[ViewVC] Diff of: jsr166/jsr166/src/jsr166y/ForkJoinPool.java

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.43 by jsr166, Tue Aug 4 00:55:13 2009 UTC vs.
Revision 1.62 by dl, Wed Aug 11 20:28:22 2010 UTC

+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.
->
+ * from non-{@code ForkJoinTask} clients, as well as management and
->
+ * monitoring operations.
+ * <p>A {@code ForkJoinPool} differs from other kinds of {@link
+ * ExecutorService} mainly by virtue of employing
+ * 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.
->
+ * ForkJoinTask}s). When setting <em>asyncMode</em> to true in
->
+ * constructors, {@code ForkJoinPool}s may also be appropriate for use
->
+ * with event-style tasks that are never joined.
+ * <p>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 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}). 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.
->
+ * 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.
+ * <p>In addition to execution and lifecycle control methods, this
+ * class provides status check methods (for example
+ * {@link #toString} returns indications of pool state in a
+ * convenient form for informal monitoring.
-+
+ * <p> 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
-+
+ * <em>NOT</em> use these pool execution methods, but instead use the
-+
+ * within-computation forms listed in the table.
-+
+ *
-+
+ * <table BORDER CELLPADDING=3 CELLSPACING=1>
-+
+ *  <tr>
-+
+ *    <td></td>
-+
+ *    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
-+
+ *    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
-+
+ *  </tr>
-+
+ *  <tr>
-+
+ *    <td> <b>Arange async execution</td>
-+
+ *    <td> {@link #execute(ForkJoinTask)}</td>
-+
+ *    <td> {@link ForkJoinTask#fork}</td>
-+
+ *  </tr>
-+
+ *  <tr>
-+
+ *    <td> <b>Await and obtain result</td>
-+
+ *    <td> {@link #invoke(ForkJoinTask)}</td>
-+
+ *    <td> {@link ForkJoinTask#invoke}</td>
-+
+ *  </tr>
-+
+ *  <tr>
-+
+ *    <td> <b>Arrange exec and obtain Future</td>
-+
+ *    <td> {@link #submit(ForkJoinTask)}</td>
-+
+ *    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
-+
+ *  </tr>
-+
+ * </table>
-+
+ *
+ * <p><b>Sample Usage.</b> 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
+ * <p><b>Implementation notes</b>: 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}.
-+
+ * <p>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
+ */
+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.)
->
+     *
->
+     * Beyond work-stealing support and essential bookkeeping, 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.  Becauae 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. Given that the creation costs of most threads on most
->
+     * systems mainly surrounds setting up runtime stacks, thread
->
+     * creation and switching is usually not much more expensive than
->
+     * stack creation and switching, and is more flexible). 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.helpJoinTask tracks joining->stealing
->
+     *      links to try to find such a task.
->
+     *
->
+     *   Compensating: Unless there are already enough live threads,
->
+     *      method helpMaintainParallelism() may create or or
->
+     *      re-activate a spare thread to compensate for blocked
->
+     *      joiners until they unblock.
->
+     *
->
+     * Because the determining 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, we rely on multiple retries of
->
+     * each. Further, because it is impossible to keep exactly the
->
+     * target (parallelism) number of threads running at any given
->
+     * time, we allow compensation during joins to fail, and enlist
->
+     * all other threads to help out whenever they are not otherwise
->
+     * occupied (i.e., mainly in method preStep).
->
+     *
->
+     * The ManagedBlocker extension API can't use helping so relies
->
+     * only on compensation in method awaitBlocker.
->
+     *
->
+     * 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 other management responsibilities. 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 accommodate
->
+     * unbalanced increments and decrements) 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 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 unusual
->
+     * code constructions here). In essence, the workers array serves
->
+     * as a WeakReference mechanism. Thus for example the event queue
->
+     * stores worker indices, not worker references. Access to the
->
+     * workers in associated methods (for example releaseEventWaiters)
->
+     * 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 shutdown, in which case
->
+     * it is OK to give up. On termination, we just clobber these
->
+     * data structures without trying to use them.
->
+     *
->
+     * 2. Bookkeeping for dynamically adding and removing workers. We
->
+     * aim to approximately maintain the given level of parallelism.
->
+     * 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.  Note however that the
->
+     * correspondance of these counts to reality is not guaranteed. In
->
+     * particular updates for unblocked threads may lag until they
->
+     * actually wake up.
->
+     *
->
+     * 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 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
->
+     * releaseEventWaiters, that removes and signals (unparks) workers
->
+     * not waiting on current count. To reduce stalls, 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. 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.  Method helpMaintainParallelism looks for
->
+     * suspended threads to resume before considering creating a new
->
+     * replacement. The spares themselves are encoded on another
->
+     * variant of a Treiber Stack, headed at field "spareWaiters".
->
+     * Note that the use of spares 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.  To avoid
->
+     * long-term build-up of spares, the oldest spare (see
->
+     * ForkJoinWorkerThread.suspendAsSpare) occasionally wakes up if
->
+     * not signalled and calls tryTrimSpare, which uses two different
->
+     * thresholds: Always killing if the number of spares is greater
->
+     * that 25% of total, and killing others only at a slower rate
->
+     * (UNUSED_SPARE_TRIM_RATE_NANOS).
