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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.41 by jsr166, Mon Aug 3 01:11:58 2009 UTC vs.
Revision 1.58 by dl, Fri Jul 23 13:07:43 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.  Normally a single {@code ForkJoinPool} is
-<
+ * used for a large number of submitted tasks. Otherwise, use would
-<
+ * not usually outweigh the construction and bookkeeping overhead of
-<
+ * creating a large set of threads.
->
+ * from non-{@code ForkJoinTask} clients, as well as management and
->
+ * monitoring operations.
-<
+ * <p>{@code ForkJoinPool}s differ from other kinds of {@link
-<
+ * Executor}s mainly in that they provide <em>work-stealing</em>: all
-<
+ * threads in the pool attempt to find and execute subtasks created by
-<
+ * other active tasks (eventually blocking if none exist). This makes
-<
+ * them efficient when most tasks spawn other subtasks (as do most
-<
+ * {@code ForkJoinTask}s), as well as the mixed execution of some
-<
+ * plain {@code Runnable}- or {@code Callable}- based activities along
-<
+ * with {@code ForkJoinTask}s. When setting {@linkplain #setAsyncMode
-<
+ * async mode}, a {@code ForkJoinPool} may also be appropriate for use
-<
+ * with fine-grained tasks that are never joined. Otherwise, other
-<
+ * {@code ExecutorService} implementations are typically more
-<
+ * appropriate choices.
->
+ * <p>A {@code ForkJoinPool} differs from other kinds of {@link
->
+ * ExecutorService} mainly by virtue of employing
->
+ * <em>work-stealing</em>: all threads in the pool attempt to find and
->
+ * execute subtasks created by other active tasks (eventually blocking
->
+ * waiting for work if none exist). This enables efficient processing
->
+ * when most tasks spawn other subtasks (as do most {@code
->
+ * ForkJoinTask}s). When setting <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} may be constructed with a given
-<
+ * parallelism level (target pool size), which it attempts to maintain
-<
+ * by dynamically adding, suspending, or resuming threads, even if
-<
+ * some tasks are waiting to join others. However, no such adjustments
-<
+ * are performed in the face of blocked IO or other unmanaged
-<
+ * synchronization. The nested {@link ManagedBlocker} interface
-<
+ * enables extension of the kinds of synchronization accommodated.
-<
+ * The target parallelism level may also be changed dynamically
-<
+ * ({@link #setParallelism}) and thread construction can be limited
-<
+ * using methods {@link #setMaximumPoolSize} and/or {@link
-<
+ * #setMaintainsParallelism}.
->
+ * <p>A {@code ForkJoinPool} is constructed with a given target
->
+ * parallelism level; by default, equal to the number of available
->
+ * processors. The pool attempts to maintain enough active (or
->
+ * available) threads by dynamically adding, suspending, or resuming
->
+ * internal worker threads, even if some tasks are stalled waiting to
->
+ * join others. However, no such adjustments are guaranteed in the
->
+ * face of blocked IO or other unmanaged synchronization. The nested
->
+ * {@link ManagedBlocker} interface enables extension of the kinds of
->
+ * synchronization accommodated.
+ * <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 follwoing
-+
+ * 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
-+
+ * bookkeeping overhead of creating a large set of threads. For
-+
+ * example, a common pool could be used for the {@code SortTasks}
-+
+ * illustrated in {@link RecursiveAction}. Because {@code
-+
+ * ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
-+
+ * daemon} mode, there is typically no need to explicitly {@link
-+
+ * #shutdown} such a pool upon program exit.
-+
+ *
-+
+ * <pre>
-+
+ * static final ForkJoinPool mainPool = new ForkJoinPool();
-+
+ * ...
-+
+ * public void sort(long[] array) {
-+
+ *   mainPool.invoke(new SortTask(array, 0, array.length));
-+
+ * }
-+
+ * </pre>
-+
+ *
+ * <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 exhuasted.
-+
+ *
+ * @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 arrange tactics for
->
+     * 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:
->
+     *
->
+     *   1. 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.
->
+     *
->
+     *   2. Unless there are already enough live threads, creating or
->
+     *      or re-activating a spare thread to compensate for the
->
+     *      (blocked) joiner until it unblocks.  Spares then suspend
->
+     *      at their next opportunity or eventually die if unused for
->
+     *      too long.  See below and the internal documentation
->
+     *      for tryAwaitJoin for more details about compensation
->
+     *      rules.
->
+     *
->
+     * 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, joins (in
->
+     * ForkJoinWorkerThread.joinTask) interleave these options until
->
+     * successful.  Creating a new spare always succeeds, but also
->
+     * increases application footprint, so we try to avoid it, within
->
+     * reason.
->
+     *
->
+     * The ManagedBlocker extension API can't use option (1) so uses a
->
+     * special version of (2) 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.
->
+     *
->
+     * 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 and reconfiguration actions that
->
+     * require wakeups of idle workers).  Each worker maintains its
->
+     * last known event count, and blocks when a scan for work did not
->
+     * find a task AND its lastEventCount matches the current
->
+     * eventCount. Waiting idle workers are recorded in a variant of
->
+     * Treiber stack headed by field eventWaiters which, when nonzero,
->
+     * encodes the thread index and count awaited for by the worker
->
+     * thread most recently calling eventSync. This thread in turn has
->
+     * a record (field nextEventWaiter) for the next waiting worker.
->
+     * In addition to allowing simpler decisions about need for
->
+     * wakeup, the event count bits in eventWaiters serve the role of
->
+     * tags to avoid ABA errors in Treiber stacks.  To reduce delays
->
+     * in task diffusion, workers not otherwise occupied may invoke
->
+     * method releaseWaiters, that removes and signals (unparks)
->
+     * workers not waiting on current count. To minimize task
->
+     * production stalls associate with signalling, any worker pushing
->
+     * a task on an empty queue invokes the weaker method signalWork,
->
+     * that only releases idle workers until it detects interference
->
+     * by other threads trying to release, and lets them take
->
+     * over. The net effect is a tree-like diffusion of signals, where
->
+     * released threads (and possibly others) help with unparks.  To
->
+     * further reduce contention effects a bit, failed CASes to
->
+     * increment field eventCount are tolerated without retries.
->
+     * Conceptually they are merged into the same event, which is OK
->
+     * when their only purpose is to enable workers to scan for work.
->
+     *
->
+     * 5. Managing suspension of extra workers. When a worker is about
->
+     * to block waiting for a join (or via ManagedBlockers), we may
->
+     * create a new thread to maintain parallelism level, or at least
->
+     * avoid starvation. Usually, extra threads are needed for only
->
+     * very short periods, yet join dependencies are such that we
->
+     * sometimes need them in bursts. Rather than create new threads
->
+     * each time this happens, we suspend no-longer-needed extra ones
->
+     * as "spares". For most purposes, we don't distinguish "extra"
->
+     * spare threads from normal "core" threads: On each call to
->
+     * preStep (the only point at which we can do this) a worker
->
+     * checks to see if there are now too many running workers, and if
->
+     * so, suspends itself.  Methods tryAwaitJoin and awaitBlocker
->
+     * look for suspended threads to resume before considering
->
+     * creating a new replacement. We don't need a special data
->
+     * structure to maintain spares; simply scanning the workers array
->
+     * looking for worker.isSuspended() is fine because the calling
->
+     * thread is otherwise not doing anything useful anyway; we are at
->
+     * least as happy if after locating a spare, the caller doesn't
->
+     * actually block because the join is ready before we try to
->
+     * adjust and compensate.  Note that this is intrinsically racy.
->
+     * One thread may become a spare at about the same time as another
->
+     * is needlessly being created. We counteract this and related
->
+     * slop in part by requiring resumed spares to immediately recheck
->
+     * (in preStep) to see whether they they should re-suspend. The
->
+     * only effective difference between "extra" and "core" threads is
->
+     * that we allow the "extra" ones to time out and die if they are
->
+     * not resumed within a keep-alive interval of a few seconds. This
->
+     * is implemented mainly within ForkJoinWorkerThread, but requires
->
+     * some coordination (isTrimmed() -- meaning killed while
->
+     * suspended) to correctly maintain pool counts.
