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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.43 by jsr166, Tue Aug 4 00:55:13 2009 UTC vs.
Revision 1.94 by dl, Tue Mar 1 10:59:04 2011 UTC

+package jsr166y;
-–
+import java.util.concurrent.*;
-–
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
-<
+import java.util.concurrent.locks.Condition;
->
+import java.util.Random;
->
+import java.util.concurrent.AbstractExecutorService;
->
+import java.util.concurrent.Callable;
->
+import java.util.concurrent.ExecutorService;
->
+import java.util.concurrent.Future;
->
+import java.util.concurrent.RejectedExecutionException;
->
+import java.util.concurrent.RunnableFuture;
->
+import java.util.concurrent.TimeUnit;
->
+import java.util.concurrent.TimeoutException;
->
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.LockSupport;
+import java.util.concurrent.locks.ReentrantLock;
-<
+import java.util.concurrent.atomic.AtomicInteger;
-<
+import java.util.concurrent.atomic.AtomicLong;
->
+import java.util.concurrent.locks.Condition;
+/**
+ * An {@link ExecutorService} for running {@link ForkJoinTask}s.
+ * A {@code ForkJoinPool} provides the entry point for submissions
-<
+ * from non-{@code ForkJoinTask}s, as well as management and
-<
+ * monitoring operations.
->
+ * from non-{@code ForkJoinTask} clients, as well as management and
->
+ * monitoring operations.
+ * <p>A {@code ForkJoinPool} differs from other kinds of {@link
+ * ExecutorService} mainly by virtue of employing
+ * execute subtasks created by other active tasks (eventually blocking
+ * waiting for work if none exist). This enables efficient processing
+ * when most tasks spawn other subtasks (as do most {@code
-<
+ * ForkJoinTask}s). A {@code ForkJoinPool} may also be used for mixed
-<
+ * execution of some plain {@code Runnable}- or {@code Callable}-
-<
+ * based activities along with {@code ForkJoinTask}s. When setting
-<
+ * {@linkplain #setAsyncMode async mode}, a {@code ForkJoinPool} may
-<
+ * also be appropriate for use with fine-grained tasks of any form
-<
+ * that are never joined. Otherwise, other {@code ExecutorService}
-<
+ * implementations are typically more appropriate choices.
->
+ * ForkJoinTask}s). When setting <em>asyncMode</em> to true in
->
+ * constructors, {@code ForkJoinPool}s may also be appropriate for use
->
+ * with event-style tasks that are never joined.
+ * <p>A {@code ForkJoinPool} is constructed with a given target
+ * parallelism level; by default, equal to the number of available
-<
+ * processors. Unless configured otherwise via {@link
-<
+ * #setMaintainsParallelism}, the pool attempts to maintain this
-<
+ * number of active (or available) threads by dynamically adding,
-<
+ * suspending, or resuming internal worker threads, even if some tasks
-<
+ * are waiting to join others. However, no such adjustments are
-<
+ * performed in the face of blocked IO or other unmanaged
-<
+ * synchronization. The nested {@link ManagedBlocker} interface
-<
+ * enables extension of the kinds of synchronization accommodated.
-<
+ * The target parallelism level may also be changed dynamically
-<
+ * ({@link #setParallelism}). The total number of threads may be
-<
+ * limited using method {@link #setMaximumPoolSize}, in which case it
-<
+ * may become possible for the activities of a pool to stall due to
-<
+ * the lack of available threads to process new tasks.
->
+ * processors. The pool attempts to maintain enough active (or
->
+ * available) threads by dynamically adding, suspending, or resuming
->
+ * internal worker threads, even if some tasks are stalled waiting to
->
+ * join others. However, no such adjustments are guaranteed in the
->
+ * face of blocked IO or other unmanaged synchronization. The nested
->
+ * {@link ManagedBlocker} interface enables extension of the kinds of
->
+ * synchronization accommodated.
+ * <p>In addition to execution and lifecycle control methods, this
+ * class provides status check methods (for example
+ * {@link #toString} returns indications of pool state in a
+ * convenient form for informal monitoring.
-+
+ * <p> As is the case with other ExecutorServices, there are three
-+
+ * main task execution methods summarized in the following
-+
+ * table. These are designed to be used by clients not already engaged
-+
+ * in fork/join computations in the current pool.  The main forms of
-+
+ * these methods accept instances of {@code ForkJoinTask}, but
-+
+ * overloaded forms also allow mixed execution of plain {@code
-+
+ * Runnable}- or {@code Callable}- based activities as well.  However,
-+
+ * tasks that are already executing in a pool should normally
-+
+ * <em>NOT</em> use these pool execution methods, but instead use the
-+
+ * within-computation forms listed in the table.
-+
+ *
-+
+ * <table BORDER CELLPADDING=3 CELLSPACING=1>
-+
+ *  <tr>
-+
+ *    <td></td>
-+
+ *    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
-+
+ *    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
-+
+ *  </tr>
-+
+ *  <tr>
-+
+ *    <td> <b>Arrange async execution</td>
-+
+ *    <td> {@link #execute(ForkJoinTask)}</td>
-+
+ *    <td> {@link ForkJoinTask#fork}</td>
-+
+ *  </tr>
-+
+ *  <tr>
-+
+ *    <td> <b>Await and obtain result</td>
-+
+ *    <td> {@link #invoke(ForkJoinTask)}</td>
-+
+ *    <td> {@link ForkJoinTask#invoke}</td>
-+
+ *  </tr>
-+
+ *  <tr>
-+
+ *    <td> <b>Arrange exec and obtain Future</td>
-+
+ *    <td> {@link #submit(ForkJoinTask)}</td>
-+
+ *    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
-+
+ *  </tr>
-+
+ * </table>
-+
+ *
+ * <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
+ * used for all parallel task execution in a program or subsystem.
+ * Otherwise, use would not usually outweigh the construction and
+ * <p><b>Implementation notes</b>: This implementation restricts the
+ * maximum number of running threads to 32767. Attempts to create
-<
+ * pools with greater than the maximum result in
->
+ * pools with greater than the maximum number result in
+ * {@code IllegalArgumentException}.
-+
+ * <p>This implementation rejects submitted tasks (that is, by throwing
-+
+ * {@link RejectedExecutionException}) only when the pool is shut down
-+
+ * or internal resources have been exhausted.
-+
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+public class ForkJoinPool extends AbstractExecutorService {
+    /*
-<
+     * See the extended comments interspersed below for design,
-<
+     * rationale, and walkthroughs.
->
+     * Implementation Overview
->
+     *
->
+     * This class provides the central bookkeeping and control for a
->
+     * set of worker threads: Submissions from non-FJ threads enter
->
+     * into a submission queue. Workers take these tasks and typically
->
+     * split them into subtasks that may be stolen by other workers.
->
+     * Preference rules give first priority to processing tasks from
->
+     * their own queues (LIFO or FIFO, depending on mode), then to
->
+     * randomized FIFO steals of tasks in other worker queues, and
->
+     * lastly to new submissions.
->
+     *
->
+     * The main throughput advantages of work-stealing stem from
->
+     * decentralized control -- workers mostly take tasks from
->
+     * themselves or each other. We cannot negate this in the
->
+     * implementation of other management responsibilities. The main
->
+     * tactic for avoiding bottlenecks is packing nearly all
->
+     * essentially atomic control state into a single 64bit volatile
->
+     * variable ("ctl"). This variable is read on the order of 10-100
->
+     * times as often as it is modified (always via CAS). (There is
->
+     * some additional control state, for example variable "shutdown"
->
+     * for which we can cope with uncoordinated updates.)  This
->
+     * streamlines synchronization and control at the expense of messy
->
+     * constructions needed to repack status bits upon updates.
->
+     * Updates tend not to contend with each other except during
->
+     * bursts while submitted tasks begin or end.  In some cases when
->
+     * they do contend, threads can instead do something else
->
+     * (usually, scan for tesks) until contention subsides.
->
+     *
->
+     * To enable packing, we restrict maximum parallelism to (1<<15)-1
->
+     * (which is far in excess of normal operating range) to allow
->
+     * ids, counts, and their negations (used for thresholding) to fit
->
+     * into 16bit fields.
->
+     *
->
+     * Recording Workers.  Workers are recorded in the "workers" array
->
+     * that is created upon pool construction and expanded if (rarely)
->
+     * necessary.  This is an array as opposed to some other data
->
+     * structure to support index-based random steals by workers.
->
+     * Updates to the array recording new workers and unrecording
->
+     * terminated ones are protected from each other by a seqLock
->
+     * (scanGuard) but the array is otherwise concurrently readable,
->
+     * and accessed directly by workers. To simplify index-based
->
+     * operations, the array size is always a power of two, and all
->
+     * readers must tolerate null slots. To avoid flailing during
->
+     * start-up, the array is presized to hold twice #parallelism
->
+     * workers (which is unlikely to need further resizing during
->
+     * execution). But to avoid dealing with so many null slots,
->
+     * variable scanGuard includes a mask for the nearest power of two
->
+     * that contains all current workers.  All worker thread creation
->
+     * is on-demand, triggered by task submissions, replacement of
->
+     * terminated workers, and/or compensation for blocked
->
+     * workers. However, all other support code is set up to work with
->
+     * other policies.  To ensure that we do not hold on to worker
->
+     * references that would prevent GC, ALL accesses to workers are
->
+     * via indices into the workers array (which is one source of some
->
+     * of the messy code constructions here). In essence, the workers
->
+     * array serves as a weak reference mechanism. Thus for example
->
+     * the wait queue field of ctl stores worker indices, not worker
->
+     * references.  Access to the workers in associated methods (for
->
+     * example signalWork) must both index-check and null-check the
->
+     * IDs. All such accesses ignore bad IDs by returning out early
->
+     * from what they are doing, since this can only be associated
->
+     * with termination, in which case it is OK to give up.
->
+     *
->
+     * All uses of the workers array, as well as queue arrays, check
->
+     * that the array is non-null (even if previously non-null). This
->
+     * allows nulling during termination, which is currently not
->
+     * necessary, but remains an option for resource-revocation-based
->
+     * shutdown schemes.
->
+     *
->
+     * Wait Queuing. Unlike HPC work-stealing frameworks, we cannot
->
+     * let workers spin indefinitely scanning for tasks when none are
->
+     * can be immediately found, and we cannot start/resume workers
->
+     * unless there appear to be tasks available.  On the other hand,
->
+     * we must quickly prod them into action when new tasks are
->
+     * submitted or generated.  We park/unpark workers after placing
->
+     * in an event wait queue when they cannot find work. This "queue"
->
+     * is actually a simple Treiber stack, headed by the "id" field of
->
+     * ctl, plus a 15bit counter value to both wake up waiters (by
->
+     * advancing their count) and avoid ABA effects. Successors are
->
+     * held in worker field "nextWait".  Queuing deals with several
->
+     * intrinsic races, mainly that a task-producing thread can miss
->
+     * seeing (and signalling) another thread that gave up looking for
->
+     * work but has not yet entered the wait queue. We solve this by
->
+     * requiring a full sweep of all workers both before (in scan())
->
+     * and after (in awaitWork()) a newly waiting worker is added to
->
+     * the wait queue. During a rescan, the worker might release some
->
+     * other queued worker rather than itself, which has the same net
->
+     * effect.
->
+     *
->
+     * Signalling.  We create or wake up workers only when there
->
+     * appears to be at least one task they might be able to find and
->
+     * execute.  When a submission is added or another worker adds a
->
+     * task to a queue that previously had two or fewer tasks, they
->
+     * signal waiting workers (or trigger creation of new ones if
->
+     * fewer than the given parallelism level -- see signalWork).
->
+     * These primary signals are buttressed by signals during rescans
->
+     * as well as those performed when a worker steals a task and
->
+     * notices that there are more tasks too; together these cover the
->
+     * signals needed in cases when more than two tasks are pushed
->
+     * but untaken.
->
+     *
->
+     * Trimming workers. To release resources after periods of lack of
->
+     * use, a worker starting to wait when the pool is quiescent will
->
+     * time out and terminate if the pool has remained quiescent for
->
+     * SHRINK_RATE nanosecs.
->
+     *
->
+     * Submissions. External submissions are maintained in an
->
+     * array-based queue that is structured identically to
->
+     * ForkJoinWorkerThread queues (which see) except for the use of
->
+     * submissionLock in method addSubmission. Unlike worker queues,
->
+     * multiple external threads can add new submissions.
->
+     *
->
+     * Compensation. Beyond work-stealing support and lifecycle
->
+     * control, the main responsibility of this framework is to take
->
+     * actions when one worker is waiting to join a task stolen (or
->
+     * always held by) another.  Because we are multiplexing many
->
+     * tasks on to a pool of workers, we can't just let them block (as
->
+     * in Thread.join).  We also cannot just reassign the joiner's
->
+     * run-time stack with another and replace it later, which would
->
+     * be a form of "continuation", that even if possible is not
->
+     * necessarily a good idea since we sometimes need both an
->
+     * unblocked task and its continuation to progress. Instead we
->
+     * combine two tactics:
->
+     *
->
+     *   Helping: Arranging for the joiner to execute some task that it
->
+     *      would be running if the steal had not occurred.  Method
->
+     *      ForkJoinWorkerThread.joinTask tracks joining->stealing
->
+     *      links to try to find such a task.
->
+     *
->
+     *   Compensating: Unless there are already enough live threads,
->
+     *      method tryPreBlock() may create or re-activate a spare
->
+     *      thread to compensate for blocked joiners until they
->
+     *      unblock.
->
+     *
->
+     * The ManagedBlocker extension API can't use helping so relies
->
+     * only on compensation in method awaitBlocker.
->
+     *
->
+     * It is impossible to keep exactly the target parallelism number
->
+     * of threads running at any given time.  Determining the
->
+     * existence of conservatively safe helping targets, the
->
+     * availability of already-created spares, and the apparent need
->
+     * to create new spares are all racy and require heuristic
->
+     * guidance, so we rely on multiple retries of each.  Currently,
->
+     * in keeping with on-demand signalling policy, we compensate only
->
+     * if blocking would leave less than one active (non-waiting,
->
+     * non-blocked) worker. Additionally, to avoid some false alarms
->
+     * due to GC, lagging counters, system activity, etc, compensated
->
+     * blocking for joins is only attempted after a number of rechecks
->
+     * proportional to the current apparent deficit (where retries are
->
+     * interspersed with Thread.yield, for good citizenship).  The
->
+     * variable blockedCount, incremented before blocking and
->
+     * decremented after, is sometimes needed to distinguish cases of
->
+     * waiting for work vs blocking on joins or other managed sync,
->
+     * but both the cases are equivalent for most pool control, so we
->
+     * can update non-atomically. (Additionally, contention on
->
+     * blockedCount alleviates some contention on ctl).
->
+     *
->
+     * Shutdown and Termination. A call to shutdownNow atomically sets
->
+     * the ctl stop bit and then (non-atomically) sets each workers
->
+     * "terminate" status, cancels all unprocessed tasks, and wakes up
->
+     * all waiting workers.  Detecting whether termination should
->
+     * commence after a non-abrupt shutdown() call requires more work
->
+     * and bookkeeping. We need consensus about quiesence (i.e., that
->
+     * there is no more work) which is reflected in active counts so
->
+     * long as there are no current blockers, as well as possible
->
+     * re-evaluations during independent changes in blocking or
->
+     * quiescing workers.