->
+     *
->
+     * 6. Deciding when to create new workers. The main dynamic
->
+     * control in this class is deciding when to create extra threads
->
+     * in method helpMaintainParallelism. We would like to keep
->
+     * exactly #parallelism threads running, which is an impossble
->
+     * task. We always need to create one when the number of running
->
+     * threads would become zero and all workers are busy. Beyond
->
+     * this, we must rely on heuristics that work well in the the
->
+     * presence of transients phenomena such as GC stalls, dynamic
->
+     * compilation, and wake-up lags. These transients are extremely
->
+     * common -- we are normally trying to fully saturate the CPUs on
->
+     * a machine, so almost any activity other than running tasks
->
+     * impedes accuracy. Our main defense is to allow some slack in
->
+     * creation thresholds, using rules that reflect the fact that the
->
+     * more threads we have running, the more likely that we are
->
+     * underestimating the number running threads. The rules also
->
+     * better cope 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 100
->
+     * 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.
->
+     *
->
+     * 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 the required read orderings (which are sometimes
->
+     * critical). 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 other coding oddities that
->
+     * help some methods perform reasonably even when interpreted (not
->
+     * compiled), at the expense of some messy constructions that
->
+     * reduce byte code counts.
->
+     *
->
+     * 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
+         * Returns a new worker thread operating in the given pool.
+         * @param pool the pool this thread works in
-<
+         * @throws NullPointerException if pool is null
->
+         * @throws NullPointerException if the pool is null
+         */
+        public ForkJoinWorkerThread newThread(ForkJoinPool pool);
+     * Default ForkJoinWorkerThreadFactory implementation; creates a
+     * 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);
+        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 plus
->
+     * one (i.e., 0xfff) must fit into a 16bit field to enable
->
+     * word-packing for some counts and indices.
->
+     */
->
+    private static final int MAX_WORKERS   = 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<ForkJoinTask<?>> 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 Phaser termination;
+    /**
+     * Creation factory for worker threads.
+    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.
-–
+     */
-–
+    private volatile WaitQueueNode spareStack;
-–
-–
+    /**
+     * Sum of per-thread steal counts, updated only when threads are
+     * idle or terminating.
+     */
-<
+    private final AtomicLong stealCount;
->
+    private volatile long stealCount;
+    /**
-<
+     * Queue for external submissions.
->
+     * The last nanoTime that a spare thread was trimmed
+     */
-<
+    private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
->
+    private volatile long trimTime;
+    /**
-<
+     * Head of Treiber stack for barrier sync. See below for explanation.
->
+     * The rate at which to trim unused spares
+     */
-<
+    private volatile WaitQueueNode syncStack;
->
+    static final long UNUSED_SPARE_TRIM_RATE_NANOS =
->
+L * 1000L * 1000L; // 1 sec
+    /**
-<
+     * The count for event barrier
->
+     * Encoded record of top of treiber stack of threads waiting for
->
+     * events. The top 32 bits contain the count being waited for. The
->
+     * bottom 16 bits contains one plus the pool index of waiting
->
+     * worker thread. (Bits 16-31 are unused.)
+     */
-<
+    private volatile long eventCount;
->
+    private volatile long eventWaiters;
->
->
+    private static final int  EVENT_COUNT_SHIFT = 32;
->
+    private static final long WAITER_ID_MASK    = (1L << 16) - 1L;
+    /**
-<
+     * Pool number, just for assigning useful names to worker threads
->
+     * 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
+     */
-<
+    private final int poolNumber;
->
+    private volatile int eventCount;
+    /**
-<
+     * The maximum allowed pool size
->
+     * Encoded record of top of treiber stack of spare threads waiting
->
+     * for resumption. The top 16 bits contain an arbitrary count to
->
+     * avoid ABA effects. The bottom 16bits contains one plus the pool
->
+     * index of waiting worker thread.
->
+     */
->
+    private volatile int spareWaiters;
->
->
+    private static final int SPARE_COUNT_SHIFT = 16;
->
+    private static final int SPARE_ID_MASK     = (1 << 16) - 1;
->
->
+    /**
->
+     * 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.
+     */
-<
+    private volatile int maxPoolSize;
->
+    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;
+    /**
-<
+     * The desired parallelism level, updated only under workerLock.
->
+     * The target parallelism level.
->
+     * Accessed directly by ForkJoinWorkerThreads.
+     */
-<
+    private volatile int parallelism;
->
+    final int parallelism;
+    /**
+     * 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 uncaught exception handler used when any worker abruptly
->
+     * terminates.
+     */
-<
+    private volatile int workerCounts;
->
+    private final Thread.UncaughtExceptionHandler ueh;
->
->
+    /**
->
+     * Pool number, just for assigning useful names to worker threads
->
+     */
->
+    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 CASing fields. Note that several of these
->
+    // are manually inlined by callers
+    /**
-<
+     * 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
->
+     * Increments running count part of workerCounts
+     */
-<
+    final void updateRunningCount(int delta) {
-<
+        int s;
-<
+        do {} while (!casWorkerCounts(s = workerCounts, s + delta));
->
+    final void incrementRunningCount() {
->
+        int c;
->
+        do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
->
+                                               c = workerCounts,
->
+                                               c + ONE_RUNNING));
+    /**
-<
+     * 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
->
+     * Tries to decrement running count unless already zero
+     */
-<
+    private void updateWorkerCount(int delta) {
-<
+        int d = delta + (delta << 16); // add to both lo and hi parts
-<
+        int s;
-<
+        do {} while (!casWorkerCounts(s = workerCounts, s + d));
->
+    final boolean tryDecrementRunningCount() {
->
+        int wc = workerCounts;
->
+        if ((wc & RUNNING_COUNT_MASK) == 0)
->
+            return false;
->
+        return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
->
+                                        wc, wc - ONE_RUNNING);
+    /**
-<
+     * 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
->
+     * Forces decrement of encoded workerCounts, awaiting nonzero if
->
+     * (rarely) necessary when other count updates lag.