->
+     *
->
+     * 6. Deciding when to create new workers. The main dynamic
->
+     * control in this class is deciding when to create extra threads,
->
+     * in methods awaitJoin and awaitBlocker. We always need to create
->
+     * one when the number of running threads would become zero and
->
+     * all workers are busy. However, this is not easy to detect
->
+     * reliably in the presence of transients so we use retries and
->
+     * allow slack (in tryAwaitJoin) to reduce false alarms.  These
->
+     * effectively reduce churn at the price of systematically
->
+     * undershooting target parallelism when many threads are blocked.
->
+     * However, biasing toward undeshooting partially compensates for
->
+     * the above mechanics to suspend extra threads, that normally
->
+     * lead to overshoot because we can only suspend workers
->
+     * in-between top-level actions. It also better copes with the
->
+     * fact that some of the methods in this class tend to never
->
+     * become compiled (but are interpreted), so some components of
->
+     * the entire set of controls might execute many times faster than
->
+     * others. And similarly for cases where the apparent lack of work
->
+     * is just due to GC stalls and other transient system activity.
->
+     *
->
+     * Beware that there is a lot of representation-level coupling
->
+     * among classes ForkJoinPool, ForkJoinWorkerThread, and
->
+     * ForkJoinTask.  For example, direct access to "workers" array by
->
+     * workers, and direct access to ForkJoinTask.status by both
->
+     * ForkJoinPool and ForkJoinWorkerThread.  There is little point
->
+     * trying to reduce this, since any associated future changes in
->
+     * representations will need to be accompanied by algorithmic
->
+     * changes anyway.
->
+     *
->
+     * Style notes: There are lots of inline assignments (of form
->
+     * "while ((local = field) != 0)") which are usually the simplest
->
+     * way to ensure read orderings. Also several occurrences of the
->
+     * unusual "do {} while(!cas...)" which is the simplest way to
->
+     * force an update of a CAS'ed variable. There are also other
->
+     * coding oddities that help some methods perform reasonably even
->
+     * when interpreted (not compiled), at the expense of messiness.
->
+     *
->
+     * 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 must
->
+     * fit into a 16bit field to enable word-packing for some counts.
+     */
-<
+    volatile ForkJoinWorkerThread[] workers;
->
+    private static final int MAX_THREADS = 0x7fff;
+    /**
-<
+     * Lock protecting access to workers.
->
+     * 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.
+     */
-<
+    private final ReentrantLock workerLock;
->
+    volatile ForkJoinWorkerThread[] workers;
+    /**
-<
+     * Condition for awaitTermination.
->
+     * Queue for external submissions.
+     */
-<
+    private final Condition termination;
->
+    private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
+    /**
-<
+     * The uncaught exception handler used when any worker
-<
+     * abruptly terminates
->
+     * Lock protecting updates to workers array.
+     */
-<
+    private Thread.UncaughtExceptionHandler ueh;
->
+    private final ReentrantLock workerLock;
+    /**
-<
+     * Creation factory for worker threads.
->
+     * Latch released upon termination.
+     */
-<
+    private final ForkJoinWorkerThreadFactory factory;
->
+    private final Phaser termination;
+    /**
-<
+     * Head of stack of threads that were created to maintain
-<
+     * parallelism when other threads blocked, but have since
-<
+     * suspended when the parallelism level rose.
->
+     * Creation factory for worker threads.
+     */
-<
+    private volatile WaitQueueNode spareStack;
->
+    private final ForkJoinWorkerThreadFactory factory;
+    /**
+     * 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.
->
+     * Encoded record of top of treiber stack of threads waiting for
->
+     * events. The top 32 bits contain the count being waited for. The
->
+     * bottom word contains one plus the pool index of waiting worker
->
+     * thread.
+     */
-<
+    private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
->
+    private volatile long eventWaiters;
->
->
+    private static final int  EVENT_COUNT_SHIFT = 32;
->
+    private static final long WAITER_ID_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
+    /**
-<
+     * Head of Treiber stack for barrier sync. See below for explanation.
->
+     * A counter for events that may wake up worker threads:
->
+     *   - Submission of a new task to the pool
->
+     *   - A worker pushing a task on an empty queue
->
+     *   - termination and reconfiguration
+     */
-<
+    private volatile WaitQueueNode syncStack;
->
+    private volatile int eventCount;
+    /**
-<
+     * The count for event barrier
-<
+     */
-<
+    private volatile long eventCount;
->
+     * 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
+    /**
-<
+     * Pool number, just for assigning useful names to worker threads
->
+     * Holds number of total (i.e., created and not yet terminated)
->
+     * and running (i.e., not blocked on joins or other managed sync)
->
+     * threads, packed together to ensure consistent snapshot when
->
+     * making decisions about creating and suspending spare
->
+     * threads. Updated only by CAS. Note that adding a new worker
->
+     * requires incrementing both counts, since workers start off in
->
+     * running state.  This field is also used for memory-fencing
->
+     * configuration parameters.
+     */
-<
+    private final int poolNumber;
->
+    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 maximum allowed pool size
->
+     * The target parallelism level.
->
+     * Accessed directly by ForkJoinWorkerThreads.
+     */
-<
+    private volatile int maxPoolSize;
->
+    final int parallelism;
+    /**
-<
+     * The desired parallelism level, updated only under workerLock.
->
+     * True if use local fifo, not default lifo, for local polling
->
+     * Read by, and replicated by ForkJoinWorkerThreads
+     */
-<
+    private volatile int parallelism;
->
+    final boolean locallyFifo;
+    /**
-<
+     * True if use local fifo, not default lifo, for local polling
->
+     * The uncaught exception handler used when any worker abruptly
->
+     * terminates.
+     */
-<
+    private volatile boolean locallyFifo;
->
+    private final Thread.UncaughtExceptionHandler ueh;
+    /**
-<
+     * Holds number of total (i.e., created and not yet terminated)
-<
+     * and running (i.e., not blocked on joins or other managed sync)
-<
+     * threads, packed into one int to ensure consistent snapshot when
-<
+     * making decisions about creating and suspending spare
-<
+     * threads. Updated only by CAS.  Note: CASes in
-<
+     * updateRunningCount and preJoin assume that running active count
-<
+     * is in low word, so need to be modified if this changes.
->
+     * Pool number, just for assigning useful names to worker threads
+     */
-<
+    private volatile int workerCounts;
->
+    private final int poolNumber;
-<
+    private static int totalCountOf(int s)           { return s >>> 16;  }
-<
+    private static int runningCountOf(int s)         { return s & shortMask; }
-<
+    private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
->
+    // Utilities for 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.  Also used by ForkJoinTask.
+     */
-<
+    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
->
+     * Tries to increment running count
+     */
-<
+    private volatile int runControl;
-<
-<
+    // RunState values. Order among values matters
-<
+    private static final int RUNNING     = 0;
-<
+    private static final int SHUTDOWN    = 1;
-<
+    private static final int TERMINATING = 2;
-<
+    private static final int TERMINATED  = 3;
-<
-<
+    private static int runStateOf(int c)             { return c >>> 16; }
-<
+    private static int activeCountOf(int c)          { return c & shortMask; }
-<
+    private static int runControlFor(int r, int a)   { return (r << 16) + a; }
->
+    final boolean tryIncrementRunningCount() {
->
+        int wc;
->
+        return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
->
+                                        wc = workerCounts, wc + ONE_RUNNING);
->
+    }
+    /**
+     * 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 nws = ws.length;
->
+            if (k < 0 || k >= nws || ws[k] != null) {
->
+                for (k = 0; k < nws && ws[k] != null; ++k)
->
+                    ;
->
+                if (k == nws)
->
+                    ws = Arrays.copyOf(ws, nws << 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 a pool size equal to the
-<
+     * number of processors available on the system, using the
-<
+     * {@linkplain #defaultForkJoinWorkerThreadFactory default thread factory}.
