--- jsr166/src/jsr166y/ForkJoinPool.java 2009/01/06 14:30:31 1.1
+++ jsr166/src/jsr166y/ForkJoinPool.java 2009/07/26 05:55:34 1.25
@@ -5,56 +5,69 @@
*/
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;
/**
- * Host for a group of ForkJoinWorkerThreads. A ForkJoinPool provides
- * the entry point for tasks submitted 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
+ * 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.
*
- *
ForkJoinPools differ from other kinds of Executor mainly in that
- * they provide work-stealing: all threads in the pool
+ *
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) but
- * possibly less so otherwise. It is however fine to combine execution
- * of some plain Runnable- or Callable- based activities with that of
- * ForkJoinTasks.
+ * 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 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 have
- * blocked waiting to join others. However, no such adjustments are
- * performed in the face of blocked IO or other unmanaged
- * synchronization. The nested ManagedBlocker interface enables
- * extension of the kinds of synchronization accommodated.
- *
- *
The target parallelism level may also be set dynamically. You
- * can limit the number of threads dynamically constructed using
- * method setMaximumPoolSize and/or
- * setMaintainParallelism.
+ * 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}.
*
*
In addition to execution and lifecycle control methods, this
* class provides status check methods (for example
- * getStealCount) that are intended to aid in developing,
+ * {@code getStealCount}) that are intended to aid in developing,
* tuning, and monitoring fork/join applications. Also, method
- * toString returns indications of pool state in a convenient
- * form for informal monitoring.
+ * {@code toString} returns indications of pool state in a
+ * convenient form for informal monitoring.
*
*
Implementation notes: This implementation restricts the
- * maximum parallelism to 32767. Attempts to create pools with greater
- * than the maximum result in IllegalArgumentExceptions.
+ * maximum number of running threads to 32767. Attempts to create
+ * pools with greater than the maximum result in
+ * IllegalArgumentExceptions.
+ *
+ * @since 1.7
+ * @author Doug Lea
*/
-public class ForkJoinPool extends AbstractExecutorService
- implements ExecutorService {
+public class ForkJoinPool extends AbstractExecutorService {
/*
* See the extended comments interspersed below for design,
@@ -78,16 +91,16 @@ public class ForkJoinPool extends Abstra
* 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 pool is null
*/
public ForkJoinWorkerThread newThread(ForkJoinPool pool);
}
/**
- * Default ForkJoinWorkerThreadFactory implementation, creates a
+ * Default ForkJoinWorkerThreadFactory implementation; creates a
* new ForkJoinWorkerThread.
*/
- public static class DefaultForkJoinWorkerThreadFactory
+ static class DefaultForkJoinWorkerThreadFactory
implements ForkJoinWorkerThreadFactory {
public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
try {
@@ -99,14 +112,13 @@ public class ForkJoinPool extends Abstra
}
/**
- * The default ForkJoinWorkerThreadFactory, used unless overridden
- * in ForkJoinPool constructors.
+ * Creates a new ForkJoinWorkerThread. This factory is used unless
+ * overridden in ForkJoinPool constructors.
*/
- private static final DefaultForkJoinWorkerThreadFactory
+ public static final ForkJoinWorkerThreadFactory
defaultForkJoinWorkerThreadFactory =
new DefaultForkJoinWorkerThreadFactory();
-
/**
* Permission required for callers of methods that may start or
* kill threads.
@@ -131,11 +143,11 @@ public class ForkJoinPool extends Abstra
new AtomicInteger();
/**
- * Array holding all worker threads in the pool. Array size must
- * be a power of two. Updates and replacements are protected by
- * workerLock, but it is always kept in a consistent enough state
- * to be randomly accessed without locking by workers performing
- * work-stealing.
+ * Array holding all worker threads in the pool. Initialized upon
+ * first use. Array size must be a power of two. Updates and
+ * replacements are protected by workerLock, but it is always kept
+ * in a consistent enough state to be randomly accessed without
+ * locking by workers performing work-stealing.
*/
volatile ForkJoinWorkerThread[] workers;
@@ -151,7 +163,7 @@ public class ForkJoinPool extends Abstra
/**
* The uncaught exception handler used when any worker
- * abrupty terminates
+ * abruptly terminates
*/
private Thread.UncaughtExceptionHandler ueh;
@@ -179,9 +191,9 @@ 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 barrierStack;
+ private volatile WaitQueueNode syncStack;
/**
* The count for event barrier
@@ -204,13 +216,18 @@ public class ForkJoinPool extends Abstra
private volatile int parallelism;
/**
+ * True if use local fifo, not default lifo, for local polling
+ */
+ private volatile boolean locallyFifo;
+
+ /**
* Holds number of total (i.e., created and not yet terminated)
* and running (i.e., not blocked on joins or other managed sync)
* threads, packed into one int to ensure consistent snapshot when
* making decisions about creating and suspending spare
* threads. Updated only by CAS. Note: CASes in
- * updateRunningCount and preJoin 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;
@@ -219,26 +236,28 @@ public class ForkJoinPool extends Abstra
private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
/**
- * Add delta (which may be negative) to running count. This must
+ * 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)
+ * 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));
}
/**
- * Add delta (which may be negative) to both total and running
+ * Adds delta (which may be negative) to both total and running
* count. This must be called upon creation and termination of
* worker threads.