->
+     *
->
+     * Style notes: There is a lot of representation-level coupling
->
+     * among classes ForkJoinPool, ForkJoinWorkerThread, and
->
+     * ForkJoinTask.  Most fields of ForkJoinWorkerThread maintain
->
+     * data structures managed by ForkJoinPool, so are directly
->
+     * accessed.  Conversely we allow access to "workers" array by
->
+     * workers, and direct access to ForkJoinTask.status by both
->
+     * ForkJoinPool and ForkJoinWorkerThread.  There is little point
->
+     * trying to reduce this, since any associated future changes in
->
+     * representations will need to be accompanied by algorithmic
->
+     * changes anyway. All together, these low-level implementation
->
+     * choices produce as much as a factor of 4 performance
->
+     * improvement compared to naive implementations, and enable the
->
+     * processing of billions of tasks per second, at the expense of
->
+     * some ugliness.
->
+     *
->
+     * Methods signalWork() and scan() are the main bottlenecks so are
->
+     * especially heavily micro-optimized/mangled.  There are lots of
->
+     * inline assignments (of form "while ((local = field) != 0)")
->
+     * which are usually the simplest way to ensure the required read
->
+     * orderings (which are sometimes critical). This leads to a
->
+     * "C"-like style of listing declarations of these locals at the
->
+     * heads of methods or blocks.  There are several occurrences of
->
+     * the unusual "do {} while (!cas...)"  which is the simplest way
->
+     * to force an update of a CAS'ed variable. There are also other
->
+     * coding oddities that help some methods perform reasonably even
->
+     * when interpreted (not compiled).
->
+     *
->
+     * The order of declarations in this file is: (1) declarations of
->
+     * statics (2) fields (along with constants used when unpacking
->
+     * some of them), listed in an order that tends to reduce
->
+     * contention among them a bit under most JVMs.  (3) internal
->
+     * control methods (4) callbacks and other support for
->
+     * ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
->
+     * methods (plus a few little helpers). (6) static block
->
+     * initializing all statics in a minimally dependent order.
+     */
-–
+    /** 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);
+     * overridden in ForkJoinPool constructors.
+     */
+    public static final ForkJoinWorkerThreadFactory
-<
+        defaultForkJoinWorkerThreadFactory =
-<
+        new DefaultForkJoinWorkerThreadFactory();
->
+        defaultForkJoinWorkerThreadFactory;
+    /**
+     * Permission required for callers of methods that may start or
+     * kill threads.
+     */
-<
+    private static final RuntimePermission modifyThreadPermission =
-<
+        new RuntimePermission("modifyThread");
->
+    private static final RuntimePermission modifyThreadPermission;
+    /**
+     * If there is a security manager, makes sure caller has
+    /**
+     * Generator for assigning sequence numbers as pool names.
+     */
-<
+    private static final AtomicInteger poolNumberGenerator =
-<
+        new AtomicInteger();
->
+    private static final AtomicInteger poolNumberGenerator;
+    /**
-<
+     * Array holding all worker threads in the pool. Initialized upon
-<
+     * first use. Array size must be a power of two.  Updates and
-<
+     * replacements are protected by workerLock, but it is always kept
-<
+     * in a consistent enough state to be randomly accessed without
-<
+     * locking by workers performing work-stealing.
->
+     * Generator for initial random seeds for worker victim
->
+     * selection. This is used only to create initial seeds. Random
->
+     * steals use a cheaper xorshift generator per steal attempt. We
->
+     * don't expect much contention on seedGenerator, so just use a
->
+     * plain Random.
+     */
-<
+    volatile ForkJoinWorkerThread[] workers;
->
+    static final Random workerSeedGenerator;
+    /**
-<
+     * Lock protecting access to workers.
->
+     * Array holding all worker threads in the pool.  Initialized upon
->
+     * construction. Array size must be a power of two.  Updates and
->
+     * replacements are protected by scanGuard, but the array is
->
+     * always kept in a consistent enough state to be randomly
->
+     * accessed without locking by workers performing work-stealing,
->
+     * as well as other traversal-based methods in this class, so long
->
+     * as reads memory-acquire by first reading ctl. All readers must
->
+     * tolerate that some array slots may be null.
+     */
-<
+    private final ReentrantLock workerLock;
->
+    ForkJoinWorkerThread[] workers;
+    /**
-<
+     * Condition for awaitTermination.
->
+     * Initial size for submission queue array. Must be a power of
->
+     * two.  In many applications, these always stay small so we use a
->
+     * small initial cap.
+     */
-<
+    private final Condition termination;
->
+    private static final int INITIAL_QUEUE_CAPACITY = 8;
->
->
+    /**
->
+     * Maximum size for submission queue array. Must be a power of two
->
+     * less than or equal to 1 << (31 - width of array entry) to
->
+     * ensure lack of index wraparound, but is capped at a lower
->
+     * value to help users trap runaway computations.
->
+     */
->
+    private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 24; // 16M
+    /**
-<
+     * The uncaught exception handler used when any worker
-<
+     * abruptly terminates
->
+     * Array serving as submission queue. Initialized upon construction.
+     */
-<
+    private Thread.UncaughtExceptionHandler ueh;
->
+    private ForkJoinTask<?>[] submissionQueue;
->
->
+    /**
->
+     * Lock protecting submissions array for addSubmission
->
+     */
->
+    private final ReentrantLock submissionLock;
->
->
+    /**
->
+     * Condition for awaitTermination, using submissionLock for
->
+     * convenience.
->
+     */
->
+    private final Condition termination;
+    /**
+     * Creation factory for worker threads.
+    private final ForkJoinWorkerThreadFactory factory;
+    /**
-<
+     * Head of stack of threads that were created to maintain
-<
+     * parallelism when other threads blocked, but have since
-<
+     * suspended when the parallelism level rose.
->
+     * The uncaught exception handler used when any worker abruptly
->
+     * terminates.
+     */
-<
+    private volatile WaitQueueNode spareStack;
->
+    final Thread.UncaughtExceptionHandler ueh;
+    /**
-<
+     * Sum of per-thread steal counts, updated only when threads are
-<
+     * idle or terminating.
->
+     * Prefix for assigning names to worker threads
+     */
-<
+    private final AtomicLong stealCount;
->
+    private final String workerNamePrefix;
+    /**
-<
+     * Queue for external submissions.
->
+     * Sum of per-thread steal counts, updated only when threads are
->
+     * idle or terminating.
+     */
-<
+    private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
->
+    private volatile long stealCount;
+    /**
-<
+     * Head of Treiber stack for barrier sync. See below for explanation.
->
+     * Main pool control -- a long packed with:
->
+     * AC: Number of active running workers minus target parallelism (16 bits)
->
+     * TC: Number of total workers minus target parallelism (16bits)
->
+     * ST: true if pool is terminating (1 bit)
->
+     * EC: the wait count of top waiting thread (15 bits)
->
+     * ID: ~poolIndex of top of Treiber stack of waiting threads (16 bits)
->
+     *
->
+     * When convenient, we can extract the upper 32 bits of counts and
->
+     * the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
->
+     * (int)ctl.  The ec field is never accessed alone, but always
->
+     * together with id and st. The offsets of counts by the target
->
+     * parallelism and the positionings of fields makes it possible to
->
+     * perform the most common checks via sign tests of fields: When
->
+     * ac is negative, there are not enough active workers, when tc is
->
+     * negative, there are not enough total workers, when id is
->
+     * negative, there is at least one waiting worker, and when e is
->
+     * negative, the pool is terminating.  To deal with these possibly
->
+     * negative fields, we use casts in and out of "short" and/or
->
+     * signed shifts to maintain signedness.
+     */
-<
+    private volatile WaitQueueNode syncStack;
->
+    volatile long ctl;
->
->
+    // bit positions/shifts for fields
->
+    private static final int  AC_SHIFT   = 48;
->
+    private static final int  TC_SHIFT   = 32;
->
+    private static final int  ST_SHIFT   = 31;
->
+    private static final int  EC_SHIFT   = 16;
->
->
+    // bounds
->
+    private static final int  MAX_ID     = 0x7fff;  // max poolIndex
->
+    private static final int  SMASK      = 0xffff;  // mask short bits
->
+    private static final int  SHORT_SIGN = 1 << 15;
->
+    private static final int  INT_SIGN   = 1 << 31;
->
->
+    // masks
->
+    private static final long STOP_BIT   = 0x0001L << ST_SHIFT;
->
+    private static final long AC_MASK    = ((long)SMASK) << AC_SHIFT;
->
+    private static final long TC_MASK    = ((long)SMASK) << TC_SHIFT;
->
->
+    // units for incrementing and decrementing
->
+    private static final long TC_UNIT    = 1L << TC_SHIFT;
->
+    private static final long AC_UNIT    = 1L << AC_SHIFT;
->
->
+    // masks and units for dealing with u = (int)(ctl >>> 32)
->
+    private static final int  UAC_SHIFT  = AC_SHIFT - 32;
->
+    private static final int  UTC_SHIFT  = TC_SHIFT - 32;
->
+    private static final int  UAC_MASK   = SMASK << UAC_SHIFT;
->
+    private static final int  UTC_MASK   = SMASK << UTC_SHIFT;
->
+    private static final int  UAC_UNIT   = 1 << UAC_SHIFT;
->
+    private static final int  UTC_UNIT   = 1 << UTC_SHIFT;
->
->
+    // masks and units for dealing with e = (int)ctl
->
+    private static final int  E_MASK     = 0x7fffffff; // no STOP_BIT
->
+    private static final int  EC_UNIT    = 1 << EC_SHIFT;
+    /**
-<
+     * The count for event barrier
->
+     * The target parallelism level.
+     */
-<
+    private volatile long eventCount;
->
+    final int parallelism;
+    /**
-<
+     * Pool number, just for assigning useful names to worker threads
->
+     * Index (mod submission queue length) of next element to take
->
+     * from submission queue.
+     */
-<
+    private final int poolNumber;
->
+    volatile int queueBase;
+    /**
-<
+     * The maximum allowed pool size
->
+     * Index (mod submission queue length) of next element to add
->
+     * in submission queue.
+     */
-<
+    private volatile int maxPoolSize;
->
+    int queueTop;
+    /**
-<
+     * The desired parallelism level, updated only under workerLock.
->
+     * True when shutdown() has been called.
+     */
-<
+    private volatile int parallelism;
->
+    volatile boolean shutdown;
+    /**
+     * True if use local fifo, not default lifo, for local polling
-+
+     * Read by, and replicated by ForkJoinWorkerThreads
+     */
-<
+    private volatile boolean locallyFifo;
->
+    final boolean locallyFifo;
+    /**
-<
+     * Holds number of total (i.e., created and not yet terminated)
-<
+     * and running (i.e., not blocked on joins or other managed sync)
-<
+     * threads, packed into one int to ensure consistent snapshot when
-<
+     * making decisions about creating and suspending spare
-<
+     * threads. Updated only by CAS.  Note: CASes in
-<
+     * updateRunningCount and preJoin assume that running active count
-<
+     * is in low word, so need to be modified if this changes.
->
+     * The number of threads in ForkJoinWorkerThreads.helpQuiescePool.
->
+     * When non-zero, suppresses automatic shutdown when active
->
+     * counts become zero.
+     */
-<
+    private volatile int workerCounts;
->
+    volatile int quiescerCount;
-<
+    private static int totalCountOf(int s)           { return s >>> 16;  }
-<
+    private static int runningCountOf(int s)         { return s & shortMask; }
-<
+    private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
->
+    /**
->
+     * The number of threads blocked in join.
->
+     */
->
+    volatile int blockedCount;
+    /**
-<
+     * Adds delta (which may be negative) to running count.  This must
-<
+     * be called before (with negative arg) and after (with positive)
-<
+     * any managed synchronization (i.e., mainly, joins).
-<
+     *
-<
+     * @param delta the number to add
->
+     * Counter for worker Thread names (unrelated to their poolIndex)
+     */
-<
+    final void updateRunningCount(int delta) {
-<
+        int s;
-<
+        do {} while (!casWorkerCounts(s = workerCounts, s + delta));
-<
+    }
->
+    private volatile int nextWorkerNumber;
+    /**
-<
+     * Adds delta (which may be negative) to both total and running
-<
+     * count.  This must be called upon creation and termination of
-<
+     * worker threads.
-<
+     *
-<
+     * @param delta the number to add
->
+     * The index for the next created worker. Accessed under scanGuard.
+     */
-<
+    private void updateWorkerCount(int delta) {
-<
+        int d = delta + (delta << 16); // add to both lo and hi parts
-<
+        int s;
-<
+        do {} while (!casWorkerCounts(s = workerCounts, s + d));
-<
+    }
->
+    private int nextWorkerIndex;
+    /**
-<
+     * Lifecycle control. High word contains runState, low word
-<
+     * contains the number of workers that are (probably) executing
-<
+     * tasks. This value is atomically incremented before a worker
-<
+     * gets a task to run, and decremented when worker has no tasks
-<
+     * and cannot find any. These two fields are bundled together to
-<
+     * support correct termination triggering.  Note: activeCount
-<
+     * CAS'es cheat by assuming active count is in low word, so need
-<
+     * to be modified if this changes
->
+     * SeqLock and index masking for for updates to workers array.
->
+     * Locked when SG_UNIT is set. Unlocking clears bit by adding
->
+     * SG_UNIT. Staleness of read-only operations can be checked by
->
+     * comparing scanGuard to value before the reads. The low 16 bits
->
+     * (i.e, anding with SMASK) hold (the smallest power of two
->
+     * covering all worker indices, minus one, and is used to avoid
->
+     * dealing with large numbers of null slots when the workers array
->
+     * is overallocated.
+     */
-<
+    private volatile int runControl;
->
+    volatile int scanGuard;
-<
+    // RunState values. Order among values matters
-<
+    private static final int RUNNING     = 0;
-<
+    private static final int SHUTDOWN    = 1;
-<
+    private static final int TERMINATING = 2;
-<
+    private static final int TERMINATED  = 3;
->
+    private static final int SG_UNIT = 1 << 16;
-<
+    private static int runStateOf(int c)             { return c >>> 16; }
-<
+    private static int activeCountOf(int c)          { return c & shortMask; }
-<
+    private static int runControlFor(int r, int a)   { return (r << 16) + a; }
->
+    /**
->
+     * The wakeup interval (in nanoseconds) for a worker waiting for a
->
+     * task when the pool is quiescent to instead try to shrink the
->
+     * number of workers.  The exact value does not matter too
->
+     * much. It must be short enough to release resources during
->
+     * sustained periods of idleness, but not so short that threads
->
+     * are continually re-created.
->
+     */
->
+    private static final long SHRINK_RATE =
->
+L * 1000L * 1000L * 1000L; // 4 seconds
+    /**
-<
+     * Tries incrementing active count; fails on contention.
-<
+     * Called by workers before/during executing tasks.
