--- jsr166/src/jsr166e/ForkJoinPool.java 2012/11/21 22:15:41 1.22
+++ jsr166/src/jsr166e/ForkJoinPool.java 2013/06/19 14:55:40 1.58
@@ -6,6 +6,7 @@
package jsr166e;
+import java.lang.Thread.UncaughtExceptionHandler;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
@@ -17,6 +18,7 @@ import java.util.concurrent.ExecutorServ
import java.util.concurrent.Future;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.RunnableFuture;
+import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;
/**
@@ -49,9 +51,9 @@ import java.util.concurrent.TimeUnit;
* level; by default, equal to the number of available processors. The
* pool attempts to maintain enough active (or available) threads by
* dynamically adding, suspending, or resuming internal worker
- * threads, even if some tasks are stalled waiting to join
- * others. However, no such adjustments are guaranteed in the face of
- * blocked IO or other unmanaged synchronization. The nested {@link
+ * threads, even if some tasks are stalled waiting to join others.
+ * However, no such adjustments are guaranteed in the face of blocked
+ * I/O or other unmanaged synchronization. The nested {@link
* ManagedBlocker} interface enables extension of the kinds of
* synchronization accommodated.
*
@@ -75,38 +77,45 @@ import java.util.concurrent.TimeUnit;
* there is little difference among choice of methods.
*
*
+ * Summary of task execution methods
*
* |
* Call from non-fork/join clients |
* Call from within fork/join computations |
*
*
- * Arrange async execution |
+ * Arrange async execution |
* {@link #execute(ForkJoinTask)} |
* {@link ForkJoinTask#fork} |
*
*
- * Await and obtain result |
+ * Await and obtain result |
* {@link #invoke(ForkJoinTask)} |
* {@link ForkJoinTask#invoke} |
*
*
- * Arrange exec and obtain Future |
+ * Arrange exec and obtain Future |
* {@link #submit(ForkJoinTask)} |
* {@link ForkJoinTask#fork} (ForkJoinTasks are Futures) |
*
*
*
* The common pool is by default constructed with default
- * parameters, but these may be controlled by setting three {@link
- * System#getProperty properties} with prefix {@code
- * java.util.concurrent.ForkJoinPool.common}: {@code parallelism} --
- * an integer greater than zero, {@code threadFactory} -- the class
- * name of a {@link ForkJoinWorkerThreadFactory}, and {@code
- * exceptionHandler} -- the class name of a {@link
- * java.lang.Thread.UncaughtExceptionHandler
- * Thread.UncaughtExceptionHandler}. Upon any error in establishing
- * these settings, default parameters are used.
+ * parameters, but these may be controlled by setting three
+ * {@linkplain System#getProperty system properties}:
+ *
+ * - {@code java.util.concurrent.ForkJoinPool.common.parallelism}
+ * - the parallelism level, a non-negative integer
+ *
- {@code java.util.concurrent.ForkJoinPool.common.threadFactory}
+ * - the class name of a {@link ForkJoinWorkerThreadFactory}
+ *
- {@code java.util.concurrent.ForkJoinPool.common.exceptionHandler}
+ * - the class name of a {@link UncaughtExceptionHandler}
+ *
+ * The system class loader is used to load these classes.
+ * Upon any error in establishing these settings, default parameters
+ * are used. It is possible to disable or limit the use of threads in
+ * the common pool by setting the parallelism property to zero, and/or
+ * using a factory that may return {@code null}.
*
* Implementation notes: This implementation restricts the
* maximum number of running threads to 32767. Attempts to create
@@ -152,32 +161,35 @@ public class ForkJoinPool extends Abstra
* (http://research.sun.com/scalable/pubs/index.html) and
* "Idempotent work stealing" by Michael, Saraswat, and Vechev,
* PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186).
- * The main differences ultimately stem from GC requirements that
- * we null out taken slots as soon as we can, to maintain as small
- * a footprint as possible even in programs generating huge
- * numbers of tasks. To accomplish this, we shift the CAS
- * arbitrating pop vs poll (steal) from being on the indices
- * ("base" and "top") to the slots themselves. So, both a
- * successful pop and poll mainly entail a CAS of a slot from
- * non-null to null. Because we rely on CASes of references, we
- * do not need tag bits on base or top. They are simple ints as
- * used in any circular array-based queue (see for example
- * ArrayDeque). Updates to the indices must still be ordered in a
- * way that guarantees that top == base means the queue is empty,
- * but otherwise may err on the side of possibly making the queue
- * appear nonempty when a push, pop, or poll have not fully
- * committed. Note that this means that the poll operation,
- * considered individually, is not wait-free. One thief cannot
- * successfully continue until another in-progress one (or, if
- * previously empty, a push) completes. However, in the
- * aggregate, we ensure at least probabilistic non-blockingness.
