--- jsr166/src/jsr166y/ForkJoinPool.java 2009/08/03 00:53:15 1.40
+++ jsr166/src/jsr166y/ForkJoinPool.java 2010/04/05 15:52:26 1.53
@@ -13,45 +13,50 @@ 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.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.CountDownLatch;
/**
* An {@link ExecutorService} for running {@link ForkJoinTask}s.
* A {@code ForkJoinPool} provides the entry point for submissions
* from non-{@code ForkJoinTask}s, as well as management and
- * monitoring operations. Normally a single {@code 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.
+ * monitoring operations.
*
- * {@code ForkJoinPool}s differ from other kinds of {@link
- * Executor}s 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
- * {@code ForkJoinTask}s), as well as the mixed execution of some
- * plain {@code Runnable}- or {@code Callable}- based activities along
- * with {@code ForkJoinTask}s. When setting {@linkplain #setAsyncMode
- * async mode}, a {@code ForkJoinPool} may also be appropriate for use
- * with fine-grained tasks that are never joined. Otherwise, other
- * {@code 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). A {@code ForkJoinPool} may also be used for mixed
+ * execution of some plain {@code Runnable}- or {@code Callable}-
+ * based activities along with {@code ForkJoinTask}s. When setting
+ * {@linkplain #setAsyncMode async mode}, a {@code ForkJoinPool} may
+ * also be appropriate for use with fine-grained tasks of any form
+ * that are never joined. Otherwise, other {@code ExecutorService}
+ * implementations are typically more appropriate choices.
*
- *
A {@code 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
+ *
A {@code ForkJoinPool} is constructed with a given target
+ * parallelism level; by default, equal to the number of available
+ * processors. Unless configured otherwise via {@link
+ * #setMaintainsParallelism}, the pool attempts to maintain this
+ * number of 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 performed in the face of blocked IO or other unmanaged
* synchronization. The nested {@link ManagedBlocker} interface
* enables extension of the kinds of synchronization accommodated.
* The target parallelism level may also be changed dynamically
- * ({@link #setParallelism}) and thread construction can be limited
- * using methods {@link #setMaximumPoolSize} and/or {@link
- * #setMaintainsParallelism}.
+ * ({@link #setParallelism}). The total number of threads may be
+ * limited using method {@link #setMaximumPoolSize}, in which case it
+ * may become possible for the activities of a pool to stall due to
+ * the lack of available threads to process new tasks. When the pool
+ * is executing tasks, these and other configuration setting methods
+ * may only gradually affect actual pool sizes. It is normally best
+ * practice to invoke these methods only when the pool is known to be
+ * quiescent.
*
*
In addition to execution and lifecycle control methods, this
* class provides status check methods (for example
@@ -60,27 +65,266 @@ import java.util.concurrent.atomic.Atomi
* {@link #toString} returns indications of pool state in a
* convenient form for informal monitoring.
*
+ *
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
+ * 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.
+ *
* @since 1.7
* @author Doug Lea
*/
public class ForkJoinPool extends AbstractExecutorService {
/*
- * See the extended comments interspersed below for design,
- * rationale, and walkthroughs.
+ * 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.
+ * The main work-stealing mechanics implemented in class
+ * ForkJoinWorkerThread 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. These mechanics do not consider
+ * affinities, loads, cache localities, etc, so rarely provide the
+ * best possible performance on a given machine, but portably
+ * provide good throughput by averaging over these factors.
+ * (Further, even if we did try to use such information, we do not
+ * usually have a basis for exploiting it. For example, some sets
+ * of tasks profit from cache affinities, but others are harmed by
+ * cache pollution effects.)
+ *
+ * The main throughput advantages of work-stealing stem from
+ * decentralized control -- workers mostly steal tasks from each
+ * other. We do not want to negate this by creating bottlenecks
+ * implementing the management responsibilities of this class. So
+ * we use a collection of techniques that avoid, reduce, or cope
+ * well with contention. These entail several instances of
+ * bit-packing into CASable fields to maintain only the minimally
+ * required atomicity. To enable such packing, we restrict maximum
+ * parallelism to (1<<15)-1 (enabling twice this to fit into a 16
+ * bit field), which is far in excess of normal operating range.
+ * Even though updates to some of these bookkeeping fields do
+ * sometimes contend with each other, they don't normally
+ * cache-contend with updates to others enough to warrant memory
+ * padding or isolation. So they are all held as fields of
+ * ForkJoinPool objects. The main capabilities are as follows:
+ *
+ * 1. Creating and removing workers. Workers are recorded in the
+ * "workers" array. 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 lock
+ * (workerLock) 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. Currently, all but the first
+ * 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.
+ *
+ * 2. Bookkeeping for dynamically adding and removing workers. We
+ * maintain a given level of parallelism (or, if
+ * maintainsParallelism is false, at least avoid starvation). When
+ * some workers are known to be blocked (on joins or via
+ * ManagedBlocker), we may create or resume others to take their
+ * place until they unblock (see below). Implementing this
+ * requires counts of the number of "running" threads (i.e., those
+ * that are neither blocked nor artifically suspended) as well as
+ * the total number. These two values are packed into one field,
+ * "workerCounts" because we need accurate snapshots when deciding
+ * to create, resume or suspend. To support these decisions,
+ * updates must be prospective (not retrospective). For example,
+ * the running count is decremented before blocking by a thread
+ * about to block, but incremented by the thread about to unblock
+ * it. (In a few cases, these prospective updates may need to be
+ * rolled back, for example when deciding to create a new worker
+ * but the thread factory fails or returns null. In these cases,
+ * we are no worse off wrt other decisions than we would be
+ * otherwise.) Updates to the workerCounts field sometimes
+ * transiently encounter a fair amount of contention when join
+ * dependencies are such that many threads block or unblock at
+ * about the same time. We alleviate this by sometimes bundling
+ * updates (for example blocking one thread on join and resuming a
+ * spare cancel each other out), and in most other cases
+ * performing an alternative action (like releasing waiters and
+ * finding spares; see below) as a more productive form of
+ * backoff.
+ *
+ * 3. Maintaining global run state. The run state of the pool
+ * consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
+ * those in other Executor implementations, as well as a count of
+ * "active" workers -- those that are, or soon will be, or
+ * recently were executing tasks. The runLevel and active count
+ * are packed together in order to correctly trigger shutdown and
+ * termination. Without care, active counts can be subject to very
+ * high contention. We substantially reduce this contention by
+ * relaxing update rules. A worker must claim active status
+ * prospectively, by activating if it sees that a submitted or
+ * stealable task exists (it may find after activating that the
+ * task no longer exists). It stays active while processing this
+ * task (if it exists) and any other local subtasks it produces,
+ * until it cannot find any other tasks. It then tries
+ * inactivating (see method preStep), but upon update contention
+ * instead scans for more tasks, later retrying inactivation if it
+ * doesn't find any.