+ *
* @param delta the number to add
*/
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));
}
/**
@@ -264,32 +283,41 @@ public class ForkJoinPool extends Abstra
private static int runControlFor(int r, int a) { return (r << 16) + a; }
/**
- * Increment active count. 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 void incrementActiveCount() {
- int c;
- do;while (!casRunControl(c = runControl, c+1));
+ final boolean tryIncrementActiveCount() {
+ int c = runControl;
+ return casRunControl(c, c+1);
}
/**
- * Decrement active count; possibly trigger termination.
+ * 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 void decrementActiveCount() {
- int c, nextc;
- do;while (!casRunControl(c = runControl, nextc = c-1));
+ final boolean tryDecrementActiveCount() {
+ int c = runControl;
+ int nextc = c - 1;
+ if (!casRunControl(c, nextc))
+ return false;
if (canTerminateOnShutdown(nextc))
terminateOnShutdown();
+ return true;
}
/**
- * Return true if argument represents zero active count and
+ * Returns 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;
}
/**
@@ -315,12 +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}("modifyThread"),
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool() {
this(Runtime.getRuntime().availableProcessors(),
@@ -328,48 +357,49 @@ public class ForkJoinPool extends Abstra
}
/**
- * Creates a ForkJoinPool with the indicated parellelism level
- * threads, and using the default ForkJoinWorkerThreadFactory,
+ * Creates a ForkJoinPool with the indicated parallelism level
+ * 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}("modifyThread"),
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool(int parallelism) {
this(parallelism, defaultForkJoinWorkerThreadFactory);
}
/**
- * Creates a ForkJoinPool with a pool size equal to the number of
+ * 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}("modifyThread"),
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
this(Runtime.getRuntime().availableProcessors(), factory);
}
/**
- * Creates a ForkJoinPool with the indicated target number of
- * worker threads and the given factory.
+ * Creates a ForkJoinPool with the given parallelism and factory.
*
* @param parallelism the targeted number of worker threads
* @param factory the factory for creating new threads
* @throws IllegalArgumentException if parallelism less than or
- * equal to zero, or greater than implementation limit.
+ * equal to zero, or greater than implementation limit
* @throws NullPointerException if factory is null
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}("modifyThread"),
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
if (parallelism <= 0 || parallelism > MAX_THREADS)
@@ -386,11 +416,12 @@ public class ForkJoinPool extends Abstra
this.termination = workerLock.newCondition();
this.stealCount = new AtomicLong();
this.submissionQueue = new LinkedTransferQueue>();
- createAndStartInitialWorkers(parallelism);
+ // worker array and workers are lazily constructed
}
/**
- * 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
*/
@@ -400,6 +431,7 @@ public class ForkJoinPool extends Abstra
if (w != null) {
w.poolIndex = index;
w.setDaemon(true);
+ w.setAsyncMode(locallyFifo);
w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
if (h != null)
w.setUncaughtExceptionHandler(h);
@@ -408,15 +440,18 @@ public class ForkJoinPool extends Abstra
}
/**
- * Return a good size for worker array given pool size.
+ * 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)));
}
/**
- * Create or resize array if necessary to hold newLength
+ * Creates or resizes array if necessary to hold newLength.
+ * Call only under exclusion.
+ *
* @return the array
*/
private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
@@ -430,39 +465,46 @@ 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;
- int len = ws.length;
- int last = len - 1;
- while (last >= 0 && ws[last] == null)
- --last;
- int newLength = arraySizeFor(last+1);
- if (newLength < len)
- workers = Arrays.copyOf(ws, newLength);
+ if (ws != null) {
+ int len = ws.length;
+ int last = len - 1;
+ while (last >= 0 && ws[last] == null)
+ --last;
+ int newLength = arraySizeFor(last+1);
+ if (newLength < len)
+ workers = Arrays.copyOf(ws, newLength);
+ }
}
/**
- * Initial worker array and worker creation and startup. (This
- * must be done under lock to avoid interference by some of the
- * newly started threads while creating others.)
+ * Initializes workers if necessary.
*/
- private void createAndStartInitialWorkers(int ps) {
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
- for (int i = 0; i < ps; ++i) {
- ForkJoinWorkerThread w = createWorker(i);
- if (w != null) {
- ws[i] = w;
- w.start();
- updateWorkerCount(1);
+ final void ensureWorkerInitialization() {
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws == null) {
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ ws = workers;
+ if (ws == null) {
+ int ps = parallelism;
+ ws = ensureWorkerArrayCapacity(ps);
+ for (int i = 0; i < ps; ++i) {
+ ForkJoinWorkerThread w = createWorker(i);
+ if (w != null) {
+ ws[i] = w;
+ w.start();
+ updateWorkerCount(1);
+ }
+ }
}
+ } finally {
+ lock.unlock();
}
- } finally {
- lock.unlock();
}
}
@@ -500,71 +542,25 @@ public class ForkJoinPool extends Abstra
}
}
- /**
- * Sets the handler for internal worker threads that terminate due
- * to unrecoverable errors encountered while executing tasks.