->
+     * Tries to create and add new worker. Assumes that worker counts
->
+     * are already updated to accommodate the worker, so adjusts on
->
+     * failure.
-<
+     * @throws SecurityException if a security manager exists and
-<
+     *         the caller is not permitted to modify threads
-<
+     *         because it does not hold {@link
-<
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
->
+     * @return new worker or null if creation failed
+     */
-<
+    public ForkJoinPool() {
-<
+        this(Runtime.getRuntime().availableProcessors(),
-<
+             defaultForkJoinWorkerThreadFactory);
->
+    private ForkJoinWorkerThread addWorker() {
->
+        ForkJoinWorkerThread w = null;
->
+        try {
->
+            w = factory.newThread(this);
->
+        } finally { // Adjust on either null or exceptional factory return
->
+            if (w == null) {
->
+                onWorkerCreationFailure();
->
+                return null;
->
+            }
->
+        }
->
+        w.start(recordWorker(w), ueh);
->
+        return w;
+    /**
-<
+     * Creates a {@code ForkJoinPool} with the indicated parallelism level
-<
+     * threads and using the
-<
+     * {@linkplain #defaultForkJoinWorkerThreadFactory default thread factory}.
-<
+     *
-<
+     * @param parallelism the number of worker threads
-<
+     * @throws IllegalArgumentException if parallelism less than or
-<
+     * equal to zero
-<
+     * @throws SecurityException if a security manager exists and
-<
+     *         the caller is not permitted to modify threads
-<
+     *         because it does not hold {@link
-<
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
->
+     * Adjusts counts upon failure to create worker
+     */
-<
+    public ForkJoinPool(int parallelism) {
-<
+        this(parallelism, defaultForkJoinWorkerThreadFactory);
->
+    private void onWorkerCreationFailure() {
->
+        for (;;) {
->
+            int wc = workerCounts;
->
+            if ((wc >>> TOTAL_COUNT_SHIFT) == 0)
->
+                Thread.yield(); // wait for other counts to settle
->
+            else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
->
+                                              wc - (ONE_RUNNING|ONE_TOTAL)))
->
+                break;
->
+        }
->
+        tryTerminate(false); // in case of failure during shutdown
+    /**
-<
+     * Creates a {@code ForkJoinPool} with parallelism equal to the
-<
+     * number of processors available on the system and using the
-<
+     * given thread factory.
->
+     * Creates and/or resumes enough workers to establish target
->
+     * parallelism, giving up if terminating or addWorker fails
-<
+     * @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")}
->
+     * TODO: recast this to support lazier creation and automated
->
+     * parallelism maintenance
+     */
-<
+    public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
-<
+        this(Runtime.getRuntime().availableProcessors(), factory);
->
+    private void ensureEnoughWorkers() {
->
+        for (;;) {
->
+            int pc = parallelism;
->
+            int wc = workerCounts;
->
+            int rc = wc & RUNNING_COUNT_MASK;
->
+            int tc = wc >>> TOTAL_COUNT_SHIFT;
->
+            if (tc < pc) {
->
+                if (runState == TERMINATING ||
->
+                    (UNSAFE.compareAndSwapInt
->
+                     (this, workerCountsOffset,
->
+                      wc, wc + (ONE_RUNNING|ONE_TOTAL)) &&
->
+                     addWorker() == null))
->
+                    break;
->
+            }
->
+            else if (tc > pc && rc < pc &&
->
+                     tc > (runState & ACTIVE_COUNT_MASK)) {
->
+                ForkJoinWorkerThread spare = null;
->
+                ForkJoinWorkerThread[] ws = workers;
->
+                int nws = ws.length;
->
+                for (int i = 0; i < nws; ++i) {
->
+                    ForkJoinWorkerThread w = ws[i];
->
+                    if (w != null && w.isSuspended()) {
->
+                        if ((workerCounts & RUNNING_COUNT_MASK) > pc ||
->
+                            runState == TERMINATING)
->
+                            return;
->
+                        if (w.tryResumeSpare())
->
+                            incrementRunningCount();
->
+                        break;
->
+                    }
->
+                }
->
+            }
->
+            else
->
+                break;
->
+        }
+    /**
-<
+     * Creates a {@code ForkJoinPool} with the given parallelism and
-<
+     * 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, else possibly replaces
->
+     * the worker.
-<
+     * @param parallelism the targeted number of worker threads
-<
+     * @param factory the factory for creating new threads
-<
+     * @throws IllegalArgumentException if parallelism less than or
-<
+     * equal to zero, or greater than implementation limit
-<
+     * @throws NullPointerException if factory is null
-<
+     * @throws SecurityException if a security manager exists and
-<
+     *         the caller is not permitted to modify threads
-<
+     *         because it does not hold {@link
-<
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
->
+     * @param w the worker
+     */
-<
+    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 workerTerminated(ForkJoinWorkerThread w) {
->
+        if (w.active) { // force inactive
->
+            w.active = false;
->
+            do {} while (!tryDecrementActiveCount());
->
+        }
->
+        forgetWorker(w);
->
->
+        // Decrement total count, and if was running, running count
->
+        // Spin (waiting for other updates) if either would be negative
->
+        int nr = w.isTrimmed() ? 0 : ONE_RUNNING;
->
+        int unit = ONE_TOTAL + nr;
->
+        for (;;) {
->
+            int wc = workerCounts;
->
+            int rc = wc & RUNNING_COUNT_MASK;
->
+            if (rc - nr < 0 || (wc >>> TOTAL_COUNT_SHIFT) == 0)
->
+                Thread.yield(); // back off if waiting for other updates
->
+            else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
->
+                                              wc, wc - unit))
->
+                break;
->
+        }
->
->
+        accumulateStealCount(w); // collect final count
->
+        if (!tryTerminate(false))
->
+            ensureEnoughWorkers();
-+
+    // Waiting for and signalling events
-+
+    /**
-<
+     * Creates a new worker thread using factory.
-<
+     *
-<
+     * @param index the index to assign worker
-<
+     * @return new worker, or null if factory failed
->
+     * Releases workers blocked on a count not equal to current count.
->
+     * @return true if any released
+     */
-<
+    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 releaseWaiters() {
->
+        long top;
->
+        while ((top = eventWaiters) != 0L) {
->
+            ForkJoinWorkerThread[] ws = workers;
->
+            int n = ws.length;
->
+            for (;;) {
->
+                int i = ((int)(top & WAITER_ID_MASK)) - 1;
->
+                if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == eventCount)
->
+                    return;
->
+                ForkJoinWorkerThread w;
->
+                if (i < n && (w = ws[i]) != null &&
->
+                    UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
->
+                                              top, w.nextWaiter)) {
->
+                    LockSupport.unpark(w);
->
+                    top = eventWaiters;
->
+                }
->
+                else
->
+                    break;      // possibly stale; reread
->
+            }
-–
+        return w;
+    /**
-<
+     * Returns a good size for worker array given pool size.
-<
+     * Currently requires size to be a power of two.
->
+     * Ensures eventCount on exit is different (mod 2^32) than on
->
+     * entry and wakes up all waiters
->
+     */
->
+    private void signalEvent() {
->
+        int c;
->
+        do {} while (!UNSAFE.compareAndSwapInt(this, eventCountOffset,
->
+                                               c = eventCount, c+1));
->
+        releaseWaiters();
->
+    }
->
->
+    /**
->
+     * Advances eventCount and releases waiters until interference by
->
+     * other releasing threads is detected.
