--- jsr166/src/jsr166y/ForkJoinPool.java 2009/07/22 01:36:51 1.13
+++ jsr166/src/jsr166y/ForkJoinPool.java 2009/12/05 11:39:03 1.52
@@ -5,57 +5,88 @@
*/
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
- * 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
- * construction and bookkeeping overhead of creating a large set of
- * threads.
+ * 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.
*
- * ForkJoinPools differ from other kinds of Executors mainly in
- * that they provide work-stealing: all threads in the pool
- * attempt to find and execute subtasks created by other active tasks
- * (eventually blocking if none exist). This makes them efficient when
- * most tasks spawn other subtasks (as do most 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.
+ *
A {@code ForkJoinPool} differs from other kinds of {@link
+ * ExecutorService} mainly by virtue of employing
+ * work-stealing: all threads in the pool attempt to find and
+ * execute subtasks created by other active tasks (eventually blocking
+ * waiting for work if none exist). This enables efficient processing
+ * when most tasks spawn other subtasks (as do most {@code
+ * ForkJoinTask}s). A {@code ForkJoinPool} may also be used for mixed
+ * execution of some plain {@code Runnable}- or {@code Callable}-
+ * based activities along with {@code ForkJoinTask}s. When setting
+ * {@linkplain #setAsyncMode async mode}, a {@code ForkJoinPool} may
+ * also be appropriate for use with fine-grained tasks of any form
+ * that are never joined. Otherwise, other {@code ExecutorService}
+ * implementations are typically more appropriate choices.
*
- *
A 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
- * the kinds of synchronization accommodated. The target parallelism
- * level may also be changed dynamically ({@code setParallelism})
- * and thread construction can be limited using methods
- * {@code setMaximumPoolSize} and/or
- * {@code setMaintainsParallelism}.
+ *
A {@code ForkJoinPool} is constructed with a given target
+ * parallelism level; by default, equal to the number of available
+ * processors. Unless configured otherwise via {@link
+ * #setMaintainsParallelism}, the pool attempts to maintain this
+ * number of active (or available) threads by dynamically adding,
+ * suspending, or resuming internal worker threads, even if some tasks
+ * are stalled waiting to join others. However, no such adjustments
+ * are performed in the face of blocked IO or other unmanaged
+ * synchronization. The nested {@link ManagedBlocker} interface
+ * enables extension of the kinds of synchronization accommodated.
+ * The target parallelism level may also be changed dynamically
+ * ({@link #setParallelism}). 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.
*
*
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.
*
+ *
Sample Usage. Normally a single {@code ForkJoinPool} is
+ * used for all parallel task execution in a program or subsystem.
+ * Otherwise, use would not usually outweigh the construction and
+ * bookkeeping overhead of creating a large set of threads. For
+ * example, a common pool could be used for the {@code SortTasks}
+ * illustrated in {@link RecursiveAction}. Because {@code
+ * ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
+ * daemon} mode, there is typically no need to explicitly {@link
+ * #shutdown} such a pool upon program exit.
+ *
+ *
+ * static final ForkJoinPool mainPool = new ForkJoinPool();
+ * ...
+ * public void sort(long[] array) {
+ * mainPool.invoke(new SortTask(array, 0, array.length));
+ * }
+ *
+ *
* Implementation notes: This implementation restricts the
* maximum number of running threads to 32767. Attempts to create
- * pools with greater than the maximum result in
- * IllegalArgumentExceptions.
+ * pools with greater than the maximum number result in
+ * {@code IllegalArgumentException}.
+ *
+ *
This implementation rejects submitted tasks (that is, by throwing
+ * {@link RejectedExecutionException}) only when the pool is shut down.
*
* @since 1.7
* @author Doug Lea
@@ -74,23 +105,23 @@ public class ForkJoinPool extends Abstra
private static final int MAX_THREADS = 0x7FFF;
/**
- * Factory for creating new ForkJoinWorkerThreads. A
- * ForkJoinWorkerThreadFactory must be defined and used for
- * ForkJoinWorkerThread subclasses that extend base functionality
- * or initialize threads with different contexts.