- * Unless set, the current default or ThreadGroup handler is used
- * as handler.
- *
- * @param h the new handler
- * @return the old handler, or 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}("modifyThread"),
- */
- public Thread.UncaughtExceptionHandler
- setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
- checkPermission();
- Thread.UncaughtExceptionHandler old = null;
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- old = ueh;
- ueh = h;
- ForkJoinWorkerThread[] ws = workers;
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread w = ws[i];
- if (w != null)
- w.setUncaughtExceptionHandler(h);
- }
- } finally {
- lock.unlock();
- }
- return old;
- }
-
- /**
- * Returns the handler for internal worker threads that terminate
- * due to unrecoverable errors encountered while executing tasks.
- * @return the handler, or null if none
- */
- public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
- Thread.UncaughtExceptionHandler h;
- final ReentrantLock lock = this.workerLock;
- lock.lock();
- try {
- h = ueh;
- } finally {
- lock.unlock();
- }
- return h;
- }
-
// Execution methods
/**
* 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)
+ ensureWorkerInitialization();
submissionQueue.offer(task);
- signalIdleWorkers(true);
+ signalIdleWorkers();
}
/**
- * 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
@@ -577,6 +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
@@ -588,7 +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) {
@@ -604,22 +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;
}
- protected RunnableFuture newTaskFor(Runnable runnable, T value) {
- return new AdaptedRunnable(runnable, value);
- }
-
- protected RunnableFuture newTaskFor(Callable callable) {
- return new AdaptedCallable(callable);
+ /**
+ * 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 {
@@ -639,6 +651,7 @@ public class ForkJoinPool extends Abstra
return true;
}
public void run() { invoke(); }
+ private static final long serialVersionUID = 5232453952276885070L;
}
/**
@@ -667,29 +680,35 @@ public class ForkJoinPool extends Abstra
}
}
public void run() { invoke(); }
+ private static final long serialVersionUID = 2838392045355241008L;
}
public List> invokeAll(Collection extends Callable> 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
*/
@@ -698,14 +717,70 @@ public class ForkJoinPool extends Abstra
}
/**
- * Sets the target paralleism level of this pool.
+ * Returns the handler for internal worker threads that terminate
+ * due to unrecoverable errors encountered while executing tasks.
+ *
+ * @return the handler, or null if none
+ */
+ public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
+ Thread.UncaughtExceptionHandler h;
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ h = ueh;
+ } finally {
+ lock.unlock();
+ }
+ return h;
+ }
+
+ /**
+ * Sets the handler for internal worker threads that terminate due
+ * to unrecoverable errors encountered while executing tasks.
+ * Unless set, the current default or ThreadGroup handler is used
+ * as handler.
+ *
+ * @param h the new handler
+ * @return the old handler, or null if none
+ * @throws SecurityException if a security manager exists and
+ * the caller is not permitted to modify threads
+ * because it does not hold {@link
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
+ */
+ public Thread.UncaughtExceptionHandler
+ setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
+ checkPermission();
+ Thread.UncaughtExceptionHandler old = null;
+ final ReentrantLock lock = this.workerLock;
+ lock.lock();
+ try {
+ old = ueh;
+ ueh = h;
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread w = ws[i];
+ if (w != null)
+ w.setUncaughtExceptionHandler(h);
+ }
+ }
+ } finally {
+ lock.unlock();
+ }
+ return old;
+ }
+
+
+ /**
+ * Sets the target parallelism level of this pool.
+ *
* @param parallelism the target parallelism
* @throws IllegalArgumentException if parallelism less than or
- * equal to zero or greater than maximum size bounds.
+ * 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}("modifyThread"),
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public void setParallelism(int parallelism) {
checkPermission();
@@ -725,13 +800,11 @@ public class ForkJoinPool extends Abstra
} finally {
lock.unlock();
}
- signalIdleWorkers(false);
+ signalIdleWorkers();
}
/**
* Returns the targeted number of worker threads in this pool.
- * This value does not necessarily reflect transient changes as
- * threads are added, removed, or abruptly terminate.
*
* @return the targeted number of worker threads in this pool
*/
@@ -742,7 +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 getParallelism when threads are created to
+ * from {@code getParallelism} when threads are created to
* maintain parallelism when others are cooperatively blocked.
*
* @return the number of worker threads
@@ -754,6 +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() {
@@ -765,8 +839,9 @@ 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.
+ * internal implementation limit
*/
public void setMaximumPoolSize(int newMax) {
if (newMax < 0 || newMax > MAX_THREADS)
@@ -779,7 +854,8 @@ 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;
+ * This setting is by default true.
