--- jsr166/src/jsr166y/ForkJoinPool.java 2009/07/26 17:33:37 1.27
+++ jsr166/src/jsr166y/ForkJoinPool.java 2011/03/04 13:29:39 1.95
@@ -6,63 +6,118 @@
package jsr166y;
-import java.util.concurrent.*;
-
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
-import java.util.concurrent.locks.Condition;
+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.TimeoutException;
+import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.LockSupport;
import java.util.concurrent.locks.ReentrantLock;
-import java.util.concurrent.atomic.AtomicInteger;
-import java.util.concurrent.atomic.AtomicLong;
+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 subtasks 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). 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 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
+ * NOT use these pool execution methods, but instead use the
+ * within-computation forms listed in the table.
+ *
+ *
+ *
+ * |
+ * 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.
+ *
+ *
+ * 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
@@ -70,28 +125,228 @@ import java.util.concurrent.atomic.Atomi
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 provides the central bookkeeping and control for a
+ * set of worker threads: Submissions from non-FJ threads enter
+ * into a submission queue. 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 worker queues, and
+ * lastly to new submissions.
+ *
+ * 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 a single 64bit volatile
+ * variable ("ctl"). This variable is read on the order of 10-100
+ * times as often as it is modified (always via CAS). (There is
+ * some additional control state, for example variable "shutdown"
+ * for which we can cope with uncoordinated updates.) This
+ * streamlines synchronization and control at the expense of messy
+ * constructions needed to repack status bits upon updates.
+ * Updates tend not to contend with each other except during
+ * bursts while submitted tasks begin or end. In some cases when
+ * they do contend, threads can instead do something else
+ * (usually, scan for tasks) until contention subsides.
+ *
+ * To enable 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.
+ *
+ * Recording Workers. Workers are recorded in the "workers" array
+ * that is created upon pool construction and expanded if (rarely)
+ * necessary. This is an array as opposed to some other data
+ * structure to support index-based random steals by workers.
+ * Updates to the array recording new workers and unrecording
+ * terminated ones are protected from each other by a seqLock
+ * (scanGuard) but the array is otherwise concurrently readable,
+ * and accessed directly by workers. To simplify index-based
+ * operations, the array size is always a power of two, and all
+ * readers must tolerate null slots. 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 scanGuard 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 workers are
+ * via indices into the workers array (which is one source of some
+ * of the messy code constructions here). In essence, the workers
+ * array serves as a weak reference mechanism. Thus for example
+ * the wait queue field of ctl stores worker indices, not worker
+ * references. Access to the workers 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 workers array, as well as queue arrays, check
+ * that the array 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.
+ *
+ * Wait 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. 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 to both wake up waiters (by advancing their
+ * count) and avoid ABA effects. Successors are held in worker
+ * field "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 both before (in scan()) and after
+ * (in tryAwaitWork()) 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 "parked" field of
+ * ForkJoinWorkerThread to reduce unnecessary calls to unpark.
+ * (Use of the parked field requires a secondary recheck to avoid
+ * missed signals.)
+ *
+ * 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 two or fewer 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
+ * as well as those performed when a worker steals a task and
+ * notices that there are more tasks too; together these cover the
+ * signals needed in cases when more than two tasks are pushed
+ * but untaken.
+ *
+ * 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.
+ *
+ * Submissions. External submissions are maintained in an
+ * array-based queue that is structured identically to
+ * ForkJoinWorkerThread queues except for the use of
+ * submissionLock in method addSubmission. Unlike the case for
+ * worker queues, multiple external threads can add new
+ * submissions, so adding requires a lock.
+ *
+ * Compensation. Beyond work-stealing support and lifecycle
+ * control, the main responsibility of this framework is to take
+ * actions 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. Method
+ * ForkJoinWorkerThread.joinTask tracks joining->stealing
+ * links to try to find such a task.
+ *
+ * Compensating: Unless there are already enough live threads,
+ * method tryPreBlock() may create or re-activate a spare
+ * thread to compensate for blocked joiners until they
+ * unblock.
+ *
+ * The ManagedBlocker extension API can't use helping so relies
+ * only on compensation in method awaitBlocker.
+ *
+ * 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 and require heuristic
+ * guidance, 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
+ * (retries are interspersed with Thread.yield, for good
+ * citizenship). The variable blockedCount, incremented before
+ * blocking and decremented after, is sometimes needed to
+ * distinguish cases of waiting for work vs blocking on joins or
+ * other managed sync. Both cases are equivalent for most pool
+ * control, so we can update non-atomically. (Additionally,
+ * contention on blockedCount alleviates some contention on ctl).
+ *
+ * Shutdown and Termination. A call to shutdownNow atomically sets
+ * the ctl stop bit and then (non-atomically) sets each workers
+ * "terminate" 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 quiesence (i.e., that
+ * there is no more work) which is reflected in active counts so
+ * long as there are no current blockers, as well as possible
+ * re-evaluations during independent changes in blocking or
+ * quiescing workers.
+ *
+ * Style notes: There is a lot of representation-level coupling
+ * among classes ForkJoinPool, ForkJoinWorkerThread, and
+ * ForkJoinTask. Most fields of ForkJoinWorkerThread maintain
+ * data structures managed by ForkJoinPool, so are directly
+ * accessed. Conversely we allow access to "workers" array by
+ * workers, and direct access to ForkJoinTask.status by both
+ * ForkJoinPool and ForkJoinWorkerThread. 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) declarations of
+ * 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) internal
+ * control methods (4) callbacks and other support for
+ * ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
+ * methods (plus a few little helpers). (6) 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);
}
@@ -100,14 +355,10 @@ public class ForkJoinPool extends Abstra
* 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);
}
}
@@ -116,15 +367,13 @@ 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
@@ -139,33 +388,59 @@ 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.
+ * Generator for initial random seeds for worker victim
+ * selection. This is used only to create initial seeds. Random
+ * steals use a cheaper xorshift generator per steal attempt. We
+ * don't expect much contention on seedGenerator, so just use a
+ * plain Random.
*/
- volatile ForkJoinWorkerThread[] workers;
+ static final Random workerSeedGenerator;
/**
- * Lock protecting access to workers.
+ * Array holding all worker threads in the pool. Initialized upon
+ * construction. Array size must be a power of two. Updates and
+ * replacements are protected by scanGuard, but the array is
+ * always kept in a consistent enough state to be randomly
+ * accessed without locking by workers performing work-stealing,
+ * as well as other traversal-based methods in this class, so long
+ * as reads memory-acquire by first reading ctl. All readers must
+ * tolerate that some array slots may be null.