->
+     *
->
+     * @param dr -- either zero or ONE_RUNNING
->
+     * @param dt == either zero or ONE_TOTAL
+     */
-<
+    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 void decrementWorkerCounts(int dr, int dt) {
->
+        for (;;) {
->
+            int wc = workerCounts;
->
+            if (wc == 0 && (runState & TERMINATED) != 0)
->
+                return; // lagging termination on a backout
->
+            if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
->
+                (wc >>> TOTAL_COUNT_SHIFT) - dt < 0)
->
+                Thread.yield();
->
+            if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
->
+                                         wc, wc - (dr + dt)))
->
+                return;
->
+        }
->
+    }
-<
+    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; }
->
+    /**
->
+     * Increments event count
->
+     */
->
+    private void advanceEventCount() {
->
+        int c;
->
+        do {} while(!UNSAFE.compareAndSwapInt(this, eventCountOffset,
->
+                                              c = eventCount, c+1));
->
+    }
+    /**
+     * 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))
-<
+            return false;
-<
+        if (canTerminateOnShutdown(nextc))
-<
+            terminateOnShutdown();
-<
+        return true;
->
+        int c;
->
+        return UNSAFE.compareAndSwapInt(this, runStateOffset,
->
+                                        c = runState, c - ONE_ACTIVE);
+    /**
-<
+     * Returns {@code true} if argument represents zero active count
-<
+     * and nonzero runstate, which is the triggering condition for
-<
+     * terminating on shutdown.
->
+     * Advances to at least the given level. Returns true if not
->
+     * already in at least the given level.
+     */
-<
+    private static boolean canTerminateOnShutdown(int c) {
-<
+        // i.e. least bit is nonzero runState bit
-<
+        return ((c & -c) >>> 16) != 0;
->
+    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
-+
+    /**
-<
+     * Transition run state to at least the given state. Return true
-<
+     * if not already at least given state.
->
+     * Records and returns a workers array index for new worker.
+     */
-<
+    private boolean transitionRunStateTo(int state) {
-<
+        for (;;) {
-<
+            int c = runControl;
-<
+            if (runStateOf(c) >= state)
-<
+                return false;
-<
+            if (casRunControl(c, runControlFor(state, activeCountOf(c))))
-<
+                return true;
->
+    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 n = ws.length;
->
+            if (k < 0 || k >= n || ws[k] != null) {
->
+                for (k = 0; k < n && ws[k] != null; ++k)
->
+                    ;
->
+                if (k == n)
->
+                    ws = Arrays.copyOf(ws, n << 1);
->
+            }
->
+            ws[k] = w;
->
+            workers = ws; // volatile array write ensures slot visibility
->
+        } finally {
->
+            lock.unlock();
-+
+        return k;
+    /**
-<
+     * Controls whether to add spares to maintain parallelism
->
+     * Nulls out record of worker in workers array
+     */
-<
+    private volatile boolean maintainsParallelism;
->
+    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();
->
+        }
->
+    }
-<
+    // Constructors
->
+    // adding and removing workers
+    /**
-<
+     * 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
-<
+     *         because it does not hold {@link
-<
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
->
+     * Tries to create and add new worker. Assumes that worker counts
->
+     * are already updated to accommodate the worker, so adjusts on
->
+     * failure.
+     */
-<
+    public ForkJoinPool() {
-<
+        this(Runtime.getRuntime().availableProcessors(),
-<
+             defaultForkJoinWorkerThreadFactory);
->
+    private void addWorker() {
->
+        ForkJoinWorkerThread w = null;
->
+        try {
->
+            w = factory.newThread(this);
->
+        } finally { // Adjust on either null or exceptional factory return
->
+            if (w == null) {
->
+                decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
->
+                tryTerminate(false); // in case of failure during shutdown
->
+            }
->
+        }
->
+        if (w != null)
->
+            w.start(recordWorker(w), ueh);
+    /**
-<
+     * Creates a {@code ForkJoinPool} with the indicated parallelism
-<
+     * level and using the {@linkplain
-<
+     * #defaultForkJoinWorkerThreadFactory default thread factory}.
->
+     * Final callback from terminating worker.  Removes record of
->
+     * worker from array, and adjusts counts. If pool is shutting
->
+     * down, tries to complete terminatation.
-<
+     * @param parallelism the parallelism level
-<
+     * @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")}
->
+     * @param w the worker
+     */
-<
+    public ForkJoinPool(int parallelism) {
-<
+        this(parallelism, defaultForkJoinWorkerThreadFactory);
->
+    final void workerTerminated(ForkJoinWorkerThread w) {
->
+        forgetWorker(w);
->
+        decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL);
->
+        while (w.stealCount != 0) // collect final count
->
+            tryAccumulateStealCount(w);
->
+        tryTerminate(false);
-+
+    // Waiting for and signalling events
-+
+    /**
-<
+     * Creates a {@code ForkJoinPool} with parallelism equal to {@link
-<
+     * java.lang.Runtime#availableProcessors}, and using the given
-<
+     * thread factory.
->
+     * Releases workers blocked on a count not equal to current count.
->
+     * Normally called after precheck that eventWaiters isn't zero to
->
+     * avoid wasted array checks.