+ *
+ * 4. Managing idle workers waiting for tasks. We cannot let
+ * workers spin indefinitely scanning for tasks when none are
+ * available. On the other hand, we must quickly prod them into
+ * action when new tasks are submitted or generated. We
+ * park/unpark these idle workers using an event-count scheme.
+ * Field eventCount is incremented upon events that may enable
+ * workers that previously could not find a task to now find one:
+ * Submission of a new task to the pool, or another worker pushing
+ * a task onto a previously empty queue. (We also use this
+ * mechanism for termination and reconfiguration actions that
+ * require wakeups of idle workers). Each worker maintains its
+ * last known event count, and blocks when a scan for work did not
+ * find a task AND its lastEventCount matches the current
+ * eventCount. Waiting idle workers are recorded in a variant of
+ * Treiber stack headed by field eventWaiters which, when nonzero,
+ * encodes the thread index and count awaited for by the worker
+ * thread most recently calling eventSync. This thread in turn has
+ * a record (field nextEventWaiter) for the next waiting worker.
+ * In addition to allowing simpler decisions about need for
+ * wakeup, the event count bits in eventWaiters serve the role of
+ * tags to avoid ABA errors in Treiber stacks. To reduce delays
+ * in task diffusion, workers not otherwise occupied may invoke
+ * method releaseWaiters, that removes and signals (unparks)
+ * workers not waiting on current count. To minimize task
+ * production stalls associate with signalling, any worker pushing
+ * a task on an empty queue invokes the weaker method signalWork,
+ * that only releases idle workers until it detects interference
+ * by other threads trying to release, and lets them take
+ * over. The net effect is a tree-like diffusion of signals, where
+ * released threads and possibly others) help with unparks. To
+ * further reduce contention effects a bit, failed CASes to
+ * increment field eventCount are tolerated without retries.
+ * Conceptually they are merged into the same event, which is OK
+ * when their only purpose is to enable workers to scan for work.
+ *
+ * 5. Managing suspension of extra workers. When a worker is about
+ * to block waiting for a join (or via ManagedBlockers), we may
+ * create a new thread to maintain parallelism level, or at least
+ * avoid starvation (see below). Usually, extra threads are needed
+ * for only very short periods, yet join dependencies are such
+ * that we sometimes need them in bursts. Rather than create new
+ * threads each time this happens, we suspend no-longer-needed
+ * extra ones as "spares". For most purposes, we don't distinguish
+ * "extra" spare threads from normal "core" threads: On each call
+ * to preStep (the only point at which we can do this) a worker
+ * checks to see if there are now too many running workers, and if
+ * so, suspends itself. Methods preJoin and doBlock look for
+ * suspended threads to resume before considering creating a new
+ * replacement. We don't need a special data structure to maintain
+ * spares; simply scanning the workers array looking for
+ * worker.isSuspended() is fine because the calling thread is
+ * otherwise not doing anything useful anyway; we are at least as
+ * happy if after locating a spare, the caller doesn't actually
+ * block because the join is ready before we try to adjust and
+ * compensate. Note that this is intrinsically racy. One thread
+ * may become a spare at about the same time as another is
+ * needlessly being created. We counteract this and related slop
+ * in part by requiring resumed spares to immediately recheck (in
+ * preStep) to see whether they they should re-suspend. The only
+ * effective difference between "extra" and "core" threads is that
+ * we allow the "extra" ones to time out and die if they are not
+ * resumed within a keep-alive interval of a few seconds. This is
+ * implemented mainly within ForkJoinWorkerThread, but requires
+ * some coordination (isTrimmed() -- meaning killed while
+ * suspended) to correctly maintain pool counts.
+ *
+ * 6. Deciding when to create new workers. The main dynamic
+ * control in this class is deciding when to create extra threads,
+ * in methods preJoin and doBlock. We always need to create one
+ * when the number of running threads becomes zero. But because
+ * blocked joins are typically dependent, we don't necessarily
+ * need or want one-to-one replacement. Using a one-to-one
+ * compensation rule often leads to enough useless overhead
+ * creating, suspending, resuming, and/or killing threads to
+ * signficantly degrade throughput. We use a rule reflecting the
+ * idea that, the more spare threads you already have, the more
+ * evidence you need to create another one; where "evidence" is
+ * expressed as the current deficit -- target minus running
+ * threads. To reduce flickering and drift around target values,
+ * the relation is quadratic: adding a spare if (dc*dc)>=(sc*pc)
+ * (where dc is deficit, sc is number of spare threads and pc is
+ * target parallelism.) This effectively reduces churn at the
+ * price of systematically undershooting target parallelism when
+ * many threads are blocked. However, biasing toward undeshooting
+ * partially compensates for the above mechanics to suspend extra
+ * threads, that normally lead to overshoot because we can only
+ * suspend workers in-between top-level actions. It also better
+ * copes with the fact that some of the methods in this class tend
+ * to never become compiled (but are interpreted), so some
+ * components of the entire set of controls might execute many
+ * times faster than others. And similarly for cases where the
+ * apparent lack of work is just due to GC stalls and other
+ * transient system activity.
+ *
+ * 7. Maintaining other configuration parameters and monitoring
+ * statistics. Updates to fields controlling parallelism level,
+ * max size, etc can only meaningfully take effect for individual
+ * threads upon their next top-level actions; i.e., between
+ * stealing/running tasks/submission, which are separated by calls
+ * to preStep. Memory ordering for these (assumed infrequent)
+ * reconfiguration calls is ensured by using reads and writes to
+ * volatile field workerCounts (that must be read in preStep anyway)
+ * as "fences" -- user-level reads are preceded by reads of
+ * workCounts, and writes are followed by no-op CAS to
+ * workerCounts. The values reported by other management and
+ * monitoring methods are either computed on demand, or are kept
+ * in fields that are only updated when threads are otherwise
+ * idle.
+ *
+ * Beware that there is a lot of representation-level coupling
+ * among classes ForkJoinPool, ForkJoinWorkerThread, and
+ * ForkJoinTask. For example, direct 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.
+ *
+ * Style notes: There are lots of inline assignments (of form
+ * "while ((local = field) != 0)") which are usually the simplest
+ * way to ensure read orderings. Also 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 a few
+ * other coding oddities that help some methods perform reasonably
+ * even when interpreted (not compiled).
+ *
+ * The order of declarations in this file is: (1) statics (2)
+ * fields (along with constants used when unpacking some of them)
+ * (3) internal control methods (4) callbacks and other support
+ * for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
+ * methods (plus a few little helpers).
*/
- /** 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 {@link ForkJoinWorkerThread}s.
* A {@code ForkJoinWorkerThreadFactory} must be defined and used
@@ -92,7 +336,7 @@ public class ForkJoinPool extends Abstra
* 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);
}
@@ -104,11 +348,7 @@ public class ForkJoinPool extends Abstra
static class DefaultForkJoinWorkerThreadFactory
implements ForkJoinWorkerThreadFactory {
public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
- try {
- return new ForkJoinWorkerThread(pool);
- } catch (OutOfMemoryError oom) {
- return null;
- }
+ return new ForkJoinWorkerThread(pool);
}
}
@@ -144,29 +384,36 @@ public class ForkJoinPool extends Abstra
new AtomicInteger();
/**
- * 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.