+ *
* @return true if maintains parallelism
*/
public boolean getMaintainsParallelism() {
@@ -790,6 +866,7 @@ 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
*/
public void setMaintainsParallelism(boolean enable) {
@@ -797,8 +874,44 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns the approximate number of worker threads that are not
- * blocked waiting to join tasks or for other managed
+ * Establishes local first-in-first-out scheduling mode for forked
+ * tasks that are never joined. This mode may be more appropriate
+ * than default locally stack-based mode in applications in which
+ * worker threads only process asynchronous tasks. This method is
+ * designed to be invoked only when 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
+ * @return the previous mode
+ */
+ public boolean setAsyncMode(boolean async) {
+ boolean oldMode = locallyFifo;
+ locallyFifo = async;
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ t.setAsyncMode(async);
+ }
+ }
+ return oldMode;
+ }
+
+ /**
+ * Returns 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
+ */
+ public boolean getAsyncMode() {
+ return locallyFifo;
+ }
+
+ /**
+ * Returns an estimate of the number of worker threads that are
+ * not blocked waiting to join tasks or for other managed
* synchronization.
*
* @return the number of worker threads
@@ -808,34 +921,37 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns the approximate number of threads that are currently
+ * 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.
+ *
+ * @return the number of active threads
*/
public int getActiveThreadCount() {
return activeCountOf(runControl);
}
/**
- * Returns the approximate number of threads that are currently
+ * 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.
+ *
+ * @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
+ * 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
*/
public boolean isQuiescent() {
@@ -847,18 +963,19 @@ 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.
+ *
+ * @return the number of steals
*/
public long getStealCount() {
return stealCount.get();
}
/**
- * 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();
@@ -867,29 +984,34 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns the total number of tasks currently held in queues by
- * worker threads (but not including tasks submitted to the pool
- * that have not begun executing). This value is only 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.
+ * Returns an estimate of the total number of tasks currently held
+ * in queues by worker threads (but not including tasks submitted
+ * to the pool that have not begun executing). This value is only
+ * 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() {
long count = 0;
ForkJoinWorkerThread[] ws = workers;
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread t = ws[i];
- if (t != null)
- count += t.getQueueSize();
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ count += t.getQueueSize();
+ }
}
return count;
}
/**
- * Returns the approximate number tasks submitted to this pool
+ * 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.
+ *
+ * @return the number of queued submissions
*/
public int getQueuedSubmissionCount() {
return submissionQueue.size();
@@ -898,7 +1020,8 @@ public class ForkJoinPool extends Abstra
/**
* Returns true if there are any tasks submitted to this pool
* that have not yet begun executing.
- * @return true if there are any queued submissions.
+ *
+ * @return {@code true} if there are any queued submissions
*/
public boolean hasQueuedSubmissions() {
return !submissionQueue.isEmpty();
@@ -908,6 +1031,7 @@ 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
*/
protected ForkJoinTask> pollSubmission() {
@@ -915,6 +1039,36 @@ 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
+ * 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
+ * neither, either or both collections when the associated
+ * 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) {
+ int n = submissionQueue.drainTo(c);
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread w = ws[i];
+ if (w != null)
+ n += w.drainTasksTo(c);
+ }
+ }
+ return n;
+ }
+
+ /**
* Returns a string identifying this pool, as well as its state,
* including indications of run state, parallelism level, and
* worker and task counts.
@@ -958,10 +1112,11 @@ 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}("modifyThread"),
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public void shutdown() {
checkPermission();
@@ -975,13 +1130,16 @@ public class ForkJoinPool extends Abstra
* 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,
- * so always returns an empty list.
+ * 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.
+ *
* @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}("modifyThread"),
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public List shutdownNow() {
checkPermission();
@@ -990,28 +1148,28 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns true if all tasks have completed following shut down.
+ * Returns {@code true} if all tasks have completed following shut down.
*
- * @return true if all tasks have completed following shut down
+ * @return {@code true} if all tasks have completed following shut down
*/
public boolean isTerminated() {
return runStateOf(runControl) == TERMINATED;
}
/**
- * Returns true if the process of termination has
+ * Returns {@code true} if the process of termination has
* commenced but possibly not yet completed.
*
- * @return true if terminating
+ * @return {@code true} if terminating
*/
public boolean isTerminating() {
return runStateOf(runControl) >= TERMINATING;
}
/**
- * Returns true if this pool has been shut down.
+ * Returns {@code true} if this pool has been shut down.
*
- * @return true if this pool has been shut down
+ * @return {@code true} if this pool has been shut down
*/
public boolean isShutdown() {
return runStateOf(runControl) >= SHUTDOWN;
@@ -1024,8 +1182,8 @@ public class ForkJoinPool extends Abstra
*
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
- * @return true if this executor terminated and
- * false if the timeout elapsed before termination
+ * @return {@code true} if this executor terminated and
+ * {@code false} if the timeout elapsed before termination
* @throws InterruptedException if interrupted while waiting
*/
public boolean awaitTermination(long timeout, TimeUnit unit)
@@ -1049,9 +1207,10 @@ 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) {
@@ -1061,41 +1220,43 @@ public class ForkJoinPool extends Abstra
lock.lock();
try {
ForkJoinWorkerThread[] ws = workers;
- int idx = w.poolIndex;
- if (idx >= 0 && idx < ws.length && ws[idx] == w)
- ws[idx] = null;
- if (totalCountOf(workerCounts) == 0) {
- terminate(); // no-op if already terminating
- transitionRunStateTo(TERMINATED);
- termination.signalAll();
- }
- else if (!isTerminating()) {
- tryShrinkWorkerArray();
- tryResumeSpare(true); // allow replacement
+ if (ws != null) {
+ int idx = w.poolIndex;
+ if (idx >= 0 && idx < ws.length && ws[idx] == w)
+ ws[idx] = null;
+ if (totalCountOf(workerCounts) == 0) {
+ terminate(); // no-op if already terminating
+ transitionRunStateTo(TERMINATED);
+ termination.signalAll();
+ }
+ else if (!isTerminating()) {
+ tryShrinkWorkerArray();
+ tryResumeSpare(true); // allow replacement
+ }
}
} finally {
lock.unlock();
}
- signalIdleWorkers(false);
+ signalIdleWorkers();
}
/**
- * Initiate termination.