-<
+     * @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")}
->
+     * @param signalling true if caller is a signalling worker so can
->
+     * exit upon (conservatively) detected contention by other threads
->
+     * who will continue to release
+     */
-<
+    public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
-<
+        this(Runtime.getRuntime().availableProcessors(), factory);
->
+    private void releaseEventWaiters(boolean signalling) {
->
+        ForkJoinWorkerThread[] ws = workers;
->
+        int n = ws.length;
->
+        long h; // head of stack
->
+        ForkJoinWorkerThread w; int id, ec;
->
+        while ((id = ((int)((h = eventWaiters) & WAITER_ID_MASK)) - 1) >= 0 &&
->
+               (int)(h >>> EVENT_COUNT_SHIFT) != (ec = eventCount) &&
->
+               id < n && (w = ws[id]) != null) {
->
+            if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
->
+                                          h, h = w.nextWaiter))
->
+                LockSupport.unpark(w);
->
+            if (signalling && (eventCount != ec || eventWaiters != h))
->
+                break;
->
+        }
+    /**
-<
+     * Creates a {@code ForkJoinPool} with the given parallelism and
-<
+     * thread factory.
-<
+     *
-<
+     * @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
-<
+     * @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")}
->
+     * Tries to advance eventCount and releases waiters. Called only
->
+     * from workers.
+     */
-<
+    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<ForkJoinTask<?>>();
-<
+        // worker array and workers are lazily constructed
->
+    final void signalWork() {
->
+        int c; // try to increment event count -- CAS failure OK
->
+        UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
->
+        if (eventWaiters != 0L)
->
+            releaseEventWaiters(true);
+    /**
-<
+     * Creates a new worker thread using factory.
->
+     * Blocks worker until terminating or event count
->
+     * advances from last value held by worker
-<
+     * @param index the index to assign worker
-<
+     * @return new worker, or null if factory failed
->
+     * @param w the calling worker thread
+     */
-<
+    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);
->
+    private void eventSync(ForkJoinWorkerThread w) {
->
+        int wec = w.lastEventCount;
->
+        long nh = (((long)wec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
->
+        long h;
->
+        while ((runState < SHUTDOWN || !tryTerminate(false)) &&
->
+               ((h = eventWaiters) == 0L ||
->
+                (int)(h >>> EVENT_COUNT_SHIFT) == wec) &&
->
+               eventCount == wec) {
->
+            if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
->
+                                          w.nextWaiter = h, nh)) {
->
+                while (runState < TERMINATING && eventCount == wec) {
->
+                    if (!tryAccumulateStealCount(w))  // transfer while idle
->
+                        continue;
->
+                    Thread.interrupted();             // clear/ignore interrupt
->
+                    if (eventCount != wec)
->
+                        break;
->
+                    LockSupport.park(w);
->
+                }
->
+                break;
->
+            }
-<
+        return w;
->
+        w.lastEventCount = eventCount;
-+
+    // Maintaining spares
-+
+    /**
-<
+     * Returns a good size for worker array given pool size.
-<
+     * Currently requires size to be a power of two.
->
+     * Pushes worker onto the spare stack
+     */
-<
+    private static int arraySizeFor(int poolSize) {
-<
+        if (poolSize <= 1)
-<
+            return 1;
-<
+        // See Hackers Delight, sec 3.2
-<
+        int c = poolSize >= MAX_THREADS ? MAX_THREADS : (poolSize - 1);
-<
+        c |= c >>>  1;
-<
+        c |= c >>>  2;
-<
+        c |= c >>>  4;
-<
+        c |= c >>>  8;
-<
+        c |= c >>> 16;
-<
+        return c + 1;
->
+    final void pushSpare(ForkJoinWorkerThread w) {
->
+        int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex+1);
->
+        do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
->
+                                               w.nextSpare = spareWaiters,ns));
+    /**
-<
+     * Creates or resizes array if necessary to hold newLength.
-<
+     * Call only under exclusion.
-<
+     *
-<
+     * @return the array
->
+     * Tries (once) to resume a spare if running count is less than
->
+     * target parallelism. Fails on contention or stale workers.
+     */
-<
+    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;
->
+    private void tryResumeSpare() {
->
+        int sw, id;
->
+        ForkJoinWorkerThread w;
->
+        ForkJoinWorkerThread[] ws;
->
+        if ((id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 &&
->
+            id < (ws = workers).length && (w = ws[id]) != null &&
->
+            (workerCounts & RUNNING_COUNT_MASK) < parallelism &&
->
+            eventWaiters == 0L &&
->
+            spareWaiters == sw &&
->
+            UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
->
+                                     sw, w.nextSpare) &&
->
+            w.tryUnsuspend()) {
->
+            int c; // try increment; if contended, finish after unpark
->
+            boolean inc = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
->
+                                                   c = workerCounts,
->
+                                                   c + ONE_RUNNING);
->
+            LockSupport.unpark(w);
->
+            if (!inc) {
->
+                do {} while(!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
->
+                                                      c = workerCounts,
->
+                                                      c + ONE_RUNNING));
->
+            }
->
+        }
+    /**
-<
+     * Tries to shrink workers into smaller array after one or more terminate.
->
+     * Callback from oldest spare occasionally waking up.  Tries
->
+     * (once) to shutdown a spare if more than 25% spare overage, or
->
+     * if UNUSED_SPARE_TRIM_RATE_NANOS have elapsed and there are at
->
+     * least #parallelism running threads. Note that we don't need CAS
->
+     * or locks here because the method is called only from the oldest
->
+     * suspended spare occasionally waking (and even misfires are OK).
