--- jsr166/src/jsr166y/ForkJoinPool.java 2009/07/22 01:36:51 1.13
+++ jsr166/src/jsr166y/ForkJoinPool.java 2009/07/29 12:05:55 1.30
@@ -5,16 +5,23 @@
*/
package jsr166y;
-import java.util.*;
+
import java.util.concurrent.*;
-import java.util.concurrent.locks.*;
-import java.util.concurrent.atomic.*;
-import sun.misc.Unsafe;
-import java.lang.reflect.*;
+
+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.concurrent.locks.LockSupport;
+import java.util.concurrent.locks.ReentrantLock;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicLong;
/**
- * An {@link ExecutorService} for running {@link ForkJoinTask}s. A
- * ForkJoinPool provides the entry point for submissions from
+ * An {@link ExecutorService} for running {@link ForkJoinTask}s.
+ * A ForkJoinPool provides the entry point for submissions from
* non-ForkJoinTasks, as well as management and monitoring operations.
* Normally a single ForkJoinPool is used for a large number of
* submitted tasks. Otherwise, use would not usually outweigh the
@@ -27,29 +34,29 @@ import java.lang.reflect.*;
* (eventually blocking if none exist). This makes them efficient when
* most tasks spawn other subtasks (as do most ForkJoinTasks), as well
* as the mixed execution of some plain Runnable- or Callable- based
- * activities along with ForkJoinTasks. When setting
- * {@code setAsyncMode}, a ForkJoinPools may also be appropriate for
- * use with fine-grained tasks that are never joined. Otherwise, other
- * ExecutorService implementations are typically more appropriate
- * choices.
+ * activities along with ForkJoinTasks. When setting {@linkplain
+ * #setAsyncMode async mode}, a ForkJoinPool may also be appropriate
+ * for use with fine-grained tasks that are never joined. Otherwise,
+ * other ExecutorService implementations are typically more
+ * appropriate choices.
*
* A ForkJoinPool may be constructed with a given parallelism level
* (target pool size), which it attempts to maintain by dynamically
* adding, suspending, or resuming threads, even if some tasks are
* waiting to join others. However, no such adjustments are performed
* in the face of blocked IO or other unmanaged synchronization. The
- * nested {@code ManagedBlocker} interface enables extension of
+ * nested {@link ManagedBlocker} interface enables extension of
* the kinds of synchronization accommodated. The target parallelism
- * level may also be changed dynamically ({@code setParallelism})
+ * level may also be changed dynamically ({@link #setParallelism})
* and thread construction can be limited using methods
- * {@code setMaximumPoolSize} and/or
- * {@code setMaintainsParallelism}.
+ * {@link #setMaximumPoolSize} and/or
+ * {@link #setMaintainsParallelism}.
*
*
In addition to execution and lifecycle control methods, this
* class provides status check methods (for example
- * {@code getStealCount}) that are intended to aid in developing,
+ * {@link #getStealCount}) that are intended to aid in developing,
* tuning, and monitoring fork/join applications. Also, method
- * {@code toString} returns indications of pool state in a
+ * {@link #toString} returns indications of pool state in a
* convenient form for informal monitoring.
*
*
Implementation notes: This implementation restricts the
@@ -90,7 +97,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Default ForkJoinWorkerThreadFactory implementation, creates a
+ * Default ForkJoinWorkerThreadFactory implementation; creates a
* new ForkJoinWorkerThread.
*/
static class DefaultForkJoinWorkerThreadFactory
@@ -184,7 +191,7 @@ public class ForkJoinPool extends Abstra
private final LinkedTransferQueue> submissionQueue;
/**
- * Head of Treiber stack for barrier sync. See below for explanation
+ * Head of Treiber stack for barrier sync. See below for explanation.
*/
private volatile WaitQueueNode syncStack;
@@ -219,8 +226,8 @@ public class ForkJoinPool extends Abstra
* 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 running active count is in low
- * word, so need to be modified if this changes
+ * updateRunningCount and preJoin assume that running active count
+ * is in low word, so need to be modified if this changes.