+ * Factory for creating new {@link ForkJoinWorkerThread}s.
+ * A {@code ForkJoinWorkerThreadFactory} must be defined and used
+ * for {@code ForkJoinWorkerThread} subclasses that extend base
+ * functionality or initialize threads with different contexts.
*/
public static interface ForkJoinWorkerThreadFactory {
/**
* 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
+ * Default ForkJoinWorkerThreadFactory implementation; creates a
* new ForkJoinWorkerThread.
*/
static class DefaultForkJoinWorkerThreadFactory
@@ -184,7 +215,7 @@ 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 +250,8 @@ 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 +263,25 @@ 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 +307,9 @@ 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 +321,7 @@ 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 +335,13 @@ 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;
}
/**
@@ -330,13 +366,14 @@ public class ForkJoinPool extends Abstra
// Constructors
/**
- * Creates a ForkJoinPool with a pool size equal to the number of
- * processors available on the system and using the default
- * ForkJoinWorkerThreadFactory,
+ * Creates a {@code ForkJoinPool} with parallelism equal to {@link
+ * java.lang.Runtime#availableProcessors}, and using the {@linkplain
+ * #defaultForkJoinWorkerThreadFactory default thread factory}.
+ *
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}{@code ("modifyThread")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool() {
this(Runtime.getRuntime().availableProcessors(),
@@ -344,47 +381,51 @@ public class ForkJoinPool extends Abstra
}
/**
- * Creates a ForkJoinPool with the indicated parallelism level
- * threads, and using the default ForkJoinWorkerThreadFactory,
- * @param parallelism the number of worker threads
+ * 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
+ * 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")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool(int parallelism) {
this(parallelism, defaultForkJoinWorkerThreadFactory);
}
/**
- * Creates a ForkJoinPool with parallelism equal to the number of
- * processors available on the system and using the given
- * ForkJoinWorkerThreadFactory,
+ * Creates a {@code ForkJoinPool} with parallelism equal to {@link
+ * java.lang.Runtime#availableProcessors}, and using the given
+ * thread factory.
+ *
* @param factory the factory for creating new threads
- * @throws NullPointerException if factory is null
+ * @throws NullPointerException if the factory is null
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}{@code ("modifyThread")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
this(Runtime.getRuntime().availableProcessors(), factory);
}
/**
- * Creates a ForkJoinPool with the given parallelism and factory.
+ * Creates a {@code ForkJoinPool} with the given parallelism and
+ * thread factory.
*
- * @param parallelism the targeted number of worker threads
+ * @param parallelism the parallelism level
* @param factory the factory for creating new threads
* @throws IllegalArgumentException if parallelism less than or
- * equal to zero, or greater than implementation limit
- * @throws NullPointerException if factory is null
+ * equal to zero, or greater than implementation limit
+ * @throws NullPointerException if the factory is null
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}{@code ("modifyThread")},
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
if (parallelism <= 0 || parallelism > MAX_THREADS)
@@ -405,9 +446,10 @@ 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
+ * @return new worker, or null if factory failed
*/
private ForkJoinWorkerThread createWorker(int index) {
Thread.UncaughtExceptionHandler h = ueh;
@@ -427,13 +469,23 @@ 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) {
+ 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;
}
/**
* 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 +499,7 @@ 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 +515,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Initialize workers if necessary
+ * Initializes workers if necessary.
*/
final void ensureWorkerInitialization() {
ForkJoinWorkerThread[] ws = workers;
@@ -474,14 +526,16 @@ public class ForkJoinPool extends Abstra
ws = workers;
if (ws == null) {
int ps = parallelism;
+ updateWorkerCount(ps);
ws = ensureWorkerArrayCapacity(ps);
for (int i = 0; i < ps; ++i) {
ForkJoinWorkerThread w = createWorker(i);
if (w != null) {
ws[i] = w;
w.start();
- updateWorkerCount(1);
}
+ else
+ updateWorkerCount(-1);
}
}
} finally {
@@ -530,6 +584,8 @@ 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)
@@ -539,11 +595,13 @@ 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
- * @throws RejectedExecutionException if pool is shut down
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
*/
public T invoke(ForkJoinTask task) {
doSubmit(task);
@@ -552,111 +610,114 @@ public class ForkJoinPool extends Abstra
/**
* Arranges for (asynchronous) execution of the given task.
