * there appear to be tasks available. On the other hand, we must
+ * quickly prod them into action when new tasks are submitted or
+ * generated. In many usages, ramp-up time to activate workers is
+ * the main limiting factor in overall performance (this is
+ * compounded at program start-up by JIT compilation and
+ * allocation). So we try to streamline this as much as possible.
+ * We park/unpark workers after placing in an event wait queue
+ * when they cannot find work. This "queue" is actually a simple
+ * Treiber stack, headed by the "id" field of ctl, plus a 15bit
+ * counter value (that reflects the number of times a worker has
+ * been inactivated) to avoid ABA effects (we need only as many
+ * version numbers as worker threads). Successors are held in
+ * field WorkQueue.nextWait. Queuing deals with several intrinsic
+ * races, mainly that a task-producing thread can miss seeing (and
+ * signalling) another thread that gave up looking for work but
+ * has not yet entered the wait queue. We solve this by requiring
+ * a full sweep of all workers (via repeated calls to method
+ * scan()) both before and after a newly waiting worker is added
+ * to the wait queue. During a rescan, the worker might release
+ * some other queued worker rather than itself, which has the same
+ * net effect. Because enqueued workers may actually be rescanning
+ * rather than waiting, we set and clear the "parker" field of
+ * WorkQueues to reduce unnecessary calls to unpark. (This
+ * requires a secondary recheck to avoid missed signals.) Note
+ * the unusual conventions about Thread.interrupts surrounding
+ * parking and other blocking: Because interrupts are used solely
+ * to alert threads to check termination, which is checked anyway
+ * upon blocking, we clear status (using Thread.interrupted)
+ * before any call to park, so that park does not immediately
+ * return due to status being set via some other unrelated call to
+ * interrupt in user code.
+ *
+ * Signalling. We create or wake up workers only when there
+ * appears to be at least one task they might be able to find and
+ * execute. When a submission is added or another worker adds a
+ * task to a queue that previously had fewer than two tasks, they
+ * signal waiting workers (or trigger creation of new ones if
+ * fewer than the given parallelism level -- see signalWork).
+ * These primary signals are buttressed by signals during rescans;
+ * together these cover the signals needed in cases when more
+ * tasks are pushed but untaken, and improve performance compared
+ * to having one thread wake up all workers.
+ *
+ * Trimming workers. To release resources after periods of lack of
+ * use, a worker starting to wait when the pool is quiescent will
+ * time out and terminate if the pool has remained quiescent for
+ * SHRINK_RATE nanosecs. This will slowly propagate, eventually
+ * terminating all workers after long periods of non-use.
+ *
+ * Shutdown and Termination. A call to shutdownNow atomically sets
+ * a runState bit and then (non-atomically) sets each worker's
+ * runState status, cancels all unprocessed tasks, and wakes up
+ * all waiting workers. Detecting whether termination should
+ * commence after a non-abrupt shutdown() call requires more work
+ * and bookkeeping. We need consensus about quiescence (i.e., that
+ * there is no more work). The active count provides a primary
+ * indication but non-abrupt shutdown still requires a rechecking
+ * scan for any workers that are inactive but not queued.
+ *
+ * Joining Tasks
+ * =============
+ *
+ * Any of several actions may be taken when one worker is waiting
+ * to join a task stolen (or always held) by another. Because we
+ * are multiplexing many tasks on to a pool of workers, we can't
+ * just let them block (as in Thread.join). We also cannot just
+ * reassign the joiner's run-time stack with another and replace
+ * it later, which would be a form of "continuation", that even if
+ * possible is not necessarily a good idea since we sometimes need
+ * both an unblocked task and its continuation to progress.
+ * Instead we combine two tactics:
+ *
+ * Helping: Arranging for the joiner to execute some task that it
+ * would be running if the steal had not occurred.
+ *
+ * Compensating: Unless there are already enough live threads,
+ * method tryCompensate() may create or re-activate a spare
+ * thread to compensate for blocked joiners until they unblock.
+ *
+ * A third form (implemented in tryRemoveAndExec and
+ * tryPollForAndExec) amounts to helping a hypothetical
+ * compensator: If we can readily tell that a possible action of a
+ * compensator is to steal and execute the task being joined, the
+ * joining thread can do so directly, without the need for a
+ * compensation thread (although at the expense of larger run-time
+ * stacks, but the tradeoff is typically worthwhile).
+ *
+ * The ManagedBlocker extension API can't use helping so relies
+ * only on compensation in method awaitBlocker.
+ *
+ * The algorithm in tryHelpStealer entails a form of "linear"
+ * helping: Each worker records (in field currentSteal) the most
+ * recent task it stole from some other worker. Plus, it records
+ * (in field currentJoin) the task it is currently actively
+ * joining. Method tryHelpStealer uses these markers to try to
+ * find a worker to help (i.e., steal back a task from and execute
+ * it) that could hasten completion of the actively joined task.
+ * In essence, the joiner executes a task that would be on its own
+ * local deque had the to-be-joined task not been stolen. This may
+ * be seen as a conservative variant of the approach in Wagner &
+ * Calder "Leapfrogging: a portable technique for implementing
+ * efficient futures" SIGPLAN Notices, 1993
+ * (http://portal.acm.org/citation.cfm?id=155354). It differs in
+ * that: (1) We only maintain dependency links across workers upon
+ * steals, rather than use per-task bookkeeping. This sometimes
+ * requires a linear scan of workers array to locate stealers, but
+ * often doesn't because stealers leave hints (that may become
+ * stale/wrong) of where to locate them. A stealHint is only a
+ * hint because a worker might have had multiple steals and the
+ * hint records only one of them (usually the most current).
+ * Hinting isolates cost to when it is needed, rather than adding
+ * to per-task overhead. (2) It is "shallow", ignoring nesting
+ * and potentially cyclic mutual steals. (3) It is intentionally
+ * racy: field currentJoin is updated only while actively joining,
+ * which means that we miss links in the chain during long-lived
+ * tasks, GC stalls etc (which is OK since blocking in such cases
+ * is usually a good idea). (4) We bound the number of attempts
+ * to find work (see MAX_HELP_DEPTH) and fall back to suspending
+ * the worker and if necessary replacing it with another.
+ *
+ * It is impossible to keep exactly the target parallelism number
+ * of threads running at any given time. Determining the
+ * existence of conservatively safe helping targets, the
+ * availability of already-created spares, and the apparent need
+ * to create new spares are all racy, so we rely on multiple
+ * retries of each. Currently, in keeping with on-demand
+ * signalling policy, we compensate only if blocking would leave
+ * less than one active (non-waiting, non-blocked) worker.
+ * Additionally, to avoid some false alarms due to GC, lagging
+ * counters, system activity, etc, compensated blocking for joins
+ * is only attempted after rechecks stabilize in
+ * ForkJoinTask.awaitJoin. (Retries are interspersed with
+ * Thread.yield, for good citizenship.)
+ *
+ * Style notes: There is a lot of representation-level coupling
+ * among classes ForkJoinPool, ForkJoinWorkerThread, and
+ * ForkJoinTask. The fields of WorkQueue maintain data structures
+ * managed by ForkJoinPool, so are directly accessed. There is
+ * little point trying to reduce this, since any associated future
+ * changes in representations will need to be accompanied by
+ * algorithmic changes anyway. All together, these low-level
+ * implementation choices produce as much as a factor of 4
+ * performance improvement compared to naive implementations, and
+ * enable the processing of billions of tasks per second, at the
+ * expense of some ugliness.
+ *
+ * Methods signalWork() and scan() are the main bottlenecks, so are
+ * especially heavily micro-optimized/mangled. There are lots of
+ * inline assignments (of form "while ((local = field) != 0)")
+ * which are usually the simplest way to ensure the required read
+ * orderings (which are sometimes critical). This leads to a
+ * "C"-like style of listing declarations of these locals at the
+ * heads of methods or blocks. There are several occurrences of
+ * the unusual "do {} while (!cas...)" which is the simplest way
+ * to force an update of a CAS'ed variable. There are also other
+ * coding oddities that help some methods perform reasonably even
+ * when interpreted (not compiled).
+ *
+ * The order of declarations in this file is:
+ * (1) statics
+ * (2) fields (along with constants used when unpacking some of
+ * them), listed in an order that tends to reduce contention
+ * among them a bit under most JVMs;
+ * (3) nested classes
+ * (4) internal control methods
+ * (5) callbacks and other support for ForkJoinTask methods
+ * (6) exported methods (plus a few little helpers)
+ * (7) static block initializing all statics in a minimally
+ * dependent order.
+ */
+
+ /**
+ * Factory for creating new {@link ForkJoinWorkerThread}s.
+ * A {@code ForkJoinWorkerThreadFactory} must be defined and used
+ * for {@code ForkJoinWorkerThread} subclasses that extend base
+ * functionality or initialize threads with different contexts.
*/
public static interface ForkJoinWorkerThreadFactory {
/**
* Returns a new worker thread operating in the given pool.
*
* @param pool the pool this thread works in
- * @throws NullPointerException if pool is null
+ * @throws NullPointerException if the pool is null
*/
public ForkJoinWorkerThread newThread(ForkJoinPool pool);
}
/**
- * Default ForkJoinWorkerThreadFactory implementation, creates a
+ * Default ForkJoinWorkerThreadFactory implementation; creates a
* new ForkJoinWorkerThread.
*/
- static class DefaultForkJoinWorkerThreadFactory
+ static class DefaultForkJoinWorkerThreadFactory
implements ForkJoinWorkerThreadFactory {
public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
- try {
- return new ForkJoinWorkerThread(pool);
- } catch (OutOfMemoryError oom) {
- return null;
- }
+ return new ForkJoinWorkerThread(pool);
}
}
@@ -109,15 +481,13 @@ public class ForkJoinPool extends Abstra
* overridden in ForkJoinPool constructors.
*/
public static final ForkJoinWorkerThreadFactory
- defaultForkJoinWorkerThreadFactory =
- new DefaultForkJoinWorkerThreadFactory();
+ defaultForkJoinWorkerThreadFactory;
/**
* Permission required for callers of methods that may start or
* kill threads.
*/
- private static final RuntimePermission modifyThreadPermission =
- new RuntimePermission("modifyThread");
+ private static final RuntimePermission modifyThreadPermission;
/**
* If there is a security manager, makes sure caller has
@@ -132,418 +502,1498 @@ public class ForkJoinPool extends Abstra
/**
* Generator for assigning sequence numbers as pool names.
*/
- private static final AtomicInteger poolNumberGenerator =
- new AtomicInteger();
+ private static final AtomicInteger poolNumberGenerator;
/**
- * Array holding all worker threads in the pool. Initialized upon
- * first use. Array size must be a power of two. Updates and
- * replacements are protected by workerLock, but it is always kept
- * in a consistent enough state to be randomly accessed without
- * locking by workers performing work-stealing.
+ * Bits and masks for control variables
+ *
+ * Field ctl is a long packed with:
+ * AC: Number of active running workers minus target parallelism (16 bits)
+ * TC: Number of total workers minus target parallelism (16 bits)
+ * ST: true if pool is terminating (1 bit)
+ * EC: the wait count of top waiting thread (15 bits)
+ * ID: ~(poolIndex >>> 1) of top of Treiber stack of waiters (16 bits)
+ *
+ * When convenient, we can extract the upper 32 bits of counts and
+ * the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
+ * (int)ctl. The ec field is never accessed alone, but always
+ * together with id and st. The offsets of counts by the target
+ * parallelism and the positionings of fields makes it possible to
+ * perform the most common checks via sign tests of fields: When
+ * ac is negative, there are not enough active workers, when tc is
+ * negative, there are not enough total workers, when id is
+ * negative, there is at least one waiting worker, and when e is
+ * negative, the pool is terminating. To deal with these possibly
+ * negative fields, we use casts in and out of "short" and/or
+ * signed shifts to maintain signedness.
+ *
+ * When a thread is queued (inactivated), its eventCount field is
+ * negative, which is the only way to tell if a worker is
+ * prevented from executing tasks, even though it must continue to
+ * scan for them to avoid queuing races.
+ *
+ * Field runState is an int packed with:
+ * SHUTDOWN: true if shutdown is enabled (1 bit)
+ * SEQ: a sequence number updated upon (de)registering workers (15 bits)
+ * MASK: mask (power of 2 - 1) covering all registered poolIndexes (16 bits)
+ *
+ * The combination of mask and sequence number enables simple
+ * consistency checks: Staleness of read-only operations on the
+ * workers and queues arrays can be checked by comparing runState
+ * before vs after the reads. The low 16 bits (i.e, anding with
+ * SMASK) hold the smallest power of two covering all worker
+ * indices, minus one. The mask for queues (vs workers) is twice
+ * this value plus 1.
+ */
+
+ // bit positions/shifts for fields
+ private static final int AC_SHIFT = 48;
+ private static final int TC_SHIFT = 32;
+ private static final int ST_SHIFT = 31;
+ private static final int EC_SHIFT = 16;
+
+ // bounds
+ private static final int MAX_ID = 0x7fff; // max poolIndex
+ private static final int SMASK = 0xffff; // mask short bits
+ private static final int SHORT_SIGN = 1 << 15;
+ private static final int INT_SIGN = 1 << 31;
+
+ // masks
+ private static final long STOP_BIT = 0x0001L << ST_SHIFT;
+ private static final long AC_MASK = ((long)SMASK) << AC_SHIFT;
+ private static final long TC_MASK = ((long)SMASK) << TC_SHIFT;
+
+ // units for incrementing and decrementing
+ private static final long TC_UNIT = 1L << TC_SHIFT;
+ private static final long AC_UNIT = 1L << AC_SHIFT;
+
+ // masks and units for dealing with u = (int)(ctl >>> 32)
+ private static final int UAC_SHIFT = AC_SHIFT - 32;
+ private static final int UTC_SHIFT = TC_SHIFT - 32;
+ private static final int UAC_MASK = SMASK << UAC_SHIFT;
+ private static final int UTC_MASK = SMASK << UTC_SHIFT;
+ private static final int UAC_UNIT = 1 << UAC_SHIFT;
+ private static final int UTC_UNIT = 1 << UTC_SHIFT;
+
+ // masks and units for dealing with e = (int)ctl
+ private static final int E_MASK = 0x7fffffff; // no STOP_BIT
+ private static final int E_SEQ = 1 << EC_SHIFT;
+
+ // runState bits
+ private static final int SHUTDOWN = 1 << 31;
+ private static final int RS_SEQ = 1 << 16;
+ private static final int RS_SEQ_MASK = 0x7fff0000;
+
+ // access mode for WorkQueue
+ static final int LIFO_QUEUE = 0;
+ static final int FIFO_QUEUE = 1;
+ static final int SHARED_QUEUE = -1;
+
+ /**
+ * The wakeup interval (in nanoseconds) for a worker waiting for a
+ * task when the pool is quiescent to instead try to shrink the
+ * number of workers. The exact value does not matter too
+ * much. It must be short enough to release resources during
+ * sustained periods of idleness, but not so short that threads
+ * are continually re-created.
+ */
+ private static final long SHRINK_RATE =
+ 4L * 1000L * 1000L * 1000L; // 4 seconds
+
+ /**
+ * The timeout value for attempted shrinkage, includes
+ * some slop to cope with system timer imprecision.
+ */
+ private static final long SHRINK_TIMEOUT = SHRINK_RATE - (SHRINK_RATE / 10);
+
+ /**
+ * The maximum stolen->joining link depth allowed in tryHelpStealer.