+ * Absolute bound for parallelism level. Twice this number must
+ * fit into a 16bit field to enable word-packing for some counts.
+ */
+ private static final int MAX_THREADS = 0x7fff;
+
+ /**
+ * Array holding all worker threads in the pool. Array size must
+ * be a power of two. Updates and replacements are protected by
+ * workerLock, 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. All readers must tolerate that some
+ * array slots may be null.
*/
volatile ForkJoinWorkerThread[] workers;
/**
- * Lock protecting access to workers.
+ * Queue for external submissions.
*/
- private final ReentrantLock workerLock;
+ private final LinkedTransferQueue> submissionQueue;
/**
- * Condition for awaitTermination.
+ * Lock protecting updates to workers array.
*/
- private final Condition termination;
+ private final ReentrantLock workerLock;
/**
- * The uncaught exception handler used when any worker
- * abruptly terminates
+ * Latch released upon termination.
*/
- private Thread.UncaughtExceptionHandler ueh;
+ private final CountDownLatch terminationLatch;
/**
* Creation factory for worker threads.
@@ -174,178 +421,675 @@ 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.
+ * Sum of per-thread steal counts, updated only when threads are
+ * idle or terminating.
*/
- private volatile WaitQueueNode spareStack;
+ private volatile long stealCount;
/**
- * Sum of per-thread steal counts, updated only when threads are
- * idle or terminating.
+ * Encoded record of top of treiber stack of threads waiting for
+ * events. The top 32 bits contain the count being waited for. The
+ * bottom word contains one plus the pool index of waiting worker
+ * thread.
*/
- private final AtomicLong stealCount;
+ private volatile long eventWaiters;
+
+ private static final int EVENT_COUNT_SHIFT = 32;
+ private static final long WAITER_INDEX_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
/**
- * Queue for external submissions.
+ * A counter for events that may wake up worker threads:
+ * - Submission of a new task to the pool
+ * - A worker pushing a task on an empty queue
+ * - termination and reconfiguration
*/
- private final LinkedTransferQueue> submissionQueue;
+ private volatile int eventCount;
/**
- * Head of Treiber stack for barrier sync. See below for explanation.
+ * Lifecycle control. The 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. Bits 16-18
+ * contain runLevel value. When all are zero, the pool is
+ * running. Level transitions are monotonic (running -> shutdown
+ * -> terminating -> terminated) so each transition adds a bit.
+ * These are bundled together to ensure consistent read for
+ * termination checks (i.e., that runLevel is at least SHUTDOWN
+ * and active threads is zero).
+ */
+ private volatile int runState;
+
+ // Note: The order among run level values matters.
+ private static final int RUNLEVEL_SHIFT = 16;
+ private static final int SHUTDOWN = 1 << RUNLEVEL_SHIFT;
+ private static final int TERMINATING = 1 << (RUNLEVEL_SHIFT + 1);
+ private static final int TERMINATED = 1 << (RUNLEVEL_SHIFT + 2);
+ private static final int ACTIVE_COUNT_MASK = (1 << RUNLEVEL_SHIFT) - 1;
+ private static final int ONE_ACTIVE = 1; // active update delta
+
+ /**
+ * 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 together to ensure consistent snapshot when
+ * making decisions about creating and suspending spare
+ * threads. Updated only by CAS. Note that adding a new worker
+ * requires incrementing both counts, since workers start off in
+ * running state. This field is also used for memory-fencing
+ * configuration parameters.
+ */
+ private volatile int workerCounts;
+
+ private static final int TOTAL_COUNT_SHIFT = 16;
+ private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1;
+ private static final int ONE_RUNNING = 1;
+ private static final int ONE_TOTAL = 1 << TOTAL_COUNT_SHIFT;
+
+ /*
+ * Fields parallelism. maxPoolSize, locallyFifo,
+ * maintainsParallelism, and ueh are non-volatile, but external
+ * reads/writes use workerCount fences to ensure visability.
*/
- private volatile WaitQueueNode syncStack;
/**
- * The count for event barrier
+ * The target parallelism level.
*/
- private volatile long eventCount;
+ private int parallelism;
/**
- * Pool number, just for assigning useful names to worker threads
+ * The maximum allowed pool size.
*/
- private final int poolNumber;
+ private int maxPoolSize;
/**
- * The maximum allowed pool size
+ * True if use local fifo, not default lifo, for local polling
+ * Replicated by ForkJoinWorkerThreads
*/
- private volatile int maxPoolSize;
+ private boolean locallyFifo;
/**
- * The desired parallelism level, updated only under workerLock.
+ * Controls whether to add spares to maintain parallelism
*/
- private volatile int parallelism;
+ private boolean maintainsParallelism;
/**
- * True if use local fifo, not default lifo, for local polling
+ * The uncaught exception handler used when any worker
+ * abruptly terminates
*/
- private volatile boolean locallyFifo;
+ private Thread.UncaughtExceptionHandler ueh;
/**
- * 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.
+ * Pool number, just for assigning useful names to worker threads
*/
- private volatile int workerCounts;
+ private final int poolNumber;
- 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; }
+ // utilities for updating fields
/**
- * 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).
+ * Adds delta to running count. Used mainly by ForkJoinTask.
*
* @param delta the number to add
*/
final void updateRunningCount(int delta) {
- int s;
- do {} while (!casWorkerCounts(s = workerCounts, s + delta));
+ int wc;
+ do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
+ wc = workerCounts,
+ wc + delta));
}
/**
- * 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
+ * Write fence for user modifications of pool parameters
+ * (parallelism. etc). Note that it doesn't matter if CAS fails.
*/
- 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 void workerCountWriteFence() {
+ int wc;
+ UNSAFE.compareAndSwapInt(this, workerCountsOffset,
+ wc = workerCounts, wc);
}
/**
- * 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
- */
- private volatile int runControl;
-
- // RunState values. Order among values matters
- private static final int RUNNING = 0;
- private static final int SHUTDOWN = 1;
- private static final int TERMINATING = 2;
- private static final int TERMINATED = 3;
-
- private static int runStateOf(int c) { return c >>> 16; }
- private static int activeCountOf(int c) { return c & shortMask; }
- private static int runControlFor(int r, int a) { return (r << 16) + a; }
+ * Read fence for external reads of pool parameters
+ * (parallelism. maxPoolSize, etc).
+ */
+ private void workerCountReadFence() {
+ int ignore = workerCounts;
+ }
/**
* Tries incrementing active count; fails on contention.
- * Called by workers before/during executing tasks.
+ * Called by workers before executing tasks.