+     */
-<
+    private static int arraySizeFor(int poolSize) {
-<
+        return (poolSize <= 1) ? 1 :
-<
+            (1 << (32 - Integer.numberOfLeadingZeros(poolSize-1)));
->
+    final void signalWork() {
->
+        int c;
->
+        UNSAFE.compareAndSwapInt(this, eventCountOffset, c=eventCount, c+1);
->
+        long top;
->
+        while ((top = eventWaiters) != 0L) {
->
+            int ec = eventCount;
->
+            ForkJoinWorkerThread[] ws = workers;
->
+            int n = ws.length;
->
+            for (;;) {
->
+                int i = ((int)(top & WAITER_ID_MASK)) - 1;
->
+                if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
->
+                    return;
->
+                ForkJoinWorkerThread w;
->
+                if (i < n && (w = ws[i]) != null &&
->
+                    UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
->
+                                              top, top = w.nextWaiter)) {
->
+                    LockSupport.unpark(w);
->
+                    if (top != eventWaiters) // let someone else take over
->
+                        return;
->
+                }
->
+                else
->
+                    break;      // possibly stale; reread
->
+            }
->
+        }
+    /**
-<
+     * Creates or resizes array if necessary to hold newLength.
-<
+     * Call only under exclusion.
->
+     * If worker is inactive, blocks until terminating or event count
->
+     * advances from last value held by worker; in any case helps
->
+     * release others.
-<
+     * @return the array
->
+     * @param w the calling worker thread
->
+     * @param retries the number of scans by caller failing to find work
->
+     * @return false if now too many threads running
+     */
-<
+    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 boolean eventSync(ForkJoinWorkerThread w, int retries) {
->
+        int wec = w.lastEventCount;
->
+        if (retries > 1) { // can only block after 2nd miss
->
+            long nextTop = (((long)wec << EVENT_COUNT_SHIFT) |
->
+                            ((long)(w.poolIndex + 1)));
->
+            long top;
->
+            while ((runState < SHUTDOWN || !tryTerminate(false)) &&
->
+                   (((int)(top = eventWaiters) & WAITER_ID_MASK) == 0 ||
->
+                    (int)(top >>> EVENT_COUNT_SHIFT) == wec) &&
->
+                   eventCount == wec) {
->
+                if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
->
+                                              w.nextWaiter = top, nextTop)) {
->
+                    accumulateStealCount(w); // transfer steals while idle
->
+                    Thread.interrupted();    // clear/ignore interrupt
->
+                    while (eventCount == wec)
->
+                        w.doPark();
->
+                    break;
->
+                }
->
+            }
->
+            wec = eventCount;
->
+        }
->
+        releaseWaiters();
->
+        int wc = workerCounts;
->
+        if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
->
+            w.lastEventCount = wec;
->
+            return true;
->
+        }
->
+        if (wec != w.lastEventCount) // back up if may re-wait
->
+            w.lastEventCount = wec - (wc >>> TOTAL_COUNT_SHIFT);
->
+        return false;
+    /**
-<
+     * Tries to shrink workers into smaller array after one or more terminate.
->
+     * Callback from workers invoked upon each top-level action (i.e.,
->
+     * stealing a task or taking a submission and running
->
+     * it). Performs one or both of the following:
->
+     *
->
+     * * If the worker cannot find work, updates its active status to
->
+     * inactive and updates activeCount unless there is contention, in
->
+     * which case it may try again (either in this or a subsequent
->
+     * call).  Additionally, awaits the next task event and/or helps
->
+     * wake up other releasable waiters.
->
+     *
->
+     * * If there are too many running threads, suspends this worker
->
+     * (first forcing inactivation if necessary).  If it is not
->
+     * resumed before a keepAlive elapses, the worker may be "trimmed"
->
+     * -- killed while suspended within suspendAsSpare. Otherwise,
->
+     * upon resume it rechecks to make sure that it is still needed.
->
+     *
->
+     * @param w the worker
->
+     * @param retries the number of scans by caller failing to find work
->
+     * find any (in which case it may block waiting for work).
+     */
-<
+    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 preStep(ForkJoinWorkerThread w, int retries) {
->
+        boolean active = w.active;
->
+        boolean inactivate = active && retries != 0;
->
+        for (;;) {
->
+            int rs, wc;
->
+            if (inactivate &&
->
+                UNSAFE.compareAndSwapInt(this, runStateOffset,
->
+                                         rs = runState, rs - ONE_ACTIVE))
->
+                inactivate = active = w.active = false;
->
+            if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= parallelism) {
->
+                if (active || eventSync(w, retries))
->
+                    break;
->
+            }
->
+            else if (!(inactivate |= active) &&  // must inactivate to suspend
->
+                UNSAFE.compareAndSwapInt(this, workerCountsOffset,
->
+                                         wc, wc - ONE_RUNNING) &&
->
+                !w.suspendAsSpare())             // false if trimmed
->
+                break;
+    /**
-<
+     * Initializes workers if necessary.
->
+     * Awaits join of the given task if enough threads, or can resume
->
+     * or create a spare. Fails (in which case the given task might
->
+     * not be done) upon contention or lack of decision about
->
+     * blocking. Returns void because caller must check
->
+     * task status on return anyway.
->
+     *
->
+     * We allow blocking if:
->
+     *
->
+     * 1. There would still be at least as many running threads as
->
+     *    parallelism level if this thread blocks.
->
+     *
->
+     * 2. A spare is resumed to replace this worker. We tolerate
->
+     *    slop in the decision to replace if a spare is found without
->
+     *    first decrementing run count.  This may release too many,
->
+     *    but if so, the superfluous ones will re-suspend via
->
+     *    preStep().
->
+     *
->
+     * 3. After #spares repeated checks, there are no fewer than #spare
->
+     *    threads not running. We allow this slack to avoid hysteresis
->
+     *    and as a hedge against lag/uncertainty of running count
->
+     *    estimates when signalling or unblocking stalls.
->
+     *
->
+     * 4. All existing workers are busy (as rechecked via repeated
->
+     *    retries by caller) and a new spare is created.
->
+     *
->
+     * If none of the above hold, we try to escape out by
->
+     * re-incrementing count and returning to caller, which can retry
->
+     * later.
->
+     *
->
+     * @param joinMe the task to join
->
+     * @param retries if negative, then serve only as a precheck
->
+     *   that the thread can be replaced by a spare. Otherwise,
->
+     *   the number of repeated calls to this method returning busy
->
+     * @return true if the call must be retried because there
->
+     *   none of the blocking checks hold
+     */
-<
+    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);
->
+    final boolean tryAwaitJoin(ForkJoinTask<?> joinMe, int retries) {
->
+        if (joinMe.status < 0) // precheck to prime loop
->
+            return false;
->
+        int pc = parallelism;
->
+        boolean running = true; // false when running count decremented
->
+        outer:for (;;) {
->
+            int wc = workerCounts;
->
+            int rc = wc & RUNNING_COUNT_MASK;
->
+            int tc = wc >>> TOTAL_COUNT_SHIFT;
->
+            if (running) { // replace with spare or decrement count
->
+                if (rc <= pc && tc > pc &&
->
+                    (retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
->
+                    ForkJoinWorkerThread[] ws = workers;
->
+                    int nws = ws.length;
->
+                    for (int i = 0; i < nws; ++i) { // search for spare
->
+                        ForkJoinWorkerThread w = ws[i];
+                        if (w != null) {
-<
+                            ws[i] = w;
-<
+                            w.start();
-<
+                            updateWorkerCount(1);
->
+                            if (joinMe.status < 0)
->
+                                return false;
->
+                            if (w.isSuspended()) {
->
+                                if ((workerCounts & RUNNING_COUNT_MASK)>=pc &&
->
+                                    w.tryResumeSpare()) {
->
+                                    running = false;
->
+                                    break outer;
->
+                                }
->
+                                continue outer; // rescan
->
+                            }
-<
+            } finally {
-<
+                lock.unlock();
->
+                if (retries < 0 || // < 0 means replacement check only
->
+                    rc == 0 || joinMe.status < 0 || workerCounts != wc ||
->
+                    !UNSAFE.compareAndSwapInt(this, workerCountsOffset,
->
+                                              wc, wc - ONE_RUNNING))
->
+                    return false; // done or inconsistent or contended
->
+                running = false;
->
+                if (rc > pc)
->
+                    break;
->
+            }
->
+            else { // allow blocking if enough threads
->
+                if (rc >= pc || joinMe.status < 0)
->
+                    break;
->
+                int sc = tc - pc + 1; // = spare threads, plus the one to add
->
+                if (retries > sc) {
->
+                    if (rc > 0 && rc >= pc - sc) // allow slack
->
+                        break;
->
+                    if (tc < MAX_THREADS &&
->
+                        tc == (runState & ACTIVE_COUNT_MASK) &&
->
+                        workerCounts == wc &&
->
+                        UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
->
+                                                 wc+(ONE_RUNNING|ONE_TOTAL))) {
->
+                        addWorker();
->
+                        break;
->
+                    }
->
+                }
->
+                if (workerCounts == wc &&        // back out to allow rescan
->
+                    UNSAFE.compareAndSwapInt (this, workerCountsOffset,
->
+                                              wc, wc + ONE_RUNNING)) {
->
+                    releaseWaiters();            // help others progress
->
+                    return true;                 // let caller retry
->
+                }
-+
+        // arrive here if can block
-+
+        joinMe.internalAwaitDone();
-+
+        int c;                      // to inline incrementRunningCount
-+
+        do {} while (!UNSAFE.compareAndSwapInt
-+
+                     (this, workerCountsOffset,
-+
+                      c = workerCounts, c + ONE_RUNNING));
-+
+        return false;
+    /**
-<
+     * Worker creation and startup for threads added via setParallelism.