->
+     * Top-level loop for worker threads: On each step: if the
->
+     * previous step swept through all queues and found no tasks, or
->
+     * there are excess threads, then possibly blocks. Otherwise,
->
+     * scans for and, if found, executes a task. Returns when pool
->
+     * and/or worker terminate.
-<
+     * @return true on success
->
+     * @param w the worker
+     */
-<
+    final boolean tryIncrementActiveCount() {
-<
+        int c = runControl;
-<
+        return casRunControl(c, c+1);
->
+    final void work(ForkJoinWorkerThread w) {
->
+        boolean swept = false;                // true on empty scans
->
+        long c;
->
+        while (!w.terminate && (int)(c = ctl) >= 0) {
->
+            int a;                            // active count
->
+            if (!swept && (a = (int)(c >> AC_SHIFT)) <= 0)
->
+                swept = scan(w, a);
->
+            else if (tryAwaitWork(w, c))
->
+                swept = false;
->
+        }
-+
+    // Signalling
-+
+    /**
-<
+     * Tries decrementing active count; fails on contention.
-<
+     * Possibly triggers termination on success.
-<
+     * Called by workers when they can't find tasks.
-<
+     *
-<
+     * @return true on success
->
+     * Wakes up or creates a worker.
+     */
-<
+    final boolean tryDecrementActiveCount() {
-<
+        int c = runControl;
-<
+        int nextc = c - 1;
-<
+        if (!casRunControl(c, nextc))
-<
+            return false;
-<
+        if (canTerminateOnShutdown(nextc))
-<
+            terminateOnShutdown();
-<
+        return true;
->
+    final void signalWork() {
->
+        /*
->
+         * The while condition is true if: (there is are too few total
->
+         * workers OR there is at least one waiter) AND (there are too
->
+         * few active workers OR the pool is terminating).  The value
->
+         * of e distinguishes the remaining cases: zero (no waiters)
->
+         * for create, negative if terminating (in which case do
->
+         * nothing), else release a waiter. The secondary checks for
->
+         * release (non-null array etc) can fail if the pool begins
->
+         * terminating after the test, and don't impose any added cost
->
+         * because JVMs must perform null and bounds checks anyway.
->
+         */
->
+        long c; int e, u;
->
+        while ((((e = (int)(c = ctl)) | (u = (int)(c >>> 32))) &
->
+                (INT_SIGN|SHORT_SIGN)) == (INT_SIGN|SHORT_SIGN) && e >= 0) {
->
+            if (e > 0) {                         // release a waiting worker
->
+                int i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
->
+                if ((ws = workers) == null ||
->
+                    (i = ~e & SMASK) >= ws.length ||
->
+                    (w = ws[i]) == null)
->
+                    break;
->
+                long nc = (((long)(w.nextWait & E_MASK)) |
->
+                           ((long)(u + UAC_UNIT) << 32));
->
+                if (w.eventCount == e &&
->
+                    UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
->
+                    w.eventCount = (e + EC_UNIT) & E_MASK;
->
+                    if (w.parked)
->
+                        UNSAFE.unpark(w);
->
+                    break;
->
+                }
->
+            }
->
+            else if (UNSAFE.compareAndSwapLong
->
+                     (this, ctlOffset, c,
->
+                      (long)(((u + UTC_UNIT) & UTC_MASK) |
->
+                             ((u + UAC_UNIT) & UAC_MASK)) << 32)) {
->
+                addWorker();
->
+                break;
->
+            }
->
+        }
+    /**
-<
+     * Returns {@code true} if argument represents zero active count
-<
+     * and nonzero runstate, which is the triggering condition for
-<
+     * terminating on shutdown.
->
+     * Variant of signalWork to help release waiters on rescans.
->
+     * Tries once to release a waiter if active count < 0.
->
+     *
->
+     * @return false if failed due to contention, else true
+     */
-<
+    private static boolean canTerminateOnShutdown(int c) {
-<
+        // i.e. least bit is nonzero runState bit
-<
+        return ((c & -c) >>> 16) != 0;
->
+    private boolean tryReleaseWaiter() {
->
+        long c; int e, i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
->
+        if ((e = (int)(c = ctl)) > 0 &&
->
+            (int)(c >> AC_SHIFT) < 0 &&
->
+            (ws = workers) != null &&
->
+            (i = ~e & SMASK) < ws.length &&
->
+            (w = ws[i]) != null) {
->
+            long nc = ((long)(w.nextWait & E_MASK) |
->
+                       ((c + AC_UNIT) & (AC_MASK|TC_MASK)));
->
+            if (w.eventCount != e ||
->
+                !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
->
+                return false;
->
+            w.eventCount = (e + EC_UNIT) & E_MASK;
->
+            if (w.parked)
->
+                UNSAFE.unpark(w);
->
+        }
->
+        return true;
-+
+    // Scanning for tasks
-+
+    /**
-<
+     * Transition run state to at least the given state. Return true
-<
+     * if not already at least given state.
->
+     * Scans for and, if found, executes one task. Scans start at a
->
+     * random index of workers array, and randomly select the first
->
+     * (2*#workers)-1 probes, and then, if all empty, resort to 2
->
+     * circular sweeps, which is necessary to check quiescence. and
->
+     * taking a submission only if no stealable tasks were found.  The
->
+     * steal code inside the loop is a specialized form of
->
+     * ForkJoinWorkerThread.deqTask, followed bookkeeping to support
->
+     * helpJoinTask and signal propagation. The code for submission
->
+     * queues is almost identical. On each steal, the worker completes
->
+     * not only the task, but also all local tasks that this task may
->
+     * have generated. On detecting staleness or contention when
->
+     * trying to take a task, this method returns without finishing
->
+     * sweep, which allows global state rechecks before retry.
->
+     *
->
+     * @param w the worker
->
+     * @param a the number of active workers
->
+     * @return true if swept all queues without finding a task
+     */
-<
+    private boolean transitionRunStateTo(int state) {
-<
+        for (;;) {
-<
+            int c = runControl;
-<
+            if (runStateOf(c) >= state)
->
+    private boolean scan(ForkJoinWorkerThread w, int a) {
->
+        int g = scanGuard; // mask 0 avoids useless scans if only one active
->
+        int m = parallelism == 1 - a? 0 : g & SMASK;
->
+        ForkJoinWorkerThread[] ws = workers;
->
+        if (ws == null || ws.length <= m)         // staleness check
->
+            return false;
->
+        for (int r = w.seed, k = r, j = -(m + m); j <= m + m; ++j) {
->
+            ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
->
+            ForkJoinWorkerThread v = ws[k & m];
->
+            if (v != null && (b = v.queueBase) != v.queueTop &&
->
+                (q = v.queue) != null && (i = (q.length - 1) & b) >= 0) {
->
+                long u = (i << ASHIFT) + ABASE;
->
+                if ((t = q[i]) != null && v.queueBase == b &&
->
+                    UNSAFE.compareAndSwapObject(q, u, t, null)) {
->
+                    int d = (v.queueBase = b + 1) - v.queueTop;
->
+                    v.stealHint = w.poolIndex;
->
+                    if (d != 0)
->
+                        signalWork();             // propagate if nonempty
->
+                    w.execTask(t);
->
+                }
->
+                r ^= r << 13; r ^= r >>> 17; w.seed = r ^ (r << 5);
->
+                return false;                     // store next seed
->
+            }
->
+            else if (j < 0) {                     // xorshift
->
+                r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;
->
+            }
->
+            else
->
+                ++k;
->
+        }
->
+        if (scanGuard != g)                       // staleness check
->
+            return false;
->
+        else {                                    // try to take submission
->
+            ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
->
+            if ((b = queueBase) != queueTop &&
->
+                (q = submissionQueue) != null &&
->
+                (i = (q.length - 1) & b) >= 0) {
->
+                long u = (i << ASHIFT) + ABASE;
->
+                if ((t = q[i]) != null && queueBase == b &&
->
+                    UNSAFE.compareAndSwapObject(q, u, t, null)) {
->
+                    queueBase = b + 1;
->
+                    w.execTask(t);
->
+                }
+                return false;
-<
+            if (casRunControl(c, runControlFor(state, activeCountOf(c))))
->
+            }
->
+            return true;                         // all queues empty
->
+        }
->
+    }
->
->
+    /**
->
+     * Tries to enqueue worker w in wait queue and await change in
->
+     * worker's eventCount.  If the pool is quiescent, possibly
->
+     * terminates worker upon exit.  Otherwise, before blocking,
->
+     * rescans queues to avoid missed signals.  Upon finding work,
->
+     * releases at least one worker (which may be the current
->
+     * worker). Rescans restart upon detected staleness or failure to
->
+     * release due to contention.
->
+     *
->
+     * @param w the calling worker
->
+     * @param c the ctl value on entry
->
+     * @return true if waited or another thread was released upon enq
->
+     */
->
+    private boolean tryAwaitWork(ForkJoinWorkerThread w, long c) {
->
+        int v = w.eventCount;
->
+        w.nextWait = (int)c;                      // w's successor record
->
+        long nc = (long)(v & E_MASK) | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
->
+        if (ctl != c || !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
->
+            long d = ctl; // return true if lost to a deq, to force scan
->
+            return (int)d != (int)c && ((d - c) & AC_MASK) >= 0L;
->
+        }
->
+        for (int sc = w.stealCount; sc != 0;) {   // accumulate stealCount
->
+            long s = stealCount;
->
+            if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s + sc))
->
+                sc = w.stealCount = 0;
->
+            else if (w.eventCount != v)
->
+                return true;                      // update next time
->
+        }
->
+        if (parallelism + (int)(nc >> AC_SHIFT) == 0 &&
->
+            blockedCount == 0 && quiescerCount == 0)
->
+            idleAwaitWork(w, nc, c, v);           // quiescent
->
+        for (boolean rescanned = false;;) {
->
+            if (w.eventCount != v)
+                return true;
-+
+            if (!rescanned) {
-+
+                int g = scanGuard, m = g & SMASK;
-+
+                ForkJoinWorkerThread[] ws = workers;
-+
+                if (ws != null && m < ws.length) {
-+
+                    rescanned = true;
-+
+                    for (int i = 0; i <= m; ++i) {
-+
+                        ForkJoinWorkerThread u = ws[i];
-+
+                        if (u != null) {
-+
+                            if (u.queueBase != u.queueTop &&
-+
+                                !tryReleaseWaiter())
-+
+                                rescanned = false; // contended
-+
+                            if (w.eventCount != v)
-+
+                                return true;
-+
+                        }
-+
+                    }
-+
+                }
-+
+                if (scanGuard != g ||              // stale
-+
+                    (queueBase != queueTop && !tryReleaseWaiter()))
-+
+                    rescanned = false;
-+
+                if (!rescanned)
-+
+                    Thread.yield();                // reduce contention
-+
+                else
-+
+                    Thread.interrupted();          // clear before park
-+
+            }
-+
+            else {
-+
+                w.parked = true;                   // must recheck
-+
+                if (w.eventCount != v) {
-+
+                    w.parked = false;
-+
+                    return true;
-+
+                }
-+
+                LockSupport.park(this);
-+
+                rescanned = w.parked = false;
-+
+            }
+    /**
-<
+     * Controls whether to add spares to maintain parallelism
-<
+     */
-<
+    private volatile boolean maintainsParallelism;
->
+     * If inactivating worker w has caused pool to become
->
+     * quiescent, check for pool termination, and wait for event
->
+     * for up to SHRINK_RATE nanosecs (rescans are unnecessary in
->
+     * this case because quiescence reflects consensus about lack
->
+     * of work). On timeout, if ctl has not changed, terminate the
->
+     * worker. Upon its termination (see deregisterWorker), it may
->
+     * wake up another worker to possibly repeat this process.
->
+     *
->
+     * @param w the calling worker
->
+     * @param currentCtl the ctl value after enqueuing w
->
+     * @param prevCtl the ctl value if w terminated
->
+     * @param v the eventCount w awaits change
->
+     */
->
+    private void idleAwaitWork(ForkJoinWorkerThread w, long currentCtl,
->
+                               long prevCtl, int v) {
->
+        if (w.eventCount == v) {
->
+            if (shutdown)
->
+                tryTerminate(false);
->
+            ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs
->
+            while (ctl == currentCtl) {
->
+                long startTime = System.nanoTime();
->
+                w.parked = true;
->
+                if (w.eventCount == v)             // must recheck
->
+                    LockSupport.parkNanos(this, SHRINK_RATE);
->
+                w.parked = false;
->
+                if (w.eventCount != v)
->
+                    break;
->
+                else if (System.nanoTime() - startTime < SHRINK_RATE)
->
+                    Thread.interrupted();          // spurious wakeup
->
+                else if (UNSAFE.compareAndSwapLong(this, ctlOffset,
->
+                                                   currentCtl, prevCtl)) {
->
+                    w.terminate = true;            // restore previous
->
+                    w.eventCount = ((int)currentCtl + EC_UNIT) & E_MASK;
->
+                    break;
->
+                }
->
+            }
->
+        }
->
+    }
-<
+    // Constructors
->
+    // Submissions
+    /**
-<
+     * Creates a {@code ForkJoinPool} with parallelism equal to {@link
-<
+     * java.lang.Runtime#availableProcessors}, and using the {@linkplain
-<
+     * #defaultForkJoinWorkerThreadFactory default thread factory}.
->
+     * Enqueues the given task in the submissionQueue.  Same idea as
->
+     * ForkJoinWorkerThread.pushTask except for use of submissionLock.
-<
+     * @throws SecurityException if a security manager exists and
-<
+     *         the caller is not permitted to modify threads
-<
+     *         because it does not hold {@link
-<
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
->
+     * @param t the task
+     */
-<
+    public ForkJoinPool() {
-<
+        this(Runtime.getRuntime().availableProcessors(),
-<
+             defaultForkJoinWorkerThreadFactory);
->
+    private void addSubmission(ForkJoinTask<?> t) {
->
+        final ReentrantLock lock = this.submissionLock;
->
+        lock.lock();
->
+        try {
->
+            ForkJoinTask<?>[] q; int s, m;
->
+            if ((q = submissionQueue) != null) {    // ignore if queue removed
->
+                long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE;
->
+                UNSAFE.putOrderedObject(q, u, t);
->
+                queueTop = s + 1;
->
+                if (s - queueBase == m)
->
+                    growSubmissionQueue();
->
+            }
->
+        } finally {
->
+            lock.unlock();
->
+        }
->
+        signalWork();
-+
+    //  (pollSubmission is defined below with exported methods)
-+
+    /**
-<
+     * Creates a {@code ForkJoinPool} with the indicated parallelism
-<
+     * level and using the {@linkplain
-<
+     * #defaultForkJoinWorkerThreadFactory default thread factory}.
-<
+     *
-<
+     * @param parallelism the parallelism level
-<
+     * @throws IllegalArgumentException if parallelism less than or
-<
+     * equal to zero
-<
+     * @throws SecurityException if a security manager exists and
-<
+     *         the caller is not permitted to modify threads
-<
+     *         because it does not hold {@link
-<
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
->
+     * Creates or doubles submissionQueue array.