+ *
* @param task the task
- * @throws NullPointerException if task is null
- * @throws RejectedExecutionException if pool is shut down
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
*/
- public void execute(ForkJoinTask task) {
+ public void execute(ForkJoinTask task) {
doSubmit(task);
}
// AbstractExecutorService methods
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public void execute(Runnable task) {
- doSubmit(new AdaptedRunnable(task, null));
+ ForkJoinTask job;
+ if (task instanceof ForkJoinTask) // avoid re-wrap
+ job = (ForkJoinTask) task;
+ else
+ job = ForkJoinTask.adapt(task, null);
+ doSubmit(job);
}
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public ForkJoinTask submit(Callable task) {
- ForkJoinTask job = new AdaptedCallable(task);
+ ForkJoinTask job = ForkJoinTask.adapt(task);
doSubmit(job);
return job;
}
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public ForkJoinTask submit(Runnable task, T result) {
- ForkJoinTask job = new AdaptedRunnable(task, result);
+ ForkJoinTask job = ForkJoinTask.adapt(task, result);
doSubmit(job);
return job;
}
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public ForkJoinTask submit(Runnable task) {
- ForkJoinTask job = new AdaptedRunnable(task, null);
+ ForkJoinTask job;
+ if (task instanceof ForkJoinTask) // avoid re-wrap
+ job = (ForkJoinTask) task;
+ else
+ job = ForkJoinTask.adapt(task, null);
doSubmit(job);
return job;
}
/**
- * Adaptor for Runnables. This implements RunnableFuture
- * to be compliant with AbstractExecutorService constraints
+ * 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
*/
- static final class AdaptedRunnable extends ForkJoinTask
- implements RunnableFuture {
- final Runnable runnable;
- final T resultOnCompletion;
- T result;
- AdaptedRunnable(Runnable runnable, T result) {
- if (runnable == null) throw new NullPointerException();
- this.runnable = runnable;
- this.resultOnCompletion = result;
- }
- public T getRawResult() { return result; }
- public void setRawResult(T v) { result = v; }
- public boolean exec() {
- runnable.run();
- result = resultOnCompletion;
- return true;
- }
- public void run() { invoke(); }
+ public ForkJoinTask submit(ForkJoinTask task) {
+ doSubmit(task);
+ return task;
}
- /**
- * Adaptor for Callables
- */
- static final class AdaptedCallable extends ForkJoinTask
- implements RunnableFuture {
- final Callable callable;
- T result;
- AdaptedCallable(Callable callable) {
- if (callable == null) throw new NullPointerException();
- this.callable = callable;
- }
- public T getRawResult() { return result; }
- public void setRawResult(T v) { result = v; }
- public boolean exec() {
- try {
- result = callable.call();
- return true;
- } catch (Error err) {
- throw err;
- } catch (RuntimeException rex) {
- throw rex;
- } catch (Exception ex) {
- throw new RuntimeException(ex);
- }
- }
- public void run() { invoke(); }
- }
+ /**
+ * @throws NullPointerException {@inheritDoc}
+ * @throws RejectedExecutionException {@inheritDoc}
+ */
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(ForkJoinTask.adapt(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 +728,8 @@ 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 +750,11 @@ 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 +782,14 @@ 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();
@@ -735,13 +798,15 @@ public class ForkJoinPool extends Abstra
final ReentrantLock lock = this.workerLock;
lock.lock();
try {
- if (!isTerminating()) {
+ if (isProcessingTasks()) {
int p = this.parallelism;
this.parallelism = parallelism;
- if (parallelism > p)
- createAndStartAddedWorkers();
- else
- trimSpares();
+ if (workers != null) {
+ if (parallelism > p)
+ createAndStartAddedWorkers();
+ else
+ trimSpares();
+ }
}
} finally {
lock.unlock();
@@ -750,9 +815,9 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns the targeted number of worker threads in this pool.