*/
- private final ReentrantLock workerLock;
+ ForkJoinWorkerThread[] workers;
/**
- * Condition for awaitTermination.
+ * Initial size for submission queue array. Must be a power of
+ * two. In many applications, these always stay small so we use a
+ * small initial cap.
*/
- private final Condition termination;
+ private static final int INITIAL_QUEUE_CAPACITY = 8;
+
+ /**
+ * Maximum size for submission queue array. Must be a power of two
+ * less than or equal to 1 << (31 - width of array entry) to
+ * ensure lack of index wraparound, but is capped at a lower
+ * value to help users trap runaway computations.
+ */
+ private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 24; // 16M
/**
- * The uncaught exception handler used when any worker
- * abruptly terminates
+ * Array serving as submission queue. Initialized upon construction.
*/
- private Thread.UncaughtExceptionHandler ueh;
+ private ForkJoinTask[] submissionQueue;
+
+ /**
+ * Lock protecting submissions array for addSubmission
+ */
+ private final ReentrantLock submissionLock;
+
+ /**
+ * Condition for awaitTermination, using submissionLock for
+ * convenience.
+ */
+ private final Condition termination;
/**
* Creation factory for worker threads.
@@ -173,446 +448,1094 @@ public class ForkJoinPool extends Abstra
private final ForkJoinWorkerThreadFactory factory;
/**
- * Head of stack of threads that were created to maintain
- * parallelism when other threads blocked, but have since
- * suspended when the parallelism level rose.
+ * The uncaught exception handler used when any worker abruptly
+ * terminates.
*/
- private volatile WaitQueueNode spareStack;
+ final Thread.UncaughtExceptionHandler ueh;
/**
- * Sum of per-thread steal counts, updated only when threads are
- * idle or terminating.
+ * Prefix for assigning names to worker threads
*/
- private final AtomicLong stealCount;
+ private final String workerNamePrefix;
/**
- * Queue for external submissions.
+ * Sum of per-thread steal counts, updated only when threads are
+ * idle or terminating.
*/
- private final LinkedTransferQueue> submissionQueue;
+ private volatile long stealCount;
/**
- * Head of Treiber stack for barrier sync. See below for explanation.
+ * Main pool control -- a long packed with:
+ * AC: Number of active running workers minus target parallelism (16 bits)
+ * TC: Number of total workers minus target parallelism (16bits)
+ * ST: true if pool is terminating (1 bit)
+ * EC: the wait count of top waiting thread (15 bits)
+ * ID: ~poolIndex of top of Treiber stack of waiting threads (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.
*/
- private volatile WaitQueueNode syncStack;
+ volatile long ctl;
+
+ // 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 EC_UNIT = 1 << EC_SHIFT;
/**
- * The count for event barrier
+ * The target parallelism level.
*/
- private volatile long eventCount;
+ final int parallelism;
/**
- * Pool number, just for assigning useful names to worker threads
+ * Index (mod submission queue length) of next element to take
+ * from submission queue. Usage is identical to that for
+ * per-worker queues -- see ForkJoinWorkerThread internal
+ * documentation.
*/
- private final int poolNumber;
+ volatile int queueBase;
/**
- * The maximum allowed pool size
+ * Index (mod submission queue length) of next element to add
+ * in submission queue. Usage is identical to that for
+ * per-worker queues -- see ForkJoinWorkerThread internal
+ * documentation.
*/
- private volatile int maxPoolSize;
+ int queueTop;
/**
- * The desired parallelism level, updated only under workerLock.
+ * True when shutdown() has been called.
*/
- private volatile int parallelism;
+ volatile boolean shutdown;
/**
* True if use local fifo, not default lifo, for local polling
+ * Read by, and replicated by ForkJoinWorkerThreads
*/
- private volatile boolean locallyFifo;
+ final boolean locallyFifo;
/**
- * 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 assume that running active count
- * is in low word, so need to be modified if this changes.
+ * The number of threads in ForkJoinWorkerThreads.helpQuiescePool.
+ * When non-zero, suppresses automatic shutdown when active
+ * counts become zero.
*/
- private volatile int workerCounts;
+ volatile int quiescerCount;
- 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; }
+ /**
+ * The number of threads blocked in join.
+ */
+ volatile int blockedCount;
/**
- * 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
+ * Counter for worker Thread names (unrelated to their poolIndex)
*/
- final void updateRunningCount(int delta) {
- int s;
- do {} while (!casWorkerCounts(s = workerCounts, s + delta));
- }
+ private volatile int nextWorkerNumber;
/**
- * 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
+ * The index for the next created worker. Accessed under scanGuard.
*/
- 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));
- }
+ private int nextWorkerIndex;
/**
- * 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
+ * SeqLock and index masking for updates to workers array. Locked
+ * when SG_UNIT is set. Unlocking clears bit by adding
+ * SG_UNIT. Staleness of read-only operations can be checked by
+ * comparing scanGuard to value before the reads. The low 16 bits
+ * (i.e, anding with SMASK) hold (the smallest power of two
+ * covering all worker indices, minus one, and is used to avoid
+ * dealing with large numbers of null slots when the workers array
+ * is overallocated.
*/
- private volatile int runControl;
+ volatile int scanGuard;
- // 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 final int SG_UNIT = 1 << 16;
- 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; }
+ /**
+ * 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
/**
- * Tries incrementing active count; fails on contention.
- * Called by workers before/during executing tasks.
+ * Top-level loop for worker threads: On each step: if the
+ * previous step swept through all queues and found no tasks, or
+ * there are excess threads, then possibly blocks. Otherwise,
+ * scans for and, if found, executes a task. Returns when pool
+ * and/or worker terminate.
*
- * @return true on success
+ * @param w the worker
*/
- final boolean tryIncrementActiveCount() {
- int c = runControl;
- return casRunControl(c, c+1);
+ final void work(ForkJoinWorkerThread w) {
+ boolean swept = false; // true on empty scans
+ long c;
+ while (!w.terminate && (int)(c = ctl) >= 0) {
+ int a; // active count
+ if (!swept && (a = (int)(c >> AC_SHIFT)) <= 0)
+ swept = scan(w, a);
+ else if (tryAwaitWork(w, c))
+ swept = false;
+ }
}
+ // Signalling
+
/**
- * 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
+ * Wakes up or creates a worker.