->
+     * Same idea as (and shares many code snippets with) tryAwaitJoin,
->
+     * but self-contained because there are no caller retries.
->
+     * TODO: Rework to use simpler API.
+     */
-<
+    private void createAndStartAddedWorkers() {
-<
+        resumeAllSpares();  // Allow spares to convert to nonspare
-<
+        int ps = parallelism;
-<
+        ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
-<
+        int len = ws.length;
-<
+        // Sweep through slots, to keep lowest indices most populated
-<
+        int k = 0;
-<
+        while (k < len) {
-<
+            if (ws[k] != null) {
-<
+                ++k;
-<
+                continue;
-<
+            }
-<
+            int s = workerCounts;
-<
+            int tc = totalCountOf(s);
-<
+            int rc = runningCountOf(s);
-<
+            if (rc >= ps || tc >= ps)
-<
+                break;
-<
+            if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
-<
+                ForkJoinWorkerThread w = createWorker(k);
-<
+                if (w != null) {
-<
+                    ws[k++] = w;
-<
+                    w.start();
->
+    final void awaitBlocker(ManagedBlocker blocker)
->
+        throws InterruptedException {
->
+        boolean done;
->
+        if (done = blocker.isReleasable())
->
+            return;
->
+        int pc = parallelism;
->
+        int retries = 0;
->
+        boolean running = true; // false when running count decremented
->
+        outer:for (;;) {
->
+            int wc = workerCounts;
->
+            int rc = wc & RUNNING_COUNT_MASK;
->
+            int tc = wc >>> TOTAL_COUNT_SHIFT;
->
+            if (running) {
->
+                if (rc <= pc && tc > pc &&
->
+                    (retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
->
+                    ForkJoinWorkerThread[] ws = workers;
->
+                    int nws = ws.length;
->
+                    for (int i = 0; i < nws; ++i) {
->
+                        ForkJoinWorkerThread w = ws[i];
->
+                        if (w != null) {
->
+                            if (done = blocker.isReleasable())
->
+                                return;
->
+                            if (w.isSuspended()) {
->
+                                if ((workerCounts & RUNNING_COUNT_MASK)>=pc &&
->
+                                    w.tryResumeSpare()) {
->
+                                    running = false;
->
+                                    break outer;
->
+                                }
->
+                                continue outer; // rescan
->
+                            }
->
+                        }
->
+                    }
-<
+                else {
-<
+                    updateWorkerCount(-1); // back out on failed creation
->
+                if (done = blocker.isReleasable())
->
+                    return;
->
+                if (rc == 0 || workerCounts != wc ||
->
+                    !UNSAFE.compareAndSwapInt(this, workerCountsOffset,
->
+                                              wc, wc - ONE_RUNNING))
->
+                    continue;
->
+                running = false;
->
+                if (rc > pc)
->
+                    break;
->
+            }
->
+            else {
->
+                if (rc >= pc || (done = blocker.isReleasable()))
+                    break;
-+
+                int sc = tc - pc + 1;
-+
+                if (retries++ > sc) {
-+
+                    if (rc > 0 && rc >= pc - sc)
-+
+                        break;
-+
+                    if (tc < MAX_THREADS &&
-+
+                        tc == (runState & ACTIVE_COUNT_MASK) &&
-+
+                        workerCounts == wc &&
-+
+                        UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
-+
+                                                 wc+(ONE_RUNNING|ONE_TOTAL))) {
-+
+                        addWorker();
-+
+                        break;
-+
+                    }
-+
+                Thread.yield();
-+
+            }
-+
+        }
-+
-+
+        try {
-+
+            if (!done)
-+
+                do {} while (!blocker.isReleasable() && !blocker.block());
-+
+        } finally {
-+
+            if (!running) {
-+
+                int c;
-+
+                do {} while (!UNSAFE.compareAndSwapInt
-+
+                             (this, workerCountsOffset,
-+
+                              c = workerCounts, c + ONE_RUNNING));
-+
+            }
-+
+        }
-+
+    }
-+
-+
+    /**
-+
+     * Possibly initiates and/or completes termination.
-+
+     *
-+
+     * @param now if true, unconditionally terminate, else only
-+
+     * if shutdown and empty queue and no active workers
-+
+     * @return true if now terminating or terminated
-+
+     */
-+
+    private boolean tryTerminate(boolean now) {
-+
+        if (now)
-+
+            advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN
-+
+        else if (runState < SHUTDOWN ||
-+
+                 !submissionQueue.isEmpty() ||
-+
+                 (runState & ACTIVE_COUNT_MASK) != 0)
-+
+            return false;
-+
-+
+        if (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
-+
+     */
-+
+    private void startTerminating() {
-+
+        for (int i = 0; i < 2; ++i) { // twice to mop up newly created workers
-+
+            cancelSubmissions();
-+
+            shutdownWorkers();
-+
+            cancelWorkerTasks();
-+
+            signalEvent();
-+
+            interruptWorkers();
-+
+        }
-+
+    }
-+
-+
+    /**
-+
+     * Clear out and cancel submissions, ignoring exceptions
-+
+     */
-+
+    private void cancelSubmissions() {
-+
+        ForkJoinTask<?> task;
-+
+        while ((task = submissionQueue.poll()) != null) {
-+
+            try {
-+
+                task.cancel(false);
-+
+            } catch (Throwable ignore) {
-+
+    /**
-+
+     * Sets all worker run states to at least shutdown,
-+
+     * also resuming suspended workers
-+
+     */
-+
+    private void shutdownWorkers() {
-+
+        ForkJoinWorkerThread[] ws = workers;
-+
+        int nws = ws.length;
-+
+        for (int i = 0; i < nws; ++i) {
-+
+            ForkJoinWorkerThread w = ws[i];
-+
+            if (w != null)
-+
+                w.shutdown();
-+
+        }
-+
+    }
-+
-+
+    /**
-+
+     * Clears out and cancels all locally queued tasks
-+
+     */
-+
+    private void cancelWorkerTasks() {
-+
+        ForkJoinWorkerThread[] ws = workers;
-+
+        int nws = ws.length;
-+
+        for (int i = 0; i < nws; ++i) {
-+
+            ForkJoinWorkerThread w = ws[i];
-+
+            if (w != null)
-+
+                w.cancelTasks();
-+
+        }
-+
+    }
-+
-+
+    /**
-+
+     * Unsticks all workers blocked on joins etc
-+
+     */
-+
+    private void interruptWorkers() {
-+
+        ForkJoinWorkerThread[] ws = workers;
-+
+        int nws = ws.length;
-+
+        for (int i = 0; i < nws; ++i) {
-+
+            ForkJoinWorkerThread w = ws[i];
-+
+            if (w != null && !w.isTerminated()) {
-+
+                try {
-+
+                    w.interrupt();
-+
+                } catch (SecurityException ignore) {
-+
+                }
-+
+            }
-+
+        }
-+
+    }
-+
-+
+    // misc support for ForkJoinWorkerThread
-+
-+
+    /**
-+
+     * Returns pool number
-+
+     */
-+
+    final int getPoolNumber() {
-+
+        return poolNumber;
-+
+    }
-+
-+
+    /**
-+
+     * Accumulates steal count from a worker, clearing
-+
+     * the worker's value
-+
+     */
-+
+    final void accumulateStealCount(ForkJoinWorkerThread w) {
-+
+        int sc = w.stealCount;
-+
+        if (sc != 0) {
-+
+            long c;
-+
+            w.stealCount = 0;
-+
+            do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
-+
+                                                    c = stealCount, c + sc));
-+
+        }
-+
+    }
-+
-+
+    /**
-+
+     * 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_THREADS)
-+
+            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();
-+
+    }
-+
-+
+    /**
-+
+     * Returns initial power of two size for workers array.