+ * Initiates termination.
*/
private void terminate() {
if (transitionRunStateTo(TERMINATING)) {
stopAllWorkers();
resumeAllSpares();
- signalIdleWorkers(true);
+ signalIdleWorkers();
cancelQueuedSubmissions();
cancelQueuedWorkerTasks();
interruptUnterminatedWorkers();
- signalIdleWorkers(true); // resignal after interrupt
+ signalIdleWorkers(); // resignal after interrupt
}
}
/**
- * Possibly terminate when on shutdown state
+ * Possibly terminates when on shutdown state.
*/
private void terminateOnShutdown() {
if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
@@ -1103,7 +1264,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Clear out and cancel submissions
+ * Clears out and cancels submissions.
*/
private void cancelQueuedSubmissions() {
ForkJoinTask> task;
@@ -1112,17 +1273,19 @@ public class ForkJoinPool extends Abstra
}
/**
- * Clean out worker queues.
+ * Cleans out worker queues.
*/
private void cancelQueuedWorkerTasks() {
final ReentrantLock lock = this.workerLock;
lock.lock();
try {
ForkJoinWorkerThread[] ws = workers;
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread t = ws[i];
- if (t != null)
- t.cancelTasks();
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ t.cancelTasks();
+ }
}
} finally {
lock.unlock();
@@ -1130,18 +1293,20 @@ public class ForkJoinPool extends Abstra
}
/**
- * Set each worker's status to terminating. Requires lock to avoid
- * conflicts with add/remove
+ * Sets each worker's status to terminating. Requires lock to avoid
+ * conflicts with add/remove.
*/
private void stopAllWorkers() {
final ReentrantLock lock = this.workerLock;
lock.lock();
try {
ForkJoinWorkerThread[] ws = workers;
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread t = ws[i];
- if (t != null)
- t.shutdownNow();
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ t.shutdownNow();
+ }
}
} finally {
lock.unlock();
@@ -1149,7 +1314,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Interrupt all unterminated workers. This is not required for
+ * Interrupts all unterminated workers. This is not required for
* sake of internal control, but may help unstick user code during
* shutdown.
*/
@@ -1158,12 +1323,14 @@ public class ForkJoinPool extends Abstra
lock.lock();
try {
ForkJoinWorkerThread[] ws = workers;
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread t = ws[i];
- if (t != null && !t.isTerminated()) {
- try {
- t.interrupt();
- } catch (SecurityException ignore) {
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null && !t.isTerminated()) {
+ try {
+ t.interrupt();
+ } catch (SecurityException ignore) {
+ }
}
}
}
@@ -1174,75 +1341,93 @@ public class ForkJoinPool extends Abstra
/*
- * Nodes for event barrier to manage idle threads.
+ * Nodes for event barrier to manage idle threads. Queue nodes
+ * are basic Treiber stack nodes, also used for spare stack.
*
* The event barrier has an event count and a wait queue (actually
* a Treiber stack). Workers are enabled to look for work when
- * the eventCount is incremented. If they fail to find some,
- * they may wait for next count. Synchronization events occur only
- * in enough contexts to maintain overall liveness:
+ * the eventCount is incremented. If they fail to find work, they
+ * may wait for next count. Upon release, threads help others wake
+ * up.
+ *
+ * Synchronization events occur only in enough contexts to
+ * maintain overall liveness:
*
* - Submission of a new task to the pool
- * - Creation or termination of a worker
+ * - Resizes or other changes to the workers array
* - pool termination
* - A worker pushing a task on an empty queue
*
- * The last case (pushing a task) occurs often enough, and is
- * heavy enough compared to simple stack pushes to require some
- * special handling: Method signalNonEmptyWorkerQueue 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, a worker in sync
- * rescans for tasks after being enqueued if it was the first to
- * enqueue, and aborts the wait if finding one, also helping to
- * signal others. This works well because the worker has nothing
- * better to do anyway, and so might as well help alleviate the
- * overhead and contention on the threads actually doing work.
- *
- * Queue nodes are basic Treiber stack nodes, also used for spare
- * stack.
+ * The case of pushing a task occurs often enough, and is heavy
+ * enough compared to simple stack pushes, to require special
+ * handling: Method signalWork returns without advancing count if
+ * the queue appears to be empty. This would ordinarily result in
+ * races causing some queued waiters not to be woken up. To avoid
+ * this, the first worker enqueued in method sync (see
+ * syncIsReleasable) rescans for tasks after being enqueued, and
+ * helps signal if any are found. This works well because the
+ * worker has nothing better to do, and so might as well help
+ * alleviate the overhead and contention on the threads actually
+ * doing work. Also, since event counts increments on task
+ * availability exist to maintain liveness (rather than to force
+ * refreshes etc), it is OK for callers to exit early if
+ * contending with another signaller.