*/
- final boolean tryDecrementActiveCount() {
- int c = runControl;
- int nextc = c - 1;
- if (!casRunControl(c, nextc))
- return false;
- if (canTerminateOnShutdown(nextc))
- terminateOnShutdown();
- 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) && e >= 0) {
+ if (e > 0) { // release a waiting worker
+ int i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
+ if ((ws = workers) == null ||
+ (i = ~e & SMASK) >= ws.length ||
+ (w = ws[i]) == null)
+ break;
+ long nc = (((long)(w.nextWait & E_MASK)) |
+ ((long)(u + UAC_UNIT) << 32));
+ if (w.eventCount == e &&
+ UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
+ w.eventCount = (e + EC_UNIT) & E_MASK;
+ if (w.parked)
+ UNSAFE.unpark(w);
+ break;
+ }
+ }
+ else if (UNSAFE.compareAndSwapLong
+ (this, ctlOffset, c,
+ (long)(((u + UTC_UNIT) & UTC_MASK) |
+ ((u + UAC_UNIT) & UAC_MASK)) << 32)) {
+ addWorker();
+ break;
+ }
+ }
}
/**
- * Returns true if argument represents zero active count and
- * nonzero runstate, which is the triggering condition for
- * terminating on shutdown.
+ * Variant of signalWork to help release waiters on rescans.
+ * Tries once to release a waiter if active count < 0.
+ *
+ * @return false if failed due to contention, else true
*/
- private static boolean canTerminateOnShutdown(int c) {
- // i.e. least bit is nonzero runState bit
- return ((c & -c) >>> 16) != 0;
+ private boolean tryReleaseWaiter() {
+ long c; int e, i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
+ if ((e = (int)(c = ctl)) > 0 &&
+ (int)(c >> AC_SHIFT) < 0 &&
+ (ws = workers) != null &&
+ (i = ~e & SMASK) < ws.length &&
+ (w = ws[i]) != null) {
+ long nc = ((long)(w.nextWait & E_MASK) |
+ ((c + AC_UNIT) & (AC_MASK|TC_MASK)));
+ if (w.eventCount != e ||
+ !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
+ return false;
+ w.eventCount = (e + EC_UNIT) & E_MASK;
+ if (w.parked)
+ UNSAFE.unpark(w);
+ }
+ return true;
}
+ // Scanning for tasks
+
/**
- * Transition run state to at least the given state. Return true
- * if not already at least given state.
+ * Scans for and, if found, executes one task. Scans start at a
+ * random index of workers array, and randomly select the first
+ * (2*#workers)-1 probes, and then, if all empty, resort to 2
+ * circular sweeps, which is necessary to check quiescence. and
+ * taking a submission only if no stealable tasks were found. The
+ * steal code inside the loop is a specialized form of
+ * ForkJoinWorkerThread.deqTask, followed bookkeeping to support
+ * helpJoinTask and signal propagation. The code for submission
+ * queues is almost identical. On each steal, the worker completes
+ * not only the task, but also all local tasks that this task may
+ * have generated. On detecting staleness or contention when
+ * trying to take a task, this method returns without finishing
+ * sweep, which allows global state rechecks before retry.
+ *
+ * @param w the worker
+ * @param a the number of active workers
+ * @return true if swept all queues without finding a task
*/
- private boolean transitionRunStateTo(int state) {
- for (;;) {
- int c = runControl;
- if (runStateOf(c) >= state)
+ private boolean scan(ForkJoinWorkerThread w, int a) {
+ int g = scanGuard; // mask 0 avoids useless scans if only one active
+ int m = parallelism == 1 - a? 0 : g & SMASK;
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws == null || ws.length <= m) // staleness check
+ return false;
+ for (int r = w.seed, k = r, j = -(m + m); j <= m + m; ++j) {
+ ForkJoinTask t; ForkJoinTask[] q; int b, i;
+ ForkJoinWorkerThread v = ws[k & m];
+ if (v != null && (b = v.queueBase) != v.queueTop &&
+ (q = v.queue) != null && (i = (q.length - 1) & b) >= 0) {
+ long u = (i << ASHIFT) + ABASE;
+ if ((t = q[i]) != null && v.queueBase == b &&
+ UNSAFE.compareAndSwapObject(q, u, t, null)) {
+ int d = (v.queueBase = b + 1) - v.queueTop;
+ v.stealHint = w.poolIndex;
+ if (d != 0)
+ signalWork(); // propagate if nonempty
+ w.execTask(t);
+ }
+ r ^= r << 13; r ^= r >>> 17; w.seed = r ^ (r << 5);
+ return false; // store next seed
+ }
+ else if (j < 0) { // xorshift
+ r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;
+ }
+ else
+ ++k;
+ }
+ if (scanGuard != g) // staleness check
+ return false;
+ else { // try to take submission
+ ForkJoinTask t; ForkJoinTask[] q; int b, i;
+ if ((b = queueBase) != queueTop &&
+ (q = submissionQueue) != null &&
+ (i = (q.length - 1) & b) >= 0) {
+ long u = (i << ASHIFT) + ABASE;
+ if ((t = q[i]) != null && queueBase == b &&
+ UNSAFE.compareAndSwapObject(q, u, t, null)) {
+ queueBase = b + 1;
+ w.execTask(t);
+ }
return false;
- if (casRunControl(c, runControlFor(state, activeCountOf(c))))
+ }
+ return true; // all queues empty
+ }
+ }
+
+ /**
+ * Tries to enqueue worker w in wait queue and await change in
+ * worker's eventCount. If the pool is quiescent, possibly
+ * terminates worker upon exit. Otherwise, before blocking,
+ * rescans queues to avoid missed signals. Upon finding work,
+ * releases at least one worker (which may be the current
+ * worker). Rescans restart upon detected staleness or failure to
+ * release due to contention. Note the unusual conventions about
+ * Thread.interrupt here and elsewhere: Because interrupts are
+ * used solely to alert threads to check termination, which is
+ * checked here anyway, 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.