+ * Returns the targeted parallelism level of this pool.
*
- * @return the targeted number of worker threads in this pool
+ * @return the targeted parallelism level of this pool
*/
public int getParallelism() {
return parallelism;
@@ -761,7 +826,7 @@ 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
@@ -772,7 +837,10 @@ 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.
+ * 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() {
@@ -781,10 +849,12 @@ public class ForkJoinPool extends Abstra
/**
* Sets the maximum number of threads allowed to exist in the
- * pool, even if there are insufficient unblocked running threads.
- * Setting this value has no effect on current pool size. It
- * controls construction of new threads.
- * @throws IllegalArgumentException if negative or greater then
+ * pool. The given value should normally be greater than or equal
+ * to the {@link #getParallelism parallelism} level. Setting this
+ * value has no effect on current pool size. It controls
+ * construction of new threads.
+ *
+ * @throws IllegalArgumentException if negative or greater than
* internal implementation limit
*/
public void setMaximumPoolSize(int newMax) {
@@ -795,11 +865,11 @@ 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 +879,8 @@ 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 +891,13 @@ 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 +914,11 @@ 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 +939,7 @@ 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 +950,24 @@ 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 +978,10 @@ 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 +989,8 @@ 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 +1005,7 @@ 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() {
@@ -944,9 +1022,10 @@ 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
+ * 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.
+ *
* @return the number of queued submissions
*/
public int getQueuedSubmissionCount() {
@@ -954,8 +1033,9 @@ 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 +1046,8 @@ 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();
@@ -976,8 +1057,8 @@ public class ForkJoinPool extends Abstra
* Removes all available unexecuted submitted and forked tasks
* from scheduling queues and adds them to the given collection,
* without altering their execution status. These may include
- * artificially generated or wrapped tasks. This method is designed
- * to be invoked only when the pool is known to be
+ * artificially generated or wrapped tasks. This method is
+ * designed to be invoked only when the pool is known to be
* quiescent. Invocations at other times may not remove all
* tasks. A failure encountered while attempting to add elements
* to collection {@code c} may result in elements being in
@@ -985,10 +1066,11 @@ 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) {
@@ -1028,7 +1110,7 @@ public class ForkJoinPool extends Abstra
}
private static String runStateToString(int rs) {
- switch(rs) {
+ switch (rs) {
case RUNNING: return "Running";
case SHUTDOWN: return "Shutting down";
case TERMINATING: return "Terminating";
@@ -1045,32 +1127,48 @@ 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();
transitionRunStateTo(SHUTDOWN);
- if (canTerminateOnShutdown(runControl))
+ 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();
+ }
}
/**
- * Attempts to stop all actively executing tasks, and cancels all
- * waiting tasks. Tasks that are in the process of being
- * submitted or executed concurrently during the course of this
- * method may or may not be rejected. Unlike some other executors,
- * this method cancels rather than collects non-executed tasks
- * upon termination, so always returns an empty list. However, you
- * can use method {@code drainTasksTo} before invoking this
- * method to transfer unexecuted tasks to another collection.
+ * Attempts to cancel and/or stop all tasks, and reject all
+ * subsequently submitted tasks. Tasks that are in the process of
+ * being submitted or executed concurrently during the course of
+ * this method may or may not be rejected. This method cancels
+ * both existing and unexecuted tasks, in order to permit
+ * termination in the presence of task dependencies. So the method
+ * always returns an empty list (unlike the case for some other
+ * Executors).
+ *
* @return an empty list
* @throws SecurityException if a security manager exists and
* 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();
@@ -1089,12 +1187,16 @@ public class ForkJoinPool extends Abstra
/**
* Returns {@code true} if the process of termination has
- * commenced but possibly not yet completed.
+ * commenced but not yet completed. This method may be useful for
+ * debugging. A return of {@code true} reported a sufficient
+ * period after shutdown may indicate that submitted tasks have
+ * ignored or suppressed interruption, causing this executor not
+ * to properly terminate.