*/
private volatile int workerCounts;
@@ -232,23 +239,25 @@ public class ForkJoinPool extends Abstra
* 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
*/
final void updateRunningCount(int delta) {
int s;
- do;while (!casWorkerCounts(s = workerCounts, s + delta));
+ do {} while (!casWorkerCounts(s = workerCounts, s + delta));
}
/**
* Adds delta (which may be negative) to both total and running
* count. This must be called upon creation and termination of
* worker threads.
+ *
* @param delta the number to add
*/
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));
+ do {} while (!casWorkerCounts(s = workerCounts, s + d));
}
/**
@@ -274,8 +283,9 @@ public class ForkJoinPool extends Abstra
private static int runControlFor(int r, int a) { return (r << 16) + a; }
/**
- * Try incrementing active count; fail on contention. Called by
- * workers before/during executing tasks.
+ * Tries incrementing active count; fails on contention.
+ * Called by workers before/during executing tasks.
+ *
* @return true on success
*/
final boolean tryIncrementActiveCount() {
@@ -287,6 +297,7 @@ public class ForkJoinPool extends Abstra
* 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
*/
final boolean tryDecrementActiveCount() {
@@ -300,12 +311,13 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns true if argument represents zero active count and
- * nonzero runstate, which is the triggering condition for
+ * Returns {@code true} if argument represents zero active count
+ * and nonzero runstate, which is the triggering condition for
* terminating on shutdown.
*/
private static boolean canTerminateOnShutdown(int c) {
- return ((c & -c) >>> 16) != 0; // i.e. least bit is nonzero runState bit
+ // i.e. least bit is nonzero runState bit
+ return ((c & -c) >>> 16) != 0;
}
/**
@@ -331,12 +343,13 @@ public class ForkJoinPool extends Abstra
/**
* Creates a ForkJoinPool with a pool size equal to the number of
- * processors available on the system and using the default
- * ForkJoinWorkerThreadFactory,
+ * processors available on the system, using the default
+ * ForkJoinWorkerThreadFactory.
+ *
* @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")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool() {
this(Runtime.getRuntime().availableProcessors(),
@@ -345,14 +358,15 @@ public class ForkJoinPool extends Abstra
/**
* Creates a ForkJoinPool with the indicated parallelism level
- * threads, and using the default ForkJoinWorkerThreadFactory,
+ * threads and using the default ForkJoinWorkerThreadFactory.
+ *
* @param parallelism the number of worker threads
* @throws IllegalArgumentException if parallelism less than or
* equal to zero
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}{@code ("modifyThread")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool(int parallelism) {
this(parallelism, defaultForkJoinWorkerThreadFactory);
@@ -361,13 +375,14 @@ public class ForkJoinPool extends Abstra
/**
* Creates a ForkJoinPool with parallelism equal to the number of
* processors available on the system and using the given
- * ForkJoinWorkerThreadFactory,
+ * ForkJoinWorkerThreadFactory.
+ *
* @param factory the factory for creating new threads
* @throws NullPointerException if factory is null
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}{@code ("modifyThread")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
this(Runtime.getRuntime().availableProcessors(), factory);
@@ -384,7 +399,7 @@ public class ForkJoinPool extends Abstra
* @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")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
if (parallelism <= 0 || parallelism > MAX_THREADS)
@@ -405,7 +420,8 @@ public class ForkJoinPool extends Abstra
}
/**
- * Create new worker using factory.
+ * Creates a new worker thread using factory.
+ *
* @param index the index to assign worker
* @return new worker, or null of factory failed
*/
@@ -427,13 +443,15 @@ public class ForkJoinPool extends Abstra
* Returns a good size for worker array given pool size.
* Currently requires size to be a power of two.