*
* @return true on success
*/
final boolean tryIncrementActiveCount() {
- int c = runControl;
- return casRunControl(c, c+1);
+ int c;
+ return UNSAFE.compareAndSwapInt(this, runStateOffset,
+ c = runState, c + ONE_ACTIVE);
}
/**
* 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
+ * Called when workers cannot find tasks to run.
*/
final boolean tryDecrementActiveCount() {
- int c = runControl;
- int nextc = c - 1;
- if (!casRunControl(c, nextc))
+ int c;
+ return UNSAFE.compareAndSwapInt(this, runStateOffset,
+ c = runState, c - ONE_ACTIVE);
+ }
+
+ /**
+ * Advances to at least the given level. Returns true if not
+ * already in at least the given level.
+ */
+ private boolean advanceRunLevel(int level) {
+ for (;;) {
+ int s = runState;
+ if ((s & level) != 0)
+ return false;
+ if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level))
+ return true;
+ }
+ }
+
+ // workers array maintenance
+
+ /**
+ * Records and returns a workers array index for new worker.
+ */
+ private int recordWorker(ForkJoinWorkerThread w) {
+ // Try using slot totalCount-1. If not available, scan and/or resize
+ int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1;
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ ForkJoinWorkerThread[] ws = workers;
+ int len = ws.length;
+ if (k < 0 || k >= len || ws[k] != null) {
+ for (k = 0; k < len && ws[k] != null; ++k)
+ ;
+ if (k == len)
+ ws = Arrays.copyOf(ws, len << 1);
+ }
+ ws[k] = w;
+ workers = ws; // volatile array write ensures slot visibility
+ } finally {
+ lock.unlock();
+ }
+ return k;
+ }
+
+ /**
+ * Nulls out record of worker in workers array
+ */
+ private void forgetWorker(ForkJoinWorkerThread w) {
+ int idx = w.poolIndex;
+ // Locking helps method recordWorker avoid unecessary expansion
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ ForkJoinWorkerThread[] ws = workers;
+ if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify
+ ws[idx] = null;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ // adding and removing workers
+
+ /**
+ * Tries to create and add new worker. Assumes that worker counts
+ * are already updated to accommodate the worker, so adjusts on
+ * failure.
+ *
+ * @return new worker or null if creation failed
+ */
+ private ForkJoinWorkerThread addWorker() {
+ ForkJoinWorkerThread w = null;
+ try {
+ w = factory.newThread(this);
+ } finally { // Adjust on either null or exceptional factory return
+ if (w == null) {
+ onWorkerCreationFailure();
+ return null;
+ }
+ }
+ w.start(recordWorker(w), locallyFifo, ueh);
+ return w;
+ }
+
+ /**
+ * Adjusts counts upon failure to create worker
+ */
+ private void onWorkerCreationFailure() {
+ int c;
+ do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
+ c = workerCounts,
+ c - (ONE_RUNNING|ONE_TOTAL)));
+ tryTerminate(false); // in case of failure during shutdown
+ }
+
+ /**
+ * Create enough total workers to establish target parallelism,
+ * giving up if terminating or addWorker fails
+ */
+ private void ensureEnoughTotalWorkers() {
+ int wc;
+ while (runState < TERMINATING &&
+ ((wc = workerCounts) >>> TOTAL_COUNT_SHIFT) < parallelism) {
+ if ((UNSAFE.compareAndSwapInt(this, workerCountsOffset,
+ wc, wc + (ONE_RUNNING|ONE_TOTAL)) &&
+ addWorker() == null))
+ break;
+ }
+ }
+
+ /**
+ * Final callback from terminating worker. Removes record of
+ * worker from array, and adjusts counts. If pool is shutting
+ * down, tries to complete terminatation, else possibly replaces
+ * the worker.
+ *
+ * @param w the worker
+ */
+ final void workerTerminated(ForkJoinWorkerThread w) {
+ if (w.active) { // force inactive
+ w.active = false;
+ do {} while (!tryDecrementActiveCount());
+ }
+ forgetWorker(w);
+
+ // decrement total count, and if was running, running count
+ int unit = w.isTrimmed()? ONE_TOTAL : (ONE_RUNNING|ONE_TOTAL);
+ int wc;
+ do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
+ wc = workerCounts, wc - unit));
+
+ accumulateStealCount(w); // collect final count
+ if (!tryTerminate(false))
+ ensureEnoughTotalWorkers();
+ }
+
+ // Waiting for and signalling events
+
+ /**
+ * Ensures eventCount on exit is different (mod 2^32) than on
+ * entry. CAS failures are OK -- any change in count suffices.
+ */
+ private void advanceEventCount() {
+ int c;
+ UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
+ }
+
+ /**
+ * Releases workers blocked on a count not equal to current count.
+ */
+ final void releaseWaiters() {
+ long top;
+ int id;
+ while ((id = (int)((top = eventWaiters) & WAITER_INDEX_MASK)) > 0 &&
+ (int)(top >>> EVENT_COUNT_SHIFT) != eventCount) {
+ ForkJoinWorkerThread[] ws = workers;
+ ForkJoinWorkerThread w;
+ if (ws.length >= id && (w = ws[id - 1]) != null &&
+ UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
+ top, w.nextWaiter))
+ LockSupport.unpark(w);
+ }
+ }
+
+ /**
+ * Advances eventCount and releases waiters until interference by
+ * other releasing threads is detected.
+ */
+ final void signalWork() {
+ int ec;
+ UNSAFE.compareAndSwapInt(this, eventCountOffset, ec=eventCount, ec+1);
+ outer:for (;;) {
+ long top = eventWaiters;
+ ec = eventCount;
+ for (;;) {
+ ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
+ int id = (int)(top & WAITER_INDEX_MASK);
+ if (id <= 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
+ return;
+ if ((ws = workers).length < id || (w = ws[id - 1]) == null ||
+ !UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
+ top, top = w.nextWaiter))
+ continue outer; // possibly stale; reread
+ LockSupport.unpark(w);
+ if (top != eventWaiters) // let someone else take over
+ return;
+ }
+ }
+ }
+
+ /**
+ * If worker is inactive, blocks until terminating or event count
+ * advances from last value held by worker; in any case helps
+ * release others.
+ *
+ * @param w the calling worker thread
+ */
+ private void eventSync(ForkJoinWorkerThread w) {
+ if (!w.active) {
+ int prev = w.lastEventCount;
+ long nextTop = (((long)prev << EVENT_COUNT_SHIFT) |
+ ((long)(w.poolIndex + 1)));
+ long top;
+ while ((runState < SHUTDOWN || !tryTerminate(false)) &&
+ (((int)(top = eventWaiters) & WAITER_INDEX_MASK) == 0 ||
+ (int)(top >>> EVENT_COUNT_SHIFT) == prev) &&
+ eventCount == prev) {
+ if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
+ w.nextWaiter = top, nextTop)) {
+ accumulateStealCount(w); // transfer steals while idle
+ Thread.interrupted(); // clear/ignore interrupt
+ while (eventCount == prev)
+ w.doPark();
+ break;
+ }
+ }
+ w.lastEventCount = eventCount;
+ }
+ releaseWaiters();
+ }
+
+ /**
+ * Callback from workers invoked upon each top-level action (i.e.,
+ * stealing a task or taking a submission and running
+ * it). Performs one or both of the following:
+ *
+ * * If the worker cannot find work, updates its active status to
+ * inactive and updates activeCount unless there is contention, in
+ * which case it may try again (either in this or a subsequent
+ * call). Additionally, awaits the next task event and/or helps
+ * wake up other releasable waiters.