*/
static final class WaitQueueNode {
WaitQueueNode next; // only written before enqueued
volatile ForkJoinWorkerThread thread; // nulled to cancel wait
final long count; // unused for spare stack
- WaitQueueNode(ForkJoinWorkerThread w, long c) {
+
+ WaitQueueNode(long c, ForkJoinWorkerThread w) {
count = c;
thread = w;
}
- final boolean signal() {
+
+ /**
+ * Wakes up waiter, returning false if known to already
+ */
+ boolean signal() {
ForkJoinWorkerThread t = thread;
+ if (t == null)
+ return false;
thread = null;
- if (t != null) {
- LockSupport.unpark(t);
- return true;
+ 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);
}
- return false;
}
}
/**
- * Release at least one thread waiting for event count to advance,
- * if one exists. If initial attempt fails, release all threads.
- * @param all if false, at first try to only release one thread
- * @return current event
+ * 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
*/
- private long releaseIdleWorkers(boolean all) {
- long c;
- for (;;) {
- WaitQueueNode q = barrierStack;
- c = eventCount;
- long qc;
- if (q == null || (qc = q.count) >= c)
- break;
- if (!all) {
- if (casBarrierStack(q, q.next) && q.signal())
- break;
- all = true;
- }
- else if (casBarrierStack(q, null)) {
+ final long ensureSync() {
+ long c = eventCount;
+ WaitQueueNode q;
+ while ((q = syncStack) != null && q.count < c) {
+ if (casBarrierStack(q, null)) {
do {
- q.signal();
+ q.signal();
} while ((q = q.next) != null);
break;
}
@@ -1251,94 +1436,111 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns current barrier event count
- * @return current barrier event count
+ * Increments event count and releases waiting threads.
*/
- final long getEventCount() {
- long ec = eventCount;
- releaseIdleWorkers(true); // release to ensure accurate result
- return ec;
- }
-
- /**
- * Increment event count and release at least one waiting thread,
- * if one exists (released threads will in turn wake up others).
- * @param all if true, try to wake up all
- */
- final void signalIdleWorkers(boolean all) {
+ private void signalIdleWorkers() {
long c;
- do;while (!casEventCount(c = eventCount, c+1));
- releaseIdleWorkers(all);
+ do {} while (!casEventCount(c = eventCount, c+1));
+ ensureSync();
}
/**
- * Wake up threads waiting to steal a task. Because method
- * sync rechecks availability, it is OK to only proceed if
- * queue appears to be non-empty.
+ * Signals threads waiting to poll a task. Because method sync
+ * rechecks availability, it is OK to only proceed if queue
+ * appears to be non-empty, and OK to skip under contention to
+ * increment count (since some other thread succeeded).
*/
- final void signalNonEmptyWorkerQueue() {
- // If CAS fails another signaller must have succeeded
+ final void signalWork() {
long c;
- if (barrierStack != null && casEventCount(c = eventCount, c+1))
- releaseIdleWorkers(false);
+ WaitQueueNode q;
+ if (syncStack != null &&
+ casEventCount(c = eventCount, c+1) &&
+ (((q = syncStack) != null && q.count <= c) &&
+ (!casBarrierStack(q, q.next) || !q.signal())))
+ ensureSync();
}
/**
- * Waits until event count advances from count, or some thread is
- * waiting on a previous count, or there is stealable work
- * available. Help wake up others on release.
+ * 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
- * @param prev previous value returned by sync (or 0)
- * @return current event count
*/
- final long sync(ForkJoinWorkerThread w, long prev) {
- updateStealCount(w);
+ final void sync(ForkJoinWorkerThread w) {
+ updateStealCount(w); // Transfer w's count while it is idle
- while (!w.isShutdown() && !isTerminating() &&
- (parallelism >= runningCountOf(workerCounts) ||
- !suspendIfSpare(w))) { // prefer suspend to waiting here
+ while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
+ long prev = w.lastEventCount;
WaitQueueNode node = null;
- boolean queued = false;
- for (;;) {
- if (!queued) {
- if (eventCount != prev)
- break;
- WaitQueueNode h = barrierStack;
- if (h != null && h.count != prev)
- break; // release below and maybe retry
- if (node == null)
- node = new WaitQueueNode(w, prev);
- queued = casBarrierStack(node.next = h, node);
- }
- else if (Thread.interrupted() ||
- node.thread == null ||
- (node.next == null && w.prescan()) ||
- eventCount != prev) {
- node.thread = null;
- if (eventCount == prev) // help trigger
- casEventCount(prev, prev+1);
+ WaitQueueNode h;
+ while (eventCount == prev &&
+ ((h = syncStack) == null || h.count == prev)) {
+ if (node == null)
+ node = new WaitQueueNode(prev, w);
+ if (casBarrierStack(node.next = h, node)) {
+ node.awaitSyncRelease(this);
break;
}
- else
- LockSupport.park(this);
}
+ 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 (releaseIdleWorkers(false) != prev)
- return ec;
+ if (prev <= ec) // help signal
+ casEventCount(ec, ec+1);
}
- return prev; // return old count if aborted
+ return true;
+ }
+
+ /**
+ * Returns true if a new sync event occurred since last call to
+ * sync or this method, if so, updating caller's count.