*/
- private static int arraySizeFor(int ps) {
- return ps <= 1? 1 : (1 << (32 - Integer.numberOfLeadingZeros(ps-1)));
+ private static int arraySizeFor(int poolSize) {
+ return (poolSize <= 1) ? 1 :
+ (1 << (32 - Integer.numberOfLeadingZeros(poolSize-1)));
}
/**
* Creates or resizes array if necessary to hold newLength.
- * Call only under exclusion or lock.
+ * Call only under exclusion.
+ *
* @return the array
*/
private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
@@ -447,7 +465,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Try to shrink workers into smaller array after one or more terminate
+ * Tries to shrink workers into smaller array after one or more terminate.
*/
private void tryShrinkWorkerArray() {
ForkJoinWorkerThread[] ws = workers;
@@ -463,7 +481,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Initialize workers if necessary
+ * Initializes workers if necessary.
*/
final void ensureWorkerInitialization() {
ForkJoinWorkerThread[] ws = workers;
@@ -530,6 +548,8 @@ public class ForkJoinPool extends Abstra
* Common code for execute, invoke and submit
*/
private void doSubmit(ForkJoinTask task) {
+ if (task == null)
+ throw new NullPointerException();
if (isShutdown())
throw new RejectedExecutionException();
if (workers == null)
@@ -539,7 +559,8 @@ public class ForkJoinPool extends Abstra
}
/**
- * Performs the given task; returning its result upon completion
+ * Performs the given task, returning its result upon completion.
+ *
* @param task the task
* @return the task's result
* @throws NullPointerException if task is null
@@ -552,6 +573,7 @@ public class ForkJoinPool extends Abstra
/**
* Arranges for (asynchronous) execution of the given task.
+ *
* @param task the task
* @throws NullPointerException if task is null
* @throws RejectedExecutionException if pool is shut down
@@ -563,7 +585,12 @@ public class ForkJoinPool extends Abstra
// AbstractExecutorService methods
public void execute(Runnable task) {
- doSubmit(new AdaptedRunnable(task, null));
+ ForkJoinTask job;
+ if (task instanceof ForkJoinTask) // avoid re-wrap
+ job = (ForkJoinTask) task;
+ else
+ job = new AdaptedRunnable(task, null);
+ doSubmit(job);
}
public ForkJoinTask submit(Callable task) {
@@ -579,14 +606,32 @@ public class ForkJoinPool extends Abstra
}
public ForkJoinTask submit(Runnable task) {
- ForkJoinTask job = new AdaptedRunnable(task, null);
+ ForkJoinTask job;
+ if (task instanceof ForkJoinTask) // avoid re-wrap
+ job = (ForkJoinTask) task;
+ else
+ job = new AdaptedRunnable(task, null);
doSubmit(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
+ */
+ public ForkJoinTask submit(ForkJoinTask task) {
+ doSubmit(task);
+ return task;
+ }
+
+ /**
* Adaptor for Runnables. This implements RunnableFuture
- * to be compliant with AbstractExecutorService constraints
+ * to be compliant with AbstractExecutorService constraints.
*/
static final class AdaptedRunnable extends ForkJoinTask
implements RunnableFuture {
@@ -606,6 +651,7 @@ public class ForkJoinPool extends Abstra
return true;
}
public void run() { invoke(); }
+ private static final long serialVersionUID = 5232453952276885070L;
}
/**
@@ -634,29 +680,35 @@ public class ForkJoinPool extends Abstra
}
}
public void run() { invoke(); }
+ private static final long serialVersionUID = 2838392045355241008L;
}
public List> invokeAll(Collection> tasks) {
- ArrayList> ts =
+ ArrayList> forkJoinTasks =
new ArrayList>(tasks.size());
- for (Callable c : tasks)
- ts.add(new AdaptedCallable(c));
- invoke(new InvokeAll(ts));
- return (List>)(List)ts;
+ for (Callable task : tasks)
+ forkJoinTasks.add(new AdaptedCallable(task));
+ invoke(new InvokeAll(forkJoinTasks));
+
+ @SuppressWarnings({"unchecked", "rawtypes"})
+ List> futures = (List>) (List) forkJoinTasks;
+ return futures;
}
static final class InvokeAll extends RecursiveAction {
final ArrayList> tasks;
InvokeAll(ArrayList> tasks) { this.tasks = tasks; }
public void compute() {
- try { invokeAll(tasks); } catch(Exception ignore) {}
+ try { invokeAll(tasks); }
+ catch (Exception ignore) {}
}
+ private static final long serialVersionUID = -7914297376763021607L;
}
// Configuration and status settings and queries
/**
- * Returns the factory used for constructing new workers
+ * Returns the factory used for constructing new workers.