->
+     *
->
+     * @param now the wake up nanoTime of caller
+     */
-<
+    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 void tryTrimSpare(long now) {
->
+        long lastTrim = trimTime;
->
+        trimTime = now;
->
+        helpMaintainParallelism(); // first, help wake up any needed spares
->
+        int sw, id;
->
+        ForkJoinWorkerThread w;
->
+        ForkJoinWorkerThread[] ws;
->
+        int pc = parallelism;
->
+        int wc = workerCounts;
->
+        if ((wc & RUNNING_COUNT_MASK) >= pc &&
->
+            (((wc >>> TOTAL_COUNT_SHIFT) - pc) > (pc >>> 2) + 1 ||// approx 25%
->
+             now - lastTrim >= UNUSED_SPARE_TRIM_RATE_NANOS) &&
->
+            (id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 &&
->
+            id < (ws = workers).length && (w = ws[id]) != null &&
->
+            UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
->
+                                     sw, w.nextSpare))
->
+            w.shutdown(false);
->
+    }
->
->
+    /**
->
+     * Does at most one of:
->
+     *
->
+     * 1. Help wake up existing workers waiting for work via
->
+     *    releaseEventWaiters. (If any exist, then it probably doesn't
->
+     *    matter right now if under target parallelism level.)
->
+     *
->
+     * 2. If below parallelism level and a spare exists, try (once)
->
+     *    to resume it via tryResumeSpare.
->
+     *
->
+     * 3. If neither of the above, tries (once) to add a new
->
+     *    worker if either there are not enough total, or if all
->
+     *    existing workers are busy, there are either no running
->
+     *    workers or the deficit is at least twice the surplus.
->
+     */
->
+    private void helpMaintainParallelism() {
->
+        // uglified to work better when not compiled
->
+        int pc, wc, rc, tc, rs; long h;
->
+        if ((h = eventWaiters) != 0L) {
->
+            if ((int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
->
+                releaseEventWaiters(false); // avoid useless call
->
+        }
->
+        else if ((pc = parallelism) >
->
+                 (rc = ((wc = workerCounts) & RUNNING_COUNT_MASK))) {
->
+            if (spareWaiters != 0)
->
+                tryResumeSpare();
->
+            else if ((rs = runState) < TERMINATING &&
->
+                     ((tc = wc >>> TOTAL_COUNT_SHIFT) < pc ||
->
+                      (tc == (rs & ACTIVE_COUNT_MASK) && // all busy
->
+                       (rc == 0 ||                       // must add
->
+                        rc < pc - ((tc - pc) << 1)) &&   // within slack
->
+                       tc < MAX_WORKERS && runState == rs)) && // recheck busy
->
+                     workerCounts == wc &&
->
+                     UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
->
+                                              wc + (ONE_RUNNING|ONE_TOTAL)))
->
+                addWorker();
->
+        }
->
+    }
->
->
+    /**
->
+     * Callback from workers invoked upon each top-level action (i.e.,
->
+     * stealing a task or taking a submission and running
->
+     * it). Performs one or more of the following:
->
+     *
->
+     * 1. If the worker cannot find work (misses > 0), updates its
->
+     *    active status to inactive and updates activeCount unless
->
+     *    this is the first miss and there is contention, in which
->
+     *    case it may try again (either in this or a subsequent
->
+     *    call).
->
+     *
->
+     * 2. If there are at least 2 misses, awaits the next task event
->
+     *    via eventSync
->
+     *
->
+     * 3. If there are too many running threads, suspends this worker
->
+     *    (first forcing inactivation if necessary).  If it is not
->
+     *    needed, it may be killed while suspended via
->
+     *    tryTrimSpare. Otherwise, upon resume it rechecks to make
->
+     *    sure that it is still needed.
->
+     *
->
+     * 4. Helps release and/or reactivate other workers via
->
+     *    helpMaintainParallelism
->
+     *
->
+     * @param w the worker
->
+     * @param misses the number of scans by caller failing to find work
->
+     * (saturating at 2 just to avoid wraparound)
->
+     */
->
+    final void preStep(ForkJoinWorkerThread w, int misses) {
->
+        boolean active = w.active;
->
+        int pc = parallelism;
->
+        for (;;) {
->
+            int wc = workerCounts;
->
+            int rc = wc & RUNNING_COUNT_MASK;
->
+            if (active && (misses > 0 || rc > pc)) {
->
+                int rs;                      // try inactivate
->
+                if (UNSAFE.compareAndSwapInt(this, runStateOffset,
->
+                                             rs = runState, rs - ONE_ACTIVE))
->
+                    active = w.active = false;
->
+                else if (misses > 1 || rc > pc ||
->
+                         (rs & ACTIVE_COUNT_MASK) >= pc)
->
+                    continue;                // force inactivate
->
+            }
->
+            if (misses > 1) {
->
+                misses = 0;                  // don't re-sync
->
+                eventSync(w);                // continue loop to recheck rc
->
+            }
->
+            else if (rc > pc) {
->
+                if (workerCounts == wc &&   // try to suspend as spare
->
+                    UNSAFE.compareAndSwapInt(this, workerCountsOffset,
->
+                                             wc, wc - ONE_RUNNING) &&
->
+                    !w.suspendAsSpare())    // false if killed
->
+                    break;
->
+            }
->
+            else {
->
+                if (rc < pc || eventWaiters != 0L)
->
+                    helpMaintainParallelism();
->
+                break;
->
+            }
+    /**
-<
+     * 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();
->
+     * Helps and/or blocks awaiting join of the given task.
->
+     * Alternates between helpJoinTask() and helpMaintainParallelism()
->
+     * as many times as there is a deficit in running count (or longer
->
+     * if running count would become zero), then blocks if task still
->
+     * not done.
->
+     *
->
+     * @param joinMe the task to join
->
+     */
->
+    final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) {
->
+        int threshold = parallelism;         // descend blocking thresholds
->
+        while (joinMe.status >= 0) {
->
+            boolean block; int wc;
->
+            worker.helpJoinTask(joinMe);
->
+            if (joinMe.status < 0)
->
+                break;
->
+            if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) {
->
+                if (threshold > 0)
->
+                    --threshold;
->
+                else
->
+                    advanceEventCount(); // force release
->
+                block = false;
->
+            }
->
+            else
->
+                block = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
->
+                                                 wc, wc - ONE_RUNNING);
->
+            helpMaintainParallelism();
->
+            if (block) {
->
+                int c;
->
+                joinMe.internalAwaitDone();
->
+                do {} while (!UNSAFE.compareAndSwapInt
->
+                             (this, workerCountsOffset,
->
+                              c = workerCounts, c + ONE_RUNNING));
->
+                break;
+    /**
-<
+     * Worker creation and startup for threads added via setParallelism.