+ *
+ * * If there are too many running threads, suspends this worker
+ * (first forcing inactivation if necessary). If it is not
+ * resumed before a keepAlive elapses, the worker may be "trimmed"
+ * -- killed while suspended within suspendAsSpare. Otherwise,
+ * upon resume it rechecks to make sure that it is still needed.
+ *
+ * @param w the worker
+ * @param worked false if the worker scanned for work but didn't
+ * find any (in which case it may block waiting for work).
+ */
+ final void preStep(ForkJoinWorkerThread w, boolean worked) {
+ boolean active = w.active;
+ boolean inactivate = !worked & active;
+ for (;;) {
+ if (inactivate) {
+ int c = runState;
+ if (UNSAFE.compareAndSwapInt(this, runStateOffset,
+ c, c - ONE_ACTIVE))
+ inactivate = active = w.active = false;
+ }
+ int wc = workerCounts;
+ if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
+ if (!worked)
+ eventSync(w);
+ return;
+ }
+ if (!(inactivate |= active) && // must inactivate to suspend
+ UNSAFE.compareAndSwapInt(this, workerCountsOffset,
+ wc, wc - ONE_RUNNING) &&
+ !w.suspendAsSpare()) // false if trimmed
+ return;
+ }
+ }
+
+ /**
+ * Adjusts counts and creates or resumes compensating threads for
+ * a worker about to block on task joinMe, returning early if
+ * joinMe becomes ready. First tries resuming an existing spare
+ * (which usually also avoids any count adjustment), but must then
+ * decrement running count to determine whether a new thread is
+ * needed. See above for fuller explanation.
+ */
+ final void preJoin(ForkJoinTask joinMe) {
+ boolean dec = false; // true when running count decremented
+ for (;;) {
+ releaseWaiters(); // help other threads progress
+
+ if (joinMe.status < 0) // surround spare search with done checks
+ return;
+ ForkJoinWorkerThread spare = null;
+ for (ForkJoinWorkerThread w : workers) {
+ if (w != null && w.isSuspended()) {
+ spare = w;
+ break;
+ }
+ }
+ if (joinMe.status < 0)
+ return;
+
+ if (spare != null && spare.tryUnsuspend()) {
+ if (dec || joinMe.requestSignal() < 0) {
+ int c;
+ do {} while (!UNSAFE.compareAndSwapInt(this,
+ workerCountsOffset,
+ c = workerCounts,
+ c + ONE_RUNNING));
+ } // else no net count change
+ LockSupport.unpark(spare);
+ return;
+ }
+
+ int wc = workerCounts; // decrement running count
+ if (!dec && (wc & RUNNING_COUNT_MASK) != 0 &&
+ (dec = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
+ wc, wc -= ONE_RUNNING)) &&
+ joinMe.requestSignal() < 0) { // cannot block
+ int c; // back out
+ do {} while (!UNSAFE.compareAndSwapInt(this,
+ workerCountsOffset,
+ c = workerCounts,
+ c + ONE_RUNNING));
+ return;
+ }
+
+ if (dec) {
+ int tc = wc >>> TOTAL_COUNT_SHIFT;
+ int pc = parallelism;
+ int dc = pc - (wc & RUNNING_COUNT_MASK); // deficit count
+ if ((dc < pc && (dc <= 0 || (dc * dc < (tc - pc) * pc) ||
+ !maintainsParallelism)) ||
+ tc >= maxPoolSize) // cannot add
+ return;
+ if (spare == null &&
+ UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
+ wc + (ONE_RUNNING|ONE_TOTAL))) {
+ addWorker();
+ return;
+ }
+ }
+ }
+ }
+
+ /**
+ * Same idea as preJoin but with too many differing details to
+ * integrate: There are no task-based signal counts, and only one
+ * way to do the actual blocking. So for simplicity it is directly
+ * incorporated into this method.
+ */
+ final void doBlock(ManagedBlocker blocker, boolean maintainPar)
+ throws InterruptedException {
+ maintainPar &= maintainsParallelism; // override
+ boolean dec = false;
+ boolean done = false;
+ for (;;) {
+ releaseWaiters();
+ if (done = blocker.isReleasable())
+ break;
+ ForkJoinWorkerThread spare = null;
+ for (ForkJoinWorkerThread w : workers) {
+ if (w != null && w.isSuspended()) {
+ spare = w;
+ break;
+ }
+ }
+ if (done = blocker.isReleasable())
+ break;
+ if (spare != null && spare.tryUnsuspend()) {
+ if (dec) {
+ int c;
+ do {} while (!UNSAFE.compareAndSwapInt(this,
+ workerCountsOffset,
+ c = workerCounts,
+ c + ONE_RUNNING));
+ }
+ LockSupport.unpark(spare);
+ break;
+ }
+ int wc = workerCounts;
+ if (!dec && (wc & RUNNING_COUNT_MASK) != 0)
+ dec = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
+ wc, wc -= ONE_RUNNING);
+ if (dec) {
+ int tc = wc >>> TOTAL_COUNT_SHIFT;
+ int pc = parallelism;
+ int dc = pc - (wc & RUNNING_COUNT_MASK);
+ if ((dc < pc && (dc <= 0 || (dc * dc < (tc - pc) * pc) ||
+ !maintainPar)) ||
+ tc >= maxPoolSize)
+ break;
+ if (spare == null &&
+ UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
+ wc + (ONE_RUNNING|ONE_TOTAL))){
+ addWorker();
+ break;
+ }
+ }
+ }
+
+ try {
+ if (!done)
+ do {} while (!blocker.isReleasable() && !blocker.block());
+ } finally {
+ if (dec) {
+ int c;
+ do {} while (!UNSAFE.compareAndSwapInt(this,
+ workerCountsOffset,
+ c = workerCounts,
+ c + ONE_RUNNING));
+ }
+ }
+ }
+
+ /**
+ * 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) {
+ if (now)
+ advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN
+ else if (runState < SHUTDOWN ||
+ !submissionQueue.isEmpty() ||
+ (runState & ACTIVE_COUNT_MASK) != 0)
return false;
- if (canTerminateOnShutdown(nextc))
- terminateOnShutdown();
+
+ if (advanceRunLevel(TERMINATING))
+ startTerminating();
+
+ // Finish now if all threads terminated; else in some subsequent call
+ if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
+ advanceRunLevel(TERMINATED);
+ terminationLatch.countDown();
+ }
return true;
}
/**
- * Returns {@code true} if argument represents zero active count
- * and nonzero runstate, which is the triggering condition for
- * terminating on shutdown.