*
* @return the factory used for constructing new workers
*/
@@ -667,7 +719,8 @@ public class ForkJoinPool extends Abstra
/**
* Returns the handler for internal worker threads that terminate
* due to unrecoverable errors encountered while executing tasks.
- * @return the handler, or null if none
+ *
+ * @return the handler, or {@code null} if none
*/
public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
Thread.UncaughtExceptionHandler h;
@@ -688,11 +741,11 @@ public class ForkJoinPool extends Abstra
* as handler.
*
* @param h the new handler
- * @return the old handler, or null if none
+ * @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")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public Thread.UncaughtExceptionHandler
setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
@@ -720,13 +773,14 @@ public class ForkJoinPool extends Abstra
/**
* 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")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public void setParallelism(int parallelism) {
checkPermission();
@@ -761,7 +815,7 @@ public class ForkJoinPool extends Abstra
/**
* Returns the number of worker threads that have started but not
* yet terminated. This result returned by this method may differ
- * from {@code getParallelism} when threads are created to
+ * from {@link #getParallelism} when threads are created to
* maintain parallelism when others are cooperatively blocked.
*
* @return the number of worker threads
@@ -773,6 +827,7 @@ public class ForkJoinPool extends Abstra
/**
* Returns the maximum number of threads allowed to exist in the
* pool, even if there are insufficient unblocked running threads.
+ *
* @return the maximum
*/
public int getMaximumPoolSize() {
@@ -784,6 +839,7 @@ public class ForkJoinPool extends Abstra
* pool, even if there are insufficient unblocked running threads.
* Setting this value has no effect on current pool size. It
* controls construction of new threads.
+ *
* @throws IllegalArgumentException if negative or greater then
* internal implementation limit
*/
@@ -795,11 +851,11 @@ public class ForkJoinPool extends Abstra
/**
- * Returns true if this pool dynamically maintains its target
- * parallelism level. If false, new threads are added only to
- * avoid possible starvation.
- * This setting is by default true;
- * @return true if maintains parallelism
+ * 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;
@@ -809,7 +865,8 @@ public class ForkJoinPool extends Abstra
* Sets whether this pool dynamically maintains its target
* parallelism level. If false, new threads are added only to
* avoid possible starvation.
- * @param enable true to maintains parallelism
+ *
+ * @param enable {@code true} to maintain parallelism
*/
public void setMaintainsParallelism(boolean enable) {
maintainsParallelism = enable;
@@ -820,12 +877,13 @@ public class ForkJoinPool extends Abstra
* tasks that are never joined. This mode may be more appropriate
* than default locally stack-based mode in applications in which
* worker threads only process asynchronous tasks. This method is
- * designed to be invoked only when pool is quiescent, and
+ * 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 true, use locally FIFO scheduling
+ * @param async if {@code true}, use locally FIFO scheduling
* @return the previous mode
+ * @see #getAsyncMode
*/
public boolean setAsyncMode(boolean async) {
boolean oldMode = locallyFifo;
@@ -842,10 +900,11 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns true if this pool uses local first-in-first-out
+ * Returns {@code true} if this pool uses local first-in-first-out
* scheduling mode for forked tasks that are never joined.
*
- * @return true if this pool uses async mode
+ * @return {@code true} if this pool uses async mode
+ * @see #setAsyncMode
*/
public boolean getAsyncMode() {
return locallyFifo;
@@ -866,6 +925,7 @@ public class ForkJoinPool extends Abstra
* Returns an estimate of the number of threads that are currently
* stealing or executing tasks. This method may overestimate the
* number of active threads.