-+
+     * @param pc the initial parallelism level
-+
+     */
-+
+    private static int initialArraySizeFor(int pc) {
-+
+        // See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
-+
+        int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
-+
+        size |= size >>> 1;
-+
+        size |= size >>> 2;
-+
+        size |= size >>> 4;
-+
+        size |= size >>> 8;
-+
+        return size + 1;
-+
+    }
-+
+    // Execution methods
+    /**
+    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();
->
+        signalEvent();
->
+        ensureEnoughWorkers();
+    /**
+     * 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;
->
+        return ueh;
-–
+    /**
-<
+     * Sets the target parallelism level of this pool.
->
+     * Returns the targeted parallelism level of this pool.
-<
+     * @param parallelism the target parallelism
-<
+     * @throws IllegalArgumentException if parallelism less than or
-<
+     * equal to zero or greater than maximum size bounds
-<
+     * @throws SecurityException if a security manager exists and
-<
+     *         the caller is not permitted to modify threads
-<
+     *         because it does not hold {@link
-<
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
-<
+     */
-<
+    public void setParallelism(int parallelism) {
-<
+        checkPermission();
-<
+        if (parallelism <= 0 || parallelism > maxPoolSize)
-<
+            throw new IllegalArgumentException();
-<
+        final ReentrantLock lock = this.workerLock;
-<
+        lock.lock();
-<
+        try {
-<
+            if (!isTerminating()) {
-<
+                int p = this.parallelism;
-<
+                this.parallelism = parallelism;
-<
+                if (parallelism > p)
-<
+                    createAndStartAddedWorkers();
-<
+                else
-<
+                    trimSpares();
-<
+            }
-<
+        } finally {
-<
+            lock.unlock();
-<
+        }
-<
+        signalIdleWorkers();
-<
+    }
-<
-<
+    /**
-<
+     * Returns the targeted number of worker threads in this pool.
-<
+     *
-<
+     * @return the targeted number of worker threads in this pool
->
+     * @return the targeted parallelism level of this pool
+     */
+    public int getParallelism() {
+        return parallelism;
+     * @return the number of worker threads
+     */
+    public int getPoolSize() {
-<
+        return totalCountOf(workerCounts);
-<
+    }
-<
-<
+    /**
-<
+     * Returns the maximum number of threads allowed to exist in the
-<
+     * pool, even if there are insufficient unblocked running threads.
-<
+     *
-<
+     * @return the maximum
-<
+     */
-<
+    public int getMaximumPoolSize() {
-<
+        return maxPoolSize;
-<
+    }
-<
-<
+    /**
-<
+     * Sets the maximum number of threads allowed to exist in the
-<
+     * pool, even if there are insufficient unblocked running threads.
-<
+     * Setting this value has no effect on current pool size. It
-<
+     * controls construction of new threads.
-<
+     *
-<
+     * @throws IllegalArgumentException if negative or greater 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 nws = ws.length;
->
+        for (int i = 0; i < nws; ++i) {
->
+            ForkJoinWorkerThread w = ws[i];
->
+            if (w != null)
->
+                count += w.getQueueSize();
+        return count;
+    protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
+        int n = submissionQueue.drainTo(c);
+        ForkJoinWorkerThread[] ws = workers;
-<
+        if (ws != null) {
-<
+            for (int i = 0; i < ws.length; ++i) {
-<
+                ForkJoinWorkerThread w = ws[i];
-<
+                if (w != null)
-<
+                    n += w.drainTasksTo(c);
-<
+            }
->
+        int nws = ws.length;
->
+        for (int i = 0; i < nws; ++i) {
->
+            ForkJoinWorkerThread w = ws[i];
->
+            if (w != null)
->
+                n += w.drainTasksTo(c);
+        return n;
+    /**
-+
+     * Returns count of total parks by existing workers.
-+
+     * Used during development only since not meaningful to users.
-+
+     */
-+
+    private int collectParkCount() {
-+
+        int count = 0;
-+
+        ForkJoinWorkerThread[] ws = workers;
-+
+        int nws = ws.length;
-+
+        for (int i = 0; i < nws; ++i) {
-+
+            ForkJoinWorkerThread w = ws[i];
-+
+            if (w != null)
-+
+                count += w.parkCount;
-+
+        }
-+
+        return count;
-+
+    }
-+
-+
+    /**
+     * Returns a string identifying this pool, as well as its state,
+     * including indications of run state, parallelism level, and
+     * worker and task counts.
+     * @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;
-+
+        //        int pk = collectParkCount();
+        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 +
-+
+            //            ", parks = " + pk +
+            "]";
-<
+    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);
+    /**
-<
+     * Attempts to stop all actively executing tasks, and cancels all
-<
+     * waiting tasks.  Tasks that are in the process of being
-<
+     * submitted or executed concurrently during the course of this
-<
+     * method may or may not be rejected. Unlike some other executors,
-<
+     * this method cancels rather than collects non-executed tasks
-<
+     * upon termination, so always returns an empty list. However, you
-<
+     * can use method {@link #drainTasksTo} before invoking this
-<
+     * method to transfer unexecuted tasks to another collection.
->
+     * Attempts to cancel and/or stop all tasks, and reject all
->
+     * subsequently submitted tasks.  Tasks that are in the process of
->
+     * being submitted or executed concurrently during the course of
->
+     * this method may or may not be rejected. This method cancels
->
+     * both existing and unexecuted tasks, in order to permit
->
+     * termination in the presence of task dependencies. So the method
->
+     * always returns an empty list (unlike the case for some other
->
+     * Executors).
+     * @return an empty list
+     * @throws SecurityException if a security manager exists and
+     */
+    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;
+    /**
+     * Returns {@code true} if the process of termination has
-<
+     * commenced but possibly not yet completed.
->
+     * commenced but not yet completed.  This method may be useful for
->
+     * debugging. A return of {@code true} reported a sufficient
->
+     * period after shutdown may indicate that submitted tasks have
->
+     * ignored or suppressed interruption, causing this executor not
->
+     * to properly terminate.
-<
+     * @return {@code true} if terminating
->
+     * @return {@code true} if terminating but not yet terminated
+     */
+    public boolean isTerminating() {
-<
+        return runStateOf(runControl) >= TERMINATING;
->
+        return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
+    /**
+     * @return {@code true} if this pool has been shut down
+     */
+    public boolean isShutdown() {
-<
+        return runStateOf(runControl) >= SHUTDOWN;
->
+        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 (!isTerminating()) {
-<
+                    tryShrinkWorkerArray();
-<
+                    tryResumeSpare(true); // allow replacement
-<
+                }
-<
+            }
-<
+        } finally {
-<
+            lock.unlock();
-<
+        }
-<
+        signalIdleWorkers();
-<
+    }
-<
-<
+    /**
-<
+     * Initiates termination.