->
+     * Basically identical to ForkJoinWorkerThread version
+     */
-<
+    public ForkJoinPool(int parallelism) {
-<
+        this(parallelism, defaultForkJoinWorkerThreadFactory);
->
+    private void growSubmissionQueue() {
->
+        ForkJoinTask<?>[] oldQ = submissionQueue;
->
+        int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY;
->
+        if (size > MAXIMUM_QUEUE_CAPACITY)
->
+            throw new RejectedExecutionException("Queue capacity exceeded");
->
+        if (size < INITIAL_QUEUE_CAPACITY)
->
+            size = INITIAL_QUEUE_CAPACITY;
->
+        ForkJoinTask<?>[] q = submissionQueue = new ForkJoinTask<?>[size];
->
+        int mask = size - 1;
->
+        int top = queueTop;
->
+        int oldMask;
->
+        if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) {
->
+            for (int b = queueBase; b != top; ++b) {
->
+                long u = ((b & oldMask) << ASHIFT) + ABASE;
->
+                Object x = UNSAFE.getObjectVolatile(oldQ, u);
->
+                if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null))
->
+                    UNSAFE.putObjectVolatile
->
+                        (q, ((b & mask) << ASHIFT) + ABASE, x);
->
+            }
->
+        }
->
+    }
->
->
+    // Blocking support
->
->
+    /**
->
+     * Tries to increment blockedCount, decrement active count
->
+     * (sometimes implicitly) and possibly release or create a
->
+     * compensating worker in preparation for blocking. Fails
->
+     * on contention or termination.
->
+     *
->
+     * @return true if the caller can block, else should recheck and retry
->
+     */
->
+    private boolean tryPreBlock() {
->
+        int b = blockedCount;
->
+        if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) {
->
+            int pc = parallelism;
->
+            do {
->
+                ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
->
+                int e, ac, tc, rc, i;
->
+                long c = ctl;
->
+                int u = (int)(c >>> 32);
->
+                if ((e = (int)c) < 0) {
->
+                                                 // skip -- terminating
->
+                }
->
+                else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 &&
->
+                         (ws = workers) != null &&
->
+                         (i = ~e & SMASK) < ws.length &&
->
+                         (w = ws[i]) != null) {
->
+                    long nc = ((long)(w.nextWait & E_MASK) |
->
+                               (c & (AC_MASK|TC_MASK)));
->
+                    if (w.eventCount == e &&
->
+                        UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
->
+                        w.eventCount = (e + EC_UNIT) & E_MASK;
->
+                        if (w.parked)
->
+                            UNSAFE.unpark(w);
->
+                        return true;             // release an idle worker
->
+                    }
->
+                }
->
+                else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
->
+                    long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
->
+                    if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
->
+                        return true;             // no compensation needed
->
+                }
->
+                else if (tc + pc < MAX_ID) {
->
+                    long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
->
+                    if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
->
+                        addWorker();
->
+                        return true;            // create a replacement
->
+                    }
->
+                }
->
+                // try to back out on any failure and let caller retry
->
+            } while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
->
+                                               b = blockedCount, b - 1));
->
+        }
->
+        return false;
+    /**
-<
+     * Creates a {@code ForkJoinPool} with parallelism equal to {@link
-<
+     * java.lang.Runtime#availableProcessors}, and using the given
-<
+     * thread factory.
-<
+     *
-<
+     * @param factory the factory for creating new threads
-<
+     * @throws NullPointerException if factory is null
-<
+     * @throws SecurityException if a security manager exists and
-<
+     *         the caller is not permitted to modify threads
-<
+     *         because it does not hold {@link
-<
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
->
+     * Decrements blockedCount and increments active count
+     */
-<
+    public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
-<
+        this(Runtime.getRuntime().availableProcessors(), factory);
->
+    private void postBlock() {
->
+        long c;
->
+        do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset,  // no mask
->
+                                                c = ctl, c + AC_UNIT));
->
+        int b;
->
+        do {} while(!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
->
+                                              b = blockedCount, b - 1));
+    /**
-<
+     * Creates a {@code ForkJoinPool} with the given parallelism and
-<
+     * thread factory.
->
+     * Possibly blocks waiting for the given task to complete, or
->
+     * cancels the task if terminating.  Fails to wait if contended.
-<
+     * @param parallelism the parallelism level
-<
+     * @param factory the factory for creating new threads
-<
+     * @throws IllegalArgumentException if parallelism less than or
-<
+     * equal to zero, or greater than implementation limit
-<
+     * @throws NullPointerException if factory is null
-<
+     * @throws SecurityException if a security manager exists and
-<
+     *         the caller is not permitted to modify threads
-<
+     *         because it does not hold {@link
-<
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
->
+     * @param joinMe the task
+     */
-<
+    public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
-<
+        if (parallelism <= 0 || parallelism > MAX_THREADS)
-<
+            throw new IllegalArgumentException();
-<
+        if (factory == null)
-<
+            throw new NullPointerException();
-<
+        checkPermission();
-<
+        this.factory = factory;
-<
+        this.parallelism = parallelism;
-<
+        this.maxPoolSize = MAX_THREADS;
-<
+        this.maintainsParallelism = true;
-<
+        this.poolNumber = poolNumberGenerator.incrementAndGet();
-<
+        this.workerLock = new ReentrantLock();
-<
+        this.termination = workerLock.newCondition();
-<
+        this.stealCount = new AtomicLong();
-<
+        this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
-<
+        // worker array and workers are lazily constructed
->
+    final void tryAwaitJoin(ForkJoinTask<?> joinMe) {
->
+        int s;
->
+        Thread.interrupted(); // clear interrupts before checking termination
->
+        if (joinMe.status >= 0) {
->
+            if (tryPreBlock()) {
->
+                joinMe.tryAwaitDone(0L);
->
+                postBlock();
->
+            }
->
+            if ((ctl & STOP_BIT) != 0L)
->
+                joinMe.cancelIgnoringExceptions();
->
+        }
+    /**
-<
+     * Creates a new worker thread using factory.
->
+     * Possibly blocks the given worker waiting for joinMe to
->
+     * complete or timeout
-<
+     * @param index the index to assign worker
-<
+     * @return new worker, or null if factory failed
->
+     * @param joinMe the task
->
+     * @param millis the wait time for underlying Object.wait
+     */
-<
+    private ForkJoinWorkerThread createWorker(int index) {
-<
+        Thread.UncaughtExceptionHandler h = ueh;
-<
+        ForkJoinWorkerThread w = factory.newThread(this);
-<
+        if (w != null) {
-<
+            w.poolIndex = index;
-<
+            w.setDaemon(true);
-<
+            w.setAsyncMode(locallyFifo);
-<
+            w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
-<
+            if (h != null)
-<
+                w.setUncaughtExceptionHandler(h);
->
+    final void timedAwaitJoin(ForkJoinTask<?> joinMe, long nanos) {
->
+        while (joinMe.status >= 0) {
->
+            Thread.interrupted();
->
+            if ((ctl & STOP_BIT) != 0L) {
->
+                joinMe.cancelIgnoringExceptions();
->
+                break;
->
+            }
->
+            if (tryPreBlock()) {
->
+                long last = System.nanoTime();
->
+                while (joinMe.status >= 0) {
->
+                    long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
->
+                    if (millis <= 0)
->
+                        break;
->
+                    joinMe.tryAwaitDone(millis);
->
+                    if (joinMe.status < 0)
->
+                        break;
->
+                    if ((ctl & STOP_BIT) != 0L) {
->
+                        joinMe.cancelIgnoringExceptions();
->
+                        break;
->
+                    }
->
+                    long now = System.nanoTime();
->
+                    nanos -= now - last;
->
+                    last = now;
->
+                }
->
+                postBlock();
->
+                break;
->
+            }
-–
+        return w;
+    /**
-<
+     * Returns a good size for worker array given pool size.
-<
+     * Currently requires size to be a power of two.
->
+     * If necessary, compensates for blocker, and blocks
+     */
-<
+    private static int arraySizeFor(int poolSize) {
-<
+        if (poolSize <= 1)
-<
+            return 1;
-<
+        // See Hackers Delight, sec 3.2
-<
+        int c = poolSize >= MAX_THREADS ? MAX_THREADS : (poolSize - 1);
-<
+        c |= c >>>  1;
-<
+        c |= c >>>  2;
-<
+        c |= c >>>  4;
-<
+        c |= c >>>  8;
-<
+        c |= c >>> 16;
-<
+        return c + 1;
->
+    private void awaitBlocker(ManagedBlocker blocker)
->
+        throws InterruptedException {
->
+        while (!blocker.isReleasable()) {
->
+            if (tryPreBlock()) {
->
+                try {
->
+                    do {} while (!blocker.isReleasable() && !blocker.block());
->
+                } finally {
->
+                    postBlock();
->
+                }
->
+                break;
->
+            }
->
+        }
-+
+    // Creating, registering and deregistring workers
-+
+    /**
-<
+     * Creates or resizes array if necessary to hold newLength.
-<
+     * Call only under exclusion.
-<
+     *
-<
+     * @return the array
->
+     * Tries to create and start a worker; minimally rolls back counts
->
+     * on failure.
+     */
-<
+    private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
-<
+        ForkJoinWorkerThread[] ws = workers;
-<
+        if (ws == null)
-<
+            return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
-<
+        else if (newLength > ws.length)
-<
+            return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
->
+    private void addWorker() {
->
+        Throwable ex = null;
->
+        ForkJoinWorkerThread t = null;
->
+        try {
->
+            t = factory.newThread(this);
->
+        } catch (Throwable e) {
->
+            ex = e;
->
+        }
->
+        if (t == null) {  // null or exceptional factory return
->
+            long c;       // adjust counts
->
+            do {} while (!UNSAFE.compareAndSwapLong
->
+                         (this, ctlOffset, c = ctl,
->
+                          (((c - AC_UNIT) & AC_MASK) |
->
+                           ((c - TC_UNIT) & TC_MASK) |
->
+                           (c & ~(AC_MASK|TC_MASK)))));
->
+            // Propagate exception if originating from an external caller
->
+            if (!tryTerminate(false) && ex != null &&
->
+                !(Thread.currentThread() instanceof ForkJoinWorkerThread))
->
+                UNSAFE.throwException(ex);
->
+        }
+        else
-<
+            return ws;
->
+            t.start();
+    /**
-<
+     * Tries to shrink workers into smaller array after one or more terminate.
->
+     * Callback from ForkJoinWorkerThread constructor to assign a
->
+     * public name
+     */
-<
+    private void tryShrinkWorkerArray() {
-<
+        ForkJoinWorkerThread[] ws = workers;
-<
+        if (ws != null) {
-<
+            int len = ws.length;
-<
+            int last = len - 1;
-<
+            while (last >= 0 && ws[last] == null)
-<
+                --last;
-<
+            int newLength = arraySizeFor(last+1);
-<
+            if (newLength < len)
-<
+                workers = Arrays.copyOf(ws, newLength);
->
+    final String nextWorkerName() {
->
+        for (int n;;) {
->
+            if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset,
->
+                                         n = nextWorkerNumber, ++n))
->
+                return workerNamePrefix + n;
+    /**
-<
+     * Initializes workers if necessary.
->
+     * Callback from ForkJoinWorkerThread constructor to
->
+     * determine its poolIndex and record in workers array.
->
+     *
->
+     * @param w the worker
->
+     * @return the worker's pool index
+     */
-<
+    final void ensureWorkerInitialization() {
-<
+        ForkJoinWorkerThread[] ws = workers;
-<
+        if (ws == null) {
-<
+            final ReentrantLock lock = this.workerLock;
-<
+            lock.lock();
-<
+            try {
-<
+                ws = workers;
-<
+                if (ws == null) {
-<
+                    int ps = parallelism;
-<
+                    ws = ensureWorkerArrayCapacity(ps);
-<
+                    for (int i = 0; i < ps; ++i) {
-<
+                        ForkJoinWorkerThread w = createWorker(i);
-<
+                        if (w != null) {
-<
+                            ws[i] = w;
-<
+                            w.start();
-<
+                            updateWorkerCount(1);
->
+    final int registerWorker(ForkJoinWorkerThread w) {
->
+        /*
->
+         * In the typical case, a new worker acquires the lock, uses
->
+         * next available index and returns quickly.  Since we should
->
+         * not block callers (ultimately from signalWork or
->
+         * tryPreBlock) waiting for the lock needed to do this, we
->
+         * instead help release other workers while waiting for the
->
+         * lock.
->
+         */
->
+        for (int g;;) {
->
+            ForkJoinWorkerThread[] ws;
->
+            if (((g = scanGuard) & SG_UNIT) == 0 &&
->
+                UNSAFE.compareAndSwapInt(this, scanGuardOffset,
->
+                                         g, g | SG_UNIT)) {
->
+                int k = nextWorkerIndex;
->
+                try {
->
+                    if ((ws = workers) != null) { // ignore on shutdown
->
+                        int n = ws.length;
->
+                        if (k < 0 || k >= n || ws[k] != null) {
->
+                            for (k = 0; k < n && ws[k] != null; ++k)
->
+                                ;
->
+                            if (k == n)
->
+                                ws = workers = Arrays.copyOf(ws, n << 1);
-+
+                        ws[k] = w;
-+
+                        nextWorkerIndex = k + 1;
-+
+                        int m = g & SMASK;
-+
+                        g = k >= m? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1);
-+
+                    }
-+
+                } finally {
-+
+                    scanGuard = g;
-+
+                }
-+
+                return k;
-+
+            }
-+
+            else if ((ws = workers) != null) { // help release others
-+
+                for (ForkJoinWorkerThread u : ws) {
-+
+                    if (u != null && u.queueBase != u.queueTop) {
-+
+                        if (tryReleaseWaiter())
-+
+                            break;
-–
+            } finally {
-–
+                lock.unlock();
+    /**
-<
+     * Worker creation and startup for threads added via setParallelism.
->
+     * Final callback from terminating worker.  Removes record of
->
+     * worker from array, and adjusts counts. If pool is shutting
->
+     * down, tries to complete termination.
->
+     *
->
+     * @param w the worker
+     */
-<
+    private void createAndStartAddedWorkers() {
-<
+        resumeAllSpares();  // Allow spares to convert to nonspare
-<
+        int ps = parallelism;
-<
+        ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
-<
+        int len = ws.length;
-<
+        // Sweep through slots, to keep lowest indices most populated
-<
+        int k = 0;
-<
+        while (k < len) {
-<
+            if (ws[k] != null) {
-<
+                ++k;
-<
+                continue;
->
+    final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) {
->
+        int idx = w.poolIndex;
->
+        int sc = w.stealCount;
->
+        int steps = 0;
->
+        // Remove from array, adjust worker counts and collect steal count.