+ * Depths for legitimate chains are unbounded, but we use a fixed
+ * constant to avoid (otherwise unchecked) cycles and to bound
+ * staleness of traversal parameters at the expense of sometimes
+ * blocking when we could be helping.
*/
- volatile ForkJoinWorkerThread[] workers;
+ private static final int MAX_HELP_DEPTH = 16;
- /**
- * Lock protecting access to workers.
+ /*
+ * Field layout order in this class tends to matter more than one
+ * would like. Runtime layout order is only loosely related to
+ * declaration order and may differ across JVMs, but the following
+ * empirically works OK on current JVMs.
+ */
+
+ volatile long ctl; // main pool control
+ final int parallelism; // parallelism level
+ final int localMode; // per-worker scheduling mode
+ int nextPoolIndex; // hint used in registerWorker
+ volatile int runState; // shutdown status, seq, and mask
+ WorkQueue[] workQueues; // main registry
+ final ReentrantLock lock; // for registration
+ final Condition termination; // for awaitTermination
+ final ForkJoinWorkerThreadFactory factory; // factory for new workers
+ final Thread.UncaughtExceptionHandler ueh; // per-worker UEH
+ final AtomicLong stealCount; // collect counts when terminated
+ final AtomicInteger nextWorkerNumber; // to create worker name string
+ final String workerNamePrefix; // Prefix for assigning worker names
+
+ /**
+ * Queues supporting work-stealing as well as external task
+ * submission. See above for main rationale and algorithms.
+ * Implementation relies heavily on "Unsafe" intrinsics
+ * and selective use of "volatile":
+ *
+ * Field "base" is the index (mod array.length) of the least valid
+ * queue slot, which is always the next position to steal (poll)
+ * from if nonempty. Reads and writes require volatile orderings
+ * but not CAS, because updates are only performed after slot
+ * CASes.
+ *
+ * Field "top" is the index (mod array.length) of the next queue
+ * slot to push to or pop from. It is written only by owner thread
+ * for push, or under lock for trySharedPush, and accessed by
+ * other threads only after reading (volatile) base. Both top and
+ * base are allowed to wrap around on overflow, but (top - base)
+ * (or more commonly -(base - top) to force volatile read of base
+ * before top) still estimates size.
+ *
+ * The array slots are read and written using the emulation of
+ * volatiles/atomics provided by Unsafe. Insertions must in
+ * general use putOrderedObject as a form of releasing store to
+ * ensure that all writes to the task object are ordered before
+ * its publication in the queue. (Although we can avoid one case
+ * of this when locked in trySharedPush.) All removals entail a
+ * CAS to null. The array is always a power of two. To ensure
+ * safety of Unsafe array operations, all accesses perform
+ * explicit null checks and implicit bounds checks via
+ * power-of-two masking.
+ *
+ * In addition to basic queuing support, this class contains
+ * fields described elsewhere to control execution. It turns out
+ * to work better memory-layout-wise to include them in this
+ * class rather than a separate class.
+ *
+ * Performance on most platforms is very sensitive to placement of
+ * instances of both WorkQueues and their arrays -- we absolutely
+ * do not want multiple WorkQueue instances or multiple queue
+ * arrays sharing cache lines. (It would be best for queue objects
+ * and their arrays to share, but there is nothing available to
+ * help arrange that). Unfortunately, because they are recorded
+ * in a common array, WorkQueue instances are often moved to be
+ * adjacent by garbage collectors. To reduce impact, we use field
+ * padding that works OK on common platforms; this effectively
+ * trades off slightly slower average field access for the sake of
+ * avoiding really bad worst-case access. (Until better JVM
+ * support is in place, this padding is dependent on transient
+ * properties of JVM field layout rules.) We also take care in
+ * allocating and sizing and resizing the array. Non-shared queue
+ * arrays are initialized (via method growArray) by workers before
+ * use. Others are allocated on first use.
*/
- private final ReentrantLock workerLock;
+ static final class WorkQueue {
+ /**
+ * Capacity of work-stealing queue array upon initialization.
+ * Must be a power of two; at least 4, but set larger to
+ * reduce cacheline sharing among queues.
+ */
+ static final int INITIAL_QUEUE_CAPACITY = 1 << 8;
- /**
- * Condition for awaitTermination.
- */
- private final Condition termination;
+ /**
+ * Maximum size for queue arrays. Must be a power of two less
+ * than or equal to 1 << (31 - width of array entry) to ensure
+ * lack of wraparound of index calculations, but defined to a
+ * value a bit less than this to help users trap runaway
+ * programs before saturating systems.
+ */
+ static final int MAXIMUM_QUEUE_CAPACITY = 1 << 26; // 64M
- /**
- * The uncaught exception handler used when any worker
- * abruptly terminates
- */
- private Thread.UncaughtExceptionHandler ueh;
+ volatile long totalSteals; // cumulative number of steals
+ int seed; // for random scanning; initialize nonzero
+ volatile int eventCount; // encoded inactivation count; < 0 if inactive
+ int nextWait; // encoded record of next event waiter
+ int rescans; // remaining scans until block
+ int nsteals; // top-level task executions since last idle
+ final int mode; // lifo, fifo, or shared
+ int poolIndex; // index of this queue in pool (or 0)
+ int stealHint; // index of most recent known stealer
+ volatile int runState; // 1: locked, -1: terminate; else 0
+ volatile int base; // index of next slot for poll
+ int top; // index of next slot for push
+ ForkJoinTask[] array; // the elements (initially unallocated)
+ final ForkJoinWorkerThread owner; // owning thread or null if shared
+ volatile Thread parker; // == owner during call to park; else null
+ ForkJoinTask currentJoin; // task being joined in awaitJoin
+ ForkJoinTask currentSteal; // current non-local task being executed
+ // Heuristic padding to ameliorate unfortunate memory placements
+ Object p00, p01, p02, p03, p04, p05, p06, p07, p08, p09, p0a;
+
+ WorkQueue(ForkJoinWorkerThread owner, int mode) {
+ this.owner = owner;
+ this.mode = mode;
+ // Place indices in the center of array (that is not yet allocated)
+ base = top = INITIAL_QUEUE_CAPACITY >>> 1;
+ }
- /**
- * Creation factory for worker threads.
- */
- private final ForkJoinWorkerThreadFactory factory;
+ /**
+ * Returns number of tasks in the queue.
+ */
+ final int queueSize() {
+ int n = base - top; // non-owner callers must read base first
+ return (n >= 0) ? 0 : -n;
+ }
- /**
- * Head of stack of threads that were created to maintain
- * parallelism when other threads blocked, but have since
- * suspended when the parallelism level rose.
- */
- private volatile WaitQueueNode spareStack;
+ /**
+ * Pushes a task. Call only by owner in unshared queues.
+ *
+ * @param task the task. Caller must ensure non-null.
+ * @param p if non-null, pool to signal if necessary
+ * @throw RejectedExecutionException if array cannot be resized
+ */
+ final void push(ForkJoinTask task, ForkJoinPool p) {
+ ForkJoinTask[] a;
+ int s = top, m, n;
+ if ((a = array) != null) { // ignore if queue removed
+ U.putOrderedObject
+ (a, (((m = a.length - 1) & s) << ASHIFT) + ABASE, task);
+ if ((n = (top = s + 1) - base) <= 2) {
+ if (p != null)
+ p.signalWork();
+ }
+ else if (n >= m)
+ growArray(true);
+ }
+ }
- /**
- * Sum of per-thread steal counts, updated only when threads are
- * idle or terminating.
- */
- private final AtomicLong stealCount;
+ /**
+ * Pushes a task if lock is free and array is either big
+ * enough or can be resized to be big enough.
+ *
+ * @param task the task. Caller must ensure non-null.
+ * @return true if submitted
+ */
+ final boolean trySharedPush(ForkJoinTask task) {
+ boolean submitted = false;
+ if (runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
+ ForkJoinTask[] a = array;
+ int s = top, n = s - base;
+ try {
+ if ((a != null && n < a.length - 1) ||
+ (a = growArray(false)) != null) { // must presize
+ int j = (((a.length - 1) & s) << ASHIFT) + ABASE;
+ U.putObject(a, (long)j, task); // don't need "ordered"
+ top = s + 1;
+ submitted = true;
+ }
+ } finally {
+ runState = 0; // unlock
+ }
+ }
+ return submitted;
+ }
- /**
- * Queue for external submissions.
- */
- private final LinkedTransferQueue> submissionQueue;
+ /**
+ * Takes next task, if one exists, in FIFO order.
+ */
+ final ForkJoinTask poll() {
+ ForkJoinTask[] a; int b, i;
+ while ((b = base) - top < 0 && (a = array) != null &&
+ (i = (a.length - 1) & b) >= 0) {
+ int j = (i << ASHIFT) + ABASE;
+ ForkJoinTask t = (ForkJoinTask)U.getObjectVolatile(a, j);
+ if (t != null && base == b &&
+ U.compareAndSwapObject(a, j, t, null)) {
+ base = b + 1;
+ return t;
+ }
+ }
+ return null;
+ }
- /**
- * Head of Treiber stack for barrier sync. See below for explanation
- */
- private volatile WaitQueueNode syncStack;
+ /**
+ * Takes next task, if one exists, in LIFO order.
+ * Call only by owner in unshared queues.
+ */
+ final ForkJoinTask pop() {
+ ForkJoinTask t; int m;
+ ForkJoinTask[] a = array;
+ if (a != null && (m = a.length - 1) >= 0) {
+ for (int s; (s = top - 1) - base >= 0;) {
+ int j = ((m & s) << ASHIFT) + ABASE;
+ if ((t = (ForkJoinTask)U.getObjectVolatile(a, j)) == null)
+ break;
+ if (U.compareAndSwapObject(a, j, t, null)) {
+ top = s;
+ return t;
+ }
+ }
+ }
+ return null;
+ }
- /**
- * The count for event barrier
- */
- private volatile long eventCount;
+ /**
+ * Takes next task, if one exists, in order specified by mode.
+ */
+ final ForkJoinTask nextLocalTask() {
+ return mode == 0 ? pop() : poll();
+ }
- /**
- * Pool number, just for assigning useful names to worker threads
- */
- private final int poolNumber;
+ /**
+ * Returns next task, if one exists, in order specified by mode.
+ */
+ final ForkJoinTask peek() {
+ ForkJoinTask[] a = array; int m;
+ if (a == null || (m = a.length - 1) < 0)
+ return null;
+ int i = mode == 0 ? top - 1 : base;
+ int j = ((i & m) << ASHIFT) + ABASE;
+ return (ForkJoinTask)U.getObjectVolatile(a, j);
+ }
+
+ /**
+ * Returns task at index b if b is current base of queue.
+ */
+ final ForkJoinTask pollAt(int b) {
+ ForkJoinTask[] a; int i;
+ ForkJoinTask task = null;
+ if ((a = array) != null && (i = ((a.length - 1) & b)) >= 0) {
+ int j = (i << ASHIFT) + ABASE;
+ ForkJoinTask t = (ForkJoinTask)U.getObjectVolatile(a, j);
+ if (t != null && base == b &&
+ U.compareAndSwapObject(a, j, t, null)) {
+ base = b + 1;
+ task = t;
+ }
+ }
+ return task;
+ }
+
+ /**
+ * Pops the given task only if it is at the current top.
+ */
+ final boolean tryUnpush(ForkJoinTask t) {
+ ForkJoinTask[] a; int s;
+ if ((a = array) != null && (s = top) != base &&
+ U.compareAndSwapObject
+ (a, (((a.length - 1) & --s) << ASHIFT) + ABASE, t, null)) {
+ top = s;
+ return true;
+ }
+ return false;
+ }
+
+ /**
+ * Polls the given task only if it is at the current base.
+ */
+ final boolean pollFor(ForkJoinTask task) {
+ ForkJoinTask[] a; int b, i;
+ if ((b = base) - top < 0 && (a = array) != null &&
+ (i = (a.length - 1) & b) >= 0) {
+ int j = (i << ASHIFT) + ABASE;
+ if (U.getObjectVolatile(a, j) == task && base == b &&
+ U.compareAndSwapObject(a, j, task, null)) {
+ base = b + 1;
+ return true;
+ }
+ }
+ return false;
+ }
+
+ /**
+ * If present, removes from queue and executes the given task, or
+ * any other cancelled task. Returns (true) immediately on any CAS
+ * or consistency check failure so caller can retry.
+ *
+ * @return false if no progress can be made
+ */
+ final boolean tryRemoveAndExec(ForkJoinTask task) {
+ boolean removed = false, empty = true, progress = true;
+ ForkJoinTask[] a; int m, s, b, n;
+ if ((a = array) != null && (m = a.length - 1) >= 0 &&
+ (n = (s = top) - (b = base)) > 0) {
+ for (ForkJoinTask t;;) { // traverse from s to b
+ int j = ((--s & m) << ASHIFT) + ABASE;
+ t = (ForkJoinTask)U.getObjectVolatile(a, j);
+ if (t == null) // inconsistent length
+ break;
+ else if (t == task) {
+ if (s + 1 == top) { // pop
+ if (!U.compareAndSwapObject(a, j, task, null))
+ break;
+ top = s;
+ removed = true;
+ }
+ else if (base == b) // replace with proxy
+ removed = U.compareAndSwapObject(a, j, task,
+ new EmptyTask());
+ break;
+ }
+ else if (t.status >= 0)
+ empty = false;
+ else if (s + 1 == top) { // pop and throw away
+ if (U.compareAndSwapObject(a, j, t, null))
+ top = s;
+ break;
+ }
+ if (--n == 0) {
+ if (!empty && base == b)
+ progress = false;
+ break;
+ }
+ }
+ }
+ if (removed)
+ task.doExec();
+ return progress;
+ }
+
+ /**
+ * Initializes or doubles the capacity of array. Call either
+ * by owner or with lock held -- it is OK for base, but not
+ * top, to move while resizings are in progress.
+ *
+ * @param rejectOnFailure if true, throw exception if capacity
+ * exceeded (relayed ultimately to user); else return null.
+ */
+ final ForkJoinTask[] growArray(boolean rejectOnFailure) {
+ ForkJoinTask[] oldA = array;
+ int size = oldA != null ? oldA.length << 1 : INITIAL_QUEUE_CAPACITY;
+ if (size <= MAXIMUM_QUEUE_CAPACITY) {
+ int oldMask, t, b;
+ ForkJoinTask[] a = array = new ForkJoinTask[size];
+ if (oldA != null && (oldMask = oldA.length - 1) >= 0 &&
+ (t = top) - (b = base) > 0) {
+ int mask = size - 1;
+ do {
+ ForkJoinTask x;
+ int oldj = ((b & oldMask) << ASHIFT) + ABASE;
+ int j = ((b & mask) << ASHIFT) + ABASE;
+ x = (ForkJoinTask)U.getObjectVolatile(oldA, oldj);
+ if (x != null &&
+ U.compareAndSwapObject(oldA, oldj, x, null))
+ U.putObjectVolatile(a, j, x);
+ } while (++b != t);
+ }
+ return a;
+ }
+ else if (!rejectOnFailure)
+ return null;
+ else
+ throw new RejectedExecutionException("Queue capacity exceeded");
+ }
+
+ /**
+ * Removes and cancels all known tasks, ignoring any exceptions.
+ */
+ final void cancelAll() {
+ ForkJoinTask.cancelIgnoringExceptions(currentJoin);
+ ForkJoinTask.cancelIgnoringExceptions(currentSteal);
+ for (ForkJoinTask t; (t = poll()) != null; )
+ ForkJoinTask.cancelIgnoringExceptions(t);
+ }
+
+ // Execution methods
+
+ /**
+ * Removes and runs tasks until empty, using local mode
+ * ordering.