+ *
+ * @param w the calling worker
+ * @param c the ctl value on entry
+ * @return true if waited or another thread was released upon enq
+ */
+ private boolean tryAwaitWork(ForkJoinWorkerThread w, long c) {
+ int v = w.eventCount;
+ w.nextWait = (int)c; // w's successor record
+ long nc = (long)(v & E_MASK) | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
+ if (ctl != c || !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
+ long d = ctl; // return true if lost to a deq, to force scan
+ return (int)d != (int)c && ((d - c) & AC_MASK) >= 0L;
+ }
+ for (int sc = w.stealCount; sc != 0;) { // accumulate stealCount
+ long s = stealCount;
+ if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s + sc))
+ sc = w.stealCount = 0;
+ else if (w.eventCount != v)
+ return true; // update next time
+ }
+ if (parallelism + (int)(nc >> AC_SHIFT) == 0 &&
+ blockedCount == 0 && quiescerCount == 0)
+ idleAwaitWork(w, nc, c, v); // quiescent
+ for (boolean rescanned = false;;) {
+ if (w.eventCount != v)
return true;
+ if (!rescanned) {
+ int g = scanGuard, m = g & SMASK;
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null && m < ws.length) {
+ rescanned = true;
+ for (int i = 0; i <= m; ++i) {
+ ForkJoinWorkerThread u = ws[i];
+ if (u != null) {
+ if (u.queueBase != u.queueTop &&
+ !tryReleaseWaiter())
+ rescanned = false; // contended
+ if (w.eventCount != v)
+ return true;
+ }
+ }
+ }
+ if (scanGuard != g || // stale
+ (queueBase != queueTop && !tryReleaseWaiter()))
+ rescanned = false;
+ if (!rescanned)
+ Thread.yield(); // reduce contention
+ else
+ Thread.interrupted(); // clear before park
+ }
+ else {
+ w.parked = true; // must recheck
+ if (w.eventCount != v) {
+ w.parked = false;
+ return true;
+ }
+ LockSupport.park(this);
+ rescanned = w.parked = false;
+ }
}
}
/**
- * Controls whether to add spares to maintain parallelism
- */
- private volatile boolean maintainsParallelism;
+ * If inactivating worker w has caused pool to become
+ * quiescent, check for pool termination, and wait for event
+ * for up to SHRINK_RATE nanosecs (rescans are unnecessary in
+ * this case because quiescence reflects consensus about lack
+ * of work). On timeout, if ctl has not changed, terminate the
+ * worker. Upon its termination (see deregisterWorker), it may
+ * wake up another worker to possibly repeat this process.
+ *
+ * @param w the calling worker
+ * @param currentCtl the ctl value after enqueuing w
+ * @param prevCtl the ctl value if w terminated
+ * @param v the eventCount w awaits change
+ */
+ private void idleAwaitWork(ForkJoinWorkerThread w, long currentCtl,
+ long prevCtl, int v) {
+ if (w.eventCount == v) {
+ if (shutdown)
+ tryTerminate(false);
+ ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs
+ while (ctl == currentCtl) {
+ long startTime = System.nanoTime();
+ w.parked = true;
+ if (w.eventCount == v) // must recheck
+ LockSupport.parkNanos(this, SHRINK_RATE);
+ w.parked = false;
+ if (w.eventCount != v)
+ break;
+ else if (System.nanoTime() - startTime < SHRINK_RATE)
+ Thread.interrupted(); // spurious wakeup
+ else if (UNSAFE.compareAndSwapLong(this, ctlOffset,
+ currentCtl, prevCtl)) {
+ w.terminate = true; // restore previous
+ w.eventCount = ((int)currentCtl + EC_UNIT) & E_MASK;
+ break;
+ }
+ }
+ }
+ }
- // Constructors
+ // Submissions
/**
- * Creates a ForkJoinPool with a pool size equal to the number of
- * processors available on the system, using the default
- * ForkJoinWorkerThreadFactory.
+ * Enqueues the given task in the submissionQueue. Same idea as
+ * ForkJoinWorkerThread.pushTask except for use of submissionLock.
*
- * @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")}
+ * @param t the task
*/
- public ForkJoinPool() {
- this(Runtime.getRuntime().availableProcessors(),
- defaultForkJoinWorkerThreadFactory);
+ private void addSubmission(ForkJoinTask t) {
+ final ReentrantLock lock = this.submissionLock;
+ lock.lock();
+ try {
+ ForkJoinTask[] q; int s, m;
+ if ((q = submissionQueue) != null) { // ignore if queue removed
+ long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE;
+ UNSAFE.putOrderedObject(q, u, t);
+ queueTop = s + 1;
+ if (s - queueBase == m)
+ growSubmissionQueue();
+ }
+ } finally {
+ lock.unlock();
+ }
+ signalWork();
}
+ // (pollSubmission is defined below with exported methods)
+
/**
- * 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")}
+ * Creates or doubles submissionQueue array.
+ * Basically identical to ForkJoinWorkerThread version.
*/
- public ForkJoinPool(int parallelism) {
- this(parallelism, defaultForkJoinWorkerThreadFactory);
+ private void growSubmissionQueue() {
+ ForkJoinTask[] oldQ = submissionQueue;
+ int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY;
+ if (size > MAXIMUM_QUEUE_CAPACITY)
+ throw new RejectedExecutionException("Queue capacity exceeded");
+ if (size < INITIAL_QUEUE_CAPACITY)
+ size = INITIAL_QUEUE_CAPACITY;
+ ForkJoinTask[] q = submissionQueue = new ForkJoinTask[size];
+ int mask = size - 1;
+ int top = queueTop;
+ int oldMask;
+ if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) {
+ for (int b = queueBase; b != top; ++b) {
+ long u = ((b & oldMask) << ASHIFT) + ABASE;
+ Object x = UNSAFE.getObjectVolatile(oldQ, u);
+ if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null))
+ UNSAFE.putObjectVolatile
+ (q, ((b & mask) << ASHIFT) + ABASE, x);
+ }
+ }
+ }
+
+ // Blocking support
+
+ /**
+ * Tries to increment blockedCount, 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
+ */
+ private boolean tryPreBlock() {
+ int b = blockedCount;
+ if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) {
+ int pc = parallelism;
+ do {
+ ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
+ int e, ac, tc, rc, i;
+ long c = ctl;
+ int u = (int)(c >>> 32);
+ if ((e = (int)c) < 0) {
+ // skip -- terminating
+ }
+ else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 &&
+ (ws = workers) != null &&
+ (i = ~e & SMASK) < ws.length &&
+ (w = ws[i]) != null) {
+ long nc = ((long)(w.nextWait & E_MASK) |
+ (c & (AC_MASK|TC_MASK)));
+ if (w.eventCount == e &&
+ UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
+ w.eventCount = (e + EC_UNIT) & E_MASK;
+ if (w.parked)
+ UNSAFE.unpark(w);
+ 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 (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
+ return true; // no compensation needed
+ }
+ else if (tc + pc < MAX_ID) {
+ long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
+ if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
+ addWorker();
+ return true; // create a replacement
+ }
+ }
+ // try to back out on any failure and let caller retry
+ } while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
+ b = blockedCount, b - 1));
+ }
+ return false;
}
/**
- * 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")}
+ * Decrements blockedCount and increments active count
*/
- public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
- this(Runtime.getRuntime().availableProcessors(), factory);
+ private void postBlock() {
+ long c;
+ do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, // no mask
+ c = ctl, c + AC_UNIT));
+ int b;
+ do {} while(!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
+ b = blockedCount, b - 1));
}
/**
- * Creates a ForkJoinPool with the given parallelism and factory.