->
+        // We can intermix failed removes or adjusts with steal updates
->
+        do {
->
+            long s, c;
->
+            int g;
->
+            if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 &&
->
+                UNSAFE.compareAndSwapInt(this, scanGuardOffset,
->
+                                         g, g |= SG_UNIT)) {
->
+                ForkJoinWorkerThread[] ws = workers;
->
+                if (ws != null && idx >= 0 &&
->
+                    idx < ws.length && ws[idx] == w)
->
+                    ws[idx] = null;    // verify
->
+                nextWorkerIndex = idx;
->
+                scanGuard = g + SG_UNIT;
->
+                steps = 1;
->
+            }
->
+            if (steps == 1 &&
->
+                UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
->
+                                          (((c - AC_UNIT) & AC_MASK) |
->
+                                           ((c - TC_UNIT) & TC_MASK) |
->
+                                           (c & ~(AC_MASK|TC_MASK)))))
->
+                steps = 2;
->
+            if (sc != 0 &&
->
+                UNSAFE.compareAndSwapLong(this, stealCountOffset,
->
+                                          s = stealCount, s + sc))
->
+                sc = 0;
->
+        } while (steps != 2 || sc != 0);
->
+        if (!tryTerminate(false)) {
->
+            if (ex != null)   // possibly replace if died abnormally
->
+                signalWork();
->
+            else
->
+                tryReleaseWaiter();
->
+        }
->
+    }
->
->
+    // Shutdown and termination
->
->
+    /**
->
+     * Possibly initiates and/or completes termination.
->
+     *
->
+     * @param now if true, unconditionally terminate, else only
->
+     * if shutdown and empty queue and no active workers
->
+     * @return true if now terminating or terminated
->
+     */
->
+    private boolean tryTerminate(boolean now) {
->
+        long c;
->
+        while (((c = ctl) & STOP_BIT) == 0) {
->
+            if (!now) {
->
+                if ((int)(c >> AC_SHIFT) != -parallelism)
->
+                    return false;
->
+                if (!shutdown || blockedCount != 0 || quiescerCount != 0 ||
->
+                    queueTop - queueBase > 0) {
->
+                    if (ctl == c) // staleness check
->
+                        return false;
->
+                    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();
->
+            if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT))
->
+                startTerminating();
->
+        }
->
+        if ((short)(c >>> TC_SHIFT) == -parallelism) {
->
+            submissionLock.lock();
->
+            termination.signalAll();
->
+            submissionLock.unlock();
->
+        }
->
+        return true;
->
+    }
->
->
+    /**
->
+     * Runs up to three passes through workers: (0) Setting
->
+     * termination status for each worker, followed by wakeups up
->
+     * queued workers (1) helping cancel tasks (2) interrupting
->
+     * lagging threads (likely in external tasks, but possibly also
->
+     * blocked in joins).  Each pass repeats previous steps because of
->
+     * potential lagging thread creation.
->
+     */
->
+    private void startTerminating() {
->
+        cancelSubmissions();
->
+        for (int pass = 0; pass < 3; ++pass) {
->
+            ForkJoinWorkerThread[] ws = workers;
->
+            if (ws != null) {
->
+                for (ForkJoinWorkerThread w : ws) {
->
+                    if (w != null) {
->
+                        w.terminate = true;
->
+                        if (pass > 0) {
->
+                            w.cancelTasks();
->
+                            if (pass > 1 && !w.isInterrupted()) {
->
+                                try {
->
+                                    w.interrupt();
->
+                                } catch (SecurityException ignore) {
->
+                                }
->
+                            }
->
+                        }
->
+                    }
-<
+                else {
-<
+                    updateWorkerCount(-1); // back out on failed creation
-<
+                    break;
->
+                terminateWaiters();
->
+            }
->
+        }
->
+    }
->
->
+    /**
->
+     * Polls and cancels all submissions. Called only during termination.
->
+     */
->
+    private void cancelSubmissions() {
->
+        while (queueBase != queueTop) {
->
+            ForkJoinTask<?> task = pollSubmission();
->
+            if (task != null) {
->
+                try {
->
+                    task.cancel(false);
->
+                } catch (Throwable ignore) {
-<
+    // Execution methods
->
+    /**
->
+     * Tries to set the termination status of waiting workers, and
->
+     * then wake them up (after which they will terminate).
->
+     */
->
+    private void terminateWaiters() {
->
+        ForkJoinWorkerThread[] ws = workers;
->
+        if (ws != null) {
->
+            ForkJoinWorkerThread w; long c; int i, e;
->
+            int n = ws.length;
->
+            while ((i = ~(e = (int)(c = ctl)) & SMASK) < n &&
->
+                   (w = ws[i]) != null && w.eventCount == (e & E_MASK)) {
->
+                if (UNSAFE.compareAndSwapLong(this, ctlOffset, c,
->
+                                              (long)(w.nextWait & E_MASK) |
->
+                                              ((c + AC_UNIT) & AC_MASK) |
->
+                                              (c & (TC_MASK|STOP_BIT)))) {
->
+                    w.terminate = true;
->
+                    w.eventCount = e + EC_UNIT;
->
+                    if (w.parked)
->
+                        UNSAFE.unpark(w);
->
+                }
->
+            }
->
+        }
->
+    }
->
->
+    // misc ForkJoinWorkerThread support
+    /**
-<
+     * Common code for execute, invoke and submit
->
+     * Increment or decrement quiescerCount. Needed only to prevent
->
+     * triggering shutdown if a worker is transiently inactive while
->
+     * checking quiescence.
->
+     *
->
+     * @param delta 1 for increment, -1 for decrement
+     */
-<
+    private <T> void doSubmit(ForkJoinTask<T> task) {
-<
+        if (task == null)
->
+    final void addQuiescerCount(int delta) {
->
+        int c;
->
+        do {} while(!UNSAFE.compareAndSwapInt(this, quiescerCountOffset,
->
+                                              c = quiescerCount, c + delta));
->
+    }
->
->
+    /**
->
+     * Directly increment or decrement active count without
->
+     * queuing. This method is used to transiently assert inactivation
->
+     * while checking quiescence.
->
+     *
->
+     * @param delta 1 for increment, -1 for decrement
->
+     */
->
+    final void addActiveCount(int delta) {
->
+        long d = delta < 0 ? -AC_UNIT : AC_UNIT;
->
+        long c;
->
+        do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
->
+                                                ((c + d) & AC_MASK) |
->
+                                                (c & ~AC_MASK)));
->
+    }
->
->
+    /**
->
+     * Returns the approximate (non-atomic) number of idle threads per
->
+     * active thread.
->
+     */
->
+    final int idlePerActive() {
->
+        // Approximate at powers of two for small values, saturate past 4
->
+        int p = parallelism;
->
+        int a = p + (int)(ctl >> AC_SHIFT);
->
+        return (a > (p >>>= 1) ? 0 :
->
+                a > (p >>>= 1) ? 1 :
->
+                a > (p >>>= 1) ? 2 :
->
+                a > (p >>>= 1) ? 4 :
->
+);
->
+    }
->
->
+    // Exported methods
->
->
+    // Constructors
->
->
+    /**
->
+     * Creates a {@code ForkJoinPool} with parallelism equal to {@link
->
+     * java.lang.Runtime#availableProcessors}, using the {@linkplain
->
+     * #defaultForkJoinWorkerThreadFactory default thread factory},
->
+     * no UncaughtExceptionHandler, and non-async LIFO processing mode.
->
+     *
->
+     * @throws SecurityException if a security manager exists and
->
+     *         the caller is not permitted to modify threads
->
+     *         because it does not hold {@link
->
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
->
+     */
->
+    public ForkJoinPool() {
->
+        this(Runtime.getRuntime().availableProcessors(),
->
+             defaultForkJoinWorkerThreadFactory, null, false);
->
+    }
->
->
+    /**
->
+     * Creates a {@code ForkJoinPool} with the indicated parallelism
->
+     * level, the {@linkplain
->
+     * #defaultForkJoinWorkerThreadFactory default thread factory},
->
+     * no UncaughtExceptionHandler, and non-async LIFO processing mode.
->
+     *
->
+     * @param parallelism the parallelism level
->
+     * @throws IllegalArgumentException if parallelism less than or
->
+     *         equal to zero, or greater than implementation limit
->
+     * @throws SecurityException if a security manager exists and
->
+     *         the caller is not permitted to modify threads
->
+     *         because it does not hold {@link
->
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
->
+     */
->
+    public ForkJoinPool(int parallelism) {
->
+        this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
->
+    }
->
->
+    /**
->
+     * Creates a {@code ForkJoinPool} with the given parameters.
->
+     *
->
+     * @param parallelism the parallelism level. For default value,
->
+     * use {@link java.lang.Runtime#availableProcessors}.
->
+     * @param factory the factory for creating new threads. For default value,
->
+     * use {@link #defaultForkJoinWorkerThreadFactory}.
->
+     * @param handler the handler for internal worker threads that
->
+     * terminate due to unrecoverable errors encountered while executing
->
+     * tasks. For default value, use {@code null}.
->
+     * @param asyncMode if true,
->
+     * establishes local first-in-first-out scheduling mode for forked
->
+     * tasks that are never joined. This mode may be more appropriate
->
+     * than default locally stack-based mode in applications in which
->
+     * worker threads only process event-style asynchronous tasks.
->
+     * For default value, use {@code false}.
->
+     * @throws IllegalArgumentException if parallelism less than or
->
+     *         equal to zero, or greater than implementation limit
->
+     * @throws NullPointerException if the factory is null
->
+     * @throws SecurityException if a security manager exists and
->
+     *         the caller is not permitted to modify threads
->
+     *         because it does not hold {@link
->
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
->
+     */
->
+    public ForkJoinPool(int parallelism,
->
+                        ForkJoinWorkerThreadFactory factory,
->
+                        Thread.UncaughtExceptionHandler handler,
->
+                        boolean asyncMode) {
->
+        checkPermission();
->
+        if (factory == null)
+            throw new NullPointerException();
-<
+        if (isShutdown())
-<
+            throw new RejectedExecutionException();
-<
+        if (workers == null)
-<
+            ensureWorkerInitialization();
-<
+        submissionQueue.offer(task);
-<
+        signalIdleWorkers();
->
+        if (parallelism <= 0 || parallelism > MAX_ID)
->
+            throw new IllegalArgumentException();
->
+        this.parallelism = parallelism;
->
+        this.factory = factory;
->
+        this.ueh = handler;
->
+        this.locallyFifo = asyncMode;
->
+        long np = (long)(-parallelism); // offset ctl counts
->
+        this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
->
+        this.submissionQueue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
->
+        // initialize workers array with room for 2*parallelism if possible
->
+        int n = parallelism << 1;
->
+        if (n >= MAX_ID)
->
+            n = MAX_ID;
->
+        else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
->
+            n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
->
+        }
->
+        workers = new ForkJoinWorkerThread[n + 1];
->
+        this.submissionLock = new ReentrantLock();
->
+        this.termination = submissionLock.newCondition();
->
+        StringBuilder sb = new StringBuilder("ForkJoinPool-");
->
+        sb.append(poolNumberGenerator.incrementAndGet());
->
+        sb.append("-worker-");
->
+        this.workerNamePrefix = sb.toString();
-+
+    // Execution methods
-+
+    /**
+     * Performs the given task, returning its result upon completion.
-+
+     * If the computation encounters an unchecked Exception or Error,
-+
+     * it is rethrown as the outcome of this invocation.  Rethrown
-+
+     * exceptions behave in the same way as regular exceptions, but,
-+
+     * when possible, contain stack traces (as displayed for example
-+
+     * using {@code ex.printStackTrace()}) of both the current thread
-+
+     * as well as the thread actually encountering the exception;
-+
+     * minimally only the latter.
+     * @param task the task
+     * @return the task's result
-<
+     * @throws NullPointerException if task is null
-<
+     * @throws RejectedExecutionException if pool is shut down
->
+     * @throws NullPointerException if the task is null
->
+     * @throws RejectedExecutionException if the task cannot be
->
+     *         scheduled for execution
+     */
+    public <T> T invoke(ForkJoinTask<T> task) {
-<
+        doSubmit(task);
-<
+        return task.join();
->
+        Thread t = Thread.currentThread();
->
+        if (task == null)
->
+            throw new NullPointerException();
->
+        if (shutdown)
->
+            throw new RejectedExecutionException();
->
+        if ((t instanceof ForkJoinWorkerThread) &&
->
+            ((ForkJoinWorkerThread)t).pool == this)
->
+            return task.invoke();  // bypass submit if in same pool
->
+        else {
->
+            addSubmission(task);
->
+            return task.join();
->
+        }
->
+    }
->
->
+    /**
->
+     * Unless terminating, forks task if within an ongoing FJ
->
+     * computation in the current pool, else submits as external task.
->
+     */
->
+    private <T> void forkOrSubmit(ForkJoinTask<T> task) {
->
+        ForkJoinWorkerThread w;
->
+        Thread t = Thread.currentThread();
->
+        if (shutdown)
->
+            throw new RejectedExecutionException();
->
+        if ((t instanceof ForkJoinWorkerThread) &&
->
+            (w = (ForkJoinWorkerThread)t).pool == this)
->
+            w.pushTask(task);
->
+        else
->
+            addSubmission(task);
+    /**
+     * Arranges for (asynchronous) execution of the given task.
+     * @param task the task
-<
+     * @throws NullPointerException if task is null
-<
+     * @throws RejectedExecutionException if pool is shut down
->
+     * @throws NullPointerException if the task is null
->
+     * @throws RejectedExecutionException if the task cannot be
->
+     *         scheduled for execution
+     */
+    public void execute(ForkJoinTask<?> task) {
-<
+        doSubmit(task);
->
+        if (task == null)
->
+            throw new NullPointerException();
->
+        forkOrSubmit(task);
+    // AbstractExecutorService methods
-+
+    /**
-+
+     * @throws NullPointerException if the task is null
-+
+     * @throws RejectedExecutionException if the task cannot be
-+
+     *         scheduled for execution
-+
+     */
+    public void execute(Runnable task) {
-+
+        if (task == null)
-+
+            throw new NullPointerException();
+        ForkJoinTask<?> job;
+        if (task instanceof ForkJoinTask<?>) // avoid re-wrap
+            job = (ForkJoinTask<?>) task;
+        else
+            job = ForkJoinTask.adapt(task, null);
-<
+        doSubmit(job);
->
+        forkOrSubmit(job);
->
+    }
->
->
+    /**
->
+     * Submits a ForkJoinTask for execution.
->
+     *
->
+     * @param task the task to submit
->
+     * @return the task
->
+     * @throws NullPointerException if the task is null
->
+     * @throws RejectedExecutionException if the task cannot be
->
+     *         scheduled for execution
->
+     */
->
+    public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
->
+        if (task == null)
->
+            throw new NullPointerException();
->
+        forkOrSubmit(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) {
-+
+        if (task == null)
-+
+            throw new NullPointerException();
+        ForkJoinTask<T> job = ForkJoinTask.adapt(task);
-<
+        doSubmit(job);
->
+        forkOrSubmit(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) {
-+
+        if (task == null)
-+
+            throw new NullPointerException();
+        ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
-<
+        doSubmit(job);
->
+        forkOrSubmit(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) {
-+
+        if (task == null)
-+
+            throw new NullPointerException();
+        ForkJoinTask<?> job;
+        if (task instanceof ForkJoinTask<?>) // avoid re-wrap
+            job = (ForkJoinTask<?>) task;
+        else
+            job = ForkJoinTask.adapt(task, null);
-<
+        doSubmit(job);
->
+        forkOrSubmit(job);
+        return job;
+    /**
-<
+     * Submits a ForkJoinTask for execution.