+ */
+ final void runLocalTasks() {
+ if (base - top < 0) {
+ for (ForkJoinTask t; (t = nextLocalTask()) != null; )
+ t.doExec();
+ }
+ }
+
+ /**
+ * Executes a top-level task and any local tasks remaining
+ * after execution.
+ *
+ * @return true unless terminating
+ */
+ final boolean runTask(ForkJoinTask t) {
+ boolean alive = true;
+ if (t != null) {
+ currentSteal = t;
+ t.doExec();
+ runLocalTasks();
+ ++nsteals;
+ currentSteal = null;
+ }
+ else if (runState < 0) // terminating
+ alive = false;
+ return alive;
+ }
+
+ /**
+ * Executes a non-top-level (stolen) task.
+ */
+ final void runSubtask(ForkJoinTask t) {
+ if (t != null) {
+ ForkJoinTask ps = currentSteal;
+ currentSteal = t;
+ t.doExec();
+ currentSteal = ps;
+ }
+ }
+
+ /**
+ * Computes next value for random probes. Scans don't require
+ * a very high quality generator, but also not a crummy one.
+ * Marsaglia xor-shift is cheap and works well enough. Note:
+ * This is manually inlined in several usages in ForkJoinPool
+ * to avoid writes inside busy scan loops.
+ */
+ final int nextSeed() {
+ int r = seed;
+ r ^= r << 13;
+ r ^= r >>> 17;
+ r ^= r << 5;
+ return seed = r;
+ }
+
+ // Unsafe mechanics
+ private static final sun.misc.Unsafe U;
+ private static final long RUNSTATE;
+ private static final int ABASE;
+ private static final int ASHIFT;
+ static {
+ int s;
+ try {
+ U = getUnsafe();
+ Class k = WorkQueue.class;
+ Class ak = ForkJoinTask[].class;
+ RUNSTATE = U.objectFieldOffset
+ (k.getDeclaredField("runState"));
+ ABASE = U.arrayBaseOffset(ak);
+ s = U.arrayIndexScale(ak);
+ } catch (Exception e) {
+ throw new Error(e);
+ }
+ if ((s & (s-1)) != 0)
+ throw new Error("data type scale not a power of two");
+ ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
+ }
+ }
/**
- * The maximum allowed pool size
+ * Class for artificial tasks that are used to replace the target
+ * of local joins if they are removed from an interior queue slot
+ * in WorkQueue.tryRemoveAndExec. We don't need the proxy to
+ * actually do anything beyond having a unique identity.
*/
- private volatile int maxPoolSize;
+ static final class EmptyTask extends ForkJoinTask {
+ EmptyTask() { status = ForkJoinTask.NORMAL; } // force done
+ public Void getRawResult() { return null; }
+ public void setRawResult(Void x) {}
+ public boolean exec() { return true; }
+ }
/**
- * The desired parallelism level, updated only under workerLock.
+ * Per-thread records for (typically non-FJ) threads that submit
+ * to pools. Cureently holds only psuedo-random seed / index that
+ * is used to choose submission queues in method doSubmit. In the
+ * future, this may incorporate a means to implement different
+ * task rejection and resubmission policies.
*/
- private volatile int parallelism;
+ static final class Submitter {
+ int seed; // seed for random submission queue selection
+
+ // Heuristic padding to ameliorate unfortunate memory placements
+ int p0, p1, p2, p3, p4, p5, p6, p7, p8, p9, pa, pb, pc, pd, pe;
+
+ Submitter() {
+ // Use identityHashCode, forced negative, for seed
+ seed = System.identityHashCode(Thread.currentThread()) | (1 << 31);
+ }
+
+ /**
+ * Computes next value for random probes. Like method
+ * WorkQueue.nextSeed, this is manually inlined in several
+ * usages to avoid writes inside busy loops.
+ */
+ final int nextSeed() {
+ int r = seed;
+ r ^= r << 13;
+ r ^= r >>> 17;
+ return seed = r ^= r << 5;
+ }
+ }
+
+ /** ThreadLocal class for Submitters */
+ static final class ThreadSubmitter extends ThreadLocal {
+ public Submitter initialValue() { return new Submitter(); }
+ }
/**
- * True if use local fifo, not default lifo, for local polling
+ * Per-thread submission bookeeping. Shared across all pools
+ * to reduce ThreadLocal pollution and because random motion
+ * to avoid contention in one pool is likely to hold for others.
*/
- private volatile boolean locallyFifo;
+ static final ThreadSubmitter submitters = new ThreadSubmitter();
/**
- * Holds number of total (i.e., created and not yet terminated)
- * and running (i.e., not blocked on joins or other managed sync)
- * threads, packed into one int to ensure consistent snapshot when
- * making decisions about creating and suspending spare
- * threads. Updated only by CAS. Note: CASes in
- * updateRunningCount and preJoin running active count is in low
- * word, so need to be modified if this changes
+ * Top-level runloop for workers
*/
- private volatile int workerCounts;
+ final void runWorker(ForkJoinWorkerThread wt) {
+ // Initialize queue array and seed in this thread
+ WorkQueue w = wt.workQueue;
+ w.growArray(false);
+ // Same initial hash as Submitters
+ w.seed = System.identityHashCode(Thread.currentThread()) | (1 << 31);
- private static int totalCountOf(int s) { return s >>> 16; }
- private static int runningCountOf(int s) { return s & shortMask; }
- private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
+ do {} while (w.runTask(scan(w)));
+ }
+
+ // Creating, registering and deregistering workers
/**
- * Adds delta (which may be negative) to running count. This must
- * be called before (with negative arg) and after (with positive)
- * any managed synchronization (i.e., mainly, joins).
- * @param delta the number to add
+ * Tries to create and start a worker
*/
- final void updateRunningCount(int delta) {
- int s;
- do;while (!casWorkerCounts(s = workerCounts, s + delta));
+ private void addWorker() {
+ Throwable ex = null;
+ ForkJoinWorkerThread w = null;
+ try {
+ if ((w = factory.newThread(this)) != null) {
+ w.start();
+ return;
+ }
+ } catch (Throwable e) {
+ ex = e;
+ }
+ deregisterWorker(w, ex);
}
/**
- * Adds delta (which may be negative) to both total and running
- * count. This must be called upon creation and termination of
- * worker threads.
- * @param delta the number to add
+ * Callback from ForkJoinWorkerThread constructor to assign a
+ * public name. This must be separate from registerWorker because
+ * it is called during the "super" constructor call in
+ * ForkJoinWorkerThread.
*/
- private void updateWorkerCount(int delta) {
- int d = delta + (delta << 16); // add to both lo and hi parts
- int s;
- do;while (!casWorkerCounts(s = workerCounts, s + d));
+ final String nextWorkerName() {
+ return workerNamePrefix.concat
+ (Integer.toString(nextWorkerNumber.addAndGet(1)));
}
/**
- * Lifecycle control. High word contains runState, low word
- * contains the number of workers that are (probably) executing
- * tasks. This value is atomically incremented before a worker
- * gets a task to run, and decremented when worker has no tasks
- * and cannot find any. These two fields are bundled together to
- * support correct termination triggering. Note: activeCount
- * CAS'es cheat by assuming active count is in low word, so need
- * to be modified if this changes
+ * Callback from ForkJoinWorkerThread constructor to establish and
+ * record its WorkQueue.
+ *
+ * @param wt the worker thread
*/
- private volatile int runControl;
-
- // RunState values. Order among values matters
- private static final int RUNNING = 0;
- private static final int SHUTDOWN = 1;
- private static final int TERMINATING = 2;
- private static final int TERMINATED = 3;
-
- private static int runStateOf(int c) { return c >>> 16; }
- private static int activeCountOf(int c) { return c & shortMask; }
- private static int runControlFor(int r, int a) { return (r << 16) + a; }
+ final void registerWorker(ForkJoinWorkerThread wt) {
+ WorkQueue w = wt.workQueue;
+ ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ int k = nextPoolIndex;
+ WorkQueue[] ws = workQueues;
+ if (ws != null) { // ignore on shutdown
+ int n = ws.length;
+ if (k < 0 || (k & 1) == 0 || k >= n || ws[k] != null) {
+ for (k = 1; k < n && ws[k] != null; k += 2)
+ ; // workers are at odd indices
+ if (k >= n) // resize
+ workQueues = ws = Arrays.copyOf(ws, n << 1);
+ }
+ w.poolIndex = k;
+ w.eventCount = ~(k >>> 1) & SMASK; // Set up wait count
+ ws[k] = w; // record worker
+ nextPoolIndex = k + 2;
+ int rs = runState;
+ int m = rs & SMASK; // recalculate runState mask
+ if (k > m)
+ m = (m << 1) + 1;
+ runState = (rs & SHUTDOWN) | ((rs + RS_SEQ) & RS_SEQ_MASK) | m;
+ }
+ } finally {
+ lock.unlock();
+ }
+ }
/**
- * Try incrementing active count; fail on contention. Called by
- * workers before/during executing tasks.
- * @return true on success
- */
- final boolean tryIncrementActiveCount() {
- int c = runControl;
- return casRunControl(c, c+1);
+ * Final callback from terminating worker, as well as failure to
+ * construct or start a worker in addWorker. Removes record of
+ * worker from array, and adjusts counts. If pool is shutting
+ * down, tries to complete termination.
+ *
+ * @param wt the worker thread or null if addWorker failed
+ * @param ex the exception causing failure, or null if none
+ */
+ final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
+ WorkQueue w = null;
+ if (wt != null && (w = wt.workQueue) != null) {
+ w.runState = -1; // ensure runState is set
+ stealCount.getAndAdd(w.totalSteals + w.nsteals);
+ int idx = w.poolIndex;
+ ReentrantLock lock = this.lock;
+ lock.lock();
+ try { // remove record from array
+ WorkQueue[] ws = workQueues;
+ if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w)
+ ws[nextPoolIndex = idx] = null;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ long c; // adjust ctl counts
+ do {} while (!U.compareAndSwapLong
+ (this, CTL, c = ctl, (((c - AC_UNIT) & AC_MASK) |
+ ((c - TC_UNIT) & TC_MASK) |
+ (c & ~(AC_MASK|TC_MASK)))));
+
+ if (!tryTerminate(false) && w != null) {
+ w.cancelAll(); // cancel remaining tasks
+ if (w.array != null) // suppress signal if never ran
+ signalWork(); // wake up or create replacement
+ }
+
+ if (ex != null) // rethrow
+ U.throwException(ex);
}
/**
- * Tries decrementing active count; fails on contention.
- * Possibly triggers termination on success.
- * Called by workers when they can't find tasks.
- * @return true on success
- */
- final boolean tryDecrementActiveCount() {
- int c = runControl;
- int nextc = c - 1;
- if (!casRunControl(c, nextc))
- return false;
- if (canTerminateOnShutdown(nextc))
- terminateOnShutdown();
- return true;
+ * Tries to add and register a new queue at the given index.
+ *
+ * @param idx the workQueues array index to register the queue
+ * @return the queue, or null if could not add because could
+ * not acquire lock or idx is unusable
+ */
+ private WorkQueue tryAddSharedQueue(int idx) {
+ WorkQueue q = null;
+ ReentrantLock lock = this.lock;
+ if (idx >= 0 && (idx & 1) == 0 && !lock.isLocked()) {
+ // create queue outside of lock but only if apparently free
+ WorkQueue nq = new WorkQueue(null, SHARED_QUEUE);
+ if (lock.tryLock()) {
+ try {
+ WorkQueue[] ws = workQueues;
+ if (ws != null && idx < ws.length) {
+ if ((q = ws[idx]) == null) {
+ int rs; // update runState seq
+ ws[idx] = q = nq;
+ runState = (((rs = runState) & SHUTDOWN) |
+ ((rs + RS_SEQ) & ~SHUTDOWN));
+ }
+ }
+ } finally {
+ lock.unlock();
+ }
+ }
+ }
+ return q;
}
+ // Maintaining ctl counts
+
/**
- * Returns true if argument represents zero active count and
- * nonzero runstate, which is the triggering condition for
- * terminating on shutdown.
+ * Increments active count; mainly called upon return from blocking.
*/
- private static boolean canTerminateOnShutdown(int c) {
- return ((c & -c) >>> 16) != 0; // i.e. least bit is nonzero runState bit
+ final void incrementActiveCount() {
+ long c;
+ do {} while (!U.compareAndSwapLong(this, CTL, c = ctl, c + AC_UNIT));
}
/**
- * Transition run state to at least the given state. Return true
- * if not already at least given state.
+ * Activates or creates a worker.
*/
- private boolean transitionRunStateTo(int state) {
- for (;;) {
- int c = runControl;
- if (runStateOf(c) >= state)
- return false;
- if (casRunControl(c, runControlFor(state, activeCountOf(c))))
- return true;
+ final void signalWork() {
+ /*
+ * The while condition is true if: (there is are too few total
+ * workers OR there is at least one waiter) AND (there are too
+ * few active workers OR the pool is terminating). The value
+ * of e distinguishes the remaining cases: zero (no waiters)
+ * for create, negative if terminating (in which case do
+ * nothing), else release a waiter. The secondary checks for
+ * release (non-null array etc) can fail if the pool begins
+ * terminating after the test, and don't impose any added cost
+ * because JVMs must perform null and bounds checks anyway.
+ */
+ long c; int e, u;
+ while ((((e = (int)(c = ctl)) | (u = (int)(c >>> 32))) &
+ (INT_SIGN|SHORT_SIGN)) == (INT_SIGN|SHORT_SIGN)) {
+ WorkQueue[] ws = workQueues; int i; WorkQueue w; Thread p;
+ if (e == 0) { // add a new worker
+ if (U.compareAndSwapLong
+ (this, CTL, c, (long)(((u + UTC_UNIT) & UTC_MASK) |
+ ((u + UAC_UNIT) & UAC_MASK)) << 32)) {
+ addWorker();
+ break;
+ }
+ }
+ else if (e > 0 && ws != null &&
+ (i = ((~e << 1) | 1) & SMASK) < ws.length &&
+ (w = ws[i]) != null &&
+ w.eventCount == (e | INT_SIGN)) {
+ if (U.compareAndSwapLong
+ (this, CTL, c, (((long)(w.nextWait & E_MASK)) |
+ ((long)(u + UAC_UNIT) << 32)))) {
+ w.eventCount = (e + E_SEQ) & E_MASK;
+ if ((p = w.parker) != null)
+ U.unpark(p); // release a waiting worker
+ break;
+ }
+ }
+ else
+ break;
}
}
/**
- * Controls whether to add spares to maintain parallelism
- */
- private volatile boolean maintainsParallelism;
+ * Tries to decrement active count (sometimes implicitly) and
+ * possibly release or create a compensating worker in preparation
+ * for blocking. Fails on contention or termination.
