--- jsr166/src/jsr166y/ForkJoinPool.java 2009/01/07 19:12:36 1.3
+++ jsr166/src/jsr166y/ForkJoinPool.java 2009/07/22 20:55:22 1.15
@@ -27,7 +27,9 @@ import java.lang.reflect.*;
* (eventually blocking if none exist). This makes them efficient when
* most tasks spawn other subtasks (as do most ForkJoinTasks), as well
* as the mixed execution of some plain Runnable- or Callable- based
- * activities along with ForkJoinTasks. Otherwise, other
+ * activities along with ForkJoinTasks. When setting
+ * 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.
*
@@ -39,7 +41,7 @@ import java.lang.reflect.*;
* nested ManagedBlocker
interface enables extension of
* the kinds of synchronization accommodated. The target parallelism
* level may also be changed dynamically (setParallelism
)
- * and dynamically thread construction can be limited using methods
+ * and thread construction can be limited using methods
* setMaximumPoolSize
and/or
* setMaintainsParallelism
.
*
@@ -131,11 +133,11 @@ 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;
@@ -181,7 +183,7 @@ public class ForkJoinPool extends Abstra
/**
* 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 +206,18 @@ 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;
@@ -264,23 +271,29 @@ 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.
+ * Try incrementing active count; fail 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.
+ * Try decrementing active count; fail on contention.
+ * Possibly trigger 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;
}
/**
@@ -385,7 +398,7 @@ 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
}
/**
@@ -399,6 +412,7 @@ 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);
@@ -415,7 +429,8 @@ public class ForkJoinPool extends Abstra
}
/**
- * Create or resize array if necessary to hold newLength
+ * Create or resize array if necessary to hold newLength.
+ * Call only under exclusion
* @return the array
*/
private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
@@ -433,35 +448,42 @@ public class ForkJoinPool extends Abstra
*/
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.)
+ * Initialize 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();
}
}
@@ -507,8 +529,10 @@ public class ForkJoinPool extends Abstra
private void doSubmit(ForkJoinTask task) {
if (isShutdown())
throw new RejectedExecutionException();
+ if (workers == null)
+ ensureWorkerInitialization();
submissionQueue.offer(task);
- signalIdleWorkers(true);
+ signalIdleWorkers();
}
/**
@@ -677,10 +701,12 @@ public class ForkJoinPool extends Abstra
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);
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread w = ws[i];
+ if (w != null)
+ w.setUncaughtExceptionHandler(h);
+ }
}
} finally {
lock.unlock();
@@ -717,7 +743,7 @@ public class ForkJoinPool extends Abstra
} finally {
lock.unlock();
}
- signalIdleWorkers(false);
+ signalIdleWorkers();
}
/**
@@ -787,6 +813,42 @@ public class ForkJoinPool extends Abstra
}
/**
+ * 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 ather 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.
@@ -868,10 +930,12 @@ public class ForkJoinPool extends Abstra
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;
}
@@ -906,6 +970,35 @@ 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
+ * artifically generated or wrapped tasks. This method id 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 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.
@@ -966,8 +1059,10 @@ 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 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
@@ -1052,22 +1147,24 @@ 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();
}
/**
@@ -1077,11 +1174,11 @@ public class ForkJoinPool extends Abstra
if (transitionRunStateTo(TERMINATING)) {
stopAllWorkers();
resumeAllSpares();
- signalIdleWorkers(true);
+ signalIdleWorkers();
cancelQueuedSubmissions();
cancelQueuedWorkerTasks();
interruptUnterminatedWorkers();
- signalIdleWorkers(true); // resignal after interrupt
+ signalIdleWorkers(); // resignal after interrupt
}
}
@@ -1110,10 +1207,12 @@ 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.cancelTasks();
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ t.cancelTasks();
+ }
}
} finally {
lock.unlock();
@@ -1129,10 +1228,12 @@ 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.shutdownNow();
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ t.shutdownNow();
+ }
}
} finally {
lock.unlock();
@@ -1149,12 +1250,14 @@ 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) {
+ }
}
}
}
@@ -1165,75 +1268,92 @@ 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() {
+
+ /**
+ * Wake 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;
+ }
+
+ /**
+ * Await release on sync
+ */
+ void awaitSyncRelease(ForkJoinPool p) {
+ while (thread != null && !p.syncIsReleasable(this))
+ LockSupport.park(this);
+ }
+
+ /**
+ * Await 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;
}
@@ -1242,82 +1362,97 @@ 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);
+ 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.
+ * Signal 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
@@ -1372,7 +1507,8 @@ 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)) {
@@ -1408,26 +1544,8 @@ public class ForkJoinPool extends Abstra
return (tc < maxPoolSize &&
(rc == 0 || totalSurplus < 0 ||
(maintainParallelism &&
- runningDeficit > totalSurplus && mayHaveQueuedWork())));
- }
-
- /**
- * 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;
+ runningDeficit > totalSurplus &&
+ ForkJoinWorkerThread.hasQueuedTasks(workers))));
}
/**
@@ -1483,7 +1601,7 @@ public class ForkJoinPool extends Abstra
}
else
updateWorkerCount(-1); // adjust on failure
- signalIdleWorkers(false);
+ signalIdleWorkers();
}
/**
@@ -1499,17 +1617,12 @@ 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));
-
// block until released by resumeSpare
- while (node.thread != null) {
- if (!Thread.interrupted())
- LockSupport.park(this);
- }
- w.activate(); // help warm up
+ node.awaitSpareRelease();
return true;
}
}
@@ -1535,8 +1648,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Pop and resume all spare threads. Same idea as
- * releaseIdleWorkers.
+ * Pop and resume all spare threads. Same idea as ensureSync.
* @return true if any spares released
*/
private boolean resumeAllSpares() {
@@ -1577,16 +1689,6 @@ 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
@@ -1692,34 +1794,51 @@ public class ForkJoinPool extends Abstra
// Temporary Unsafe mechanics for preliminary release
+ private static Unsafe getUnsafe() throws Throwable {
+ try {
+ return Unsafe.getUnsafe();
+ } catch (SecurityException se) {
+ try {
+ return java.security.AccessController.doPrivileged
+ (new java.security.PrivilegedExceptionAction() {
+ public Unsafe run() throws Exception {
+ return getUnsafePrivileged();
+ }});
+ } catch (java.security.PrivilegedActionException e) {
+ throw e.getCause();
+ }
+ }
+ }
+
+ private static Unsafe getUnsafePrivileged()
+ throws NoSuchFieldException, IllegalAccessException {
+ Field f = Unsafe.class.getDeclaredField("theUnsafe");
+ f.setAccessible(true);
+ return (Unsafe) f.get(null);
+ }
+
+ private static long fieldOffset(String fieldName)
+ throws NoSuchFieldException {
+ return _unsafe.objectFieldOffset
+ (ForkJoinPool.class.getDeclaredField(fieldName));
+ }
static final Unsafe _unsafe;
static final long eventCountOffset;
static final long workerCountsOffset;
static final long runControlOffset;
- static final long barrierStackOffset;
+ static final long syncStackOffset;
static final long spareStackOffset;
static {
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) {
+ _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);
}
}
@@ -1737,6 +1856,6 @@ public class ForkJoinPool extends Abstra
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);
}
}