-<
+     */
-<
+    private void terminate() {
-<
+        if (transitionRunStateTo(TERMINATING)) {
-<
+            stopAllWorkers();
-<
+            resumeAllSpares();
-<
+            signalIdleWorkers();
-<
+            cancelQueuedSubmissions();
-<
+            cancelQueuedWorkerTasks();
-<
+            interruptUnterminatedWorkers();
-<
+            signalIdleWorkers(); // resignal after interrupt
-<
+        }
-<
+    }
-<
-<
+    /**
-<
+     * Possibly terminates when on shutdown state.
-<
+     */
-<
+    private void terminateOnShutdown() {
-<
+        if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
-<
+            terminate();
-<
+    }
-<
-<
+    /**
-<
+     * Clears out and cancels submissions.
-<
+     */
-<
+    private void cancelQueuedSubmissions() {
-<
+        ForkJoinTask<?> task;
-<
+        while ((task = pollSubmission()) != null)
-<
+            task.cancel(false);
-<
+    }
-<
-<
+    /**
-<
+     * Cleans out worker queues.
-<
+     */
-<
+    private void cancelQueuedWorkerTasks() {
-<
+        final ReentrantLock lock = this.workerLock;
-<
+        lock.lock();
-<
+        try {
-<
+            ForkJoinWorkerThread[] ws = workers;
-<
+            if (ws != null) {
-<
+                for (int i = 0; i < ws.length; ++i) {
-<
+                    ForkJoinWorkerThread t = ws[i];
-<
+                    if (t != null)
-<
+                        t.cancelTasks();
-<
+                }
-<
+            }
-<
+        } finally {
-<
+            lock.unlock();
-<
+        }
-<
+    }
-<
-<
+    /**
-<
+     * Sets each worker's status to terminating. Requires lock to avoid
-<
+     * conflicts with add/remove.
-<
+     */
-<
+    private void stopAllWorkers() {
-<
+        final ReentrantLock lock = this.workerLock;
-<
+        lock.lock();
-<
+        try {
-<
+            ForkJoinWorkerThread[] ws = workers;
-<
+            if (ws != null) {
-<
+                for (int i = 0; i < ws.length; ++i) {
-<
+                    ForkJoinWorkerThread t = ws[i];
-<
+                    if (t != null)
-<
+                        t.shutdownNow();
-<
+                }
-<
+            }
-<
+        } finally {
-<
+            lock.unlock();
-<
+        }
-<
+    }
-<
-<
+    /**
-<
+     * Interrupts all unterminated workers.  This is not required for
-<
+     * sake of internal control, but may help unstick user code during
-<
+     * shutdown.
-<
+     */
-<
+    private void interruptUnterminatedWorkers() {
-<
+        final ReentrantLock lock = this.workerLock;
-<
+        lock.lock();
-<
+        try {
-<
+            ForkJoinWorkerThread[] ws = workers;
-<
+            if (ws != null) {
-<
+                for (int i = 0; i < ws.length; ++i) {
-<
+                    ForkJoinWorkerThread t = ws[i];
-<
+                    if (t != null && !t.isTerminated()) {
-<
+                        try {
-<
+                            t.interrupt();
-<
+                        } catch (SecurityException ignore) {
-<
+                        }
-<
+                    }
-<
+                }
-<
+            }
-<
+        } finally {
-<
+            lock.unlock();
-<
+        }
-<
+    }
-<
-<
-<
+    /*
-<
+     * Nodes for event barrier to manage idle threads.  Queue nodes
-<
+     * are basic Treiber stack nodes, also used for spare stack.
-<
+     *
-<
+     * The event barrier has an event count and a wait queue (actually
-<
+     * a Treiber stack).  Workers are enabled to look for work when
-<
+     * the eventCount is incremented. If they fail to find work, they
-<
+     * may wait for next count. Upon release, threads help others wake
-<
+     * up.
-<
+     *
-<
+     * Synchronization events occur only in enough contexts to
-<
+     * maintain overall liveness:
-<
+     *
-<
+     *   - Submission of a new task to the pool
-<
+     *   - Resizes or other changes to the workers array
-<
+     *   - pool termination
-<
+     *   - A worker pushing a task on an empty queue
-<
+     *
-<
+     * The case of pushing a task occurs often enough, and is heavy
-<
+     * enough compared to simple stack pushes, to require special
-<
+     * handling: Method signalWork returns without advancing count if
-<
+     * the queue appears to be empty.  This would ordinarily result in
-<
+     * races causing some queued waiters not to be woken up. To avoid
-<
+     * this, the first worker enqueued in method sync (see
-<
+     * syncIsReleasable) rescans for tasks after being enqueued, and
-<
+     * helps signal if any are found. This works well because the
-<
+     * worker has nothing better to do, and so might as well help
-<
+     * alleviate the overhead and contention on the threads actually
-<
+     * doing work.  Also, since event counts increments on task
-<
+     * availability exist to maintain liveness (rather than to force
-<
+     * refreshes etc), it is OK for callers to exit early if
-<
+     * contending with another signaller.
-<
+     */
-<
+    static final class WaitQueueNode {
-<
+        WaitQueueNode next; // only written before enqueued
-<
+        volatile ForkJoinWorkerThread thread; // nulled to cancel wait
-<
+        final long count; // unused for spare stack
-<
-<
+        WaitQueueNode(long c, ForkJoinWorkerThread w) {
-<
+            count = c;
-<
+            thread = w;
-<
+        }
-<
-<
+        /**
-<
+         * Wakes up waiter, returning false if known to already
-<
+         */
-<
+        boolean signal() {
-<
+            ForkJoinWorkerThread t = thread;
-<
+            if (t == null)
-<
+                return false;
-<
+            thread = null;
-<
+            LockSupport.unpark(t);
-<
+            return true;
-<
+        }
-<
-<
+        /**
-<
+         * Awaits release on sync.
-<
+         */
-<
+        void awaitSyncRelease(ForkJoinPool p) {
-<
+            while (thread != null && !p.syncIsReleasable(this))
-<
+                LockSupport.park(this);
-<
+        }
-<
-<
+        /**
-<
+         * Awaits resumption as spare.
-<
+         */
-<
+        void awaitSpareRelease() {
-<
+            while (thread != null) {
-<
+                if (!Thread.interrupted())
-<
+                    LockSupport.park(this);
-<
+            }
-<
+        }
-<
+    }
-<
-<
+    /**
-<
+     * Ensures that no thread is waiting for count to advance from the
-<
+     * current value of eventCount read on entry to this method, by
-<
+     * releasing waiting threads if necessary.
-<
+     *
-<
+     * @return the count
-<
+     */
-<
+    final long ensureSync() {
-<
+        long c = eventCount;
-<
+        WaitQueueNode q;
-<
+        while ((q = syncStack) != null && q.count < c) {
-<
+            if (casBarrierStack(q, null)) {
-<
+                do {
-<
+                    q.signal();
-<
+                } while ((q = q.next) != null);
-<
+                break;
-<
+            }
-<
+        }
-<
+        return c;
-<
+    }
-<
-<
+    /**
-<
+     * Increments event count and releases waiting threads.
-<
+     */
-<
+    private void signalIdleWorkers() {
-<
+        long c;
-<
+        do {} while (!casEventCount(c = eventCount, c+1));
-<
+        ensureSync();
-<
+    }
-<
-<
+    /**
-<
+     * Signals threads waiting to poll a task. Because method sync
-<
+     * rechecks availability, it is OK to only proceed if queue
-<
+     * appears to be non-empty, and OK to skip under contention to
-<
+     * increment count (since some other thread succeeded).