*
- * @return {@code true} if terminating
+ * @return {@code true} if terminating but not yet terminated
*/
public boolean isTerminating() {
- return runStateOf(runControl) >= TERMINATING;
+ return runStateOf(runControl) == TERMINATING;
}
/**
@@ -1107,6 +1209,14 @@ public class ForkJoinPool extends Abstra
}
/**
+ * Returns true if pool is not terminating or terminated.
+ * Used internally to suppress execution when terminating.
+ */
+ final boolean isProcessingTasks() {
+ return runStateOf(runControl) < TERMINATING;
+ }
+
+ /**
* Blocks until all tasks have completed execution after a shutdown
* request, or the timeout occurs, or the current thread is
* interrupted, whichever happens first.
@@ -1138,9 +1248,10 @@ 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) {
@@ -1159,7 +1270,7 @@ public class ForkJoinPool extends Abstra
transitionRunStateTo(TERMINATED);
termination.signalAll();
}
- else if (!isTerminating()) {
+ else if (isProcessingTasks()) {
tryShrinkWorkerArray();
tryResumeSpare(true); // allow replacement
}
@@ -1171,7 +1282,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Initiate termination.
+ * Initiates termination.
*/
private void terminate() {
if (transitionRunStateTo(TERMINATING)) {
@@ -1269,7 +1380,6 @@ public class ForkJoinPool extends Abstra
}
}
-
/*
* Nodes for event barrier to manage idle threads. Queue nodes
* are basic Treiber stack nodes, also used for spare stack.
@@ -1293,15 +1403,14 @@ public class ForkJoinPool extends Abstra
* 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.
+ * this, the first worker enqueued in method sync 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
@@ -1314,32 +1423,13 @@ public class ForkJoinPool extends Abstra
}
/**
- * Wakes up waiter, returning false if known to already
+ * Wakes up waiter, also clearing thread field
*/
- boolean signal() {
+ void 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);
+ if (t != null) {
+ thread = null;
+ LockSupport.unpark(t);
}
}
}
@@ -1348,9 +1438,8 @@ 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() {
+ final void ensureSync() {
long c = eventCount;
WaitQueueNode q;
while ((q = syncStack) != null && q.count < c) {
@@ -1361,7 +1450,6 @@ public class ForkJoinPool extends Abstra
break;
}
}
- return c;
}
/**
@@ -1369,93 +1457,82 @@ 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();
}
/**
* 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).
+ * appears to be non-empty, and OK if CAS to increment count
+ * fails (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();
+ if (syncStack != null) {
+ long c = eventCount;
+ casEventCount(c, c+1);
+ WaitQueueNode q = syncStack;
+ if (q != null && q.count <= c) {
+ if (casBarrierStack(q, q.next))
+ q.signal();
+ else
+ ensureSync(); // awaken all on contention
+ }
+ }
}
/**
- * Waits until event count advances from last value held by
- * caller, or if excess threads, caller is resumed as spare, or
+ * Possibly blocks until event count advances from last value held
+ * by caller, or if excess threads, caller is resumed as spare, or
* caller or pool is terminating. Updates caller's event on exit.