+ * Possibly blocks waiting for the given task to complete, or
+ * cancels the task if terminating. Fails to wait if contended.
*
- * @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")}
+ * @param joinMe the task
*/
- 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
+ final void tryAwaitJoin(ForkJoinTask joinMe) {
+ int s;
+ Thread.interrupted(); // clear interrupts before checking termination
+ if (joinMe.status >= 0) {
+ if (tryPreBlock()) {
+ joinMe.tryAwaitDone(0L);
+ postBlock();
+ }
+ else if ((ctl & STOP_BIT) != 0L)
+ joinMe.cancelIgnoringExceptions();
+ }
}
/**
- * Creates a new worker thread using factory.
+ * Possibly blocks the given worker waiting for joinMe to
+ * complete or timeout
*
- * @param index the index to assign worker
- * @return new worker, or null of factory failed
+ * @param joinMe the task
+ * @param millis the wait time for underlying Object.wait
*/
- 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);
+ final void timedAwaitJoin(ForkJoinTask joinMe, long nanos) {
+ while (joinMe.status >= 0) {
+ Thread.interrupted();
+ if ((ctl & STOP_BIT) != 0L) {
+ joinMe.cancelIgnoringExceptions();
+ break;
+ }
+ if (tryPreBlock()) {
+ long last = System.nanoTime();
+ while (joinMe.status >= 0) {
+ long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
+ if (millis <= 0)
+ break;
+ joinMe.tryAwaitDone(millis);
+ if (joinMe.status < 0)
+ break;
+ if ((ctl & STOP_BIT) != 0L) {
+ joinMe.cancelIgnoringExceptions();
+ break;
+ }
+ long now = System.nanoTime();
+ nanos -= now - last;
+ last = now;
+ }
+ postBlock();
+ break;
+ }
}
- return w;
}
/**
- * Returns a good size for worker array given pool size.
- * Currently requires size to be a power of two.
+ * If necessary, compensates for blocker, and blocks
*/
- private static int arraySizeFor(int poolSize) {
- return (poolSize <= 1) ? 1 :
- (1 << (32 - Integer.numberOfLeadingZeros(poolSize-1)));
+ private void awaitBlocker(ManagedBlocker blocker)
+ throws InterruptedException {
+ while (!blocker.isReleasable()) {
+ if (tryPreBlock()) {
+ try {
+ do {} while (!blocker.isReleasable() && !blocker.block());
+ } finally {
+ postBlock();
+ }
+ break;
+ }
+ }
}
+ // Creating, registering and deregistring workers
+
/**
- * Creates or resizes array if necessary to hold newLength.
- * Call only under exclusion.
- *
- * @return the array
+ * Tries to create and start a worker; minimally rolls back counts
+ * on failure.
*/
- 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));
+ private void addWorker() {
+ Throwable ex = null;
+ ForkJoinWorkerThread t = null;
+ try {
+ t = factory.newThread(this);
+ } catch (Throwable e) {
+ ex = e;
+ }
+ if (t == null) { // null or exceptional factory return
+ long c; // adjust counts
+ do {} while (!UNSAFE.compareAndSwapLong
+ (this, ctlOffset, c = ctl,
+ (((c - AC_UNIT) & AC_MASK) |
+ ((c - TC_UNIT) & TC_MASK) |
+ (c & ~(AC_MASK|TC_MASK)))));
+ // Propagate exception if originating from an external caller
+ if (!tryTerminate(false) && ex != null &&
+ !(Thread.currentThread() instanceof ForkJoinWorkerThread))
+ UNSAFE.throwException(ex);
+ }
else
- return ws;
+ t.start();
}
/**
- * Tries to shrink workers into smaller array after one or more terminate.
+ * Callback from ForkJoinWorkerThread constructor to assign a
+ * public name
*/
- 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);
+ final String nextWorkerName() {
+ for (int n;;) {
+ if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset,
+ n = nextWorkerNumber, ++n))
+ return workerNamePrefix + n;
+ }
+ }
+
+ /**
+ * Callback from ForkJoinWorkerThread constructor to
+ * determine its poolIndex and record in workers array.
+ *
+ * @param w the worker
+ * @return the worker's pool index
+ */
+ final int registerWorker(ForkJoinWorkerThread w) {
+ /*
+ * In the typical case, a new worker acquires the lock, uses
+ * next available index and returns quickly. Since we should
+ * not block callers (ultimately from signalWork or
+ * tryPreBlock) waiting for the lock needed to do this, we
+ * instead help release other workers while waiting for the
+ * lock.
+ */
+ for (int g;;) {
+ ForkJoinWorkerThread[] ws;
+ if (((g = scanGuard) & SG_UNIT) == 0 &&
+ UNSAFE.compareAndSwapInt(this, scanGuardOffset,
+ g, g | SG_UNIT)) {
+ int k = nextWorkerIndex;
+ try {
+ if ((ws = workers) != null) { // ignore on shutdown
+ int n = ws.length;
+ if (k < 0 || k >= n || ws[k] != null) {
+ for (k = 0; k < n && ws[k] != null; ++k)
+ ;
+ if (k == n)
+ ws = workers = Arrays.copyOf(ws, n << 1);
+ }
+ ws[k] = w;
+ nextWorkerIndex = k + 1;
+ int m = g & SMASK;
+ g = k >= m? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1);
+ }
+ } finally {
+ scanGuard = g;
+ }
+ return k;
+ }
+ else if ((ws = workers) != null) { // help release others
+ for (ForkJoinWorkerThread u : ws) {
+ if (u != null && u.queueBase != u.queueTop) {
+ if (tryReleaseWaiter())
+ break;
+ }
+ }
+ }
}
}
/**
- * Initializes workers if necessary.
+ * Final callback from terminating worker. Removes record of
+ * worker from array, and adjusts counts. If pool is shutting
+ * down, tries to complete termination.
+ *
+ * @param w the worker
*/
- final void ensureWorkerInitialization() {
- ForkJoinWorkerThread[] ws = workers;
- if (ws == null) {
- final ReentrantLock lock = this.workerLock;
+ final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) {
+ int idx = w.poolIndex;
+ int sc = w.stealCount;
+ int steps = 0;
+ // Remove from array, adjust worker counts and collect steal count.