->
+     * Same idea as awaitJoin, but no helping
+     */
-<
+    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;
->
+    final void awaitBlocker(ManagedBlocker blocker)
->
+        throws InterruptedException {
->
+        int threshold = parallelism;
->
+        while (!blocker.isReleasable()) {
->
+            boolean block; int wc;
->
+            if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) {
->
+                if (threshold > 0)
->
+                    --threshold;
->
+                else
->
+                    advanceEventCount();
->
+                block = false;
-<
+            int s = workerCounts;
-<
+            int tc = totalCountOf(s);
-<
+            int rc = runningCountOf(s);
-<
+            if (rc >= ps || tc >= ps)
->
+            else
->
+                block = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
->
+                                                 wc, wc - ONE_RUNNING);
->
+            helpMaintainParallelism();
->
+            if (block) {
->
+                try {
->
+                    do {} while (!blocker.isReleasable() && !blocker.block());
->
+                } finally {
->
+                    int c;
->
+                    do {} while (!UNSAFE.compareAndSwapInt
->
+                                 (this, workerCountsOffset,
->
+                                  c = workerCounts, c + ONE_RUNNING));
->
+                }
+                break;
-<
+            if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
-<
+                ForkJoinWorkerThread w = createWorker(k);
->
+            }
->
+        }
->
+    }
->
->
+    /**
->
+     * 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 (advanceRunLevel(TERMINATING))
->
+            startTerminating();
->
->
+        // Finish now if all threads terminated; else in some subsequent call
->
+        if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
->
+            advanceRunLevel(TERMINATED);
->
+            termination.arrive();
->
+        }
->
+        return true;
->
+    }
->
->
+    /**
->
+     * Actions on transition to TERMINATING
->
+     *
->
+     * Runs up to four passes through workers: (0) shutting down each
->
+     * quietly (without waking up if parked) to quickly spread
->
+     * notifications without unnecessary bouncing around event queues
->
+     * etc (1) wake up and help cancel tasks (2) interrupt (3) mop up
->
+     * races with interrupted workers
->
+     */
->
+    private void startTerminating() {
->
+        cancelSubmissions();
->
+        for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
->
+            advanceEventCount();
->
+            eventWaiters = 0L; // clobber lists
->
+            spareWaiters = 0;
->
+            ForkJoinWorkerThread[] ws = workers;
->
+            int n = ws.length;
->
+            for (int i = 0; i < n; ++i) {
->
+                ForkJoinWorkerThread w = ws[i];
+                if (w != null) {
-<
+                    ws[k++] = w;
-<
+                    w.start();
-<
+                }
-<
+                else {
-<
+                    updateWorkerCount(-1); // back out on failed creation
-<
+                    break;
->
+                    w.shutdown(true);
->
+                    if (passes > 0 && !w.isTerminated()) {
->
+                        w.cancelTasks();
->
+                        LockSupport.unpark(w);
->
+                        if (passes > 1) {
->
+                            try {
->
+                                w.interrupt();
->
+                            } catch (SecurityException ignore) {
->
+                            }
->
+                        }
->
+                    }
-+
+    /**
-+
+     * Clear out and cancel submissions, ignoring exceptions
-+
+     */
-+
+    private void cancelSubmissions() {
-+
+        ForkJoinTask<?> task;
-+
+        while ((task = submissionQueue.poll()) != null) {
-+
+            try {
-+
+                task.cancel(false);
-+
+            } catch (Throwable ignore) {
-+
+            }
-+
+        }
-+
+    }
-+
-+
+    // misc support for ForkJoinWorkerThread
-+
-+
+    /**
-+
+     * Returns pool number
-+
+     */
-+
+    final int getPoolNumber() {
-+
+        return poolNumber;
-+
+    }
-+
-+
+    /**
-+
+     * Tries to accumulates steal count from a worker, clearing
-+
+     * the worker's value.
-+
+     *
-+
+     * @return true if worker steal count now zero
-+
+     */
-+
+    final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
-+
+        int sc = w.stealCount;
-+
+        long c = stealCount;
-+
+        // CAS even if zero, for fence effects
-+
+        if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
-+
+            if (sc != 0)
-+
+                w.stealCount = 0;
-+
+            return true;
-+
+        }
-+
+        return sc == 0;
-+
+    }
-+
-+
+    /**
-+
+     * Returns the approximate (non-atomic) number of idle threads per
-+
+     * active thread.
-+
+     */
-+
+    final int idlePerActive() {
-+
+        int pc = parallelism; // use parallelism, not rc
-+
+        int ac = runState;    // no mask -- artifically boosts during shutdown
-+
+        // Use exact results for small values, saturate past 4
-+
+        return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
-+
+    }
-+
-+
+    // Public and protected 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</code>.
-+
+     * @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</code>.