+ *
+ * @return true if the caller can block, else should recheck and retry
+ */
+ final boolean tryCompensate() {
+ WorkQueue[] ws; WorkQueue w; Thread p;
+ int pc = parallelism, e, u, ac, tc, i;
+ long c = ctl;
+
+ if ((e = (int)c) >= 0) {
+ if ((ac = ((u = (int)(c >>> 32)) >> UAC_SHIFT)) <= 0 &&
+ e != 0 && (ws = workQueues) != null &&
+ (i = ((~e << 1) | 1) & SMASK) < ws.length &&
+ (w = ws[i]) != null) {
+ if (w.eventCount == (e | INT_SIGN) &&
+ U.compareAndSwapLong
+ (this, CTL, c, ((long)(w.nextWait & E_MASK) |
+ (c & (AC_MASK|TC_MASK))))) {
+ w.eventCount = (e + E_SEQ) & E_MASK;
+ if ((p = w.parker) != null)
+ U.unpark(p);
+ return true; // release an idle worker
+ }
+ }
+ else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
+ long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
+ if (U.compareAndSwapLong(this, CTL, c, nc))
+ return true; // no compensation needed
+ }
+ else if (tc + pc < MAX_ID) {
+ long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
+ if (U.compareAndSwapLong(this, CTL, c, nc)) {
+ addWorker();
+ return true; // create replacement
+ }
+ }
+ }
+ return false;
+ }
- // Constructors
+ // Submissions
/**
- * Creates a ForkJoinPool with a pool size equal to the number of
- * processors available on the system and using the default
- * ForkJoinWorkerThreadFactory,
- * @throws SecurityException if a security manager exists and
- * the caller is not permitted to modify threads
- * because it does not hold {@link
- * java.lang.RuntimePermission}{@code ("modifyThread")},
+ * Unless shutting down, adds the given task to a submission queue
+ * at submitter's current queue index. If no queue exists at the
+ * index, one is created unless pool lock is busy. If the queue
+ * and/or lock are busy, another index is randomly chosen.
*/
- public ForkJoinPool() {
- this(Runtime.getRuntime().availableProcessors(),
- defaultForkJoinWorkerThreadFactory);
+ private void doSubmit(ForkJoinTask task) {
+ if (task == null)
+ throw new NullPointerException();
+ Submitter s = submitters.get();
+ for (int r = s.seed;;) {
+ WorkQueue q; int k;
+ int rs = runState, m = rs & SMASK;
+ WorkQueue[] ws = workQueues;
+ if (rs < 0 || ws == null) // shutting down
+ throw new RejectedExecutionException();
+ if (ws.length > m && // k must be at index
+ ((q = ws[k = (r << 1) & m]) != null ||
+ (q = tryAddSharedQueue(k)) != null) &&
+ q.trySharedPush(task)) {
+ signalWork();
+ return;
+ }
+ r ^= r << 13; // xorshift seed to new position
+ r ^= r >>> 17;
+ if (((s.seed = r ^= r << 5) & m) == 0)
+ Thread.yield(); // occasionally yield if busy
+ }
+ }
+
+
+ // Scanning for tasks
+
+ /**
+ * Scans for and, if found, returns one task, else possibly
+ * inactivates the worker. This method operates on single reads of
+ * volatile state and is designed to be re-invoked continuously in
+ * part because it returns upon detecting inconsistencies,
+ * contention, or state changes that indicate possible success on
+ * re-invocation.
+ *
+ * The scan searches for tasks across queues, randomly selecting
+ * the first #queues probes, favoring steals 2:1 over submissions
+ * (by exploiting even/odd indexing), and then performing a
+ * circular sweep of all queues. The scan terminates upon either
+ * finding a non-empty queue, or completing a full sweep. If the
+ * worker is not inactivated, it takes and returns a task from
+ * this queue. On failure to find a task, we take one of the
+ * following actions, after which the caller will retry calling
+ * this method unless terminated.
+ *
+ * * If not a complete sweep, try to release a waiting worker. If
+ * the scan terminated because the worker is inactivated, then the
+ * released worker will often be the calling worker, and it can
+ * succeed obtaining a task on the next call. Or maybe it is
+ * another worker, but with same net effect. Releasing in other
+ * cases as well ensures that we have enough workers running.
+ *
+ * * If the caller has run a task since the the last empty scan,
+ * return (to allow rescan) if other workers are not also yet
+ * enqueued. Field WorkQueue.rescans counts down on each scan to
+ * ensure eventual inactivation, and occasional calls to
+ * Thread.yield to help avoid interference with more useful
+ * activities on the system.
+ *
+ * * If pool is terminating, terminate the worker.
+ *
+ * * If not already enqueued, try to inactivate and enqueue the
+ * worker on wait queue.
+ *
+ * * If already enqueued and none of the above apply, either park
+ * awaiting signal, or if this is the most recent waiter and pool
+ * is quiescent, relay to idleAwaitWork to check for termination
+ * and possibly shrink pool.
+ *
+ * @param w the worker (via its WorkQueue)
+ * @return a task or null of none found
+ */
+ private final ForkJoinTask scan(WorkQueue w) {
+ boolean swept = false; // true after full empty scan
+ WorkQueue[] ws; // volatile read order matters
+ int r = w.seed, ec = w.eventCount; // ec is negative if inactive
+ int rs = runState, m = rs & SMASK;
+ if ((ws = workQueues) != null && ws.length > m) {
+ ForkJoinTask task = null;
+ for (int k = 0, j = -2 - m; ; ++j) {
+ WorkQueue q; int b;
+ if (j < 0) { // random probes while j negative
+ r ^= r << 13; r ^= r >>> 17; k = (r ^= r << 5) | (j & 1);
+ } // worker (not submit) for odd j
+ else // cyclic scan when j >= 0
+ k += (m >>> 1) | 1; // step by half to reduce bias
+
+ if ((q = ws[k & m]) != null && (b = q.base) - q.top < 0) {
+ if (ec >= 0)
+ task = q.pollAt(b); // steal
+ break;
+ }
+ else if (j > m) {
+ if (rs == runState) // staleness check
+ swept = true;
+ break;
+ }
+ }
+ w.seed = r; // save seed for next scan
+ if (task != null)
+ return task;
+ }
+
+ // Decode ctl on empty scan
+ long c = ctl; int e = (int)c, a = (int)(c >> AC_SHIFT), nr, ns;
+ if (!swept) { // try to release a waiter
+ WorkQueue v; Thread p;
+ if (e > 0 && a < 0 && ws != null &&
+ (v = ws[((~e << 1) | 1) & m]) != null &&
+ v.eventCount == (e | INT_SIGN) && U.compareAndSwapLong
+ (this, CTL, c, ((long)(v.nextWait & E_MASK) |
+ ((c + AC_UNIT) & (AC_MASK|TC_MASK))))) {
+ v.eventCount = (e + E_SEQ) & E_MASK;
+ if ((p = v.parker) != null)
+ U.unpark(p);
+ }
+ }
+ else if ((nr = w.rescans) > 0) { // continue rescanning
+ int ac = a + parallelism;
+ if ((w.rescans = (ac < nr) ? ac : nr - 1) > 0 && w.seed < 0 &&
+ w.eventCount == ec)
+ Thread.yield(); // 1 bit randomness for yield call
+ }
+ else if (e < 0) // pool is terminating
+ w.runState = -1;
+ else if (ec >= 0) { // try to enqueue
+ long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
+ w.nextWait = e;
+ w.eventCount = ec | INT_SIGN; // mark as inactive
+ if (!U.compareAndSwapLong(this, CTL, c, nc))
+ w.eventCount = ec; // back out on CAS failure
+ else if ((ns = w.nsteals) != 0) { // set rescans if ran task
+ if (a <= 0) // ... unless too many active
+ w.rescans = a + parallelism;
+ w.nsteals = 0;
+ w.totalSteals += ns;
+ }
+ }
+ else{ // already queued
+ if (parallelism == -a)
+ idleAwaitWork(w); // quiescent
+ if (w.eventCount == ec) {
+ Thread.interrupted(); // clear status
+ ForkJoinWorkerThread wt = w.owner;
+ U.putObject(wt, PARKBLOCKER, this);
+ w.parker = wt; // emulate LockSupport.park
+ if (w.eventCount == ec) // recheck
+ U.park(false, 0L); // block
+ w.parker = null;
+ U.putObject(wt, PARKBLOCKER, null);
+ }
+ }
+ return null;
+ }
+
+ /**
+ * If inactivating worker w has caused pool to become quiescent,
+ * checks for pool termination, and, so long as this is not the
+ * only worker, waits for event for up to SHRINK_RATE nanosecs.
+ * On timeout, if ctl has not changed, terminates the worker,
+ * which will in turn wake up another worker to possibly repeat
+ * this process.
+ *
+ * @param w the calling worker
+ */
+ private void idleAwaitWork(WorkQueue w) {
+ long c; int nw, ec;
+ if (!tryTerminate(false) &&
+ (int)((c = ctl) >> AC_SHIFT) + parallelism == 0 &&
+ (ec = w.eventCount) == ((int)c | INT_SIGN) &&
+ (nw = w.nextWait) != 0) {
+ long nc = ((long)(nw & E_MASK) | // ctl to restore on timeout
+ ((c + AC_UNIT) & AC_MASK) | (c & TC_MASK));
+ ForkJoinTask.helpExpungeStaleExceptions(); // help clean
+ ForkJoinWorkerThread wt = w.owner;
+ while (ctl == c) {
+ long startTime = System.nanoTime();
+ Thread.interrupted(); // timed variant of version in scan()
+ U.putObject(wt, PARKBLOCKER, this);
+ w.parker = wt;
+ if (ctl == c)
+ U.park(false, SHRINK_RATE);
+ w.parker = null;
+ U.putObject(wt, PARKBLOCKER, null);
+ if (ctl != c)
+ break;
+ if (System.nanoTime() - startTime >= SHRINK_TIMEOUT &&
+ U.compareAndSwapLong(this, CTL, c, nc)) {
+ w.runState = -1; // shrink
+ w.eventCount = (ec + E_SEQ) | E_MASK;
+ break;
+ }
+ }
+ }
}
/**
- * Creates a ForkJoinPool with the indicated parallelism level
- * threads, and using the default ForkJoinWorkerThreadFactory,
- * @param parallelism the number of worker threads
- * @throws IllegalArgumentException if parallelism less than or
- * equal to zero
- * @throws SecurityException if a security manager exists and
- * the caller is not permitted to modify threads
- * because it does not hold {@link
- * java.lang.RuntimePermission}{@code ("modifyThread")},
- */
- public ForkJoinPool(int parallelism) {
- this(parallelism, defaultForkJoinWorkerThreadFactory);
+ * Tries to locate and execute tasks for a stealer of the given
+ * task, or in turn one of its stealers, Traces currentSteal ->
+ * currentJoin links looking for a thread working on a descendant
+ * of the given task and with a non-empty queue to steal back and
+ * execute tasks from. The first call to this method upon a
+ * waiting join will often entail scanning/search, (which is OK
+ * because the joiner has nothing better to do), but this method
+ * leaves hints in workers to speed up subsequent calls. The
+ * implementation is very branchy to cope with potential
+ * inconsistencies or loops encountering chains that are stale,
+ * unknown, or of length greater than MAX_HELP_DEPTH links. All
+ * of these cases are dealt with by just retrying by caller.
+ *
+ * @param joiner the joining worker
+ * @param task the task to join
+ * @return true if found or ran a task (and so is immediately retryable)
+ */
+ final boolean tryHelpStealer(WorkQueue joiner, ForkJoinTask task) {
+ ForkJoinTask subtask; // current target
+ boolean progress = false;
+ int depth = 0; // current chain depth
+ int m = runState & SMASK;
+ WorkQueue[] ws = workQueues;
+
+ if (ws != null && ws.length > m && (subtask = task).status >= 0) {
+ outer:for (WorkQueue j = joiner;;) {
+ // Try to find the stealer of subtask, by first using hint
+ WorkQueue stealer = null;
+ WorkQueue v = ws[j.stealHint & m];
+ if (v != null && v.currentSteal == subtask)
+ stealer = v;
+ else {
+ for (int i = 1; i <= m; i += 2) {
+ if ((v = ws[i]) != null && v.currentSteal == subtask) {
+ stealer = v;
+ j.stealHint = i; // save hint
+ break;
+ }
+ }
+ if (stealer == null)
+ break;
+ }
+
+ for (WorkQueue q = stealer;;) { // Try to help stealer
+ ForkJoinTask t; int b;
+ if (task.status < 0)
+ break outer;
+ if ((b = q.base) - q.top < 0) {
+ progress = true;
+ if (subtask.status < 0)
+ break outer; // stale
+ if ((t = q.pollAt(b)) != null) {
+ stealer.stealHint = joiner.poolIndex;
+ joiner.runSubtask(t);
+ }
+ }
+ else { // empty - try to descend to find stealer's stealer
+ ForkJoinTask next = stealer.currentJoin;
+ if (++depth == MAX_HELP_DEPTH || subtask.status < 0 ||
+ next == null || next == subtask)
+ break outer; // max depth, stale, dead-end, cyclic
+ subtask = next;
+ j = stealer;
+ break;
+ }
+ }
+ }
+ }
+ return progress;
}
/**
- * Creates a ForkJoinPool with parallelism equal to the number of
- * processors available on the system and using the given
- * ForkJoinWorkerThreadFactory,
- * @param factory the factory for creating new threads
- * @throws NullPointerException if factory is null
- * @throws SecurityException if a security manager exists and
- * the caller is not permitted to modify threads
- * because it does not hold {@link
- * java.lang.RuntimePermission}{@code ("modifyThread")},
+ * If task is at base of some steal queue, steals and executes it.
+ *
+ * @param joiner the joining worker
+ * @param task the task
*/
- public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
- this(Runtime.getRuntime().availableProcessors(), factory);
+ final void tryPollForAndExec(WorkQueue joiner, ForkJoinTask task) {
+ WorkQueue[] ws;
+ int m = runState & SMASK;
+ if ((ws = workQueues) != null && ws.length > m) {
+ for (int j = 1; j <= m && task.status >= 0; j += 2) {
+ WorkQueue q = ws[j];
+ if (q != null && q.pollFor(task)) {
+ joiner.runSubtask(task);
+ break;
+ }
+ }
+ }
}
/**
- * Creates a ForkJoinPool with the given parallelism and factory.
- *
- * @param parallelism the targeted number of worker threads
- * @param factory the factory for creating new threads
- * @throws IllegalArgumentException if parallelism less than or
- * equal to zero, or greater than implementation limit
- * @throws NullPointerException if factory is null
- * @throws SecurityException if a security manager exists and
- * the caller is not permitted to modify threads
- * because it does not hold {@link
- * java.lang.RuntimePermission}{@code ("modifyThread")},
- */
- public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
- if (parallelism <= 0 || parallelism > MAX_THREADS)
- throw new IllegalArgumentException();
- if (factory == null)
- throw new NullPointerException();
- checkPermission();
- this.factory = factory;
- this.parallelism = parallelism;
- this.maxPoolSize = MAX_THREADS;
- this.maintainsParallelism = true;
- this.poolNumber = poolNumberGenerator.incrementAndGet();
- this.workerLock = new ReentrantLock();
- this.termination = workerLock.newCondition();
- this.stealCount = new AtomicLong();
- this.submissionQueue = new LinkedTransferQueue>();
- // worker array and workers are lazily constructed
+ * Returns a non-empty steal queue, if one is found during a random,
+ * then cyclic scan, else null. This method must be retried by
+ * caller if, by the time it tries to use the queue, it is empty.