+ // We can intermix failed removes or adjusts with steal updates
+ do {
+ long s, c;
+ int g;
+ if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 &&
+ UNSAFE.compareAndSwapInt(this, scanGuardOffset,
+ g, g |= SG_UNIT)) {
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null && idx >= 0 &&
+ idx < ws.length && ws[idx] == w)
+ ws[idx] = null; // verify
+ nextWorkerIndex = idx;
+ scanGuard = g + SG_UNIT;
+ steps = 1;
+ }
+ if (steps == 1 &&
+ UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
+ (((c - AC_UNIT) & AC_MASK) |
+ ((c - TC_UNIT) & TC_MASK) |
+ (c & ~(AC_MASK|TC_MASK)))))
+ steps = 2;
+ if (sc != 0 &&
+ UNSAFE.compareAndSwapLong(this, stealCountOffset,
+ s = stealCount, s + sc))
+ sc = 0;
+ } while (steps != 2 || sc != 0);
+ if (!tryTerminate(false)) {
+ if (ex != null) // possibly replace if died abnormally
+ signalWork();
+ else
+ tryReleaseWaiter();
+ }
+ }
+
+ // Shutdown and termination
+
+ /**
+ * Possibly initiates and/or completes termination.
+ *
+ * @param now if true, unconditionally terminate, else only
+ * if shutdown and empty queue and no active workers
+ * @return true if now terminating or terminated
+ */
+ private boolean tryTerminate(boolean now) {
+ long c;
+ while (((c = ctl) & STOP_BIT) == 0) {
+ if (!now) {
+ if ((int)(c >> AC_SHIFT) != -parallelism)
+ return false;
+ if (!shutdown || blockedCount != 0 || quiescerCount != 0 ||
+ queueBase != queueTop) {
+ if (ctl == c) // staleness check
+ return false;
+ continue;
+ }
+ }
+ if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT))
+ startTerminating();
+ }
+ if ((short)(c >>> TC_SHIFT) == -parallelism) { // signal when 0 workers
+ final ReentrantLock lock = this.submissionLock;
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);
+ termination.signalAll();
+ } finally {
+ lock.unlock();
+ }
+ }
+ return true;
+ }
+
+ /**
+ * Runs up to three passes through workers: (0) Setting
+ * termination status for each worker, followed by wakeups up to
+ * queued workers; (1) helping cancel 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 startTerminating() {
+ cancelSubmissions();
+ for (int pass = 0; pass < 3; ++pass) {
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ for (ForkJoinWorkerThread w : ws) {
+ if (w != null) {
+ w.terminate = true;
+ if (pass > 0) {
+ w.cancelTasks();
+ if (pass > 1 && !w.isInterrupted()) {
+ try {
+ w.interrupt();
+ } catch (SecurityException ignore) {
+ }
+ }
}
}
}
- } finally {
- lock.unlock();
+ terminateWaiters();
}
}
}
/**
- * Worker creation and startup for threads added via setParallelism.
+ * Polls and cancels all submissions. Called only during termination.
*/
- 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 cancelSubmissions() {
+ while (queueBase != queueTop) {
+ ForkJoinTask task = pollSubmission();
+ if (task != null) {
+ try {
+ task.cancel(false);
+ } catch (Throwable ignore) {
}
- else {
- updateWorkerCount(-1); // back out on failed creation
- break;
+ }
+ }
+ }
+
+ /**
+ * Tries to set the termination status of waiting workers, and
+ * then wakes them up (after which they will terminate).
+ */
+ private void terminateWaiters() {
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ ForkJoinWorkerThread w; long c; int i, e;
+ int n = ws.length;
+ while ((i = ~(e = (int)(c = ctl)) & SMASK) < n &&
+ (w = ws[i]) != null && w.eventCount == (e & E_MASK)) {
+ if (UNSAFE.compareAndSwapLong(this, ctlOffset, c,
+ (long)(w.nextWait & E_MASK) |
+ ((c + AC_UNIT) & AC_MASK) |
+ (c & (TC_MASK|STOP_BIT)))) {
+ w.terminate = true;
+ w.eventCount = e + EC_UNIT;
+ if (w.parked)
+ UNSAFE.unpark(w);
}
}
}
}
- // Execution methods
+ // misc ForkJoinWorkerThread support
/**
- * Common code for execute, invoke and submit
+ * Increment or decrement quiescerCount. Needed only to prevent
+ * triggering shutdown if a worker is transiently inactive while
+ * checking quiescence.
+ *
+ * @param delta 1 for increment, -1 for decrement
*/
- private void doSubmit(ForkJoinTask task) {
- if (task == null)
+ final void addQuiescerCount(int delta) {
+ int c;
+ do {} while(!UNSAFE.compareAndSwapInt(this, quiescerCountOffset,
+ c = quiescerCount, c + delta));
+ }
+
+ /**
+ * Directly increment or decrement active count without
+ * queuing. This method is used to transiently assert inactivation
+ * while checking quiescence.
+ *
+ * @param delta 1 for increment, -1 for decrement
+ */
+ final void addActiveCount(int delta) {
+ long d = delta < 0 ? -AC_UNIT : AC_UNIT;
+ long c;
+ do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
+ ((c + d) & AC_MASK) |
+ (c & ~AC_MASK)));
+ }
+
+ /**
+ * Returns the approximate (non-atomic) number of idle threads per
+ * active thread.
+ */
+ 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);
+ }
+
+ // 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);
+ }
+
+ /**
+ * 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")}
+ */
+ public ForkJoinPool(int parallelism) {
+ this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
+ }
+
+ /**
+ * 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 (isShutdown())
- throw new RejectedExecutionException();
- if (workers == null)
- ensureWorkerInitialization();
- submissionQueue.offer(task);
- signalIdleWorkers();
+ if (parallelism <= 0 || parallelism > MAX_ID)
+ throw new IllegalArgumentException();
+ this.parallelism = parallelism;
+ this.factory = factory;
+ this.ueh = handler;
+ this.locallyFifo = asyncMode;
+ long np = (long)(-parallelism); // offset ctl counts
+ this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
+ this.submissionQueue = new ForkJoinTask[INITIAL_QUEUE_CAPACITY];
+ // initialize workers 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;
+ }
+ workers = new ForkJoinWorkerThread[n + 1];
+ this.submissionLock = new ReentrantLock();
+ this.termination = submissionLock.newCondition();
+ StringBuilder sb = new StringBuilder("ForkJoinPool-");
+ sb.append(poolNumberGenerator.incrementAndGet());
+ sb.append("-worker-");
+ this.workerNamePrefix = sb.toString();
}
+ // 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);
- return task.join();
+ Thread t = Thread.currentThread();
+ if (task == null)
+ throw new NullPointerException();
+ if (shutdown)
+ throw new RejectedExecutionException();
+ if ((t instanceof ForkJoinWorkerThread) &&
+ ((ForkJoinWorkerThread)t).pool == this)
+ return task.invoke(); // bypass submit if in same pool
+ else {
+ addSubmission(task);
+ return task.join();
+ }
+ }
+
+ /**
+ * Unless terminating, forks task if within an ongoing FJ
+ * computation in the current pool, else submits as external task.