-+
+     * @throws IllegalArgumentException if parallelism less than or
-+
+     *         equal to zero, or greater than implementation limit
-+
+     * @throws NullPointerException if the factory is null
-+
+     * @throws SecurityException if a security manager exists and
-+
+     *         the caller is not permitted to modify threads
-+
+     *         because it does not hold {@link
-+
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
-+
+     */
-+
+    public ForkJoinPool(int parallelism,
-+
+                        ForkJoinWorkerThreadFactory factory,
-+
+                        Thread.UncaughtExceptionHandler handler,
-+
+                        boolean asyncMode) {
-+
+        checkPermission();
-+
+        if (factory == null)
-+
+            throw new NullPointerException();
-+
+        if (parallelism <= 0 || parallelism > MAX_WORKERS)
-+
+            throw new IllegalArgumentException();
-+
+        this.parallelism = parallelism;
-+
+        this.factory = factory;
-+
+        this.ueh = handler;
-+
+        this.locallyFifo = asyncMode;
-+
+        int arraySize = initialArraySizeFor(parallelism);
-+
+        this.workers = new ForkJoinWorkerThread[arraySize];
-+
+        this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
-+
+        this.workerLock = new ReentrantLock();
-+
+        this.termination = new Phaser(1);
-+
+        this.poolNumber = poolNumberGenerator.incrementAndGet();
-+
+        this.trimTime = System.nanoTime();
-+
+    }
-+
-+
+    /**
-+
+     * 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_WORKERS < (1 >>> 16)
-+
+        int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
-+
+        size |= size >>> 1;
-+
+        size |= size >>> 2;
-+
+        size |= size >>> 4;
-+
+        size |= size >>> 8;
-+
+        return size + 1;
-+
+    }
-+
+    // Execution methods
+    /**
+    private <T> void doSubmit(ForkJoinTask<T> task) {
+        if (task == null)
+            throw new NullPointerException();
-<
+        if (isShutdown())
->
+        if (runState >= SHUTDOWN)
+            throw new RejectedExecutionException();
-–
+        if (workers == null)
-–
+            ensureWorkerInitialization();
+        submissionQueue.offer(task);
-<
+        signalIdleWorkers();
->
+        advanceEventCount();
->
+        helpMaintainParallelism();         // start or wake up workers
+    /**
+     * Performs the given task, returning its result upon completion.
-+
+     * If the caller is already engaged in a fork/join computation in
-+
+     * the current pool, this method is equivalent in effect to
-+
+     * {@link ForkJoinTask#invoke}.
+     * @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> T invoke(ForkJoinTask<T> task) {
+        doSubmit(task);
+    /**
+     * Arranges for (asynchronous) execution of the given task.
-+
+     * If the caller is already engaged in a fork/join computation in
-+
+     * the current pool, this method is equivalent in effect to
-+
+     * {@link ForkJoinTask#fork}.
+     * @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);
+    // 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
+        doSubmit(job);
-+
+    /**
-+
+     * Submits a ForkJoinTask for execution.
-+
+     * If the caller is already engaged in a fork/join computation in
-+
+     * the current pool, this method is equivalent in effect to
-+
+     * {@link ForkJoinTask#fork}.
-+
+     *
-+
+     * @param task the task to submit
-+
+     * @return the task
-+
+     * @throws NullPointerException if the task is null
-+
+     * @throws RejectedExecutionException if the task cannot be
-+
+     *         scheduled for execution
-+
+     */
-+
+    public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
-+
+        doSubmit(task);
-+
+        return task;
-+
+    }
-+
-+
+    /**
-+
+     * @throws NullPointerException if the task is null
-+
+     * @throws RejectedExecutionException if the task cannot be
-+
+     *         scheduled for execution
-+
+     */
+    public <T> ForkJoinTask<T> submit(Callable<T> task) {
+        ForkJoinTask<T> 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 <T> ForkJoinTask<T> submit(Runnable task, T result) {
+        ForkJoinTask<T> 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
+    /**
-<
+     * Submits a ForkJoinTask for execution.
-<
+     *
-<
+     * @param task the task to submit
-<
+     * @return the task
-<
+     * @throws RejectedExecutionException if the task cannot be
-<
+     *         scheduled for execution
-<
+     * @throws NullPointerException if the task is null
->
+     * @throws NullPointerException       {@inheritDoc}
->
+     * @throws RejectedExecutionException {@inheritDoc}
+     */
-–
+    public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
-–
+        doSubmit(task);
-–
+        return task;
-–
+    }
-–
-–
+    public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
+        ArrayList<ForkJoinTask<T>> forkJoinTasks =
+            new ArrayList<ForkJoinTask<T>>(tasks.size());
+        invoke(new InvokeAll<T>(forkJoinTasks));
+        @SuppressWarnings({"unchecked", "rawtypes"})
-<
+        List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
->
+            List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
+        return futures;
+        private static final long serialVersionUID = -7914297376763021607L;
-–
+    // Configuration and status settings and queries
-–
+    /**
+     * Returns the factory used for constructing new workers.
+     * @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;
-<
+    }
-<
-<
+    /**
-<
+     * Sets the handler for internal worker threads that terminate due
-<
+     * to unrecoverable errors encountered while executing tasks.
-<
+     * Unless set, the current default or ThreadGroup handler is used
-<
+     * as handler.
-<
+     *
-<
+     * @param h the new handler
-<
+     * @return the old handler, or {@code 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 (isProcessingTasks()) {
-<
+                int p = this.parallelism;
-<
+                this.parallelism = parallelism;
-<
+                if (parallelism > p)
-<
+                    createAndStartAddedWorkers();
-<
+                else
-<
+                    trimSpares();
-<
+            }
-<
+        } finally {
-<
+            lock.unlock();
-<
+        }
-<
+        signalIdleWorkers();
->
+        return ueh;
+    /**
+     * @return the number of worker threads
+     */
+    public int getPoolSize() {
-<
+        return totalCountOf(workerCounts);
-<
+    }
-<
-<
+    /**
-<
+     * Returns the maximum number of threads allowed to exist in the
-<
+     * 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() {
-<
+        return maxPoolSize;
-<
+    }
-<
-<
+    /**
-<
+     * Sets the maximum number of threads allowed to exist in the
-<
+     * pool.  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
-<
+     */
-<
+    public void setMaximumPoolSize(int newMax) {
-<
+        if (newMax < 0 || newMax > MAX_THREADS)
-<
+            throw new IllegalArgumentException();
-<
+        maxPoolSize = newMax;
-<
+    }
-<
-<
-<
+    /**
-<
+     * Returns {@code 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 {@code 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 {@code true} to maintain 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 the pool is quiescent, and
-<
+     * typically only before any tasks are submitted. The effects of
-<
+     * invocations at other times may be unpredictable.