+ */
+ private WorkQueue findNonEmptyStealQueue(WorkQueue w) {
+ int r = w.seed; // Same idea as scan(), but ignoring submissions
+ for (WorkQueue[] ws;;) {
+ int m = runState & SMASK;
+ if ((ws = workQueues) == null)
+ return null;
+ if (ws.length > m) {
+ WorkQueue q;
+ for (int n = m << 2, k = r, j = -n;;) {
+ r ^= r << 13; r ^= r >>> 17; r ^= r << 5;
+ if ((q = ws[(k | 1) & m]) != null && q.base - q.top < 0) {
+ w.seed = r;
+ return q;
+ }
+ else if (j > n)
+ return null;
+ else
+ k = (j++ < 0) ? r : k + ((m >>> 1) | 1);
+
+ }
+ }
+ }
}
/**
- * Create new worker using factory.
- * @param index the index to assign worker
- * @return new worker, or null of factory failed
- */
- private ForkJoinWorkerThread createWorker(int index) {
- Thread.UncaughtExceptionHandler h = ueh;
- ForkJoinWorkerThread w = factory.newThread(this);
- if (w != null) {
- w.poolIndex = index;
- w.setDaemon(true);
- w.setAsyncMode(locallyFifo);
- w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
- if (h != null)
- w.setUncaughtExceptionHandler(h);
+ * Runs tasks until {@code isQuiescent()}. We piggyback on
+ * active count ctl maintenance, but rather than blocking
+ * when tasks cannot be found, we rescan until all others cannot
+ * find tasks either.
+ */
+ final void helpQuiescePool(WorkQueue w) {
+ for (boolean active = true;;) {
+ w.runLocalTasks(); // exhaust local queue
+ WorkQueue q = findNonEmptyStealQueue(w);
+ if (q != null) {
+ ForkJoinTask t;
+ if (!active) { // re-establish active count
+ long c;
+ active = true;
+ do {} while (!U.compareAndSwapLong
+ (this, CTL, c = ctl, c + AC_UNIT));
+ }
+ if ((t = q.poll()) != null)
+ w.runSubtask(t);
+ }
+ else {
+ long c;
+ if (active) { // decrement active count without queuing
+ active = false;
+ do {} while (!U.compareAndSwapLong
+ (this, CTL, c = ctl, c -= AC_UNIT));
+ }
+ else
+ c = ctl; // re-increment on exit
+ if ((int)(c >> AC_SHIFT) + parallelism == 0) {
+ do {} while (!U.compareAndSwapLong
+ (this, CTL, c = ctl, c + AC_UNIT));
+ break;
+ }
+ }
}
- return w;
}
/**
- * Returns a good size for worker array given pool size.
- * Currently requires size to be a power of two.
+ * Gets and removes a local or stolen task for the given worker.
+ *
+ * @return a task, if available
*/
- private static int arraySizeFor(int ps) {
- return ps <= 1? 1 : (1 << (32 - Integer.numberOfLeadingZeros(ps-1)));
+ final ForkJoinTask nextTaskFor(WorkQueue w) {
+ for (ForkJoinTask t;;) {
+ WorkQueue q;
+ if ((t = w.nextLocalTask()) != null)
+ return t;
+ if ((q = findNonEmptyStealQueue(w)) == null)
+ return null;
+ if ((t = q.poll()) != null)
+ return t;
+ }
}
/**
- * Creates or resizes array if necessary to hold newLength.
- * Call only under exclusion or lock.
- * @return the array
+ * Returns the approximate (non-atomic) number of idle threads per
+ * active thread to offset steal queue size for method
+ * ForkJoinTask.getSurplusQueuedTaskCount().
*/
- private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
- ForkJoinWorkerThread[] ws = workers;
- if (ws == null)
- return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
- else if (newLength > ws.length)
- return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
- else
- return ws;
+ final int idlePerActive() {
+ // Approximate at powers of two for small values, saturate past 4
+ int p = parallelism;
+ int a = p + (int)(ctl >> AC_SHIFT);
+ return (a > (p >>>= 1) ? 0 :
+ a > (p >>>= 1) ? 1 :
+ a > (p >>>= 1) ? 2 :
+ a > (p >>>= 1) ? 4 :
+ 8);
}
+ // Termination
+
/**
- * Try to shrink workers into smaller array after one or more terminate
+ * Sets SHUTDOWN bit of runState under lock
*/
- private void tryShrinkWorkerArray() {
- ForkJoinWorkerThread[] ws = workers;
- if (ws != null) {
- int len = ws.length;
- int last = len - 1;
- while (last >= 0 && ws[last] == null)
- --last;
- int newLength = arraySizeFor(last+1);
- if (newLength < len)
- workers = Arrays.copyOf(ws, newLength);
+ private void enableShutdown() {
+ ReentrantLock lock = this.lock;
+ if (runState >= 0) {
+ lock.lock(); // don't need try/finally
+ runState |= SHUTDOWN;
+ lock.unlock();
}
}
/**
- * Initialize workers if necessary
- */
- final void ensureWorkerInitialization() {
- ForkJoinWorkerThread[] ws = workers;
- if (ws == null) {
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- ws = workers;
- if (ws == null) {
- int ps = parallelism;
- ws = ensureWorkerArrayCapacity(ps);
- for (int i = 0; i < ps; ++i) {
- ForkJoinWorkerThread w = createWorker(i);
- if (w != null) {
- ws[i] = w;
- w.start();
- updateWorkerCount(1);
- }
+ * Possibly initiates and/or completes termination. Upon
+ * termination, cancels all queued tasks and then
+ *
+ * @param now if true, unconditionally terminate, else only
+ * if no work and no active workers
+ * @return true if now terminating or terminated
+ */
+ private boolean tryTerminate(boolean now) {
+ for (long c;;) {
+ if (((c = ctl) & STOP_BIT) != 0) { // already terminating
+ if ((short)(c >>> TC_SHIFT) == -parallelism) {
+ ReentrantLock lock = this.lock; // signal when no workers
+ lock.lock(); // don't need try/finally
+ termination.signalAll(); // signal when 0 workers
+ lock.unlock();
+ }
+ return true;
+ }
+ if (!now) {
+ if ((int)(c >> AC_SHIFT) != -parallelism || runState >= 0 ||
+ hasQueuedSubmissions())
+ return false;
+ // Check for unqueued inactive workers. One pass suffices.
+ WorkQueue[] ws = workQueues; WorkQueue w;
+ if (ws != null) {
+ int n = ws.length;
+ for (int i = 1; i < n; i += 2) {
+ if ((w = ws[i]) != null && w.eventCount >= 0)
+ return false;
}
}
- } finally {
- lock.unlock();
}
+ if (U.compareAndSwapLong(this, CTL, c, c | STOP_BIT))
+ startTerminating();
}
}
/**
- * Worker creation and startup for threads added via setParallelism.
+ * Initiates termination: Runs three passes through workQueues:
+ * (0) Setting termination status, followed by wakeups of queued
+ * workers; (1) cancelling all tasks; (2) interrupting lagging
+ * threads (likely in external tasks, but possibly also blocked in
+ * joins). Each pass repeats previous steps because of potential
+ * lagging thread creation.
*/
- private void createAndStartAddedWorkers() {
- resumeAllSpares(); // Allow spares to convert to nonspare
- int ps = parallelism;
- ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
- int len = ws.length;
- // Sweep through slots, to keep lowest indices most populated
- int k = 0;
- while (k < len) {
- if (ws[k] != null) {
- ++k;
- continue;
- }
- int s = workerCounts;
- int tc = totalCountOf(s);
- int rc = runningCountOf(s);
- if (rc >= ps || tc >= ps)
- break;
- if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
- ForkJoinWorkerThread w = createWorker(k);
- if (w != null) {
- ws[k++] = w;
- w.start();
+ private void startTerminating() {
+ for (int pass = 0; pass < 3; ++pass) {
+ WorkQueue[] ws = workQueues;
+ if (ws != null) {
+ WorkQueue w; Thread wt;
+ int n = ws.length;
+ for (int j = 0; j < n; ++j) {
+ if ((w = ws[j]) != null) {
+ w.runState = -1;
+ if (pass > 0) {
+ w.cancelAll();
+ if (pass > 1 && (wt = w.owner) != null &&
+ !wt.isInterrupted()) {
+ try {
+ wt.interrupt();
+ } catch (SecurityException ignore) {
+ }
+ }
+ }
+ }
}
- else {
- updateWorkerCount(-1); // back out on failed creation
- break;
+ // Wake up workers parked on event queue
+ int i, e; long c; Thread p;
+ while ((i = ((~(e = (int)(c = ctl)) << 1) | 1) & SMASK) < n &&
+ (w = ws[i]) != null &&
+ w.eventCount == (e | INT_SIGN)) {
+ long nc = ((long)(w.nextWait & E_MASK) |
+ ((c + AC_UNIT) & AC_MASK) |
+ (c & (TC_MASK|STOP_BIT)));
+ if (U.compareAndSwapLong(this, CTL, c, nc)) {
+ w.eventCount = (e + E_SEQ) & E_MASK;
+ if ((p = w.parker) != null)
+ U.unpark(p);
+ }
}
}
}
}
- // Execution methods
+ // Exported methods
+
+ // Constructors
+
+ /**
+ * Creates a {@code ForkJoinPool} with parallelism equal to {@link
+ * java.lang.Runtime#availableProcessors}, using the {@linkplain
+ * #defaultForkJoinWorkerThreadFactory default thread factory},
+ * no UncaughtExceptionHandler, and non-async LIFO processing mode.
+ *
+ * @throws SecurityException if a security manager exists and
+ * the caller is not permitted to modify threads
+ * because it does not hold {@link
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
+ */
+ public ForkJoinPool() {
+ this(Runtime.getRuntime().availableProcessors(),
+ defaultForkJoinWorkerThreadFactory, null, false);
+ }
/**
- * Common code for execute, invoke and submit
+ * Creates a {@code ForkJoinPool} with the indicated parallelism
+ * level, the {@linkplain
+ * #defaultForkJoinWorkerThreadFactory default thread factory},
+ * no UncaughtExceptionHandler, and non-async LIFO processing mode.
+ *
+ * @param parallelism the parallelism level
+ * @throws IllegalArgumentException if parallelism less than or
+ * equal to zero, or greater than implementation limit
+ * @throws SecurityException if a security manager exists and
+ * the caller is not permitted to modify threads
+ * because it does not hold {@link
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
- private void doSubmit(ForkJoinTask task) {
- if (isShutdown())
- throw new RejectedExecutionException();
- if (workers == null)
- ensureWorkerInitialization();
- submissionQueue.offer(task);
- signalIdleWorkers();
+ public ForkJoinPool(int parallelism) {
+ this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
}
/**
- * Performs the given task; returning its result upon completion
+ * Creates a {@code ForkJoinPool} with the given parameters.
+ *
+ * @param parallelism the parallelism level. For default value,
+ * use {@link java.lang.Runtime#availableProcessors}.
+ * @param factory the factory for creating new threads. For default value,
+ * use {@link #defaultForkJoinWorkerThreadFactory}.
+ * @param handler the handler for internal worker threads that
+ * terminate due to unrecoverable errors encountered while executing
+ * tasks. For default value, use {@code null}.
+ * @param asyncMode if true,
+ * establishes local first-in-first-out scheduling mode for forked
+ * tasks that are never joined. This mode may be more appropriate
+ * than default locally stack-based mode in applications in which
+ * worker threads only process event-style asynchronous tasks.
+ * For default value, use {@code false}.
+ * @throws IllegalArgumentException if parallelism less than or
+ * equal to zero, or greater than implementation limit
+ * @throws NullPointerException if the factory is null
+ * @throws SecurityException if a security manager exists and
+ * the caller is not permitted to modify threads
+ * because it does not hold {@link
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
+ */
+ public ForkJoinPool(int parallelism,
+ ForkJoinWorkerThreadFactory factory,
+ Thread.UncaughtExceptionHandler handler,
+ boolean asyncMode) {
+ checkPermission();
+ if (factory == null)
+ throw new NullPointerException();
+ if (parallelism <= 0 || parallelism > MAX_ID)
+ throw new IllegalArgumentException();
+ this.parallelism = parallelism;
+ this.factory = factory;
+ this.ueh = handler;
+ this.localMode = asyncMode ? FIFO_QUEUE : LIFO_QUEUE;
+ this.nextPoolIndex = 1;
+ long np = (long)(-parallelism); // offset ctl counts
+ this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
+ // initialize workQueues array with room for 2*parallelism if possible
+ int n = parallelism << 1;
+ if (n >= MAX_ID)
+ n = MAX_ID;
+ else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
+ n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
+ }
+ this.workQueues = new WorkQueue[(n + 1) << 1];
+ ReentrantLock lck = this.lock = new ReentrantLock();
+ this.termination = lck.newCondition();
+ this.stealCount = new AtomicLong();
+ this.nextWorkerNumber = new AtomicInteger();
+ StringBuilder sb = new StringBuilder("ForkJoinPool-");
+ sb.append(poolNumberGenerator.incrementAndGet());
+ sb.append("-worker-");
+ this.workerNamePrefix = sb.toString();
+ // Create initial submission queue
+ WorkQueue sq = tryAddSharedQueue(0);
+ if (sq != null)
+ sq.growArray(false);
+ }
+
+ // Execution methods
+
+ /**
+ * Performs the given task, returning its result upon completion.
+ * If the computation encounters an unchecked Exception or Error,
+ * it is rethrown as the outcome of this invocation. Rethrown
+ * exceptions behave in the same way as regular exceptions, but,
+ * when possible, contain stack traces (as displayed for example
+ * using {@code ex.printStackTrace()}) of both the current thread
+ * as well as the thread actually encountering the exception;
+ * minimally only the latter.
+ *
* @param task the task
* @return the task's result
- * @throws NullPointerException if task is null
- * @throws RejectedExecutionException if pool is shut down
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
*/
public T invoke(ForkJoinTask task) {
doSubmit(task);
@@ -552,111 +2002,119 @@ public class ForkJoinPool extends Abstra
/**
* Arranges for (asynchronous) execution of the given task.
+ *
* @param task the task
- * @throws NullPointerException if task is null
- * @throws RejectedExecutionException if pool is shut down
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
*/
- public void execute(ForkJoinTask task) {
+ public void execute(ForkJoinTask task) {
doSubmit(task);
}
// AbstractExecutorService methods
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public void execute(Runnable task) {
- doSubmit(new AdaptedRunnable(task, null));
+ if (task == null)
+ throw new NullPointerException();
+ ForkJoinTask job;
+ if (task instanceof ForkJoinTask) // avoid re-wrap
+ job = (ForkJoinTask) task;
+ else
+ job = ForkJoinTask.adapt(task, null);
+ doSubmit(job);
}
+ /**
+ * Submits a ForkJoinTask for execution.