+ */
+ private void forkOrSubmit(ForkJoinTask task) {
+ ForkJoinWorkerThread w;
+ Thread t = Thread.currentThread();
+ if (shutdown)
+ throw new RejectedExecutionException();
+ if ((t instanceof ForkJoinWorkerThread) &&
+ (w = (ForkJoinWorkerThread)t).pool == this)
+ w.pushTask(task);
+ else
+ addSubmission(task);
}
/**
* 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) {
- doSubmit(task);
+ public void execute(ForkJoinTask task) {
+ if (task == null)
+ throw new NullPointerException();
+ forkOrSubmit(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) {
+ if (task == null)
+ throw new NullPointerException();
ForkJoinTask job;
if (task instanceof ForkJoinTask) // avoid re-wrap
job = (ForkJoinTask) task;
else
- job = new AdaptedRunnable(task, null);
- doSubmit(job);
- }
-
- public ForkJoinTask submit(Callable task) {
- ForkJoinTask job = new AdaptedCallable(task);
- doSubmit(job);
- return job;
- }
-
- public ForkJoinTask submit(Runnable task, T result) {
- ForkJoinTask job = new AdaptedRunnable(task, result);
- doSubmit(job);
- return job;
- }
-
- public ForkJoinTask submit(Runnable task) {
- ForkJoinTask job;
- if (task instanceof ForkJoinTask) // avoid re-wrap
- job = (ForkJoinTask) task;
- else
- job = new AdaptedRunnable(task, null);
- doSubmit(job);
- return job;
+ job = ForkJoinTask.adapt(task, null);
+ forkOrSubmit(job);
}
/**
@@ -620,78 +1543,73 @@ public class ForkJoinPool extends Abstra
*
* @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
- * @throws NullPointerException if the task is null
*/
public ForkJoinTask submit(ForkJoinTask task) {
- doSubmit(task);
+ if (task == null)
+ throw new NullPointerException();
+ forkOrSubmit(task);
return task;
}
/**
- * Adaptor for Runnables. This implements RunnableFuture
- * to be compliant with AbstractExecutorService constraints.
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
+ public ForkJoinTask submit(Callable task) {
+ if (task == null)
+ throw new NullPointerException();
+ ForkJoinTask job = ForkJoinTask.adapt(task);
+ forkOrSubmit(job);
+ return job;
+ }
+
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
*/
- 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(); }
- private static final long serialVersionUID = 5232453952276885070L;
+ public ForkJoinTask submit(Runnable task, T result) {
+ if (task == null)
+ throw new NullPointerException();
+ ForkJoinTask job = ForkJoinTask.adapt(task, result);
+ forkOrSubmit(job);
+ return job;
}
/**
- * 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(); }
- private static final long serialVersionUID = 2838392045355241008L;
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
+ public ForkJoinTask submit(Runnable task) {
+ if (task == null)
+ throw new NullPointerException();
+ ForkJoinTask job;
+ if (task instanceof ForkJoinTask) // avoid re-wrap
+ job = (ForkJoinTask) task;
+ else
+ job = ForkJoinTask.adapt(task, null);
+ forkOrSubmit(job);
+ return job;
}
+ /**
+ * @throws NullPointerException {@inheritDoc}
+ * @throws RejectedExecutionException {@inheritDoc}
+ */
public List> invokeAll(Collection> tasks) {
ArrayList> forkJoinTasks =
new ArrayList>(tasks.size());
for (Callable task : tasks)
- forkJoinTasks.add(new AdaptedCallable(task));
+ forkJoinTasks.add(ForkJoinTask.adapt(task));
invoke(new InvokeAll(forkJoinTasks));
@SuppressWarnings({"unchecked", "rawtypes"})
- List> futures = (List>) (List) forkJoinTasks;
+ List> futures = (List>) (List) forkJoinTasks;
return futures;
}
@@ -705,8 +1623,6 @@ public class ForkJoinPool extends Abstra
private static final long serialVersionUID = -7914297376763021607L;
}
- // Configuration and status settings and queries
-
/**
* Returns the factory used for constructing new workers.
*
@@ -720,93 +1636,16 @@ 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
+ * @return the handler, or {@code 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;
+ return ueh;
}
/**
- * 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.
+ * Returns the targeted parallelism level of this pool.
*
- * @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")}
- */
- 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();
- }
-
- /**
- * Returns the targeted number of worker threads in 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;
@@ -814,96 +1653,21 @@ 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);
- }
-
- /**
- * 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;
+ return parallelism + (short)(ctl >>> TC_SHIFT);
}
/**
- * 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;
@@ -912,12 +1676,14 @@ public class ForkJoinPool extends Abstra
/**
* 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 r = parallelism + (int)(ctl >> AC_SHIFT);
+ return r <= 0? 0 : r; // suppress momentarily negative values
}
/**
@@ -928,34 +1694,23 @@ public class ForkJoinPool extends Abstra
* @return the number of active threads
*/
public int getActiveThreadCount() {
- return activeCountOf(runControl);
+ int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount;
+ return r <= 0? 0 : r; // suppress momentarily negative values
}
/**
- * 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;
- }
-
- /**
- * 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.