-<
+     *
-<
+     * @param async if {@code true}, use locally FIFO scheduling
-<
+     * @return the previous mode
-<
+     * @see #getAsyncMode
-<
+     */
-<
+    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 workerCounts >>> TOTAL_COUNT_SHIFT;
+    /**
+     * scheduling mode for forked tasks that are never joined.
+     * @return {@code true} if this pool uses async mode
-–
+     * @see #setAsyncMode
+     */
+    public boolean getAsyncMode() {
+        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;
+    /**
+     * @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;
+    /**
+     * @return {@code true} if all threads are currently idle
+     */
+    public boolean isQuiescent() {
-<
+        return activeCountOf(runControl) == 0;
->
+        return (runState & ACTIVE_COUNT_MASK) == 0;
+    /**
+     * @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;
+    /**
+    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();
-<
+            }
->
+        int n = ws.length;
->
+        for (int i = 0; i < n; ++i) {
->
+            ForkJoinWorkerThread w = ws[i];
->
+            if (w != null)
->
+                count += w.getQueueSize();
+        return count;
+     * @return the number of elements transferred
+     */
+    protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
-<
+        int n = submissionQueue.drainTo(c);
->
+        int count = 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);
-<
+            }
->
+        int n = ws.length;
->
+        for (int i = 0; i < n; ++i) {
->
+            ForkJoinWorkerThread w = ws[i];
->
+            if (w != null)
->
+                count += w.drainTasksTo(c);
-<
+        return n;
->
+        return count;
+    /**
+     * @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.
+     */
+    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);
+    /**
+     */
+    public List<Runnable> shutdownNow() {
+        checkPermission();
-<
+        terminate();
->
+        tryTerminate(true);
+        return Collections.emptyList();
+     * @return {@code true} if all tasks have completed following shut down
+     */
+    public boolean isTerminated() {
-<
+        return runStateOf(runControl) == TERMINATED;
->
+        return runState >= TERMINATED;
+    /**
+     * @return {@code true} if terminating but not yet terminated
+     */
+    public boolean isTerminating() {
-<
+        return runStateOf(runControl) == TERMINATING;
->
+        return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
+    /**
+     * @return {@code true} if this pool has been shut down
+     */
+    public boolean isShutdown() {
-<
+        return runStateOf(runControl) >= SHUTDOWN;
-<
+    }
-<
-<
+    /**
-<
+     * Returns true if pool is not terminating or terminated.
-<
+     * Used internally to suppress execution when terminating.
-<
+     */
-<
+    final boolean isProcessingTasks() {
-<
+        return runStateOf(runControl) < TERMINATING;
->
+        return runState >= SHUTDOWN;
+    /**
+     */
+    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 (isProcessingTasks()) {
-–
+                    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() && isProcessingTasks() && !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 termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
->
+        } catch(TimeoutException ex) {
+            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 && isProcessingTasks() && (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 {@link ForkJoinPool}s.
-<
+     * <p>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).
->
+     * <p>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). 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.
+     * <p>For example, here is a ManagedBlocker based on a
+     * ReentrantLock:
+     *     return hasLock || (hasLock = lock.tryLock());
+     *   }
+     * }}</pre>
-+
+     *
-+
+     * <p>Here is a class that possibly blocks waiting for an
-+
+     * item on a given queue:
-+
+     *  <pre> {@code
-+
+     * class QueueTaker<E> implements ManagedBlocker {
-+
+     *   final BlockingQueue<E> queue;
-+
+     *   volatile E item = null;
-+
+     *   QueueTaker(BlockingQueue<E> 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;
-+
+     *   }
-+
+     * }}</pre>
+     */
+    public static interface ManagedBlocker {
+        /**
+     * Blocks in accord with the given blocker.  If the current thread
+     * is a {@link ForkJoinWorkerThread}, this method possibly
+     * arranges for a spare thread to be activated if necessary to
-<
+     * ensure parallelism while the current thread is blocked.
-<
+     *
-<
+     * <p>If {@code maintainParallelism} is {@code 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.
->
+     * ensure sufficient parallelism while the current thread is blocked.
+     * <p>If the caller is not a {@link ForkJoinTask}, this method is
+     * behaviorally equivalent to
+     * first be expanded to ensure parallelism, and later adjusted.
+     * @param blocker the blocker
-–
+     * @param maintainParallelism if {@code 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.  These rely on undocumented
+    // 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 final long spareWaitersOffset =
->
+        objectFieldOffset("spareWaiters",ForkJoinPool.class);
+    private static long objectFieldOffset(String field, Class<?> klazz) {
+        try {

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents): Revision 1.43 by jsr166, Tue Aug 4 00:55:13 2009 UTC vs. Revision 1.62 by dl, Wed Aug 11 20:28:22 2010 UTC

Diff Legend

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.43 by jsr166, Tue Aug 4 00:55:13 2009 UTC vs.
Revision 1.62 by dl, Wed Aug 11 20:28:22 2010 UTC