+ * Actions on transition to TERMINATING
+ */
+ private void startTerminating() {
+ // Clear out and cancel submissions, ignoring exceptions
+ ForkJoinTask task;
+ while ((task = submissionQueue.poll()) != null) {
+ try {
+ task.cancel(false);
+ } catch (Throwable ignore) {
+ }
+ }
+ // Propagate run level
+ for (ForkJoinWorkerThread w : workers) {
+ if (w != null)
+ w.shutdown(); // also resumes suspended workers
+ }
+ // Ensure no straggling local tasks
+ for (ForkJoinWorkerThread w : workers) {
+ if (w != null)
+ w.cancelTasks();
+ }
+ // Wake up idle workers
+ advanceEventCount();
+ releaseWaiters();
+ // Unstick pending joins
+ for (ForkJoinWorkerThread w : workers) {
+ if (w != null && !w.isTerminated()) {
+ try {
+ w.interrupt();
+ } catch (SecurityException ignore) {
+ }
+ }
+ }
+ }
+
+ // misc support for ForkJoinWorkerThread
+
+ /**
+ * Returns pool number
*/
- private static boolean canTerminateOnShutdown(int c) {
- // i.e. least bit is nonzero runState bit
- return ((c & -c) >>> 16) != 0;
+ final int getPoolNumber() {
+ return poolNumber;
}
/**
- * Transition run state to at least the given state. Return true
- * if not already at least given state.
+ * Accumulates steal count from a worker, clearing
+ * the worker's value
*/
- private boolean transitionRunStateTo(int state) {
- for (;;) {
- int c = runControl;
- if (runStateOf(c) >= state)
- return false;
- if (casRunControl(c, runControlFor(state, activeCountOf(c))))
- return true;
+ final void accumulateStealCount(ForkJoinWorkerThread w) {
+ int sc = w.stealCount;
+ if (sc != 0) {
+ long c;
+ w.stealCount = 0;
+ do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
+ c = stealCount, c + sc));
}
}
/**
- * Controls whether to add spares to maintain parallelism
+ * Returns the approximate (non-atomic) number of idle threads per
+ * active thread.
+ */
+ final int idlePerActive() {
+ int ac = runState; // no mask -- artifically boosts during shutdown
+ int pc = parallelism; // use targeted parallelism, not rc
+ // Use exact results for small values, saturate past 4
+ return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
+ }
+
+ /**
+ * Returns the approximate (non-atomic) difference between running
+ * and active counts.
*/
- private volatile boolean maintainsParallelism;
+ final int inactiveCount() {
+ return (workerCounts & RUNNING_COUNT_MASK) -
+ (runState & ACTIVE_COUNT_MASK);
+ }
+
+ // Public and protected methods
// Constructors
/**
- * Creates a ForkJoinPool with a pool size equal to the number of
- * processors available on the system, using the default
- * ForkJoinWorkerThreadFactory.
+ * Creates a {@code ForkJoinPool} with parallelism equal to {@link
+ * java.lang.Runtime#availableProcessors}, and using the {@linkplain
+ * #defaultForkJoinWorkerThreadFactory default thread factory}.
*
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
@@ -358,12 +1102,13 @@ public class ForkJoinPool extends Abstra
}
/**
- * Creates a ForkJoinPool with the indicated parallelism level
- * threads and using the default ForkJoinWorkerThreadFactory.
+ * Creates a {@code ForkJoinPool} with the indicated parallelism
+ * level and using the {@linkplain
+ * #defaultForkJoinWorkerThreadFactory default thread factory}.
*
- * @param parallelism the number of worker threads
+ * @param parallelism the parallelism level
* @throws IllegalArgumentException if parallelism less than or
- * equal to zero
+ * 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
@@ -374,12 +1119,12 @@ public class ForkJoinPool extends Abstra
}
/**
- * Creates a ForkJoinPool with parallelism equal to the number of
- * processors available on the system and using the given
- * ForkJoinWorkerThreadFactory.
+ * Creates a {@code ForkJoinPool} with parallelism equal to {@link
+ * java.lang.Runtime#availableProcessors}, and using the given
+ * thread factory.
*
* @param factory the factory for creating new threads
- * @throws NullPointerException if factory is null
+ * @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
@@ -390,157 +1135,52 @@ public class ForkJoinPool extends Abstra
}
/**
- * Creates a ForkJoinPool with the given parallelism and factory.
+ * Creates a {@code ForkJoinPool} with the given parallelism and
+ * thread factory.
*
- * @param parallelism the targeted number of worker threads
+ * @param parallelism the parallelism level
* @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
+ * 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) {
- if (parallelism <= 0 || parallelism > MAX_THREADS)
- throw new IllegalArgumentException();
+ checkPermission();
if (factory == null)
throw new NullPointerException();
- checkPermission();
- this.factory = factory;
+ if (parallelism <= 0 || parallelism > MAX_THREADS)
+ throw new IllegalArgumentException();
+ this.poolNumber = poolNumberGenerator.incrementAndGet();
+ int arraySize = initialArraySizeFor(parallelism);
this.parallelism = parallelism;
+ this.factory = factory;
this.maxPoolSize = MAX_THREADS;
this.maintainsParallelism = true;
- this.poolNumber = poolNumberGenerator.incrementAndGet();
- this.workerLock = new ReentrantLock();
- this.termination = workerLock.newCondition();
- this.stealCount = new AtomicLong();
+ this.workers = new ForkJoinWorkerThread[arraySize];
this.submissionQueue = new LinkedTransferQueue>();
- // worker array and workers are lazily constructed
- }
-
- /**
- * Creates a new worker thread using factory.
- *
- * @param index the index to assign worker
- * @return new worker, or null of factory failed
- */
- private ForkJoinWorkerThread createWorker(int index) {
- Thread.UncaughtExceptionHandler h = ueh;
- ForkJoinWorkerThread w = factory.newThread(this);
- if (w != null) {
- w.poolIndex = index;
- w.setDaemon(true);
- w.setAsyncMode(locallyFifo);
- w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
- if (h != null)
- w.setUncaughtExceptionHandler(h);
- }
- return w;
- }
-
- /**
- * Returns a good size for worker array given pool size.
- * Currently requires size to be a power of two.
- */
- private static int arraySizeFor(int poolSize) {
- return (poolSize <= 1) ? 1 :
- (1 << (32 - Integer.numberOfLeadingZeros(poolSize-1)));
- }
-
- /**
- * Creates or resizes array if necessary to hold newLength.
- * Call only under exclusion.
- *
- * @return the array
- */
- private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
- ForkJoinWorkerThread[] ws = workers;
- if (ws == null)
- return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
- else if (newLength > ws.length)
- return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
- else
- return ws;
- }
-
- /**
- * Tries to shrink workers into smaller array after one or more terminate.