+ * 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 true if all threads are currently idle
+ * @return {@code true} if all threads are currently idle
*/
public boolean isQuiescent() {
- return activeCountOf(runControl) == 0;
+ return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 0;
}
/**
@@ -970,17 +1725,7 @@ public class ForkJoinPool extends Abstra
* @return the number of steals
*/
public long getStealCount() {
- return stealCount.get();
- }
-
- /**
- * Accumulates 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);
+ return stealCount;
}
/**
@@ -995,36 +1740,35 @@ public class ForkJoinPool extends Abstra
*/
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();
- }
+ ForkJoinWorkerThread[] ws;
+ if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
+ (ws = workers) != null) {
+ for (ForkJoinWorkerThread w : ws)
+ if (w != null)
+ count -= w.queueBase - w.queueTop; // must read base first
}
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();
+ return -queueBase + queueTop;
}
/**
- * 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();
+ return queueBase != queueTop;
}
/**
@@ -1032,18 +1776,30 @@ public class ForkJoinPool extends Abstra
* 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();
+ ForkJoinTask t; ForkJoinTask[] q; int b, i;
+ while ((b = queueBase) != queueTop &&
+ (q = submissionQueue) != null &&
+ (i = (q.length - 1) & b) >= 0) {
+ long u = (i << ASHIFT) + ABASE;
+ if ((t = q[i]) != null &&
+ queueBase == b &&
+ UNSAFE.compareAndSwapObject(q, u, t, null)) {
+ queueBase = b + 1;
+ 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
@@ -1055,17 +1811,23 @@ public class ForkJoinPool extends Abstra
* @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;
+ while (queueBase != queueTop) {
+ ForkJoinTask t = pollSubmission();
+ if (t != null) {
+ c.add(t);
+ ++count;
}
}
- return n;
+ ForkJoinWorkerThread[] ws;
+ if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
+ (ws = workers) != null) {
+ for (ForkJoinWorkerThread w : ws)
+ if (w != null)
+ count += w.drainTasksTo(c);
+ }
+ return count;
}
/**
@@ -1076,36 +1838,33 @@ 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 pc = parallelism;
+ long c = ctl;
+ int tc = pc + (short)(c >>> TC_SHIFT);
+ int rc = pc + (int)(c >> AC_SHIFT);
+ if (rc < 0) // ignore transient negative
+ rc = 0;
+ int ac = rc + blockedCount;
+ String level;
+ if ((c & STOP_BIT) != 0)
+ level = (tc == 0)? "Terminated" : "Terminating";
+ else
+ level = shutdown? "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.
@@ -1120,20 +1879,19 @@ public class ForkJoinPool extends Abstra
*/
public void shutdown() {
checkPermission();
- transitionRunStateTo(SHUTDOWN);
- if (canTerminateOnShutdown(runControl))
- terminateOnShutdown();
+ shutdown = true;
+ 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
@@ -1143,7 +1901,8 @@ public class ForkJoinPool extends Abstra
*/
public List shutdownNow() {
checkPermission();
- terminate();
+ shutdown = true;
+ tryTerminate(true);
return Collections.emptyList();
}
@@ -1153,17 +1912,35 @@ 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);
+ }
+
+ /**
+ * Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
+ */
+ final boolean isAtLeastTerminating() {
+ return (ctl & STOP_BIT) != 0L;
}
/**
@@ -1172,7 +1949,7 @@ public class ForkJoinPool extends Abstra
* @return {@code true} if this pool has been shut down
*/
public boolean isShutdown() {
- return runStateOf(runControl) >= SHUTDOWN;
+ return shutdown;
}
/**
@@ -1189,7 +1966,7 @@ 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.submissionLock;
lock.lock();
try {
for (;;) {
@@ -1204,580 +1981,23 @@ public class ForkJoinPool extends Abstra
}
}
- // Shutdown and termination support
-
- /**
- * Callback from terminating worker. Nulls out the corresponding
- * workers slot, and if terminating, tries to terminate; else
- * tries 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();
- }
-
- /**
- * Initiates 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
- *
- * 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.
- *
- * 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 {@code isReleasable}
- * before actually blocking.).
+ * in {@link ForkJoinPool}s.
+ *
+ * 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.
*
*
For example, here is a ManagedBlocker based on a
* ReentrantLock:
@@ -1795,126 +2015,131 @@ public class ForkJoinPool extends Abstra
* 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)
*/
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 it activates
- * a thread only if necessary to avoid complete starvation. This
- * option may be preferable when blockages use timeouts, or are
- * almost always brief.
+ * 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 ForkJoinTask, this method is behaviorally
- * equivalent to
+ *
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 ForkJoinTask, then the pool may first
- * be expanded to ensure parallelism, and later adjusted.
+ *
+ * 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);
- }
+ if (t instanceof ForkJoinWorkerThread) {
+ ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
+ w.pool.awaitBlocker(blocker);
+ }
+ else {
+ do {} while (!blocker.isReleasable() && !blocker.block());
}
}
- 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 UNSAFE = getUnsafe();
- private static final long eventCountOffset =
- objectFieldOffset("eventCount", ForkJoinPool.class);
- private static final long workerCountsOffset =
- objectFieldOffset("workerCounts", ForkJoinPool.class);
- private static final long runControlOffset =
- objectFieldOffset("runControl", ForkJoinPool.class);
- private static final long syncStackOffset =
- objectFieldOffset("syncStack",ForkJoinPool.class);
- private static final long spareStackOffset =
- objectFieldOffset("spareStack", ForkJoinPool.class);
-
- 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);
- }
-
- private static long objectFieldOffset(String field, Class klazz) {
+ private static final sun.misc.Unsafe UNSAFE;
+ private static final long ctlOffset;
+ private static final long stealCountOffset;
+ private static final long blockedCountOffset;
+ private static final long quiescerCountOffset;
+ private static final long scanGuardOffset;
+ private static final long nextWorkerNumberOffset;
+ private static final long ABASE;
+ private static final int ASHIFT;
+
+ static {
+ poolNumberGenerator = new AtomicInteger();
+ workerSeedGenerator = new Random();
+ modifyThreadPermission = new RuntimePermission("modifyThread");
+ defaultForkJoinWorkerThreadFactory =
+ new DefaultForkJoinWorkerThreadFactory();
+ int s;
try {
- return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
- } catch (NoSuchFieldException e) {
- // Convert Exception to corresponding Error
- NoSuchFieldError error = new NoSuchFieldError(field);
- error.initCause(e);
- throw error;
- }
+ UNSAFE = getUnsafe();
+ Class k = ForkJoinPool.class;
+ ctlOffset = UNSAFE.objectFieldOffset
+ (k.getDeclaredField("ctl"));
+ stealCountOffset = UNSAFE.objectFieldOffset
+ (k.getDeclaredField("stealCount"));
+ blockedCountOffset = UNSAFE.objectFieldOffset
+ (k.getDeclaredField("blockedCount"));
+ quiescerCountOffset = UNSAFE.objectFieldOffset
+ (k.getDeclaredField("quiescerCount"));
+ scanGuardOffset = UNSAFE.objectFieldOffset
+ (k.getDeclaredField("scanGuard"));
+ nextWorkerNumberOffset = UNSAFE.objectFieldOffset
+ (k.getDeclaredField("nextWorkerNumber"));
+ Class a = ForkJoinTask[].class;
+ ABASE = UNSAFE.arrayBaseOffset(a);
+ s = UNSAFE.arrayIndexScale(a);
+ } 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);
}
/**