+ */
+ final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
+ long lc = w.lastEventCount;
+ long ec = ensureSync();
+ if (ec == lc)
+ return false;
+ w.lastEventCount = ec;
+ return true;
}
// Parallelism maintenance
/**
- * Decrement running count; if too low, add spare.
+ * Decrements running count; if too low, adds spare.
*
* Conceptually, all we need to do here is add or resume a
* spare thread when one is about to block (and remove or
* suspend it later when unblocked -- see suspendIfSpare).
* However, implementing this idea requires coping with
- * several problems: We have imperfect information about the
+ * 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
@@ -1352,7 +1554,7 @@ public class ForkJoinPool extends Abstra
* only be suspended or removed when they are idle, not
* immediately when they aren't needed. So adding threads will
* raise parallelism level for longer than necessary. Also,
- * FJ applications often enounter highly transient peaks when
+ * FJ applications often encounter highly transient peaks when
* many threads are blocked joining, but for less time than it
* takes to create or resume spares.
*
@@ -1361,12 +1563,14 @@ 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)
@@ -1381,7 +1585,8 @@ 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)) {
@@ -1405,6 +1610,7 @@ public class ForkJoinPool extends Abstra
* 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
*/
@@ -1417,31 +1623,14 @@ public class ForkJoinPool extends Abstra
return (tc < maxPoolSize &&
(rc == 0 || totalSurplus < 0 ||
(maintainParallelism &&
- runningDeficit > totalSurplus && mayHaveQueuedWork())));
+ runningDeficit > totalSurplus &&
+ ForkJoinWorkerThread.hasQueuedTasks(workers))));
}
/**
- * Returns true if at least one worker queue appears to be
- * nonempty. This is expensive but not often called. It is not
- * critical that this be accurate, but if not, more or fewer
- * running threads than desired might be maintained.
- */
- private boolean mayHaveQueuedWork() {
- ForkJoinWorkerThread[] ws = workers;
- int len = ws.length;
- ForkJoinWorkerThread v;
- for (int i = 0; i < len; ++i) {
- if ((v = ws[i]) != null && v.getRawQueueSize() > 0) {
- releaseIdleWorkers(false); // help wake up stragglers
- return true;
- }
- }
- return false;
- }
-
- /**
- * Add a spare worker if lock available and no more than the
- * expected numbers of threads exist
+ * 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) {
@@ -1474,7 +1663,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Add the kth spare worker. On entry, pool coounts are already
+ * Adds the kth spare worker. On entry, pool counts are already
* adjusted to reflect addition.
*/
private void createAndStartSpare(int k) {
@@ -1486,21 +1675,22 @@ public class ForkJoinPool extends Abstra
for (k = 0; k < len && ws[k] != null; ++k)
;
}
- if (k < len && (w = createWorker(k)) != null) {
+ if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
ws[k] = w;
w.start();
}
else
updateWorkerCount(-1); // adjust on failure
- signalIdleWorkers(false);
+ signalIdleWorkers();
}
/**
- * Suspend calling thread w if there are excess threads. Called
- * only from sync. Spares are enqueued in a Treiber stack
- * using the same WaitQueueNodes as barriers. They are resumed
- * mainly in preJoin, but are also woken on pool events that
- * require all threads to check run state.
+ * Suspends calling thread w if there are excess threads. Called
+ * only from sync. Spares are enqueued in a Treiber stack using
+ * the same WaitQueueNodes as barriers. They are resumed mainly
+ * in preJoin, but are also woken on pool events that require all
+ * threads to check run state.
+ *
* @param w the caller
*/
private boolean suspendIfSpare(ForkJoinWorkerThread w) {
@@ -1508,17 +1698,12 @@ public class ForkJoinPool extends Abstra
int s;
while (parallelism < runningCountOf(s = workerCounts)) {
if (node == null)
- node = new WaitQueueNode(w, 0);
+ 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
- while (node.thread != null) {
- if (!Thread.interrupted())
- LockSupport.park(this);
- }
- w.activate(); // help warm up
+ node.awaitSpareRelease();
return true;
}
}
@@ -1526,7 +1711,8 @@ public class ForkJoinPool extends Abstra
}
/**
- * Try to pop and resume a spare thread.
+ * Tries to pop and resume a spare thread.
+ *
* @param updateCount if true, increment running count on success
* @return true if successful
*/
@@ -1544,8 +1730,8 @@ public class ForkJoinPool extends Abstra
}
/**
- * Pop and resume all spare threads. Same idea as
- * releaseIdleWorkers.
+ * Pops and resumes all spare threads. Same idea as ensureSync.