-<
+     *
-<
+     * @param task the task to submit
-<
+     * @return the task
-<
+     * @throws RejectedExecutionException if the task cannot be
-<
+     *         scheduled for execution
-<
+     * @throws NullPointerException if the task is null
->
+     * @throws NullPointerException       {@inheritDoc}
->
+     * @throws RejectedExecutionException {@inheritDoc}
+     */
-–
+    public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
-–
+        doSubmit(task);
-–
+        return task;
-–
+    }
-–
-–
+    public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
+        ArrayList<ForkJoinTask<T>> forkJoinTasks =
+            new ArrayList<ForkJoinTask<T>>(tasks.size());
+        invoke(new InvokeAll<T>(forkJoinTasks));
+        @SuppressWarnings({"unchecked", "rawtypes"})
-<
+        List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
->
+            List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
+        return futures;
+        private static final long serialVersionUID = -7914297376763021607L;
-–
+    // Configuration and status settings and queries
-–
+    /**
+     * Returns the factory used for constructing new workers.
+     * @return the handler, or {@code null} if none
+     */
+    public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
-<
+        Thread.UncaughtExceptionHandler h;
-<
+        final ReentrantLock lock = this.workerLock;
-<
+        lock.lock();
-<
+        try {
-<
+            h = ueh;
-<
+        } finally {
-<
+            lock.unlock();
-<
+        }
-<
+        return h;
-<
+    }
-<
-<
+    /**
-<
+     * Sets the handler for internal worker threads that terminate due
-<
+     * to unrecoverable errors encountered while executing tasks.
-<
+     * Unless set, the current default or ThreadGroup handler is used
-<
+     * as handler.
-<
+     *
-<
+     * @param h the new handler
-<
+     * @return the old handler, or {@code null} if none
-<
+     * @throws SecurityException if a security manager exists and
-<
+     *         the caller is not permitted to modify threads
-<
+     *         because it does not hold {@link
-<
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
-<
+     */
-<
+    public Thread.UncaughtExceptionHandler
-<
+        setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
-<
+        checkPermission();
-<
+        Thread.UncaughtExceptionHandler old = null;
-<
+        final ReentrantLock lock = this.workerLock;
-<
+        lock.lock();
-<
+        try {
-<
+            old = ueh;
-<
+            ueh = h;
-<
+            ForkJoinWorkerThread[] ws = workers;
-<
+            if (ws != null) {
-<
+                for (int i = 0; i < ws.length; ++i) {
-<
+                    ForkJoinWorkerThread w = ws[i];
-<
+                    if (w != null)
-<
+                        w.setUncaughtExceptionHandler(h);
-<
+                }
-<
+            }
-<
+        } finally {
-<
+            lock.unlock();
-<
+        }
-<
+        return old;
-<
+    }
-<
-<
-<
+    /**
-<
+     * Sets the target parallelism level of this pool.
-<
+     *
-<
+     * @param parallelism the target parallelism
-<
+     * @throws IllegalArgumentException if parallelism less than or
-<
+     * equal to zero or greater than maximum size bounds
-<
+     * @throws SecurityException if a security manager exists and
-<
+     *         the caller is not permitted to modify threads
-<
+     *         because it does not hold {@link
-<
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
-<
+     */
-<
+    public void setParallelism(int parallelism) {
-<
+        checkPermission();
-<
+        if (parallelism <= 0 || parallelism > maxPoolSize)
-<
+            throw new IllegalArgumentException();
-<
+        final ReentrantLock lock = this.workerLock;
-<
+        lock.lock();
-<
+        try {
-<
+            if (isProcessingTasks()) {
-<
+                int p = this.parallelism;
-<
+                this.parallelism = parallelism;
-<
+                if (parallelism > p)
-<
+                    createAndStartAddedWorkers();
-<
+                else
-<
+                    trimSpares();
-<
+            }
-<
+        } finally {
-<
+            lock.unlock();
-<
+        }
-<
+        signalIdleWorkers();
->
+        return ueh;
+    /**
+    /**
+     * Returns the number of worker threads that have started but not
-<
+     * yet terminated.  This result returned by this method may differ
->
+     * yet terminated.  The result returned by this method may differ
+     * from {@link #getParallelism} when threads are created to
+     * maintain parallelism when others are cooperatively blocked.
+     * @return the number of worker threads
+     */
+    public int getPoolSize() {
-<
+        return totalCountOf(workerCounts);
-<
+    }
-<
-<
+    /**
-<
+     * Returns the maximum number of threads allowed to exist in the
-<
+     * pool.  Unless set using {@link #setMaximumPoolSize}, the
-<
+     * maximum is an implementation-defined value designed only to
-<
+     * prevent runaway growth.
-<
+     *
-<
+     * @return the maximum
-<
+     */
-<
+    public int getMaximumPoolSize() {
-<
+        return maxPoolSize;
-<
+    }
-<
-<
+    /**
-<
+     * Sets the maximum number of threads allowed to exist in the
-<
+     * pool.  Setting this value has no effect on current pool
-<
+     * size. It controls construction of new threads.
-<
+     *
-<
+     * @throws IllegalArgumentException if negative or greater than
-<
+     * internal implementation limit
-<
+     */
-<
+    public void setMaximumPoolSize(int newMax) {
-<
+        if (newMax < 0 || newMax > MAX_THREADS)
-<
+            throw new IllegalArgumentException();
-<
+        maxPoolSize = newMax;
-<
+    }
-<
-<
-<
+    /**
-<
+     * Returns {@code true} if this pool dynamically maintains its
-<
+     * target parallelism level. If false, new threads are added only
-<
+     * to avoid possible starvation.  This setting is by default true.
-<
+     *
-<
+     * @return {@code true} if maintains parallelism
-<
+     */
-<
+    public boolean getMaintainsParallelism() {
-<
+        return maintainsParallelism;
-<
+    }
-<
-<
+    /**
-<
+     * Sets whether this pool dynamically maintains its target
-<
+     * parallelism level. If false, new threads are added only to
-<
+     * avoid possible starvation.
-<
+     *
-<
+     * @param enable {@code true} to maintain parallelism
-<
+     */
-<
+    public void setMaintainsParallelism(boolean enable) {
-<
+        maintainsParallelism = enable;
-<
+    }
-<
-<
+    /**
-<
+     * Establishes local first-in-first-out scheduling mode for forked
-<
+     * tasks that are never joined. This mode may be more appropriate
-<
+     * than default locally stack-based mode in applications in which
-<
+     * worker threads only process asynchronous tasks.  This method is
-<
+     * designed to be invoked only when the pool is quiescent, and
-<
+     * typically only before any tasks are submitted. The effects of
-<
+     * invocations at other times may be unpredictable.
-<
+     *
-<
+     * @param async if {@code true}, use locally FIFO scheduling
-<
+     * @return the previous mode
-<
+     * @see #getAsyncMode
-<
+     */
-<
+    public boolean setAsyncMode(boolean async) {
-<
+        boolean oldMode = locallyFifo;
-<
+        locallyFifo = async;
-<
+        ForkJoinWorkerThread[] ws = workers;
-<
+        if (ws != null) {
-<
+            for (int i = 0; i < ws.length; ++i) {
-<
+                ForkJoinWorkerThread t = ws[i];
-<
+                if (t != null)
-<
+                    t.setAsyncMode(async);
-<
+            }
-<
+        }
-<
+        return oldMode;
->
+        return parallelism + (short)(ctl >>> TC_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);
->
+        int r = parallelism + (int)(ctl >> AC_SHIFT);
->
+        return r <= 0? 0 : r; // suppress momentarily negative values
+    /**
+     * @return the number of active threads
+     */
+    public int getActiveThreadCount() {
-<
+        return activeCountOf(runControl);
-<
+    }
-<
-<
+    /**
-<
+     * Returns an estimate of the number of threads that are currently
-<
+     * idle waiting for tasks. This method may underestimate the
-<
+     * number of idle threads.
-<
+     *
-<
+     * @return the number of idle threads
-<
+     */
-<
+    final int getIdleThreadCount() {
-<
+        int c = runningCountOf(workerCounts) - activeCountOf(runControl);
-<
+        return (c <= 0) ? 0 : c;
->
+        int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount;
->
+        return r <= 0? 0 : r; // suppress momentarily negative values
+    /**
+     * @return {@code true} if all threads are currently idle
+     */
+    public boolean isQuiescent() {
-<
+        return activeCountOf(runControl) == 0;
->
+        return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 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();
-<
+            }
->
+        ForkJoinWorkerThread[] ws;
->
+        if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
->
+            (ws = workers) != null) {
->
+            for (ForkJoinWorkerThread w : ws)
->
+                if (w != null)
->
+                    count -= w.queueBase - w.queueTop; // must read base first
+        return count;
+    /**
+     * Returns an estimate of the number of tasks submitted to this
-<
+     * pool that have not yet begun executing.  This method takes time
-<
+     * proportional to the number of submissions.
->
+     * pool that have not yet begun executing.  This method may take
->
+     * time proportional to the number of submissions.
+     * @return the number of queued submissions
+     */
+    public int getQueuedSubmissionCount() {
-<
+        return submissionQueue.size();
->
+        return -queueBase + queueTop;
+    /**
+     * @return {@code true} if there are any queued submissions
+     */
+    public boolean hasQueuedSubmissions() {
-<
+        return !submissionQueue.isEmpty();
->
+        return queueBase != queueTop;
+    /**
+     * @return the next submission, or {@code null} if none
+     */
+    protected ForkJoinTask<?> pollSubmission() {
-<
+        return submissionQueue.poll();
->
+        ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
->
+        while ((b = queueBase) != queueTop &&
->
+               (q = submissionQueue) != null &&
->
+               (i = (q.length - 1) & b) >= 0) {
->
+            long u = (i << ASHIFT) + ABASE;
->
+            if ((t = q[i]) != null &&
->
+                queueBase == b &&
->
+                UNSAFE.compareAndSwapObject(q, u, t, null)) {
->
+                queueBase = b + 1;
->
+                return t;
->
+            }
->
+        }
->
+        return null;
+    /**
+     * @return the number of elements transferred
+     */
+    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 count = 0;
->
+        while (queueBase != queueTop) {
->
+            ForkJoinTask<?> t = pollSubmission();
->
+            if (t != null) {
->
+                c.add(t);
->
+                ++count;
-<
+        return n;
->
+        ForkJoinWorkerThread[] ws;
->
+        if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
->
+            (ws = workers) != null) {
->
+            for (ForkJoinWorkerThread w : ws)
->
+                if (w != null)
->
+                    count += w.drainTasksTo(c);
->
+        }
->
+        return count;
+    /**
+     * @return a string identifying this pool, as well as its state
+     */
+    public String toString() {
-–
+        int ps = parallelism;
-–
+        int wc = workerCounts;
-–
+        int rc = runControl;
+        long st = getStealCount();
+        long qt = getQueuedTaskCount();
+        long qs = getQueuedSubmissionCount();
-+
+        int pc = parallelism;
-+
+        long c = ctl;
-+
+        int tc = pc + (short)(c >>> TC_SHIFT);
-+
+        int rc = pc + (int)(c >> AC_SHIFT);
-+
+        if (rc < 0) // ignore transient negative
-+
+            rc = 0;
-+
+        int ac = rc + blockedCount;
-+
+        String level;
-+
+        if ((c & STOP_BIT) != 0)
-+
+            level = (tc == 0)? "Terminated" : "Terminating";
-+
+        else
-+
+            level = shutdown? "Shutting down" : "Running";
+        return super.toString() +
-<
+            "[" + runStateToString(runStateOf(rc)) +
-<
+            ", parallelism = " + ps +
-<
+            ", size = " + totalCountOf(wc) +
-<
+            ", active = " + activeCountOf(rc) +
-<
+            ", running = " + runningCountOf(wc) +
->
+            "[" + level +
->
+            ", parallelism = " + pc +
->
+            ", size = " + tc +
->
+            ", active = " + ac +
->
+            ", running = " + rc +
+            ", steals = " + st +
+            ", tasks = " + qt +
+            ", submissions = " + qs +
+            "]";
-–
+    private static String runStateToString(int rs) {
-–
+        switch(rs) {
-–
+        case RUNNING: return "Running";
-–
+        case SHUTDOWN: return "Shutting down";
-–
+        case TERMINATING: return "Terminating";
-–
+        case TERMINATED: return "Terminated";
-–
+        default: throw new Error("Unknown run state");
-–
+        }
-–
+    }
-–
-–
+    // lifecycle control
-–
+    /**
+     * Initiates an orderly shutdown in which previously submitted
+     * tasks are executed, but no new tasks will be accepted.
+     */
+    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();
-<
+        }
->
+        shutdown = true;
->
+        tryTerminate(false);
+    /**
+     */
+    public List<Runnable> shutdownNow() {
+        checkPermission();
-<
+        terminate();
->
+        shutdown = true;
->
+        tryTerminate(true);
+        return Collections.emptyList();
+     * @return {@code true} if all tasks have completed following shut down
+     */
+    public boolean isTerminated() {
-<
+        return runStateOf(runControl) == TERMINATED;
->
+        long c = ctl;
->
+        return ((c & STOP_BIT) != 0L &&
->
+                (short)(c >>> TC_SHIFT) == -parallelism);
+    /**
+     * 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.
->
+     * ignored or suppressed interruption, or are waiting for IO,
->
+     * causing this executor not to properly terminate. (See the
->
+     * advisory notes for class {@link ForkJoinTask} stating that
->
+     * tasks should not normally entail blocking operations.  But if
->
+     * they do, they must abort them on interrupt.)
+     * @return {@code true} if terminating but not yet terminated
+     */
+    public boolean isTerminating() {
-<
+        return runStateOf(runControl) == TERMINATING;
->
+        long c = ctl;
->
+        return ((c & STOP_BIT) != 0L &&
->
+                (short)(c >>> TC_SHIFT) != -parallelism);
+    /**
-<
+     * Returns {@code true} if this pool has been shut down.
-<
+     *
-<
+     * @return {@code true} if this pool has been shut down
->
+     * Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
+     */
-<
+    public boolean isShutdown() {
-<
+        return runStateOf(runControl) >= SHUTDOWN;
->
+    final boolean isAtLeastTerminating() {
->
+        return (ctl & STOP_BIT) != 0L;
+    /**
-<
+     * Returns true if pool is not terminating or terminated.
-<
+     * Used internally to suppress execution when terminating.
->
+     * Returns {@code true} if this pool has been shut down.
->
+     *
->
+     * @return {@code true} if this pool has been shut down
+     */
-<
+    final boolean isProcessingTasks() {
-<
+        return runStateOf(runControl) < TERMINATING;
->
+    public boolean isShutdown() {
->
+        return shutdown;
+    /**
+    public boolean awaitTermination(long timeout, TimeUnit unit)
+        throws InterruptedException {
+        long nanos = unit.toNanos(timeout);
-<
+        final ReentrantLock lock = this.workerLock;
->
+        final ReentrantLock lock = this.submissionLock;
+        lock.lock();
+        try {
+            for (;;) {
-–
+    // Shutdown and termination support
-–
-–
+    /**
-–
+     * Callback from terminating worker. Nulls out the corresponding
-–
+     * workers slot, and if terminating, tries to terminate; else
-–
+     * tries to shrink workers array.