+ *
* @param w the calling worker thread
*/
final void sync(ForkJoinWorkerThread w) {
updateStealCount(w); // Transfer w's count while it is idle
- while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
+ if (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) {
long prev = w.lastEventCount;
WaitQueueNode node = null;
WaitQueueNode h;
- while (eventCount == prev &&
+ long c;
+ while ((c = 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);
+ if (!Thread.interrupted() &&
+ node.thread != null &&
+ eventCount == prev &&
+ (h != null || // cover signalWork race
+ (!ForkJoinWorkerThread.hasQueuedTasks(workers) &&
+ eventCount == prev)))
+ LockSupport.park(this);
+ c = eventCount;
+ if (node.thread != null) { // help signal if not unparked
+ node.thread = null;
+ if (c == prev)
+ casEventCount(prev, prev + 1);
+ }
break;
}
}
- long ec = ensureSync();
- if (ec != prev) {
- w.lastEventCount = ec;
- break;
- }
- }
- }
-
- /**
- * Returns 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 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);
+ w.lastEventCount = c;
+ ensureSync();
}
- return true;
}
/**
- * 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;
- long ec = ensureSync();
- if (ec == lc)
- return false;
- w.lastEventCount = ec;
- return true;
+ long wc = w.lastEventCount;
+ long c = eventCount;
+ if (wc != c)
+ w.lastEventCount = c;
+ ensureSync();
+ return wc != c || wc != eventCount;
}
// Parallelism maintenance
@@ -1467,7 +1544,7 @@ 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 +1567,13 @@ 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))) {
if (!needSpare(counts, maintainParallelism))
break;
if (joinMe.status < 0)
@@ -1510,7 +1588,8 @@ 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 +1607,13 @@ 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 +1633,7 @@ 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) {
@@ -1597,7 +1678,7 @@ public class ForkJoinPool extends Abstra
for (k = 0; k < len && ws[k] != null; ++k)
;
}
- if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
+ if (k < len && isProcessingTasks() && (w = createWorker(k)) != null) {
ws[k] = w;
w.start();
}
@@ -1612,27 +1693,35 @@ 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) {
WaitQueueNode node = null;
- int s;
- while (parallelism < runningCountOf(s = workerCounts)) {
+ for (;;) {
+ int s = workerCounts;
+ int rc = runningCountOf(s);
+ int tc = totalCountOf(s);
+ int ps = parallelism;
+ // use tc as bound if rc transiently out of sync
+ if (tc <= ps || rc <= ps)
+ return false; // not a spare
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;
- }
+ if (casWorkerCounts(s, workerCountsFor(tc, rc - 1)))
+ break;
}
- return false;
+ // push onto stack
+ do {} while (!casSpareStack(node.next = spareStack, node));
+ // block until released by resumeSpare
+ while (!Thread.interrupted() && node.thread != null)
+ LockSupport.park(this);
+ return true;
}
/**
* Tries to pop and resume a spare thread.
+ *
* @param updateCount if true, increment running count on success
* @return true if successful
*/
@@ -1651,6 +1740,7 @@ public class ForkJoinPool extends Abstra
/**
* Pops and resumes all spare threads. Same idea as ensureSync.
+ *
* @return true if any spares released
*/
private boolean resumeAllSpares() {
@@ -1692,81 +1782,86 @@ 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.).
+ * in {@link ForkJoinPool}s.
+ *
+ * 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).
+ *
*
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();
}
/**
* Blocks in accord with the given blocker. If the current thread
- * 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
- * it ({@link #getMaintainsParallelism}), this method attempts to
- * maintain the pool's nominal parallelism. Otherwise if 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;
- *
- * If the caller is a ForkJoinTask, then the pool may first
- * be expanded to ensure parallelism, and later adjusted.
+ * 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.
+ *
+ * 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.
+ *
+ *
If the caller is not a {@link ForkJoinTask}, this method is
+ * behaviorally equivalent to
+ *
{@code
+ * while (!blocker.isReleasable())
+ * if (blocker.block())
+ * return;
+ * }
+ *
+ * If the caller is a {@code 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 +1876,34 @@ 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
+ // AbstractExecutorService overrides. These rely on undocumented
+ // fact that ForkJoinTask.adapt returns ForkJoinTasks that also
+ // implement RunnableFuture.
protected RunnableFuture newTaskFor(Runnable runnable, T value) {
- return new AdaptedRunnable(runnable, value);
+ return (RunnableFuture) ForkJoinTask.adapt(runnable, value);
}
protected RunnableFuture newTaskFor(Callable callable) {
- return new AdaptedCallable(callable);
- }
-
-
- // 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();
- }
- }
+ return (RunnableFuture) ForkJoinTask.adapt(callable);
}
- 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));
- }
+ // Unsafe mechanics
- 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 +1920,43 @@ 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());
+ }
+ }
+ }
}