- */
- 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);
- }
+ this.workerLock = new ReentrantLock();
+ this.terminationLatch = new CountDownLatch(1);
+ // Start first worker; remaining workers added upon first submission
+ workerCounts = ONE_RUNNING | ONE_TOTAL;
+ addWorker();
}
/**
- * Initializes workers if necessary.
- */
- final void ensureWorkerInitialization() {
- ForkJoinWorkerThread[] ws = workers;
- if (ws == null) {
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- ws = workers;
- if (ws == null) {
- int ps = parallelism;
- ws = ensureWorkerArrayCapacity(ps);
- for (int i = 0; i < ps; ++i) {
- ForkJoinWorkerThread w = createWorker(i);
- if (w != null) {
- ws[i] = w;
- w.start();
- updateWorkerCount(1);
- }
- }
- }
- } finally {
- lock.unlock();
- }
- }
- }
-
- /**
- * Worker creation and startup for threads added via setParallelism.
- */
- 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();
- }
- else {
- updateWorkerCount(-1); // back out on failed creation
- break;
- }
- }
- }
+ * Returns initial power of two size for workers array.
+ * @param pc the initial parallelism level
+ */
+ private static int initialArraySizeFor(int pc) {
+ // See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
+ int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
+ size |= size >>> 1;
+ size |= size >>> 2;
+ size |= size >>> 4;
+ size |= size >>> 8;
+ return size + 1;
}
// Execution methods
@@ -551,12 +1191,13 @@ public class ForkJoinPool extends Abstra
private void doSubmit(ForkJoinTask task) {
if (task == null)
throw new NullPointerException();
- if (isShutdown())
+ if (runState >= SHUTDOWN)
throw new RejectedExecutionException();
- if (workers == null)
- ensureWorkerInitialization();
submissionQueue.offer(task);
- signalIdleWorkers();
+ advanceEventCount();
+ releaseWaiters();
+ if ((workerCounts >>> TOTAL_COUNT_SHIFT) < parallelism)
+ ensureEnoughTotalWorkers();
}
/**
@@ -564,8 +1205,9 @@ public class ForkJoinPool extends Abstra
*
* @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);
@@ -576,8 +1218,9 @@ public class ForkJoinPool extends Abstra
* Arranges for (asynchronous) execution of the given task.
*
* @param task the task
- * @throws NullPointerException if task is null
- * @throws RejectedExecutionException if pool is shut down
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
*/
public void execute(ForkJoinTask task) {
doSubmit(task);
@@ -585,6 +1228,11 @@ public class ForkJoinPool extends Abstra
// AbstractExecutorService methods
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public void execute(Runnable task) {
ForkJoinTask job;
if (task instanceof ForkJoinTask) // avoid re-wrap
@@ -594,18 +1242,33 @@ public class ForkJoinPool extends Abstra
doSubmit(job);
}
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public ForkJoinTask submit(Callable task) {
ForkJoinTask job = ForkJoinTask.adapt(task);
doSubmit(job);
return job;
}
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public ForkJoinTask submit(Runnable task, T result) {
ForkJoinTask job = ForkJoinTask.adapt(task, result);
doSubmit(job);
return job;
}
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public ForkJoinTask submit(Runnable task) {
ForkJoinTask job;
if (task instanceof ForkJoinTask) // avoid re-wrap
@@ -621,16 +1284,19 @@ 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);
return task;
}
-
+ /**
+ * @throws NullPointerException {@inheritDoc}
+ * @throws RejectedExecutionException {@inheritDoc}
+ */
public List> invokeAll(Collection> tasks) {
ArrayList> forkJoinTasks =
new ArrayList>(tasks.size());
@@ -653,8 +1319,6 @@ 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.
*
@@ -671,15 +1335,8 @@ public class ForkJoinPool extends Abstra
* @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;
+ workerCountReadFence();
+ return ueh;
}
/**
@@ -698,27 +1355,19 @@ public class ForkJoinPool extends Abstra
public Thread.UncaughtExceptionHandler
setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
checkPermission();
- Thread.UncaughtExceptionHandler old = null;
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- old = ueh;
+ workerCountReadFence();
+ Thread.UncaughtExceptionHandler old = ueh;
+ if (h != old) {
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);
- }
+ workerCountWriteFence();
+ for (ForkJoinWorkerThread w : workers) {
+ if (w != null)
+ w.setUncaughtExceptionHandler(h);
}
- } finally {
- lock.unlock();
}
return old;
}
-
/**
* Sets the target parallelism level of this pool.
*
@@ -734,29 +1383,32 @@ public class ForkJoinPool extends Abstra
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();
+ workerCountReadFence();
+ int pc = this.parallelism;
+ if (pc != parallelism) {
+ this.parallelism = parallelism;
+ workerCountWriteFence();
+ // Release spares. If too many, some will die after re-suspend
+ for (ForkJoinWorkerThread w : workers) {
+ if (w != null && w.tryUnsuspend()) {
+ updateRunningCount(1);
+ LockSupport.unpark(w);
+ }
}
- } finally {
- lock.unlock();
+ ensureEnoughTotalWorkers();
+ advanceEventCount();
+ releaseWaiters(); // force config recheck by existing workers
}
- signalIdleWorkers();
}
/**
- * Returns the targeted number of worker threads in this pool.
+ * Returns the targeted parallelism level of this pool.
*
- * @return the targeted number of worker threads in this pool
+ * @return the targeted parallelism level of this pool
*/
public int getParallelism() {
+ // workerCountReadFence(); // inlined below
+ int ignore = workerCounts;
return parallelism;
}
@@ -769,24 +1421,28 @@ public class ForkJoinPool extends Abstra
* @return the number of worker threads
*/
public int getPoolSize() {
- return totalCountOf(workerCounts);
+ return workerCounts >>> TOTAL_COUNT_SHIFT;
}
/**
* Returns the maximum number of threads allowed to exist in the
- * pool, even if there are insufficient unblocked running threads.
+ * pool. Unless set using {@link #setMaximumPoolSize}, the
+ * maximum is an implementation-defined value designed only to
+ * prevent runaway growth.
*
* @return the maximum
*/
public int getMaximumPoolSize() {
+ workerCountReadFence();
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.
+ * pool. The given value should normally be greater than or equal
+ * to the {@link #getParallelism parallelism} level. Setting this
+ * value has no effect on current pool size. It controls
+ * construction of new threads.