+ *
+ * @param task the task to submit
+ * @return the task
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
+ public ForkJoinTask submit(ForkJoinTask task) {
+ doSubmit(task);
+ return task;
+ }
+
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public ForkJoinTask submit(Callable task) {
- ForkJoinTask job = new AdaptedCallable(task);
+ if (task == null)
+ throw new NullPointerException();
+ ForkJoinTask job = ForkJoinTask.adapt(task);
doSubmit(job);
return job;
}
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public ForkJoinTask submit(Runnable task, T result) {
- ForkJoinTask job = new AdaptedRunnable(task, result);
+ if (task == null)
+ throw new NullPointerException();
+ ForkJoinTask job = ForkJoinTask.adapt(task, result);
doSubmit(job);
return job;
}
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public ForkJoinTask submit(Runnable task) {
- ForkJoinTask job = new AdaptedRunnable(task, null);
+ if (task == null)
+ throw new NullPointerException();
+ ForkJoinTask job;
+ if (task instanceof ForkJoinTask) // avoid re-wrap
+ job = (ForkJoinTask) task;
+ else
+ job = ForkJoinTask.adapt(task, null);
doSubmit(job);
return job;
}
/**
- * Adaptor for Runnables. This implements RunnableFuture
- * to be compliant with AbstractExecutorService constraints
+ * @throws NullPointerException {@inheritDoc}
+ * @throws RejectedExecutionException {@inheritDoc}
*/
- static final class AdaptedRunnable extends ForkJoinTask
- implements RunnableFuture {
- final Runnable runnable;
- final T resultOnCompletion;
- T result;
- AdaptedRunnable(Runnable runnable, T result) {
- if (runnable == null) throw new NullPointerException();
- this.runnable = runnable;
- this.resultOnCompletion = result;
- }
- public T getRawResult() { return result; }
- public void setRawResult(T v) { result = v; }
- public boolean exec() {
- runnable.run();
- result = resultOnCompletion;
- return true;
- }
- public void run() { invoke(); }
- }
-
- /**
- * Adaptor for Callables
- */
- static final class AdaptedCallable extends ForkJoinTask
- implements RunnableFuture {
- final Callable callable;
- T result;
- AdaptedCallable(Callable callable) {
- if (callable == null) throw new NullPointerException();
- this.callable = callable;
- }
- public T getRawResult() { return result; }
- public void setRawResult(T v) { result = v; }
- public boolean exec() {
- try {
- result = callable.call();
- return true;
- } catch (Error err) {
- throw err;
- } catch (RuntimeException rex) {
- throw rex;
- } catch (Exception ex) {
- throw new RuntimeException(ex);
- }
- }
- public void run() { invoke(); }
- }
-
public List> invokeAll(Collection> tasks) {
- ArrayList> ts =
+ ArrayList> forkJoinTasks =
new ArrayList>(tasks.size());
- for (Callable c : tasks)
- ts.add(new AdaptedCallable(c));
- invoke(new InvokeAll(ts));
- return (List>)(List)ts;
+ for (Callable task : tasks)
+ forkJoinTasks.add(ForkJoinTask.adapt(task));
+ invoke(new InvokeAll(forkJoinTasks));
+
+ @SuppressWarnings({"unchecked", "rawtypes"})
+ List> futures = (List>) (List) forkJoinTasks;
+ return futures;
}
static final class InvokeAll extends RecursiveAction {
final ArrayList> tasks;
InvokeAll(ArrayList> tasks) { this.tasks = tasks; }
public void compute() {
- try { invokeAll(tasks); } catch(Exception ignore) {}
+ try { invokeAll(tasks); }
+ catch (Exception ignore) {}
}
+ private static final long serialVersionUID = -7914297376763021607L;
}
- // Configuration and status settings and queries
-
/**
- * Returns the factory used for constructing new workers
+ * Returns the factory used for constructing new workers.
*
* @return the factory used for constructing new workers
*/
@@ -667,92 +2125,17 @@ public class ForkJoinPool extends Abstra
/**
* Returns the handler for internal worker threads that terminate
* due to unrecoverable errors encountered while executing tasks.
- * @return the handler, or null if none
- */
- public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
- Thread.UncaughtExceptionHandler h;
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- h = ueh;
- } finally {
- lock.unlock();
- }
- return h;
- }
-
- /**
- * Sets the handler for internal worker threads that terminate due
- * to unrecoverable errors encountered while executing tasks.
- * Unless set, the current default or ThreadGroup handler is used
- * as handler.
*
- * @param h the new handler
- * @return the old handler, or null if none
- * @throws SecurityException if a security manager exists and
- * the caller is not permitted to modify threads
- * because it does not hold {@link
- * java.lang.RuntimePermission}{@code ("modifyThread")},
- */
- public Thread.UncaughtExceptionHandler
- setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
- checkPermission();
- Thread.UncaughtExceptionHandler old = null;
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- old = ueh;
- ueh = h;
- ForkJoinWorkerThread[] ws = workers;
- if (ws != null) {
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread w = ws[i];
- if (w != null)
- w.setUncaughtExceptionHandler(h);
- }
- }
- } finally {
- lock.unlock();
- }
- return old;
- }
-
-
- /**
- * Sets the target parallelism level of this pool.
- * @param parallelism the target parallelism
- * @throws IllegalArgumentException if parallelism less than or
- * equal to zero or greater than maximum size bounds
- * @throws SecurityException if a security manager exists and
- * the caller is not permitted to modify threads
- * because it does not hold {@link
- * java.lang.RuntimePermission}{@code ("modifyThread")},
+ * @return the handler, or {@code null} if none
*/
- public void setParallelism(int parallelism) {
- checkPermission();
- if (parallelism <= 0 || parallelism > maxPoolSize)
- throw new IllegalArgumentException();
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- if (!isTerminating()) {
- int p = this.parallelism;
- this.parallelism = parallelism;
- if (parallelism > p)
- createAndStartAddedWorkers();
- else
- trimSpares();
- }
- } finally {
- lock.unlock();
- }
- signalIdleWorkers();
+ public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
+ return ueh;
}
/**
- * Returns the targeted number of worker threads in this pool.
+ * Returns the targeted parallelism level of this pool.
*
- * @return the targeted number of worker threads in this pool
+ * @return the targeted parallelism level of this pool
*/
public int getParallelism() {
return parallelism;
@@ -760,141 +2143,77 @@ public class ForkJoinPool extends Abstra
/**
* Returns the number of worker threads that have started but not
- * yet terminated. This result returned by this method may differ
- * from {@code getParallelism} when threads are created to
+ * yet terminated. The result returned by this method may differ
+ * from {@link #getParallelism} when threads are created to
* maintain parallelism when others are cooperatively blocked.
*
* @return the number of worker threads
*/
public int getPoolSize() {
- return totalCountOf(workerCounts);
+ return parallelism + (short)(ctl >>> TC_SHIFT);
}
/**
- * Returns the maximum number of threads allowed to exist in the
- * pool, even if there are insufficient unblocked running threads.
- * @return the maximum
- */
- public int getMaximumPoolSize() {
- return maxPoolSize;
- }
-
- /**
- * Sets the maximum number of threads allowed to exist in the
- * pool, even if there are insufficient unblocked running threads.
- * Setting this value has no effect on current pool size. It
- * controls construction of new threads.
- * @throws IllegalArgumentException if negative or greater then
- * internal implementation limit
- */
- public void setMaximumPoolSize(int newMax) {
- if (newMax < 0 || newMax > MAX_THREADS)
- throw new IllegalArgumentException();
- maxPoolSize = newMax;
- }
-
-
- /**
- * Returns true if this pool dynamically maintains its target
- * parallelism level. If false, new threads are added only to
- * avoid possible starvation.
- * This setting is by default true;
- * @return true if maintains parallelism
- */
- public boolean getMaintainsParallelism() {
- return maintainsParallelism;
- }
-
- /**
- * Sets whether this pool dynamically maintains its target
- * parallelism level. If false, new threads are added only to
- * avoid possible starvation.
- * @param enable true to maintains parallelism
- */
- public void setMaintainsParallelism(boolean enable) {
- maintainsParallelism = enable;
- }
-
- /**
- * Establishes local first-in-first-out scheduling mode for forked
- * tasks that are never joined. This mode may be more appropriate
- * than default locally stack-based mode in applications in which
- * worker threads only process asynchronous tasks. This method is
- * designed to be invoked only when pool is quiescent, and
- * typically only before any tasks are submitted. The effects of
- * invocations at other times may be unpredictable.
- *
- * @param async if true, use locally FIFO scheduling
- * @return the previous mode
- */
- public boolean setAsyncMode(boolean async) {
- boolean oldMode = locallyFifo;
- locallyFifo = async;
- ForkJoinWorkerThread[] ws = workers;
- if (ws != null) {
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread t = ws[i];
- if (t != null)
- t.setAsyncMode(async);
- }
- }
- return oldMode;
- }
-
- /**
- * Returns true if this pool uses local first-in-first-out
+ * Returns {@code true} if this pool uses local first-in-first-out
* scheduling mode for forked tasks that are never joined.
*
- * @return true if this pool uses async mode
+ * @return {@code true} if this pool uses async mode
*/
public boolean getAsyncMode() {
- return locallyFifo;
+ return localMode != 0;
}
/**
* Returns an estimate of the number of worker threads that are
* not blocked waiting to join tasks or for other managed
- * synchronization.
+ * synchronization. This method may overestimate the
+ * number of running threads.
*
* @return the number of worker threads
*/
public int getRunningThreadCount() {
- return runningCountOf(workerCounts);
+ int rc = 0;
+ WorkQueue[] ws; WorkQueue w;
+ if ((ws = workQueues) != null) {
+ int n = ws.length;
+ for (int i = 1; i < n; i += 2) {
+ Thread.State s; ForkJoinWorkerThread wt;
+ if ((w = ws[i]) != null && (wt = w.owner) != null &&
+ w.eventCount >= 0 &&
+ (s = wt.getState()) != Thread.State.BLOCKED &&
+ s != Thread.State.WAITING &&
+ s != Thread.State.TIMED_WAITING)
+ ++rc;
+ }
+ }
+ return rc;
}
/**
* Returns an estimate of the number of threads that are currently
* stealing or executing tasks. This method may overestimate the
* number of active threads.
+ *
* @return the number of active threads
*/
public int getActiveThreadCount() {
- return activeCountOf(runControl);
- }
-
- /**
- * Returns an estimate of the number of threads that are currently
- * idle waiting for tasks. This method may underestimate the
- * number of idle threads.
- * @return the number of idle threads
- */
- final int getIdleThreadCount() {
- int c = runningCountOf(workerCounts) - activeCountOf(runControl);
- return (c <= 0)? 0 : c;
+ int r = parallelism + (int)(ctl >> AC_SHIFT);
+ return (r <= 0) ? 0 : r; // suppress momentarily negative values
}
/**
- * Returns true if all worker threads are currently idle. An idle
- * worker is one that cannot obtain a task to execute because none
- * are available to steal from other threads, and there are no
- * pending submissions to the pool. This method is conservative:
- * It might not return true immediately upon idleness of all
- * threads, but will eventually become true if threads remain
- * inactive.
- * @return true if all threads are currently idle
+ * Returns {@code true} if all worker threads are currently idle.
+ * An idle worker is one that cannot obtain a task to execute
+ * because none are available to steal from other threads, and
+ * there are no pending submissions to the pool. This method is
+ * conservative; it might not return {@code true} immediately upon
+ * idleness of all threads, but will eventually become true if
+ * threads remain inactive.
+ *
+ * @return {@code true} if all threads are currently idle
*/
public boolean isQuiescent() {
- return activeCountOf(runControl) == 0;
+ return (int)(ctl >> AC_SHIFT) + parallelism == 0;
}
/**
@@ -902,23 +2221,23 @@ public class ForkJoinPool extends Abstra
* one thread's work queue by another. The reported value
* underestimates the actual total number of steals when the pool
* is not quiescent. This value may be useful for monitoring and
- * tuning fork/join programs: In general, steal counts should be
+ * tuning fork/join programs: in general, steal counts should be
* high enough to keep threads busy, but low enough to avoid
* overhead and contention across threads.
+ *
* @return the number of steals
*/
public long getStealCount() {
- return stealCount.get();
- }
-
- /**
- * Accumulate steal count from a worker. Call only
- * when worker known to be idle.
- */
- private void updateStealCount(ForkJoinWorkerThread w) {
- int sc = w.getAndClearStealCount();
- if (sc != 0)
- stealCount.addAndGet(sc);
+ long count = stealCount.get();
+ WorkQueue[] ws; WorkQueue w;
+ if ((ws = workQueues) != null) {
+ int n = ws.length;
+ for (int i = 1; i < n; i += 2) {
+ if ((w = ws[i]) != null)
+ count += w.totalSteals;
+ }
+ }
+ return count;
}
/**
@@ -928,56 +2247,85 @@ public class ForkJoinPool extends Abstra
* an approximation, obtained by iterating across all threads in
* the pool. This method may be useful for tuning task
* granularities.
+ *
* @return the number of queued tasks
*/
public long getQueuedTaskCount() {
long count = 0;
- ForkJoinWorkerThread[] ws = workers;
- if (ws != null) {
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread t = ws[i];
- if (t != null)
- count += t.getQueueSize();
+ WorkQueue[] ws; WorkQueue w;
+ if ((ws = workQueues) != null) {
+ int n = ws.length;
+ for (int i = 1; i < n; i += 2) {
+ if ((w = ws[i]) != null)
+ count += w.queueSize();
}
}
return count;
}
/**
- * Returns an estimate of the number tasks submitted to this pool
- * that have not yet begun executing. This method takes time
- * proportional to the number of submissions.
+ * Returns an estimate of the number of tasks submitted to this
+ * pool that have not yet begun executing. This method may take
+ * time proportional to the number of submissions.
+ *
* @return the number of queued submissions
*/
public int getQueuedSubmissionCount() {
- return submissionQueue.size();
+ int count = 0;
+ WorkQueue[] ws; WorkQueue w;
+ if ((ws = workQueues) != null) {
+ int n = ws.length;
+ for (int i = 0; i < n; i += 2) {
+ if ((w = ws[i]) != null)
+ count += w.queueSize();
+ }
+ }
+ return count;
}
/**
- * Returns true if there are any tasks submitted to this pool
- * that have not yet begun executing.
+ * Returns {@code true} if there are any tasks submitted to this
+ * pool that have not yet begun executing.
+ *
* @return {@code true} if there are any queued submissions
*/
public boolean hasQueuedSubmissions() {
- return !submissionQueue.isEmpty();
+ WorkQueue[] ws; WorkQueue w;
+ if ((ws = workQueues) != null) {
+ int n = ws.length;
+ for (int i = 0; i < n; i += 2) {
+ if ((w = ws[i]) != null && w.queueSize() != 0)
+ return true;
+ }
+ }
+ return false;
}
/**
* Removes and returns the next unexecuted submission if one is
* available. This method may be useful in extensions to this
* class that re-assign work in systems with multiple pools.
- * @return the next submission, or null if none
+ *
+ * @return the next submission, or {@code null} if none
*/
protected ForkJoinTask pollSubmission() {
- return submissionQueue.poll();
+ WorkQueue[] ws; WorkQueue w; ForkJoinTask t;
+ if ((ws = workQueues) != null) {
+ int n = ws.length;
+ for (int i = 0; i < n; i += 2) {
+ if ((w = ws[i]) != null && (t = w.poll()) != null)
+ return t;
+ }
+ }
+ return null;
}
/**
* Removes all available unexecuted submitted and forked tasks
* from scheduling queues and adds them to the given collection,
* without altering their execution status. These may include
- * artificially generated or wrapped tasks. This method is designed
- * to be invoked only when the pool is known to be
+ * artificially generated or wrapped tasks. This method is
+ * designed to be invoked only when the pool is known to be
* quiescent. Invocations at other times may not remove all
* tasks. A failure encountered while attempting to add elements
* to collection {@code c} may result in elements being in
@@ -985,20 +2333,25 @@ public class ForkJoinPool extends Abstra
* exception is thrown. The behavior of this operation is
* undefined if the specified collection is modified while the
* operation is in progress.