+ *
* @return the number of active threads
*/
public int getActiveThreadCount() {
@@ -876,22 +936,24 @@ public class ForkJoinPool extends Abstra
* Returns an estimate of the number of threads that are currently
* idle waiting for tasks. This method may underestimate the
* number of idle threads.
+ *
* @return the number of idle threads
*/
final int getIdleThreadCount() {
int c = runningCountOf(workerCounts) - activeCountOf(runControl);
- return (c <= 0)? 0 : c;
+ return (c <= 0) ? 0 : c;
}
/**
- * Returns true if all worker threads are currently idle. An idle
- * worker is one that cannot obtain a task to execute because none
- * are available to steal from other threads, and there are no
- * pending submissions to the pool. This method is conservative:
- * It might not return true immediately upon idleness of all
- * threads, but will eventually become true if threads remain
- * inactive.
- * @return true if all threads are currently idle
+ * Returns {@code true} if all worker threads are currently idle.
+ * An idle worker is one that cannot obtain a task to execute
+ * because none are available to steal from other threads, and
+ * there are no pending submissions to the pool. This method is
+ * conservative; it might not return {@code true} immediately upon
+ * idleness of all threads, but will eventually become true if
+ * threads remain inactive.
+ *
+ * @return {@code true} if all threads are currently idle
*/
public boolean isQuiescent() {
return activeCountOf(runControl) == 0;
@@ -902,9 +964,10 @@ public class ForkJoinPool extends Abstra
* one thread's work queue by another. The reported value
* underestimates the actual total number of steals when the pool
* is not quiescent. This value may be useful for monitoring and
- * tuning fork/join programs: In general, steal counts should be
+ * tuning fork/join programs: in general, steal counts should be
* high enough to keep threads busy, but low enough to avoid
* overhead and contention across threads.
+ *
* @return the number of steals
*/
public long getStealCount() {
@@ -912,8 +975,8 @@ public class ForkJoinPool extends Abstra
}
/**
- * Accumulate steal count from a worker. Call only
- * when worker known to be idle.
+ * Accumulates steal count from a worker.
+ * Call only when worker known to be idle.
*/
private void updateStealCount(ForkJoinWorkerThread w) {
int sc = w.getAndClearStealCount();
@@ -928,6 +991,7 @@ public class ForkJoinPool extends Abstra
* an approximation, obtained by iterating across all threads in
* the pool. This method may be useful for tuning task
* granularities.
+ *
* @return the number of queued tasks
*/
public long getQueuedTaskCount() {
@@ -947,6 +1011,7 @@ public class ForkJoinPool extends Abstra
* Returns an estimate of the number tasks submitted to this pool
* that have not yet begun executing. This method takes time
* proportional to the number of submissions.
+ *
* @return the number of queued submissions
*/
public int getQueuedSubmissionCount() {
@@ -954,8 +1019,9 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns true if there are any tasks submitted to this pool
- * that have not yet begun executing.
+ * Returns {@code true} if there are any tasks submitted to this
+ * pool that have not yet begun executing.
+ *
* @return {@code true} if there are any queued submissions
*/
public boolean hasQueuedSubmissions() {
@@ -966,7 +1032,8 @@ public class ForkJoinPool extends Abstra
* Removes and returns the next unexecuted submission if one is
* available. This method may be useful in extensions to this
* class that re-assign work in systems with multiple pools.
- * @return the next submission, or null if none
+ *
+ * @return the next submission, or {@code null} if none
*/
protected ForkJoinTask pollSubmission() {
return submissionQueue.poll();
@@ -985,10 +1052,11 @@ public class ForkJoinPool extends Abstra
* exception is thrown. The behavior of this operation is
* undefined if the specified collection is modified while the
* operation is in progress.