-–
+     *
-–
+     * @param w the worker
-–
+     */
-–
+    final void workerTerminated(ForkJoinWorkerThread w) {
-–
+        updateStealCount(w);
-–
+        updateWorkerCount(-1);
-–
+        final ReentrantLock lock = this.workerLock;
-–
+        lock.lock();
-–
+        try {
-–
+            ForkJoinWorkerThread[] ws = workers;
-–
+            if (ws != null) {
-–
+                int idx = w.poolIndex;
-–
+                if (idx >= 0 && idx < ws.length && ws[idx] == w)
-–
+                    ws[idx] = null;
-–
+                if (totalCountOf(workerCounts) == 0) {
-–
+                    terminate(); // no-op if already terminating
-–
+                    transitionRunStateTo(TERMINATED);
-–
+                    termination.signalAll();
-–
+                }
-–
+                else if (isProcessingTasks()) {
-–
+                    tryShrinkWorkerArray();
-–
+                    tryResumeSpare(true); // allow replacement
-–
+                }
-–
+            }
-–
+        } finally {
-–
+            lock.unlock();
-–
+        }
-–
+        signalIdleWorkers();
-–
+    }
-–
-–
+    /**
-–
+     * Initiates termination.
-–
+     */
-–
+    private void terminate() {
-–
+        if (transitionRunStateTo(TERMINATING)) {
-–
+            stopAllWorkers();
-–
+            resumeAllSpares();
-–
+            signalIdleWorkers();
-–
+            cancelQueuedSubmissions();
-–
+            cancelQueuedWorkerTasks();
-–
+            interruptUnterminatedWorkers();
-–
+            signalIdleWorkers(); // resignal after interrupt
-–
+        }
-–
+    }
-–
-–
+    /**
-–
+     * Possibly terminates when on shutdown state.
-–
+     */
-–
+    private void terminateOnShutdown() {
-–
+        if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
-–
+            terminate();
-–
+    }
-–
-–
+    /**
-–
+     * Clears out and cancels submissions.
-–
+     */
-–
+    private void cancelQueuedSubmissions() {
-–
+        ForkJoinTask<?> task;
-–
+        while ((task = pollSubmission()) != null)
-–
+            task.cancel(false);
-–
+    }
-–
-–
+    /**
-–
+     * Cleans out worker queues.
-–
+     */
-–
+    private void cancelQueuedWorkerTasks() {
-–
+        final ReentrantLock lock = this.workerLock;
-–
+        lock.lock();
-–
+        try {
-–
+            ForkJoinWorkerThread[] ws = workers;
-–
+            if (ws != null) {
-–
+                for (int i = 0; i < ws.length; ++i) {
-–
+                    ForkJoinWorkerThread t = ws[i];
-–
+                    if (t != null)
-–
+                        t.cancelTasks();
-–
+                }
-–
+            }
-–
+        } finally {
-–
+            lock.unlock();
-–
+        }
-–
+    }
-–
-–
+    /**
-–
+     * Sets each worker's status to terminating. Requires lock to avoid
-–
+     * conflicts with add/remove.
-–
+     */
-–
+    private void stopAllWorkers() {
-–
+        final ReentrantLock lock = this.workerLock;
-–
+        lock.lock();
-–
+        try {
-–
+            ForkJoinWorkerThread[] ws = workers;
-–
+            if (ws != null) {
-–
+                for (int i = 0; i < ws.length; ++i) {
-–
+                    ForkJoinWorkerThread t = ws[i];
-–
+                    if (t != null)
-–
+                        t.shutdownNow();
-–
+                }
-–
+            }
-–
+        } finally {
-–
+            lock.unlock();
-–
+        }
-–
+    }
-–
-–
+    /**
-–
+     * Interrupts all unterminated workers.  This is not required for
-–
+     * sake of internal control, but may help unstick user code during
-–
+     * shutdown.
-–
+     */
-–
+    private void interruptUnterminatedWorkers() {
-–
+        final ReentrantLock lock = this.workerLock;
-–
+        lock.lock();
-–
+        try {
-–
+            ForkJoinWorkerThread[] ws = workers;
-–
+            if (ws != null) {
-–
+                for (int i = 0; i < ws.length; ++i) {
-–
+                    ForkJoinWorkerThread t = ws[i];
-–
+                    if (t != null && !t.isTerminated()) {
-–
+                        try {
-–
+                            t.interrupt();
-–
+                        } catch (SecurityException ignore) {
-–
+                        }
-–
+                    }
-–
+                }
-–
+            }
-–
+        } finally {
-–
+            lock.unlock();
-–
+        }
-–
+    }
-–
-–
-–
+    /*
-–
+     * Nodes for event barrier to manage idle threads.  Queue nodes
-–
+     * are basic Treiber stack nodes, also used for spare stack.
-–
+     *
-–
+     * The event barrier has an event count and a wait queue (actually
-–
+     * a Treiber stack).  Workers are enabled to look for work when
-–
+     * the eventCount is incremented. If they fail to find work, they
-–
+     * may wait for next count. Upon release, threads help others wake
-–
+     * up.
-–
+     *
-–
+     * Synchronization events occur only in enough contexts to
-–
+     * maintain overall liveness:
-–
+     *
-–
+     *   - Submission of a new task to the pool
-–
+     *   - Resizes or other changes to the workers array
-–
+     *   - pool termination
-–
+     *   - A worker pushing a task on an empty queue
-–
+     *
-–
+     * The case of pushing a task occurs often enough, and is heavy
-–
+     * enough compared to simple stack pushes, to require special
-–
+     * handling: Method signalWork returns without advancing count if
-–
+     * the queue appears to be empty.  This would ordinarily result in
-–
+     * races causing some queued waiters not to be woken up. To avoid
-–
+     * this, the first worker enqueued in method sync (see
-–
+     * syncIsReleasable) rescans for tasks after being enqueued, and
-–
+     * helps signal if any are found. This works well because the
-–
+     * worker has nothing better to do, and so might as well help
-–
+     * alleviate the overhead and contention on the threads actually
-–
+     * doing work.  Also, since event counts increments on task
-–
+     * availability exist to maintain liveness (rather than to force
-–
+     * refreshes etc), it is OK for callers to exit early if
-–
+     * contending with another signaller.
-–
+     */
-–
+    static final class WaitQueueNode {
-–
+        WaitQueueNode next; // only written before enqueued
-–
+        volatile ForkJoinWorkerThread thread; // nulled to cancel wait
-–
+        final long count; // unused for spare stack
-–
-–
+        WaitQueueNode(long c, ForkJoinWorkerThread w) {
-–
+            count = c;
-–
+            thread = w;
-–
+        }
-–
-–
+        /**
-–
+         * Wakes up waiter, returning false if known to already
-–
+         */
-–
+        boolean signal() {
-–
+            ForkJoinWorkerThread t = thread;
-–
+            if (t == null)
-–
+                return false;
-–
+            thread = null;
-–
+            LockSupport.unpark(t);
-–
+            return true;
-–
+        }
-–
-–
+        /**
-–
+         * Awaits release on sync.
-–
+         */
-–
+        void awaitSyncRelease(ForkJoinPool p) {
-–
+            while (thread != null && !p.syncIsReleasable(this))
-–
+                LockSupport.park(this);
-–
+        }
-–
-–
+        /**
-–
+         * Awaits resumption as spare.
-–
+         */
-–
+        void awaitSpareRelease() {
-–
+            while (thread != null) {
-–
+                if (!Thread.interrupted())
-–
+                    LockSupport.park(this);
-–
+            }
-–
+        }
-–
+    }
-–
-–
+    /**
-–
+     * Ensures that no thread is waiting for count to advance from the
-–
+     * current value of eventCount read on entry to this method, by
-–
+     * releasing waiting threads if necessary.
-–
+     *
-–
+     * @return the count
-–
+     */
-–
+    final long ensureSync() {
-–
+        long c = eventCount;
-–
+        WaitQueueNode q;
-–
+        while ((q = syncStack) != null && q.count < c) {
-–
+            if (casBarrierStack(q, null)) {
-–
+                do {
-–
+                    q.signal();
-–
+                } while ((q = q.next) != null);
-–
+                break;
-–
+            }
-–
+        }
-–
+        return c;
-–
+    }
-–
-–
+    /**
-–
+     * Increments event count and releases waiting threads.
-–
+     */
-–
+    private void signalIdleWorkers() {
-–
+        long c;
-–
+        do {} while (!casEventCount(c = eventCount, c+1));
-–
+        ensureSync();
-–
+    }
-–
-–
+    /**
-–
+     * Signals threads waiting to poll a task. Because method sync
-–
+     * rechecks availability, it is OK to only proceed if queue
-–
+     * appears to be non-empty, and OK to skip under contention to
-–
+     * increment count (since some other thread succeeded).
-–
+     */
-–
+    final void signalWork() {
-–
+        long c;
-–
+        WaitQueueNode q;
-–
+        if (syncStack != null &&
-–
+            casEventCount(c = eventCount, c+1) &&
-–
+            (((q = syncStack) != null && q.count <= c) &&
-–
+             (!casBarrierStack(q, q.next) || !q.signal())))
-–
+            ensureSync();
-–
+    }
-–
-–
+    /**
-–
+     * Waits until event count advances from last value held by
-–
+     * caller, or if excess threads, caller is resumed as spare, or
-–
+     * caller or pool is terminating. Updates caller's event on exit.
-–
+     *
-–
+     * @param w the calling worker thread
-–
+     */
-–
+    final void sync(ForkJoinWorkerThread w) {
-–
+        updateStealCount(w); // Transfer w's count while it is idle
-–
-–
+        while (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) {
-–
+            long prev = w.lastEventCount;
-–
+            WaitQueueNode node = null;
-–
+            WaitQueueNode h;
-–
+            while (eventCount == prev &&
-–
+                   ((h = syncStack) == null || h.count == prev)) {
-–
+                if (node == null)
-–
+                    node = new WaitQueueNode(prev, w);
-–
+                if (casBarrierStack(node.next = h, node)) {
-–
+                    node.awaitSyncRelease(this);
-–
+                    break;
-–
+                }
-–
+            }
-–
+            long ec = ensureSync();
-–
+            if (ec != prev) {
-–
+                w.lastEventCount = ec;
-–
+                break;
-–
+            }
-–
+        }
-–
+    }
-–
-–
+    /**
-–
+     * Returns {@code true} if worker waiting on sync can proceed:
-–
+     *  - on signal (thread == null)
-–
+     *  - on event count advance (winning race to notify vs signaller)
-–
+     *  - on interrupt
-–
+     *  - if the first queued node, we find work available
-–
+     * If node was not signalled and event count not advanced on exit,
-–
+     * then we also help advance event count.
-–
+     *
-–
+     * @return {@code true} if node can be released
-–
+     */
-–
+    final boolean syncIsReleasable(WaitQueueNode node) {
-–
+        long prev = node.count;
-–
+        if (!Thread.interrupted() && node.thread != null &&
-–
+            (node.next != null ||
-–
+             !ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
-–
+            eventCount == prev)
-–
+            return false;
-–
+        if (node.thread != null) {
-–
+            node.thread = null;
-–
+            long ec = eventCount;
-–
+            if (prev <= ec) // help signal
-–
+                casEventCount(ec, ec+1);
-–
+        }
-–
+        return true;
-–
+    }
-–
-–
+    /**
-–
+     * Returns {@code true} if a new sync event occurred since last
-–
+     * call to sync or this method, if so, updating caller's count.
-–
+     */
-–
+    final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
-–
+        long lc = w.lastEventCount;
-–
+        long ec = ensureSync();
-–
+        if (ec == lc)
-–
+            return false;
-–
+        w.lastEventCount = ec;
-–
+        return true;
-–
+    }
-–
-–
+    //  Parallelism maintenance
-–
-–
+    /**
-–
+     * Decrements running count; if too low, adds spare.
-–
+     *
-–
+     * Conceptually, all we need to do here is add or resume a
-–
+     * spare thread when one is about to block (and remove or
-–
+     * suspend it later when unblocked -- see suspendIfSpare).
-–
+     * However, implementing this idea requires coping with
-–
+     * several problems: we have imperfect information about the
-–
+     * states of threads. Some count updates can and usually do
-–
+     * lag run state changes, despite arrangements to keep them
-–
+     * accurate (for example, when possible, updating counts
-–
+     * before signalling or resuming), especially when running on
-–
+     * dynamic JVMs that don't optimize the infrequent paths that
-–
+     * update counts. Generating too many threads can make these
-–
+     * problems become worse, because excess threads are more
-–
+     * likely to be context-switched with others, slowing them all
-–
+     * down, especially if there is no work available, so all are
-–
+     * busy scanning or idling.  Also, excess spare threads can
-–
+     * only be suspended or removed when they are idle, not
-–
+     * immediately when they aren't needed. So adding threads will
-–
+     * raise parallelism level for longer than necessary.  Also,
-–
+     * FJ applications often encounter highly transient peaks when
-–
+     * many threads are blocked joining, but for less time than it
-–
+     * takes to create or resume spares.
-–
+     *
-–
+     * @param joinMe if non-null, return early if done
-–
+     * @param maintainParallelism if true, try to stay within
-–
+     * target counts, else create only to avoid starvation
-–
+     * @return true if joinMe known to be done
-–
+     */
-–
+    final boolean preJoin(ForkJoinTask<?> joinMe,
-–
+                          boolean maintainParallelism) {
-–
+        maintainParallelism &= maintainsParallelism; // overrride
-–
+        boolean dec = false;  // true when running count decremented
-–
+        while (spareStack == null || !tryResumeSpare(dec)) {
-–
+            int counts = workerCounts;
-–
+            if (dec || (dec = casWorkerCounts(counts, --counts))) {
-–
+                // CAS cheat
-–
+                if (!needSpare(counts, maintainParallelism))
-–
+                    break;
-–
+                if (joinMe.status < 0)
-–
+                    return true;
-–
+                if (tryAddSpare(counts))
-–
+                    break;
-–
+            }
-–
+        }
-–
+        return false;
-–
+    }
-–
-–
+    /**
-–
+     * Same idea as preJoin
-–
+     */
-–
+    final boolean preBlock(ManagedBlocker blocker,
-–
+                           boolean maintainParallelism) {
-–
+        maintainParallelism &= maintainsParallelism;
-–
+        boolean dec = false;
-–
+        while (spareStack == null || !tryResumeSpare(dec)) {
-–
+            int counts = workerCounts;
-–
+            if (dec || (dec = casWorkerCounts(counts, --counts))) {
-–
+                if (!needSpare(counts, maintainParallelism))
-–
+                    break;
-–
+                if (blocker.isReleasable())
-–
+                    return true;
-–
+                if (tryAddSpare(counts))
-–
+                    break;
-–
+            }
-–
+        }
-–
+        return false;
-–
+    }
-–
-–
+    /**
-–
+     * Returns {@code true} if a spare thread appears to be needed.