*
* @throws IllegalArgumentException if negative or greater than
* internal implementation limit
@@ -795,9 +1451,9 @@ public class ForkJoinPool extends Abstra
if (newMax < 0 || newMax > MAX_THREADS)
throw new IllegalArgumentException();
maxPoolSize = newMax;
+ workerCountWriteFence();
}
-
/**
* Returns {@code true} if this pool dynamically maintains its
* target parallelism level. If false, new threads are added only
@@ -806,6 +1462,7 @@ public class ForkJoinPool extends Abstra
* @return {@code true} if maintains parallelism
*/
public boolean getMaintainsParallelism() {
+ workerCountReadFence();
return maintainsParallelism;
}
@@ -818,6 +1475,7 @@ public class ForkJoinPool extends Abstra
*/
public void setMaintainsParallelism(boolean enable) {
maintainsParallelism = enable;
+ workerCountWriteFence();
}
/**
@@ -834,14 +1492,14 @@ public class ForkJoinPool extends Abstra
* @see #getAsyncMode
*/
public boolean setAsyncMode(boolean async) {
+ workerCountReadFence();
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);
+ if (oldMode != async) {
+ locallyFifo = async;
+ workerCountWriteFence();
+ for (ForkJoinWorkerThread w : workers) {
+ if (w != null)
+ w.setAsyncMode(async);
}
}
return oldMode;
@@ -855,18 +1513,20 @@ public class ForkJoinPool extends Abstra
* @see #setAsyncMode
*/
public boolean getAsyncMode() {
+ workerCountReadFence();
return locallyFifo;
}
/**
* 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);
+ return workerCounts & RUNNING_COUNT_MASK;
}
/**
@@ -877,19 +1537,7 @@ public class ForkJoinPool extends Abstra
* @return the number of active threads
*/
public int getActiveThreadCount() {
- return activeCountOf(runControl);
- }
-
- /**
- * Returns an estimate of the number of threads that are currently
- * idle waiting for tasks. This method may underestimate the
- * number of idle threads.
- *
- * @return the number of idle threads
- */
- final int getIdleThreadCount() {
- int c = runningCountOf(workerCounts) - activeCountOf(runControl);
- return (c <= 0) ? 0 : c;
+ return runState & ACTIVE_COUNT_MASK;
}
/**
@@ -904,7 +1552,7 @@ public class ForkJoinPool extends Abstra
* @return {@code true} if all threads are currently idle
*/
public boolean isQuiescent() {
- return activeCountOf(runControl) == 0;
+ return (runState & ACTIVE_COUNT_MASK) == 0;
}
/**
@@ -919,17 +1567,7 @@ 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;
}
/**
@@ -944,13 +1582,9 @@ 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();
- }
+ for (ForkJoinWorkerThread w : workers) {
+ if (w != null)
+ count += w.getQueueSize();
}
return count;
}
@@ -991,8 +1625,8 @@ public class ForkJoinPool extends Abstra
* 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
@@ -1006,13 +1640,9 @@ public class ForkJoinPool extends Abstra
*/
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);
- }
+ for (ForkJoinWorkerThread w : workers) {
+ if (w != null)
+ n += w.drainTasksTo(c);
}
return n;
}
@@ -1025,36 +1655,34 @@ 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 wc = workerCounts;
+ int tc = wc >>> TOTAL_COUNT_SHIFT;
+ int rc = wc & RUNNING_COUNT_MASK;
+ int pc = parallelism;
+ int rs = runState;
+ int ac = rs & ACTIVE_COUNT_MASK;
return super.toString() +
- "[" + runStateToString(runStateOf(rc)) +
- ", parallelism = " + ps +
- ", size = " + totalCountOf(wc) +
- ", active = " + activeCountOf(rc) +
- ", running = " + runningCountOf(wc) +
+ "[" + runLevelToString(rs) +
+ ", 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");
- }
+ private static String runLevelToString(int s) {
+ return ((s & TERMINATED) != 0 ? "Terminated" :
+ ((s & TERMINATING) != 0 ? "Terminating" :
+ ((s & SHUTDOWN) != 0 ? "Shutting down" :
+ "Running")));
}
- // lifecycle control
-
/**
* Initiates an orderly shutdown in which previously submitted
* tasks are executed, but no new tasks will be accepted.
@@ -1069,34 +1697,19 @@ public class ForkJoinPool extends Abstra
*/
public void shutdown() {
checkPermission();
- transitionRunStateTo(SHUTDOWN);
- if (canTerminateOnShutdown(runControl)) {
- if (workers == null) { // shutting down before workers created
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- if (workers == null) {
- terminate();
- transitionRunStateTo(TERMINATED);
- termination.signalAll();
- }
- } finally {
- lock.unlock();
- }
- }
- terminateOnShutdown();
- }
+ advanceRunLevel(SHUTDOWN);
+ 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 {@link #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
@@ -1106,7 +1719,7 @@ public class ForkJoinPool extends Abstra
*/
public List shutdownNow() {
checkPermission();
- terminate();
+ tryTerminate(true);
return Collections.emptyList();
}
@@ -1116,17 +1729,21 @@ public class ForkJoinPool extends Abstra
* @return {@code true} if all tasks have completed following shut down
*/
public boolean isTerminated() {
- return runStateOf(runControl) == TERMINATED;
+ return runState >= TERMINATED;
}
/**
* 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, causing this executor not
+ * to properly terminate.
*
- * @return {@code true} if terminating
+ * @return {@code true} if terminating but not yet terminated
*/
public boolean isTerminating() {
- return runStateOf(runControl) >= TERMINATING;
+ return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
}
/**
@@ -1135,7 +1752,7 @@ public class ForkJoinPool extends Abstra
* @return {@code true} if this pool has been shut down
*/
public boolean isShutdown() {
- return runStateOf(runControl) >= SHUTDOWN;
+ return runState >= SHUTDOWN;
}
/**
@@ -1151,587 +1768,7 @@ public class ForkJoinPool extends Abstra
*/
public boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException {
- long nanos = unit.toNanos(timeout);
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- for (;;) {
- if (isTerminated())
- return true;
- if (nanos <= 0)
- return false;
- nanos = termination.awaitNanos(nanos);
- }
- } finally {
- lock.unlock();
- }
- }
-
- // 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 {@code 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 {@code 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 {@code 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 {@code 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);
- }
- }
+ return terminationLatch.await(timeout, unit);
}
/**
@@ -1814,20 +1851,16 @@ public class ForkJoinPool extends Abstra
boolean maintainParallelism)
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) t).pool.
+ doBlock(blocker, maintainParallelism);
+ else
+ awaitBlocker(blocker);
}
+ /**
+ * Performs Non-FJ blocking
+ */
private static void awaitBlocker(ManagedBlocker blocker)
throws InterruptedException {
do {} while (!blocker.isReleasable() && !blocker.block());
@@ -1848,32 +1881,17 @@ public class ForkJoinPool extends Abstra
// 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 final long runStateOffset =
+ objectFieldOffset("runState", ForkJoinPool.class);
+ private static final long eventCountOffset =
+ objectFieldOffset("eventCount", ForkJoinPool.class);
+ private static final long eventWaitersOffset =
+ objectFieldOffset("eventWaiters",ForkJoinPool.class);
+ private static final long stealCountOffset =
+ objectFieldOffset("stealCount",ForkJoinPool.class);
+
private static long objectFieldOffset(String field, Class klazz) {
try {