+ *
* @param c the collection to transfer elements into
* @return the number of elements transferred
*/
- protected int drainTasksTo(Collection> c) {
+ protected int drainTasksTo(Collection> c) {
int n = submissionQueue.drainTo(c);
ForkJoinWorkerThread[] ws = workers;
if (ws != null) {
@@ -1045,10 +1113,11 @@ public class ForkJoinPool extends Abstra
* Invocation has no additional effect if already shut down.
* Tasks that are in the process of being submitted concurrently
* during the course of this method may or may not be rejected.
+ *
* @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")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public void shutdown() {
checkPermission();
@@ -1064,13 +1133,14 @@ public class ForkJoinPool extends Abstra
* method may or may not be rejected. Unlike some other executors,
* this method cancels rather than collects non-executed tasks
* upon termination, so always returns an empty list. However, you
- * can use method {@code drainTasksTo} before invoking this
+ * can use method {@link #drainTasksTo} before invoking this
* method to transfer unexecuted tasks to another collection.
+ *
* @return an empty list
* @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")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public List shutdownNow() {
checkPermission();
@@ -1138,9 +1208,10 @@ public class ForkJoinPool extends Abstra
// Shutdown and termination support
/**
- * Callback from terminating worker. Null out the corresponding
- * workers slot, and if terminating, try to terminate, else try to
- * shrink workers array.
+ * 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) {
@@ -1171,7 +1242,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Initiate termination.
+ * Initiates termination.
*/
private void terminate() {
if (transitionRunStateTo(TERMINATING)) {
@@ -1348,6 +1419,7 @@ public class ForkJoinPool extends Abstra
* 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() {
@@ -1369,7 +1441,7 @@ public class ForkJoinPool extends Abstra
*/
private void signalIdleWorkers() {
long c;
- do;while (!casEventCount(c = eventCount, c+1));
+ do {} while (!casEventCount(c = eventCount, c+1));
ensureSync();
}
@@ -1393,6 +1465,7 @@ public class ForkJoinPool extends Abstra
* 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) {
@@ -1420,14 +1493,15 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns true if worker waiting on sync can proceed:
+ * 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
+ * - on interrupt
* - if the first queued node, we find work available
* If node was not signalled and event count not advanced on exit,
* then we also help advance event count.
- * @return true if node can be released
+ *
+ * @return {@code true} if node can be released
*/
final boolean syncIsReleasable(WaitQueueNode node) {
long prev = node.count;
@@ -1446,8 +1520,8 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns true if a new sync event occurred since last call to
- * sync or this method, if so, updating caller's count.
+ * 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;
@@ -1467,7 +1541,7 @@ public class ForkJoinPool extends Abstra
* 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
+ * 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
@@ -1490,12 +1564,14 @@ public class ForkJoinPool extends Abstra
* target counts, else create only to avoid starvation
* @return true if joinMe known to be done
*/
- final boolean preJoin(ForkJoinTask joinMe, boolean maintainParallelism) {
+ 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 (dec || (dec = casWorkerCounts(counts, --counts))) {
+ // CAS cheat
if (!needSpare(counts, maintainParallelism))
break;
if (joinMe.status < 0)
@@ -1510,7 +1586,8 @@ public class ForkJoinPool extends Abstra
/**
* Same idea as preJoin
*/
- final boolean preBlock(ManagedBlocker blocker, boolean maintainParallelism){
+ final boolean preBlock(ManagedBlocker blocker,
+ boolean maintainParallelism) {
maintainParallelism &= maintainsParallelism;
boolean dec = false;
while (spareStack == null || !tryResumeSpare(dec)) {
@@ -1528,12 +1605,13 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns true if a spare thread appears to be needed. If
- * maintaining parallelism, returns true when the deficit in
+ * 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
*/
@@ -1553,6 +1631,7 @@ public class ForkJoinPool extends Abstra
/**
* 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) {
@@ -1612,6 +1691,7 @@ public class ForkJoinPool extends Abstra
* 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) {
@@ -1622,7 +1702,7 @@ public class ForkJoinPool extends Abstra
node = new WaitQueueNode(0, w);
if (casWorkerCounts(s, s-1)) { // representation-dependent
// push onto stack
- do;while (!casSpareStack(node.next = spareStack, node));
+ do {} while (!casSpareStack(node.next = spareStack, node));
// block until released by resumeSpare
node.awaitSpareRelease();
return true;
@@ -1633,6 +1713,7 @@ public class ForkJoinPool extends Abstra
/**
* Tries to pop and resume a spare thread.