-<
+     */
-<
+    final void signalWork() {
-<
+        long c;
-<
+        WaitQueueNode q;
-<
+        if (syncStack != null &&
-<
+            casEventCount(c = eventCount, c+1) &&
-<
+            (((q = syncStack) != null && q.count <= c) &&
-<
+             (!casBarrierStack(q, q.next) || !q.signal())))
-<
+            ensureSync();
-<
+    }
-<
-<
+    /**
-<
+     * Waits until event count advances from last value held by
-<
+     * caller, or if excess threads, caller is resumed as spare, or
-<
+     * caller or pool is terminating. Updates caller's event on exit.
-<
+     *
-<
+     * @param w the calling worker thread
-<
+     */
-<
+    final void sync(ForkJoinWorkerThread w) {
-<
+        updateStealCount(w); // Transfer w's count while it is idle
-<
-<
+        while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
-<
+            long prev = w.lastEventCount;
-<
+            WaitQueueNode node = null;
-<
+            WaitQueueNode h;
-<
+            while (eventCount == prev &&
-<
+                   ((h = syncStack) == null || h.count == prev)) {
-<
+                if (node == null)
-<
+                    node = new WaitQueueNode(prev, w);
-<
+                if (casBarrierStack(node.next = h, node)) {
-<
+                    node.awaitSyncRelease(this);
-<
+                    break;
-<
+                }
-<
+            }
-<
+            long ec = ensureSync();
-<
+            if (ec != prev) {
-<
+                w.lastEventCount = ec;
-<
+                break;
-<
+            }
-<
+        }
-<
+    }
-<
-<
+    /**
-<
+     * Returns {@code true} if worker waiting on sync can proceed:
-<
+     *  - on signal (thread == null)
-<
+     *  - on event count advance (winning race to notify vs signaller)
-<
+     *  - on interrupt
-<
+     *  - if the first queued node, we find work available
-<
+     * If node was not signalled and event count not advanced on exit,
-<
+     * then we also help advance event count.
-<
+     *
-<
+     * @return {@code true} if node can be released
-<
+     */
-<
+    final boolean syncIsReleasable(WaitQueueNode node) {
-<
+        long prev = node.count;
-<
+        if (!Thread.interrupted() && node.thread != null &&
-<
+            (node.next != null ||
-<
+             !ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
-<
+            eventCount == prev)
->
+            return 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 && !isTerminating() && (w = createWorker(k)) != null) {
-–
+            ws[k] = w;
-–
+            w.start();
-–
+        }
-–
+        else
-–
+            updateWorkerCount(-1); // adjust on failure
-–
+        signalIdleWorkers();
-–
+    }
-–
-–
+    /**
-–
+     * Suspends calling thread w if there are excess threads.  Called
-–
+     * only from sync.  Spares are enqueued in a Treiber stack using
-–
+     * the same WaitQueueNodes as barriers.  They are resumed mainly
-–
+     * in preJoin, but are also woken on pool events that require all
-–
+     * threads to check run state.
-–
+     *
-–
+     * @param w the caller
-–
+     */
-–
+    private boolean suspendIfSpare(ForkJoinWorkerThread w) {
-–
+        WaitQueueNode node = null;
-–
+        int s;
-–
+        while (parallelism < runningCountOf(s = workerCounts)) {
-–
+            if (node == null)
-–
+                node = new WaitQueueNode(0, w);
-–
+            if (casWorkerCounts(s, s-1)) { // representation-dependent
-–
+                // push onto stack
-–
+                do {} while (!casSpareStack(node.next = spareStack, node));
-–
+                // block until released by resumeSpare
-–
+                node.awaitSpareRelease();
-–
+                return true;
-–
+            }
-–
+        }
-–
+        return false;
-–
+    }
-–
-–
+    /**
-–
+     * Tries to pop and resume a spare thread.
-–
+     *
-–
+     * @param updateCount if true, increment running count on success
-–
+     * @return true if successful
-–
+     */
-–
+    private boolean tryResumeSpare(boolean updateCount) {
-–
+        WaitQueueNode q;
-–
+        while ((q = spareStack) != null) {
-–
+            if (casSpareStack(q, q.next)) {
-–
+                if (updateCount)
-–
+                    updateRunningCount(1);
-–
+                q.signal();
-–
+                return true;
-–
+            }
-–
+        }
-–
+        return false;
-–
+    }
-–
-–
+    /**
-–
+     * Pops and resumes all spare threads. Same idea as ensureSync.
-–
+     *
-–
+     * @return true if any spares released
-–
+     */
-–
+    private boolean resumeAllSpares() {
-–
+        WaitQueueNode q;
-–
+        while ( (q = spareStack) != null) {
-–
+            if (casSpareStack(q, null)) {
-–
+                do {
-–
+                    updateRunningCount(1);
-–
+                    q.signal();
-–
+                } while ((q = q.next) != null);
-–
+                return true;
-–
+            }
-–
+        }
-–
+        return false;
-–
+    }
-–
-–
+    /**
-–
+     * Pops and shuts down excessive spare threads. Call only while
-–
+     * holding lock. This is not guaranteed to eliminate all excess
-–
+     * threads, only those suspended as spares, which are the ones
-–
+     * unlikely to be needed in the future.
-–
+     */
-–
+    private void trimSpares() {
-–
+        int surplus = totalCountOf(workerCounts) - parallelism;
-–
+        WaitQueueNode q;
-–
+        while (surplus > 0 && (q = spareStack) != null) {
-–
+            if (casSpareStack(q, null)) {
-–
+                do {
-–
+                    updateRunningCount(1);
-–
+                    ForkJoinWorkerThread w = q.thread;
-–
+                    if (w != null && surplus > 0 &&
-–
+                        runningCountOf(workerCounts) > 0 && w.shutdown())
-–
+                        --surplus;
-–
+                    q.signal();
-–
+                } while ((q = q.next) != null);
-–
+            }
+     * 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) t).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
+    // fact that ForkJoinTask.adapt returns ForkJoinTasks that also
+    // implement RunnableFuture.
+    // Unsafe mechanics
+    private static final sun.misc.Unsafe UNSAFE = getUnsafe();
-–
+    private static final long eventCountOffset =
-–
+        objectFieldOffset("eventCount", ForkJoinPool.class);
+    private static final long workerCountsOffset =
+        objectFieldOffset("workerCounts", ForkJoinPool.class);
-<
+    private static final long runControlOffset =
-<
+        objectFieldOffset("runControl", ForkJoinPool.class);
-<
+    private static final long syncStackOffset =
-<
+        objectFieldOffset("syncStack",ForkJoinPool.class);
-<
+    private static final long spareStackOffset =
-<
+        objectFieldOffset("spareStack", ForkJoinPool.class);
-<
-<
+    private boolean casEventCount(long cmp, long val) {
-<
+        return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
-<
+    }
-<
+    private boolean casWorkerCounts(int cmp, int val) {
-<
+        return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
-<
+    }
-<
+    private boolean casRunControl(int cmp, int val) {
-<
+        return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
-<
+    }
-<
+    private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
-<
+        return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
-<
+    }
-<
+    private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
-<
+        return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
-<
+    }
->
+    private static final long runStateOffset =
->
+        objectFieldOffset("runState", ForkJoinPool.class);
->
+    private static final long eventCountOffset =
->
+        objectFieldOffset("eventCount", ForkJoinPool.class);
->
+    private static final long eventWaitersOffset =
->
+        objectFieldOffset("eventWaiters",ForkJoinPool.class);
->
+    private static final long stealCountOffset =
->
+        objectFieldOffset("stealCount",ForkJoinPool.class);
+    private static long objectFieldOffset(String field, Class<?> klazz) {
+        try {

Diff Legend

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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents): Revision 1.41 by jsr166, Mon Aug 3 01:11:58 2009 UTC vs. Revision 1.58 by dl, Fri Jul 23 13:07:43 2010 UTC

Diff Legend

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.41 by jsr166, Mon Aug 3 01:11:58 2009 UTC vs.
Revision 1.58 by dl, Fri Jul 23 13:07:43 2010 UTC