-–
+     * If maintaining parallelism, returns true when the deficit in
-–
+     * running threads is more than the surplus of total threads, and
-–
+     * there is apparently some work to do.  This self-limiting rule
-–
+     * means that the more threads that have already been added, the
-–
+     * less parallelism we will tolerate before adding another.
-–
+     *
-–
+     * @param counts current worker counts
-–
+     * @param maintainParallelism try to maintain parallelism
-–
+     */
-–
+    private boolean needSpare(int counts, boolean maintainParallelism) {
-–
+        int ps = parallelism;
-–
+        int rc = runningCountOf(counts);
-–
+        int tc = totalCountOf(counts);
-–
+        int runningDeficit = ps - rc;
-–
+        int totalSurplus = tc - ps;
-–
+        return (tc < maxPoolSize &&
-–
+                (rc == 0 || totalSurplus < 0 ||
-–
+                 (maintainParallelism &&
-–
+                  runningDeficit > totalSurplus &&
-–
+                  ForkJoinWorkerThread.hasQueuedTasks(workers))));
-–
+    }
-–
-–
+    /**
-–
+     * Adds a spare worker if lock available and no more than the
-–
+     * expected numbers of threads exist.
-–
+     *
-–
+     * @return true if successful
-–
+     */
-–
+    private boolean tryAddSpare(int expectedCounts) {
-–
+        final ReentrantLock lock = this.workerLock;
-–
+        int expectedRunning = runningCountOf(expectedCounts);
-–
+        int expectedTotal = totalCountOf(expectedCounts);
-–
+        boolean success = false;
-–
+        boolean locked = false;
-–
+        // confirm counts while locking; CAS after obtaining lock
-–
+        try {
-–
+            for (;;) {
-–
+                int s = workerCounts;
-–
+                int tc = totalCountOf(s);
-–
+                int rc = runningCountOf(s);
-–
+                if (rc > expectedRunning || tc > expectedTotal)
-–
+                    break;
-–
+                if (!locked && !(locked = lock.tryLock()))
-–
+                    break;
-–
+                if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
-–
+                    createAndStartSpare(tc);
-–
+                    success = true;
-–
+                    break;
-–
+                }
-–
+            }
-–
+        } finally {
-–
+            if (locked)
-–
+                lock.unlock();
-–
+        }
-–
+        return success;
-–
+    }
-–
-–
+    /**
-–
+     * Adds the kth spare worker. On entry, pool counts are already
-–
+     * adjusted to reflect addition.
-–
+     */
-–
+    private void createAndStartSpare(int k) {
-–
+        ForkJoinWorkerThread w = null;
-–
+        ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
-–
+        int len = ws.length;
-–
+        // Probably, we can place at slot k. If not, find empty slot
-–
+        if (k < len && ws[k] != null) {
-–
+            for (k = 0; k < len && ws[k] != null; ++k)
-–
+                ;
-–
+        }
-–
+        if (k < len && isProcessingTasks() && (w = createWorker(k)) != null) {
-–
+            ws[k] = w;
-–
+            w.start();
-–
+        }
-–
+        else
-–
+            updateWorkerCount(-1); // adjust on failure
-–
+        signalIdleWorkers();
-–
+    }
-–
-–
+    /**
-–
+     * Suspends calling thread w if there are excess threads.  Called
-–
+     * only from sync.  Spares are enqueued in a Treiber stack using
-–
+     * the same WaitQueueNodes as barriers.  They are resumed mainly
-–
+     * in preJoin, but are also woken on pool events that require all
-–
+     * threads to check run state.
-–
+     *
-–
+     * @param w the caller
-–
+     */
-–
+    private boolean suspendIfSpare(ForkJoinWorkerThread w) {
-–
+        WaitQueueNode node = null;
-–
+        int s;
-–
+        while (parallelism < runningCountOf(s = workerCounts)) {
-–
+            if (node == null)
-–
+                node = new WaitQueueNode(0, w);
-–
+            if (casWorkerCounts(s, s-1)) { // representation-dependent
-–
+                // push onto stack
-–
+                do {} while (!casSpareStack(node.next = spareStack, node));
-–
+                // block until released by resumeSpare
-–
+                node.awaitSpareRelease();
-–
+                return true;
-–
+            }
-–
+        }
-–
+        return false;
-–
+    }
-–
-–
+    /**
-–
+     * Tries to pop and resume a spare thread.
-–
+     *
-–
+     * @param updateCount if true, increment running count on success
-–
+     * @return true if successful
-–
+     */
-–
+    private boolean tryResumeSpare(boolean updateCount) {
-–
+        WaitQueueNode q;
-–
+        while ((q = spareStack) != null) {
-–
+            if (casSpareStack(q, q.next)) {
-–
+                if (updateCount)
-–
+                    updateRunningCount(1);
-–
+                q.signal();
-–
+                return true;
-–
+            }
-–
+        }
-–
+        return false;
-–
+    }
-–
-–
+    /**
-–
+     * Pops and resumes all spare threads. Same idea as ensureSync.
-–
+     *
-–
+     * @return true if any spares released
-–
+     */
-–
+    private boolean resumeAllSpares() {
-–
+        WaitQueueNode q;
-–
+        while ( (q = spareStack) != null) {
-–
+            if (casSpareStack(q, null)) {
-–
+                do {
-–
+                    updateRunningCount(1);
-–
+                    q.signal();
-–
+                } while ((q = q.next) != null);
-–
+                return true;
-–
+            }
-–
+        }
-–
+        return false;
-–
+    }
-–
-–
+    /**
-–
+     * Pops and shuts down excessive spare threads. Call only while
-–
+     * holding lock. This is not guaranteed to eliminate all excess
-–
+     * threads, only those suspended as spares, which are the ones
-–
+     * unlikely to be needed in the future.
-–
+     */
-–
+    private void trimSpares() {
-–
+        int surplus = totalCountOf(workerCounts) - parallelism;
-–
+        WaitQueueNode q;
-–
+        while (surplus > 0 && (q = spareStack) != null) {
-–
+            if (casSpareStack(q, null)) {
-–
+                do {
-–
+                    updateRunningCount(1);
-–
+                    ForkJoinWorkerThread w = q.thread;
-–
+                    if (w != null && surplus > 0 &&
-–
+                        runningCountOf(workerCounts) > 0 && w.shutdown())
-–
+                        --surplus;
-–
+                    q.signal();
-–
+                } while ((q = q.next) != null);
-–
+            }
-–
+        }
-–
+    }
-–
+    /**
+     * Interface for extending managed parallelism for tasks running
+     * in {@link ForkJoinPool}s.
-<
+     * <p>A {@code ManagedBlocker} provides two methods.
-<
+     * Method {@code isReleasable} must return {@code true} if
-<
+     * blocking is not necessary. Method {@code block} blocks the
-<
+     * current thread if necessary (perhaps internally invoking
-<
+     * {@code isReleasable} before actually blocking).
->
+     * <p>A {@code ManagedBlocker} provides two methods.  Method
->
+     * {@code isReleasable} must return {@code true} if blocking is
->
+     * not necessary. Method {@code block} blocks the current thread
->
+     * if necessary (perhaps internally invoking {@code isReleasable}
->
+     * before actually blocking). These actions are performed by any
->
+     * thread invoking {@link ForkJoinPool#managedBlock}.  The
->
+     * unusual methods in this API accommodate synchronizers that may,
->
+     * but don't usually, block for long periods. Similarly, they
->
+     * allow more efficient internal handling of cases in which
->
+     * additional workers may be, but usually are not, needed to
->
+     * ensure sufficient parallelism.  Toward this end,
->
+     * implementations of method {@code isReleasable} must be amenable
->
+     * to repeated invocation.
+     * <p>For example, here is a ManagedBlocker based on a
+     * ReentrantLock:
+     *     return hasLock || (hasLock = lock.tryLock());
+     *   }
+     * }}</pre>
-+
+     *
-+
+     * <p>Here is a class that possibly blocks waiting for an
-+
+     * item on a given queue:
-+
+     *  <pre> {@code
-+
+     * class QueueTaker<E> implements ManagedBlocker {
-+
+     *   final BlockingQueue<E> queue;
-+
+     *   volatile E item = null;
-+
+     *   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
-+
+     *   public boolean block() throws InterruptedException {
-+
+     *     if (item == null)
-+
+     *       item = queue.take();
-+
+     *     return true;
-+
+     *   }
-+
+     *   public boolean isReleasable() {
-+
+     *     return item != null || (item = queue.poll()) != null;
-+
+     *   }
-+
+     *   public E getItem() { // call after pool.managedBlock completes
-+
+     *     return item;
-+
+     *   }
-+
+     * }}</pre>
+     */
+    public static interface ManagedBlocker {
+        /**
+     * Blocks in accord with the given blocker.  If the current thread
+     * is a {@link ForkJoinWorkerThread}, this method possibly
+     * arranges for a spare thread to be activated if necessary to
-<
+     * ensure parallelism while the current thread is blocked.
-<
+     *
-<
+     * <p>If {@code maintainParallelism} is {@code true} and the pool
-<
+     * supports it ({@link #getMaintainsParallelism}), this method
-<
+     * attempts to maintain the pool's nominal parallelism. Otherwise
-<
+     * it activates a thread only if necessary to avoid complete
-<
+     * starvation. This option may be preferable when blockages use
-<
+     * timeouts, or are almost always brief.
->
+     * ensure sufficient parallelism while the current thread is blocked.
+     * <p>If the caller is not a {@link ForkJoinTask}, this method is
+     * behaviorally equivalent to
+     * first be expanded to ensure parallelism, and later adjusted.
+     * @param blocker the blocker
-–
+     * @param maintainParallelism if {@code true} and supported by
-–
+     * this pool, attempt to maintain the pool's nominal parallelism;
-–
+     * otherwise activate a thread only if necessary to avoid
-–
+     * complete starvation.
+     * @throws InterruptedException if blocker.block did so
+     */
-<
+    public static void managedBlock(ManagedBlocker blocker,
-<
+                                    boolean maintainParallelism)
->
+    public static void managedBlock(ManagedBlocker blocker)
+        throws InterruptedException {
+        Thread t = Thread.currentThread();
-<
+        ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ?
-<
+                             ((ForkJoinWorkerThread) t).pool : null);
-<
+        if (!blocker.isReleasable()) {
-<
+            try {
-<
+                if (pool == null ||
-<
+                    !pool.preBlock(blocker, maintainParallelism))
-<
+                    awaitBlocker(blocker);
-<
+            } finally {
-<
+                if (pool != null)
-<
+                    pool.updateRunningCount(1);
-<
+            }
->
+        if (t instanceof ForkJoinWorkerThread) {
->
+            ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
->
+            w.pool.awaitBlocker(blocker);
->
+        }
->
+        else {
->
+            do {} while (!blocker.isReleasable() && !blocker.block());
-–
+    }
-–
-–
+    private static void awaitBlocker(ManagedBlocker blocker)
-–
+        throws InterruptedException {
-–
+        do {} while (!blocker.isReleasable() && !blocker.block());
+    // AbstractExecutorService overrides.  These rely on undocumented
+    // Unsafe mechanics
-<
-<
+    private static final sun.misc.Unsafe UNSAFE = getUnsafe();
-<
+    private static final long eventCountOffset =
-<
+        objectFieldOffset("eventCount", ForkJoinPool.class);
-<
+    private static final long workerCountsOffset =
-<
+        objectFieldOffset("workerCounts", ForkJoinPool.class);
-<
+    private static final long runControlOffset =
-<
+        objectFieldOffset("runControl", ForkJoinPool.class);
-<
+    private static final long syncStackOffset =
-<
+        objectFieldOffset("syncStack",ForkJoinPool.class);
-<
+    private static final long spareStackOffset =
-<
+        objectFieldOffset("spareStack", ForkJoinPool.class);
-<
-<
+    private boolean casEventCount(long cmp, long val) {
-<
+        return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
-<
+    }
-<
+    private boolean casWorkerCounts(int cmp, int val) {
-<
+        return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
-<
+    }
-<
+    private boolean casRunControl(int cmp, int val) {
-<
+        return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
-<
+    }
-<
+    private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
-<
+        return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
-<
+    }
-<
+    private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
-<
+        return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
-<
+    }
-<
-<
+    private static long objectFieldOffset(String field, Class<?> klazz) {
->
+    private static final sun.misc.Unsafe UNSAFE;
->
+    private static final long ctlOffset;
->
+    private static final long stealCountOffset;
->
+    private static final long blockedCountOffset;
->
+    private static final long quiescerCountOffset;
->
+    private static final long scanGuardOffset;
->
+    private static final long nextWorkerNumberOffset;
->
+    private static final long ABASE;
->
+    private static final int ASHIFT;
->
->
+    static {
->
+        poolNumberGenerator = new AtomicInteger();
->
+        workerSeedGenerator = new Random();
->
+        modifyThreadPermission = new RuntimePermission("modifyThread");
->
+        defaultForkJoinWorkerThreadFactory =
->
+            new DefaultForkJoinWorkerThreadFactory();
->
+        int s;
+        try {
-<
+            return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
-<
+        } catch (NoSuchFieldException e) {
-<
+            // Convert Exception to corresponding Error
-<
+            NoSuchFieldError error = new NoSuchFieldError(field);
-<
+            error.initCause(e);
-<
+            throw error;
-<
+        }
->
+            UNSAFE = getUnsafe();
->
+            Class k = ForkJoinPool.class;
->
+            ctlOffset = UNSAFE.objectFieldOffset
->
+                (k.getDeclaredField("ctl"));
->
+            stealCountOffset = UNSAFE.objectFieldOffset
->
+                (k.getDeclaredField("stealCount"));
->
+            blockedCountOffset = UNSAFE.objectFieldOffset
->
+                (k.getDeclaredField("blockedCount"));
->
+            quiescerCountOffset = UNSAFE.objectFieldOffset
->
+                (k.getDeclaredField("quiescerCount"));
->
+            scanGuardOffset = UNSAFE.objectFieldOffset
->
+                (k.getDeclaredField("scanGuard"));
->
+            nextWorkerNumberOffset = UNSAFE.objectFieldOffset
->
+                (k.getDeclaredField("nextWorkerNumber"));
->
+            Class a = ForkJoinTask[].class;
->
+            ABASE = UNSAFE.arrayBaseOffset(a);
->
+            s = UNSAFE.arrayIndexScale(a);
->
+        } catch (Exception e) {
->
+            throw new Error(e);
->
+        }
->
+        if ((s & (s-1)) != 0)
->
+            throw new Error("data type scale not a power of two");
->
+        ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
+    /**

Diff Legend

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+Removed lines
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+Added lines
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+Changed lines
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+Changed lines

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents): Revision 1.43 by jsr166, Tue Aug 4 00:55:13 2009 UTC vs. Revision 1.94 by dl, Tue Mar 1 10:59:04 2011 UTC

Diff Legend

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.43 by jsr166, Tue Aug 4 00:55:13 2009 UTC vs.
Revision 1.94 by dl, Tue Mar 1 10:59:04 2011 UTC