+ *
* @param c the collection to transfer elements into
* @return the number of elements transferred
*/
- protected int drainTasksTo(Collection> c) {
- int n = submissionQueue.drainTo(c);
- ForkJoinWorkerThread[] ws = workers;
- if (ws != null) {
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread w = ws[i];
- if (w != null)
- n += w.drainTasksTo(c);
+ protected int drainTasksTo(Collection> c) {
+ int count = 0;
+ WorkQueue[] ws; WorkQueue w; ForkJoinTask t;
+ if ((ws = workQueues) != null) {
+ int n = ws.length;
+ for (int i = 0; i < n; ++i) {
+ if ((w = ws[i]) != null) {
+ while ((t = w.poll()) != null) {
+ c.add(t);
+ ++count;
+ }
+ }
}
}
- return n;
+ return count;
}
/**
@@ -1009,72 +2362,71 @@ public class ForkJoinPool extends Abstra
* @return a string identifying this pool, as well as its state
*/
public String toString() {
- int ps = parallelism;
- int wc = workerCounts;
- int rc = runControl;
long st = getStealCount();
long qt = getQueuedTaskCount();
long qs = getQueuedSubmissionCount();
+ int rc = getRunningThreadCount();
+ int pc = parallelism;
+ long c = ctl;
+ int tc = pc + (short)(c >>> TC_SHIFT);
+ int ac = pc + (int)(c >> AC_SHIFT);
+ if (ac < 0) // ignore transient negative
+ ac = 0;
+ String level;
+ if ((c & STOP_BIT) != 0)
+ level = (tc == 0) ? "Terminated" : "Terminating";
+ else
+ level = runState < 0 ? "Shutting down" : "Running";
return super.toString() +
- "[" + runStateToString(runStateOf(rc)) +
- ", parallelism = " + ps +
- ", size = " + totalCountOf(wc) +
- ", active = " + activeCountOf(rc) +
- ", running = " + runningCountOf(wc) +
+ "[" + level +
+ ", parallelism = " + pc +
+ ", size = " + tc +
+ ", active = " + ac +
+ ", running = " + rc +
", steals = " + st +
", tasks = " + qt +
", submissions = " + qs +
"]";
}
- private static String runStateToString(int rs) {
- switch(rs) {
- case RUNNING: return "Running";
- case SHUTDOWN: return "Shutting down";
- case TERMINATING: return "Terminating";
- case TERMINATED: return "Terminated";
- default: throw new Error("Unknown run state");
- }
- }
-
- // lifecycle control
-
/**
* Initiates an orderly shutdown in which previously submitted
* tasks are executed, but no new tasks will be accepted.
* Invocation has no additional effect if already shut down.
* Tasks that are in the process of being submitted concurrently
* during the course of this method may or may not be rejected.
+ *
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}{@code ("modifyThread")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public void shutdown() {
checkPermission();
- transitionRunStateTo(SHUTDOWN);
- if (canTerminateOnShutdown(runControl))
- terminateOnShutdown();
+ enableShutdown();
+ tryTerminate(false);
}
/**
- * Attempts to stop all actively executing tasks, and cancels all
- * waiting tasks. Tasks that are in the process of being
- * submitted or executed concurrently during the course of this
- * method may or may not be rejected. Unlike some other executors,
- * this method cancels rather than collects non-executed tasks
- * upon termination, so always returns an empty list. However, you
- * can use method {@code drainTasksTo} before invoking this
- * method to transfer unexecuted tasks to another collection.
+ * Attempts to cancel and/or stop all tasks, and reject all
+ * subsequently submitted tasks. Tasks that are in the process of
+ * being submitted or executed concurrently during the course of
+ * this method may or may not be rejected. This method cancels
+ * both existing and unexecuted tasks, in order to permit
+ * termination in the presence of task dependencies. So the method
+ * always returns an empty list (unlike the case for some other
+ * Executors).
+ *
* @return an empty list
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}{@code ("modifyThread")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public List shutdownNow() {
checkPermission();
- terminate();
+ enableShutdown();
+ tryTerminate(true);
return Collections.emptyList();
}
@@ -1084,17 +2436,28 @@ public class ForkJoinPool extends Abstra
* @return {@code true} if all tasks have completed following shut down
*/
public boolean isTerminated() {
- return runStateOf(runControl) == TERMINATED;
+ long c = ctl;
+ return ((c & STOP_BIT) != 0L &&
+ (short)(c >>> TC_SHIFT) == -parallelism);
}
/**
* Returns {@code true} if the process of termination has
- * commenced but possibly not yet completed.
+ * commenced but not yet completed. This method may be useful for
+ * debugging. A return of {@code true} reported a sufficient
+ * period after shutdown may indicate that submitted tasks have
+ * ignored or suppressed interruption, or are waiting for IO,
+ * causing this executor not to properly terminate. (See the
+ * advisory notes for class {@link ForkJoinTask} stating that
+ * tasks should not normally entail blocking operations. But if
+ * they do, they must abort them on interrupt.)
*
- * @return {@code true} if terminating
+ * @return {@code true} if terminating but not yet terminated
*/
public boolean isTerminating() {
- return runStateOf(runControl) >= TERMINATING;
+ long c = ctl;
+ return ((c & STOP_BIT) != 0L &&
+ (short)(c >>> TC_SHIFT) != -parallelism);
}
/**
@@ -1103,7 +2466,7 @@ public class ForkJoinPool extends Abstra
* @return {@code true} if this pool has been shut down
*/
public boolean isShutdown() {
- return runStateOf(runControl) >= SHUTDOWN;
+ return runState < 0;
}
/**
@@ -1120,7 +2483,7 @@ public class ForkJoinPool extends Abstra
public boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException {
long nanos = unit.toNanos(timeout);
- final ReentrantLock lock = this.workerLock;
+ final ReentrantLock lock = this.lock;
lock.lock();
try {
for (;;) {
@@ -1135,729 +2498,182 @@ public class ForkJoinPool extends Abstra
}
}
- // Shutdown and termination support
-
- /**
- * Callback from terminating worker. Null out the corresponding
- * workers slot, and if terminating, try to terminate, else try to
- * shrink workers array.
- * @param w the worker
- */
- final void workerTerminated(ForkJoinWorkerThread w) {
- updateStealCount(w);
- updateWorkerCount(-1);
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- ForkJoinWorkerThread[] ws = workers;
- if (ws != null) {
- int idx = w.poolIndex;
- if (idx >= 0 && idx < ws.length && ws[idx] == w)
- ws[idx] = null;
- if (totalCountOf(workerCounts) == 0) {
- terminate(); // no-op if already terminating
- transitionRunStateTo(TERMINATED);
- termination.signalAll();
- }
- else if (!isTerminating()) {
- tryShrinkWorkerArray();
- tryResumeSpare(true); // allow replacement
- }
- }
- } finally {
- lock.unlock();
- }
- signalIdleWorkers();
- }
-
/**
- * Initiate termination.
- */
- private void terminate() {
- if (transitionRunStateTo(TERMINATING)) {
- stopAllWorkers();
- resumeAllSpares();
- signalIdleWorkers();
- cancelQueuedSubmissions();
- cancelQueuedWorkerTasks();
- interruptUnterminatedWorkers();
- signalIdleWorkers(); // resignal after interrupt
- }
- }
-
- /**
- * Possibly terminates when on shutdown state.
- */
- private void terminateOnShutdown() {
- if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
- terminate();
- }
-
- /**
- * Clears out and cancels submissions.
- */
- private void cancelQueuedSubmissions() {
- ForkJoinTask task;
- while ((task = pollSubmission()) != null)
- task.cancel(false);
- }
-
- /**
- * Cleans out worker queues.
- */
- private void cancelQueuedWorkerTasks() {
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- ForkJoinWorkerThread[] ws = workers;
- if (ws != null) {
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread t = ws[i];
- if (t != null)
- t.cancelTasks();
- }
- }
- } finally {
- lock.unlock();
- }
- }
-
- /**
- * Sets each worker's status to terminating. Requires lock to avoid
- * conflicts with add/remove.
- */
- private void stopAllWorkers() {
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- ForkJoinWorkerThread[] ws = workers;
- if (ws != null) {
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread t = ws[i];
- if (t != null)
- t.shutdownNow();
- }
- }
- } finally {
- lock.unlock();
- }
- }
-
- /**
- * Interrupts all unterminated workers. This is not required for
- * sake of internal control, but may help unstick user code during
- * shutdown.
- */
- private void interruptUnterminatedWorkers() {
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- ForkJoinWorkerThread[] ws = workers;
- if (ws != null) {
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread t = ws[i];
- if (t != null && !t.isTerminated()) {
- try {
- t.interrupt();
- } catch (SecurityException ignore) {
- }
- }
- }
- }
- } finally {
- lock.unlock();
- }
- }
-
-
- /*
- * Nodes for event barrier to manage idle threads. Queue nodes
- * are basic Treiber stack nodes, also used for spare stack.
- *
- * The event barrier has an event count and a wait queue (actually
- * a Treiber stack). Workers are enabled to look for work when
- * the eventCount is incremented. If they fail to find work, they
- * may wait for next count. Upon release, threads help others wake
- * up.
- *
- * Synchronization events occur only in enough contexts to
- * maintain overall liveness:
- *
- * - Submission of a new task to the pool
- * - Resizes or other changes to the workers array
- * - pool termination
- * - A worker pushing a task on an empty queue
+ * Interface for extending managed parallelism for tasks running
+ * in {@link ForkJoinPool}s.
*
- * The case of pushing a task occurs often enough, and is heavy
- * enough compared to simple stack pushes, to require special
- * handling: Method signalWork returns without advancing count if
- * the queue appears to be empty. This would ordinarily result in
- * races causing some queued waiters not to be woken up. To avoid
- * this, the first worker enqueued in method sync (see
- * syncIsReleasable) rescans for tasks after being enqueued, and
- * helps signal if any are found. This works well because the
- * worker has nothing better to do, and so might as well help
- * alleviate the overhead and contention on the threads actually
- * doing work. Also, since event counts increments on task
- * availability exist to maintain liveness (rather than to force
- * refreshes etc), it is OK for callers to exit early if
- * contending with another signaller.
- */
- static final class WaitQueueNode {
- WaitQueueNode next; // only written before enqueued
- volatile ForkJoinWorkerThread thread; // nulled to cancel wait
- final long count; // unused for spare stack
-
- WaitQueueNode(long c, ForkJoinWorkerThread w) {
- count = c;
- thread = w;
- }
-
- /**
- * Wakes up waiter, returning false if known to already
- */
- boolean signal() {
- ForkJoinWorkerThread t = thread;
- if (t == null)
- return false;
- thread = null;
- LockSupport.unpark(t);
- return true;
- }
-
- /**
- * Awaits release on sync.
- */
- void awaitSyncRelease(ForkJoinPool p) {
- while (thread != null && !p.syncIsReleasable(this))
- LockSupport.park(this);
- }
-
- /**
- * Awaits resumption as spare.
- */
- void awaitSpareRelease() {
- while (thread != null) {
- if (!Thread.interrupted())
- LockSupport.park(this);
- }
- }
- }
-
- /**
- * Ensures that no thread is waiting for count to advance from the
- * current value of eventCount read on entry to this method, by
- * releasing waiting threads if necessary.
- * @return the count
- */
- final long ensureSync() {
- long c = eventCount;
- WaitQueueNode q;
- while ((q = syncStack) != null && q.count < c) {
- if (casBarrierStack(q, null)) {
- do {
- q.signal();
- } while ((q = q.next) != null);
- break;
- }
- }
- return c;
- }
-
- /**
- * Increments event count and releases waiting threads.
- */
- private void signalIdleWorkers() {
- long c;
- do;while (!casEventCount(c = eventCount, c+1));
- ensureSync();
- }
-
- /**
- * Signals threads waiting to poll a task. Because method sync
- * rechecks availability, it is OK to only proceed if queue
- * appears to be non-empty, and OK to skip under contention to
- * increment count (since some other thread succeeded).
- */
- final void signalWork() {
- long c;
- WaitQueueNode q;
- if (syncStack != null &&
- casEventCount(c = eventCount, c+1) &&
- (((q = syncStack) != null && q.count <= c) &&
- (!casBarrierStack(q, q.next) || !q.signal())))
- ensureSync();
- }
-
- /**
- * Waits until event count advances from last value held by
- * caller, or if excess threads, caller is resumed as spare, or
- * caller or pool is terminating. Updates caller's event on exit.
- * @param w the calling worker thread
- */
- final void sync(ForkJoinWorkerThread w) {
- updateStealCount(w); // Transfer w's count while it is idle
-
- while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
- long prev = w.lastEventCount;
- WaitQueueNode node = null;
- WaitQueueNode h;
- while (eventCount == prev &&
- ((h = syncStack) == null || h.count == prev)) {
- if (node == null)
- node = new WaitQueueNode(prev, w);
- if (casBarrierStack(node.next = h, node)) {
- node.awaitSyncRelease(this);
- break;
- }
- }
- long ec = ensureSync();
- if (ec != prev) {
- w.lastEventCount = ec;
- break;
- }
- }
- }
-
- /**
- * Returns true if worker waiting on sync can proceed:
- * - on signal (thread == null)
- * - on event count advance (winning race to notify vs signaller)
- * - on Interrupt
- * - if the first queued node, we find work available
- * If node was not signalled and event count not advanced on exit,
- * then we also help advance event count.
- * @return true if node can be released
- */
- final boolean syncIsReleasable(WaitQueueNode node) {
- long prev = node.count;
- if (!Thread.interrupted() && node.thread != null &&
- (node.next != null ||
- !ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
- eventCount == prev)
- return false;
- if (node.thread != null) {
- node.thread = null;
- long ec = eventCount;
- if (prev <= ec) // help signal
- casEventCount(ec, ec+1);
- }
- return true;
- }
-
- /**
- * Returns true if a new sync event occurred since last call to
- * sync or this method, if so, updating caller's count.
- */
- final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
- long lc = w.lastEventCount;
- long ec = ensureSync();
- if (ec == lc)
- return false;
- w.lastEventCount = ec;
- return true;
- }
-
- // Parallelism maintenance
-
- /**
- * Decrements running count; if too low, adds spare.
+ * A {@code ManagedBlocker} provides two methods. Method
+ * {@code isReleasable} must return {@code true} if blocking is
+ * not necessary. Method {@code block} blocks the current thread
+ * if necessary (perhaps internally invoking {@code isReleasable}
+ * before actually blocking). These actions are performed by any
+ * thread invoking {@link ForkJoinPool#managedBlock}. The
+ * unusual methods in this API accommodate synchronizers that may,
+ * but don't usually, block for long periods. Similarly, they
+ * allow more efficient internal handling of cases in which
+ * additional workers may be, but usually are not, needed to
+ * ensure sufficient parallelism. Toward this end,
+ * implementations of method {@code isReleasable} must be amenable
+ * to repeated invocation.
*
- * Conceptually, all we need to do here is add or resume a
- * spare thread when one is about to block (and remove or
- * suspend it later when unblocked -- see suspendIfSpare).
- * However, implementing this idea requires coping with
- * several problems: We have imperfect information about the
- * states of threads. Some count updates can and usually do
- * lag run state changes, despite arrangements to keep them
- * accurate (for example, when possible, updating counts
- * before signalling or resuming), especially when running on
- * dynamic JVMs that don't optimize the infrequent paths that
- * update counts. Generating too many threads can make these
- * problems become worse, because excess threads are more
- * likely to be context-switched with others, slowing them all
- * down, especially if there is no work available, so all are
- * busy scanning or idling. Also, excess spare threads can
- * only be suspended or removed when they are idle, not
- * immediately when they aren't needed. So adding threads will
- * raise parallelism level for longer than necessary. Also,
- * FJ applications often encounter highly transient peaks when
- * many threads are blocked joining, but for less time than it
- * takes to create or resume spares.