+ *
* @return true if any spares released
*/
private boolean resumeAllSpares() {
@@ -1563,7 +1749,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Pop and shutdown excessive spare threads. Call only while
+ * Pops and shuts down excessive spare threads. Call only while
* holding lock. This is not guaranteed to eliminate all excess
* threads, only those suspended as spares, which are the ones
* unlikely to be needed in the future.
@@ -1586,48 +1772,39 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns approximate number of spares, just for diagnostics.
- */
- private int countSpares() {
- int sum = 0;
- for (WaitQueueNode q = spareStack; q != null; q = q.next)
- ++sum;
- return sum;
- }
-
- /**
* Interface for extending managed parallelism for tasks running
* in ForkJoinPools. A ManagedBlocker provides two methods.
- * Method isReleasable must return true if blocking is not
- * necessary. Method block blocks the current thread
- * if necessary (perhaps internally invoking isReleasable before
- * actually blocking.).
+ * Method {@code isReleasable} must return 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).
+ * if isReleasable would return true)
* @throws InterruptedException if interrupted while waiting
- * (the method is not required to do so, but is allowe to).
+ * (the method is not required to do so, but is allowed to)
*/
boolean block() throws InterruptedException;
@@ -1642,20 +1819,20 @@ 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
- * maintainParallelism is true and the pool supports it
- * (see getMaintainsParallelism), this method attempts to
- * maintain the pool's nominal parallelism. Otherwise if activates
+ * {@code maintainParallelism} is 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 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.
*
@@ -1664,14 +1841,14 @@ public class ForkJoinPool extends Abstra
* 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.
+ * @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 ||
@@ -1686,56 +1863,82 @@ 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);
+ }
+
+ protected RunnableFuture newTaskFor(Callable callable) {
+ return new AdaptedCallable(callable);
}
- // Temporary Unsafe mechanics for preliminary release
+ // Unsafe mechanics for jsr166y 3rd party package.
+ 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 {
+ return getUnsafeByReflection();
+ }});
+ } catch (java.security.PrivilegedActionException e) {
+ throw new RuntimeException("Could not initialize intrinsics",
+ e.getCause());
+ }
+ }
+ }
- static final Unsafe _unsafe;
- static final long eventCountOffset;
- static final long workerCountsOffset;
- static final long runControlOffset;
- static final long barrierStackOffset;
- static final long spareStackOffset;
+ private static sun.misc.Unsafe getUnsafeByReflection()
+ throws NoSuchFieldException, IllegalAccessException {
+ java.lang.reflect.Field f =
+ sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
+ f.setAccessible(true);
+ return (sun.misc.Unsafe) f.get(null);
+ }
- static {
+ private static long fieldOffset(String fieldName, Class> klazz) {
try {
- if (ForkJoinPool.class.getClassLoader() != null) {
- Field f = Unsafe.class.getDeclaredField("theUnsafe");
- f.setAccessible(true);
- _unsafe = (Unsafe)f.get(null);
- }
- else
- _unsafe = Unsafe.getUnsafe();
- eventCountOffset = _unsafe.objectFieldOffset
- (ForkJoinPool.class.getDeclaredField("eventCount"));
- workerCountsOffset = _unsafe.objectFieldOffset
- (ForkJoinPool.class.getDeclaredField("workerCounts"));
- runControlOffset = _unsafe.objectFieldOffset
- (ForkJoinPool.class.getDeclaredField("runControl"));
- barrierStackOffset = _unsafe.objectFieldOffset
- (ForkJoinPool.class.getDeclaredField("barrierStack"));
- spareStackOffset = _unsafe.objectFieldOffset
- (ForkJoinPool.class.getDeclaredField("spareStack"));
- } catch (Exception e) {
- throw new RuntimeException("Could not initialize intrinsics", e);
+ return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName));
+ } catch (NoSuchFieldException e) {
+ // Convert Exception to Error
+ NoSuchFieldError error = new NoSuchFieldError(fieldName);
+ error.initCause(e);
+ throw error;
}
}
+ private static final sun.misc.Unsafe UNSAFE = getUnsafe();
+ private static final long eventCountOffset =
+ fieldOffset("eventCount", ForkJoinPool.class);
+ private static final long workerCountsOffset =
+ fieldOffset("workerCounts", ForkJoinPool.class);
+ private static final long runControlOffset =
+ fieldOffset("runControl", ForkJoinPool.class);
+ private static final long syncStackOffset =
+ fieldOffset("syncStack",ForkJoinPool.class);
+ private static final long spareStackOffset =
+ fieldOffset("spareStack", ForkJoinPool.class);
+
private boolean casEventCount(long cmp, long val) {
- return _unsafe.compareAndSwapLong(this, eventCountOffset, cmp, val);
+ return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
}
private boolean casWorkerCounts(int cmp, int val) {
- return _unsafe.compareAndSwapInt(this, workerCountsOffset, cmp, val);
+ return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
}
private boolean casRunControl(int cmp, int val) {
- return _unsafe.compareAndSwapInt(this, runControlOffset, cmp, val);
+ return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
}
private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
- return _unsafe.compareAndSwapObject(this, spareStackOffset, cmp, val);
+ return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
}
private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
- return _unsafe.compareAndSwapObject(this, barrierStackOffset, cmp, val);
+ return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
}
}