+ *
* @param updateCount if true, increment running count on success
* @return true if successful
*/
@@ -1651,6 +1732,7 @@ public class ForkJoinPool extends Abstra
/**
* Pops and resumes all spare threads. Same idea as ensureSync.
+ *
* @return true if any spares released
*/
private boolean resumeAllSpares() {
@@ -1693,41 +1775,42 @@ public class ForkJoinPool extends Abstra
/**
* Interface for extending managed parallelism for tasks running
* in ForkJoinPools. A ManagedBlocker provides two methods.
- * Method {@code isReleasable} must return true if blocking is not
- * necessary. Method {@code block} blocks the current thread
- * if necessary (perhaps internally invoking isReleasable before
- * actually blocking.).
+ * 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.).
+ *
* For example, here is a ManagedBlocker based on a
* ReentrantLock:
- *
- * class ManagedLocker implements ManagedBlocker {
- * final ReentrantLock lock;
- * boolean hasLock = false;
- * ManagedLocker(ReentrantLock lock) { this.lock = lock; }
- * public boolean block() {
- * if (!hasLock)
- * lock.lock();
- * return true;
- * }
- * public boolean isReleasable() {
- * return hasLock || (hasLock = lock.tryLock());
- * }
+ * {@code
+ * class ManagedLocker implements ManagedBlocker {
+ * final ReentrantLock lock;
+ * boolean hasLock = false;
+ * ManagedLocker(ReentrantLock lock) { this.lock = lock; }
+ * public boolean block() {
+ * if (!hasLock)
+ * lock.lock();
+ * return true;
+ * }
+ * public boolean isReleasable() {
+ * return hasLock || (hasLock = lock.tryLock());
* }
- *
+ * }}
*/
public static interface ManagedBlocker {
/**
* Possibly blocks the current thread, for example waiting for
* a lock or condition.
- * @return true if no additional blocking is necessary (i.e.,
- * if isReleasable would return true)
+ *
+ * @return {@code true} if no additional blocking is necessary
+ * (i.e., if isReleasable would return true)
* @throws InterruptedException if interrupted while waiting
- * (the method is not required to do so, but is allowed to).
+ * (the method is not required to do so, but is allowed to)
*/
boolean block() throws InterruptedException;
/**
- * Returns true if blocking is unnecessary.
+ * Returns {@code true} if blocking is unnecessary.
*/
boolean isReleasable();
}
@@ -1737,36 +1820,36 @@ public class ForkJoinPool extends Abstra
* is a ForkJoinWorkerThread, this method possibly arranges for a
* spare thread to be activated if necessary to ensure parallelism
* while the current thread is blocked. If
- * {@code maintainParallelism} is true and the pool supports
+ * {@code maintainParallelism} is {@code true} and the pool supports
* it ({@link #getMaintainsParallelism}), this method attempts to
- * maintain the pool's nominal parallelism. Otherwise if activates
+ * 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.
*
* If the caller is not a ForkJoinTask, this method is behaviorally
* equivalent to
- *
- * while (!blocker.isReleasable())
- * if (blocker.block())
- * return;
- *
+ * {@code
+ * while (!blocker.isReleasable())
+ * if (blocker.block())
+ * return;
+ * }
* If the caller is a ForkJoinTask, then the pool may first
* be expanded to ensure parallelism, and later adjusted.
*
* @param blocker the blocker
- * @param maintainParallelism if true and supported by this pool,
- * attempt to maintain the pool's nominal parallelism; otherwise
- * activate a thread only if necessary to avoid complete
- * starvation.