- *
- * @param joinMe if non-null, return early if done
- * @param maintainParallelism if true, try to stay within
- * target counts, else create only to avoid starvation
- * @return true if joinMe known to be done
- */
- final boolean preJoin(ForkJoinTask joinMe, boolean maintainParallelism) {
- maintainParallelism &= maintainsParallelism; // overrride
- boolean dec = false; // true when running count decremented
- while (spareStack == null || !tryResumeSpare(dec)) {
- int counts = workerCounts;
- if (dec || (dec = casWorkerCounts(counts, --counts))) { // CAS cheat
- if (!needSpare(counts, maintainParallelism))
- break;
- if (joinMe.status < 0)
- return true;
- if (tryAddSpare(counts))
- break;
- }
- }
- return false;
- }
-
- /**
- * Same idea as preJoin
- */
- final boolean preBlock(ManagedBlocker blocker, boolean maintainParallelism){
- maintainParallelism &= maintainsParallelism;
- boolean dec = false;
- while (spareStack == null || !tryResumeSpare(dec)) {
- int counts = workerCounts;
- if (dec || (dec = casWorkerCounts(counts, --counts))) {
- if (!needSpare(counts, maintainParallelism))
- break;
- if (blocker.isReleasable())
- return true;
- if (tryAddSpare(counts))
- break;
- }
- }
- return false;
- }
-
- /**
- * Returns true if a spare thread appears to be needed. If
- * maintaining parallelism, returns true when the deficit in
- * running threads is more than the surplus of total threads, and
- * there is apparently some work to do. This self-limiting rule
- * means that the more threads that have already been added, the
- * less parallelism we will tolerate before adding another.
- * @param counts current worker counts
- * @param maintainParallelism try to maintain parallelism
- */
- private boolean needSpare(int counts, boolean maintainParallelism) {
- int ps = parallelism;
- int rc = runningCountOf(counts);
- int tc = totalCountOf(counts);
- int runningDeficit = ps - rc;
- int totalSurplus = tc - ps;
- return (tc < maxPoolSize &&
- (rc == 0 || totalSurplus < 0 ||
- (maintainParallelism &&
- runningDeficit > totalSurplus &&
- ForkJoinWorkerThread.hasQueuedTasks(workers))));
- }
-
- /**
- * Adds a spare worker if lock available and no more than the
- * expected numbers of threads exist.
- * @return true if successful
- */
- private boolean tryAddSpare(int expectedCounts) {
- final ReentrantLock lock = this.workerLock;
- int expectedRunning = runningCountOf(expectedCounts);
- int expectedTotal = totalCountOf(expectedCounts);
- boolean success = false;
- boolean locked = false;
- // confirm counts while locking; CAS after obtaining lock
- try {
- for (;;) {
- int s = workerCounts;
- int tc = totalCountOf(s);
- int rc = runningCountOf(s);
- if (rc > expectedRunning || tc > expectedTotal)
- break;
- if (!locked && !(locked = lock.tryLock()))
- break;
- if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
- createAndStartSpare(tc);
- success = true;
- break;
- }
- }
- } finally {
- if (locked)
- lock.unlock();
- }
- return success;
- }
-
- /**
- * Adds the kth spare worker. On entry, pool counts are already
- * adjusted to reflect addition.
- */
- private void createAndStartSpare(int k) {
- ForkJoinWorkerThread w = null;
- ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
- int len = ws.length;
- // Probably, we can place at slot k. If not, find empty slot
- if (k < len && ws[k] != null) {
- for (k = 0; k < len && ws[k] != null; ++k)
- ;
- }
- if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
- ws[k] = w;
- w.start();
- }
- else
- updateWorkerCount(-1); // adjust on failure
- signalIdleWorkers();
- }
-
- /**
- * Suspends calling thread w if there are excess threads. Called
- * only from sync. Spares are enqueued in a Treiber stack using
- * the same WaitQueueNodes as barriers. They are resumed mainly
- * in preJoin, but are also woken on pool events that require all
- * threads to check run state.
- * @param w the caller
- */
- private boolean suspendIfSpare(ForkJoinWorkerThread w) {
- WaitQueueNode node = null;
- int s;
- while (parallelism < runningCountOf(s = workerCounts)) {
- if (node == null)
- node = new WaitQueueNode(0, w);
- if (casWorkerCounts(s, s-1)) { // representation-dependent
- // push onto stack
- do;while (!casSpareStack(node.next = spareStack, node));
- // block until released by resumeSpare
- node.awaitSpareRelease();
- return true;
- }
- }
- return false;
- }
-
- /**
- * Tries to pop and resume a spare thread.
- * @param updateCount if true, increment running count on success
- * @return true if successful
- */
- private boolean tryResumeSpare(boolean updateCount) {
- WaitQueueNode q;
- while ((q = spareStack) != null) {
- if (casSpareStack(q, q.next)) {
- if (updateCount)
- updateRunningCount(1);
- q.signal();
- return true;
- }
- }
- return false;
- }
-
- /**
- * Pops and resumes all spare threads. Same idea as ensureSync.
- * @return true if any spares released
- */
- private boolean resumeAllSpares() {
- WaitQueueNode q;
- while ( (q = spareStack) != null) {
- if (casSpareStack(q, null)) {
- do {
- updateRunningCount(1);
- q.signal();
- } while ((q = q.next) != null);
- return true;
- }
- }
- return false;
- }
-
- /**
- * Pops and shuts down excessive spare threads. Call only while
- * holding lock. This is not guaranteed to eliminate all excess
- * threads, only those suspended as spares, which are the ones
- * unlikely to be needed in the future.
- */
- private void trimSpares() {
- int surplus = totalCountOf(workerCounts) - parallelism;
- WaitQueueNode q;
- while (surplus > 0 && (q = spareStack) != null) {
- if (casSpareStack(q, null)) {
- do {
- updateRunningCount(1);
- ForkJoinWorkerThread w = q.thread;
- if (w != null && surplus > 0 &&
- runningCountOf(workerCounts) > 0 && w.shutdown())
- --surplus;
- q.signal();
- } while ((q = q.next) != null);
- }
- }
- }
-
- /**
- * Interface for extending managed parallelism for tasks running
- * in ForkJoinPools. A ManagedBlocker provides two methods.
- * Method {@code isReleasable} must return true if blocking is not
- * necessary. Method {@code block} blocks the current thread
- * if necessary (perhaps internally invoking isReleasable before
- * actually blocking.).
*
For example, here is a ManagedBlocker based on a
* ReentrantLock:
- *
- * class ManagedLocker implements ManagedBlocker {
- * final ReentrantLock lock;
- * boolean hasLock = false;
- * ManagedLocker(ReentrantLock lock) { this.lock = lock; }
- * public boolean block() {
- * if (!hasLock)
- * lock.lock();
- * return true;
- * }
- * public boolean isReleasable() {
- * return hasLock || (hasLock = lock.tryLock());
- * }
+ * {@code
+ * class ManagedLocker implements ManagedBlocker {
+ * final ReentrantLock lock;
+ * boolean hasLock = false;
+ * ManagedLocker(ReentrantLock lock) { this.lock = lock; }
+ * public boolean block() {
+ * if (!hasLock)
+ * lock.lock();
+ * return true;
+ * }
+ * public boolean isReleasable() {
+ * return hasLock || (hasLock = lock.tryLock());
* }
- *
+ * }}
+ *
+ * Here is a class that possibly blocks waiting for an
+ * item on a given queue:
+ *
{@code
+ * class QueueTaker implements ManagedBlocker {
+ * final BlockingQueue queue;
+ * volatile E item = null;
+ * QueueTaker(BlockingQueue q) { this.queue = q; }
+ * public boolean block() throws InterruptedException {
+ * if (item == null)
+ * item = queue.take();
+ * return true;
+ * }
+ * public boolean isReleasable() {
+ * return item != null || (item = queue.poll()) != null;
+ * }
+ * public E getItem() { // call after pool.managedBlock completes
+ * return item;
+ * }
+ * }}
*/
public static interface ManagedBlocker {
/**
* Possibly blocks the current thread, for example waiting for
* a lock or condition.
- * @return true if no additional blocking is necessary (i.e.,
- * if isReleasable would return true)
+ *
+ * @return {@code true} if no additional blocking is necessary
+ * (i.e., if isReleasable would return true)
* @throws InterruptedException if interrupted while waiting
- * (the method is not required to do so, but is allowed to).
+ * (the method is not required to do so, but is allowed to)
*/
boolean block() throws InterruptedException;
/**
- * Returns true if blocking is unnecessary.
+ * Returns {@code true} if blocking is unnecessary.
*/
boolean isReleasable();
}
/**
* Blocks in accord with the given blocker. If the current thread
- * is a ForkJoinWorkerThread, this method possibly arranges for a
- * spare thread to be activated if necessary to ensure parallelism
- * while the current thread is blocked. If
- * {@code maintainParallelism} is true and the pool supports
- * it ({@link #getMaintainsParallelism}), this method attempts to
- * maintain the pool's nominal parallelism. Otherwise if activates
- * a thread only if necessary to avoid complete starvation. This
- * option may be preferable when blockages use timeouts, or are
- * almost always brief.
- *
- * If the caller is not a ForkJoinTask, this method is behaviorally
- * equivalent to
- *
- * while (!blocker.isReleasable())
- * if (blocker.block())
- * return;
- *
- * If the caller is a ForkJoinTask, then the pool may first
- * be expanded to ensure parallelism, and later adjusted.
+ * is a {@link ForkJoinWorkerThread}, this method possibly
+ * arranges for a spare thread to be activated if necessary to
+ * ensure sufficient parallelism while the current thread is blocked.
+ *
+ * If the caller is not a {@link ForkJoinTask}, this method is
+ * behaviorally equivalent to
+ *
{@code
+ * while (!blocker.isReleasable())
+ * if (blocker.block())
+ * return;
+ * }
+ *
+ * If the caller is a {@code ForkJoinTask}, then the pool may
+ * first be expanded to ensure parallelism, and later adjusted.
*
* @param blocker the blocker
- * @param maintainParallelism if true and supported by this pool,
- * attempt to maintain the pool's nominal parallelism; otherwise
- * activate a thread only if necessary to avoid complete
- * starvation.
* @throws InterruptedException if blocker.block did so
*/
- public static void managedBlock(ManagedBlocker blocker,
- boolean maintainParallelism)
+ public static void managedBlock(ManagedBlocker blocker)
throws InterruptedException {
Thread t = Thread.currentThread();
- ForkJoinPool pool = (t instanceof ForkJoinWorkerThread?
- ((ForkJoinWorkerThread)t).pool : null);
- if (!blocker.isReleasable()) {
- try {
- if (pool == null ||
- !pool.preBlock(blocker, maintainParallelism))
- awaitBlocker(blocker);
- } finally {
- if (pool != null)
- pool.updateRunningCount(1);
+ ForkJoinPool p = ((t instanceof ForkJoinWorkerThread) ?
+ ((ForkJoinWorkerThread)t).pool : null);
+ while (!blocker.isReleasable()) {
+ if (p == null || p.tryCompensate()) {
+ try {
+ do {} while (!blocker.isReleasable() && !blocker.block());
+ } finally {
+ if (p != null)
+ p.incrementActiveCount();
+ }
+ break;
}
}
}
- private static void awaitBlocker(ManagedBlocker blocker)
- throws InterruptedException {
- do;while (!blocker.isReleasable() && !blocker.block());
- }
-
- // AbstractExecutorService overrides
+ // AbstractExecutorService overrides. These rely on undocumented
+ // fact that ForkJoinTask.adapt returns ForkJoinTasks that also
+ // implement RunnableFuture.
protected RunnableFuture newTaskFor(Runnable runnable, T value) {
- return new AdaptedRunnable(runnable, value);
+ return (RunnableFuture) ForkJoinTask.adapt(runnable, value);
}
protected RunnableFuture newTaskFor(Callable callable) {
- return new AdaptedCallable(callable);
+ return (RunnableFuture) ForkJoinTask.adapt(callable);
}
+ // Unsafe mechanics
+ private static final sun.misc.Unsafe U;
+ private static final long CTL;
+ private static final long RUNSTATE;
+ private static final long PARKBLOCKER;
- // Temporary Unsafe mechanics for preliminary release
- private static Unsafe getUnsafe() throws Throwable {
+ static {
+ poolNumberGenerator = new AtomicInteger();
+ modifyThreadPermission = new RuntimePermission("modifyThread");
+ defaultForkJoinWorkerThreadFactory =
+ new DefaultForkJoinWorkerThreadFactory();
+ int s;
try {
- return Unsafe.getUnsafe();
+ U = getUnsafe();
+ Class k = ForkJoinPool.class;
+ Class tk = Thread.class;
+ CTL = U.objectFieldOffset
+ (k.getDeclaredField("ctl"));
+ RUNSTATE = U.objectFieldOffset
+ (k.getDeclaredField("runState"));
+ PARKBLOCKER = U.objectFieldOffset
+ (tk.getDeclaredField("parkBlocker"));
+ } catch (Exception e) {
+ throw new Error(e);
+ }
+ }
+
+ /**
+ * Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package.
+ * Replace with a simple call to Unsafe.getUnsafe when integrating
+ * into a jdk.
+ *
+ * @return a sun.misc.Unsafe
+ */
+ private static sun.misc.Unsafe getUnsafe() {
+ try {
+ return sun.misc.Unsafe.getUnsafe();
} catch (SecurityException se) {
try {
return java.security.AccessController.doPrivileged
- (new java.security.PrivilegedExceptionAction() {
- public Unsafe run() throws Exception {
- return getUnsafePrivileged();
+ (new java.security
+ .PrivilegedExceptionAction() {
+ public sun.misc.Unsafe run() throws Exception {
+ java.lang.reflect.Field f = sun.misc
+ .Unsafe.class.getDeclaredField("theUnsafe");
+ f.setAccessible(true);
+ return (sun.misc.Unsafe) f.get(null);
}});
} catch (java.security.PrivilegedActionException e) {
- throw e.getCause();
+ throw new RuntimeException("Could not initialize intrinsics",
+ e.getCause());
}
}
}
- private static Unsafe getUnsafePrivileged()
- throws NoSuchFieldException, IllegalAccessException {
- Field f = Unsafe.class.getDeclaredField("theUnsafe");
- f.setAccessible(true);
- return (Unsafe) f.get(null);
- }
-
- private static long fieldOffset(String fieldName)
- throws NoSuchFieldException {
- return UNSAFE.objectFieldOffset
- (ForkJoinPool.class.getDeclaredField(fieldName));
- }
-
- static final Unsafe UNSAFE;
- static final long eventCountOffset;
- static final long workerCountsOffset;
- static final long runControlOffset;
- static final long syncStackOffset;
- static final long spareStackOffset;
-
- static {
- try {
- UNSAFE = getUnsafe();
- eventCountOffset = fieldOffset("eventCount");
- workerCountsOffset = fieldOffset("workerCounts");
- runControlOffset = fieldOffset("runControl");
- syncStackOffset = fieldOffset("syncStack");
- spareStackOffset = fieldOffset("spareStack");
- } catch (Throwable e) {
- throw new RuntimeException("Could not initialize intrinsics", e);
- }
- }
-
- private boolean casEventCount(long cmp, long val) {
- return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
- }
- private boolean casWorkerCounts(int cmp, int val) {
- return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
- }
- private boolean casRunControl(int cmp, int val) {
- return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
- }
- private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
- return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
- }
- private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
- return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
- }
}