+ * @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)
throws InterruptedException {
Thread t = Thread.currentThread();
- ForkJoinPool pool = (t instanceof ForkJoinWorkerThread?
- ((ForkJoinWorkerThread)t).pool : null);
+ ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ?
+ ((ForkJoinWorkerThread) t).pool : null);
if (!blocker.isReleasable()) {
try {
if (pool == null ||
@@ -1781,69 +1864,32 @@ public class ForkJoinPool extends Abstra
private static void awaitBlocker(ManagedBlocker blocker)
throws InterruptedException {
- do;while (!blocker.isReleasable() && !blocker.block());
+ do {} while (!blocker.isReleasable() && !blocker.block());
}
// AbstractExecutorService overrides
protected RunnableFuture newTaskFor(Runnable runnable, T value) {
- return new AdaptedRunnable(runnable, value);
+ return new AdaptedRunnable(runnable, value);
}
protected RunnableFuture newTaskFor(Callable callable) {
- return new AdaptedCallable(callable);
+ return new AdaptedCallable(callable);
}
+ // Unsafe mechanics
- // Temporary Unsafe mechanics for preliminary release
- private static Unsafe getUnsafe() throws Throwable {
- try {
- return Unsafe.getUnsafe();
- } catch (SecurityException se) {
- try {
- return java.security.AccessController.doPrivileged
- (new java.security.PrivilegedExceptionAction() {
- public Unsafe run() throws Exception {
- return getUnsafePrivileged();
- }});
- } catch (java.security.PrivilegedActionException e) {
- throw e.getCause();
- }
- }
- }
-
- private static Unsafe getUnsafePrivileged()
- throws NoSuchFieldException, IllegalAccessException {
- Field f = Unsafe.class.getDeclaredField("theUnsafe");
- f.setAccessible(true);
- return (Unsafe) f.get(null);
- }
-
- private static long fieldOffset(String fieldName)
- throws NoSuchFieldException {
- return UNSAFE.objectFieldOffset
- (ForkJoinPool.class.getDeclaredField(fieldName));
- }
-
- static final Unsafe UNSAFE;
- static final long eventCountOffset;
- static final long workerCountsOffset;
- static final long runControlOffset;
- static final long syncStackOffset;
- static final long spareStackOffset;
-
- static {
- try {
- UNSAFE = getUnsafe();
- eventCountOffset = fieldOffset("eventCount");
- workerCountsOffset = fieldOffset("workerCounts");
- runControlOffset = fieldOffset("runControl");
- syncStackOffset = fieldOffset("syncStack");
- spareStackOffset = fieldOffset("spareStack");
- } catch (Throwable e) {
- throw new RuntimeException("Could not initialize intrinsics", e);
- }
- }
+ 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);
@@ -1860,4 +1906,43 @@ public class ForkJoinPool extends Abstra
private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
}
+
+ private static long objectFieldOffset(String field, Class klazz) {
+ 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;
+ }
+ }
+
+ /**
+ * Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package.
+ * Replace with a simple call to Unsafe.getUnsafe when integrating
+ * into a jdk.
+ *
+ * @return a sun.misc.Unsafe
+ */
+ private static sun.misc.Unsafe getUnsafe() {
+ try {
+ return sun.misc.Unsafe.getUnsafe();
+ } catch (SecurityException se) {
+ try {
+ return java.security.AccessController.doPrivileged
+ (new java.security
+ .PrivilegedExceptionAction() {
+ public sun.misc.Unsafe run() throws Exception {
+ java.lang.reflect.Field f = sun.misc
+ .Unsafe.class.getDeclaredField("theUnsafe");
+ f.setAccessible(true);
+ return (sun.misc.Unsafe) f.get(null);
+ }});
+ } catch (java.security.PrivilegedActionException e) {
+ throw new RuntimeException("Could not initialize intrinsics",
+ e.getCause());
+ }
+ }
+ }
}