- * If an attempted steal fails, a thief always chooses a different
- * random victim target to try next. So, in order for one thief to
- * progress, it suffices for any in-progress poll or new push on
- * any empty queue to complete. (This is why we normally use
- * method pollAt and its variants that try once at the apparent
- * base index, else consider alternative actions, rather than
- * method poll.)
+ * See also "Correct and Efficient Work-Stealing for Weak Memory
+ * Models" by Le, Pop, Cohen, and Nardelli, PPoPP 2013
+ * (http://www.di.ens.fr/~zappa/readings/ppopp13.pdf) for an
+ * analysis of memory ordering (atomic, volatile etc) issues. The
+ * main differences ultimately stem from GC requirements that we
+ * null out taken slots as soon as we can, to maintain as small a
+ * footprint as possible even in programs generating huge numbers
+ * of tasks. To accomplish this, we shift the CAS arbitrating pop
+ * vs poll (steal) from being on the indices ("base" and "top") to
+ * the slots themselves. So, both a successful pop and poll
+ * mainly entail a CAS of a slot from non-null to null. Because
+ * we rely on CASes of references, we do not need tag bits on base
+ * or top. They are simple ints as used in any circular
+ * array-based queue (see for example ArrayDeque). Updates to the
+ * indices must still be ordered in a way that guarantees that top
+ * == base means the queue is empty, but otherwise may err on the
+ * side of possibly making the queue appear nonempty when a push,
+ * pop, or poll have not fully committed. Note that this means
+ * that the poll operation, considered individually, is not
+ * wait-free. One thief cannot successfully continue until another
+ * in-progress one (or, if previously empty, a push) completes.
+ * However, in the aggregate, we ensure at least probabilistic
+ * non-blockingness. If an attempted steal fails, a thief always
+ * chooses a different random victim target to try next. So, in
+ * order for one thief to progress, it suffices for any
+ * in-progress poll or new push on any empty queue to
+ * complete. (This is why we normally use method pollAt and its
+ * variants that try once at the apparent base index, else
+ * consider alternative actions, rather than method poll.)
*
* This approach also enables support of a user mode in which local
* task processing is in FIFO, not LIFO order, simply by using
@@ -196,18 +208,18 @@ public class ForkJoinPool extends Abstra
* for work-stealing (this would contaminate lifo/fifo
* processing). Instead, we randomly associate submission queues
* with submitting threads, using a form of hashing. The
- * ThreadLocal Submitter class contains a value initially used as
- * a hash code for choosing existing queues, but may be randomly
- * repositioned upon contention with other submitters. In
- * essence, submitters act like workers except that they are
- * restricted to executing local tasks that they submitted (or in
- * the case of CountedCompleters, others with the same root task).
- * However, because most shared/external queue operations are more
- * expensive than internal, and because, at steady state, external
- * submitters will compete for CPU with workers, ForkJoinTask.join
- * and related methods disable them from repeatedly helping to
- * process tasks if all workers are active. Insertion of tasks in
- * shared mode requires a lock (mainly to protect in the case of
+ * Submitter probe value serves as a hash code for
+ * choosing existing queues, and may be randomly repositioned upon
+ * contention with other submitters. In essence, submitters act
+ * like workers except that they are restricted to executing local
+ * tasks that they submitted (or in the case of CountedCompleters,
+ * others with the same root task). However, because most
+ * shared/external queue operations are more expensive than
+ * internal, and because, at steady state, external submitters
+ * will compete for CPU with workers, ForkJoinTask.join and
+ * related methods disable them from repeatedly helping to process
+ * tasks if all workers are active. Insertion of tasks in shared
+ * mode requires a lock (mainly to protect in the case of
* resizing) but we use only a simple spinlock (using bits in
* field qlock), because submitters encountering a busy queue move
* on to try or create other queues -- they block only when
@@ -297,37 +309,35 @@ public class ForkJoinPool extends Abstra
* has not yet entered the wait queue. We solve this by requiring
* a full sweep of all workers (via repeated calls to method
* scan()) both before and after a newly waiting worker is added
- * to the wait queue. During a rescan, the worker might release
- * some other queued worker rather than itself, which has the same
- * net effect. Because enqueued workers may actually be rescanning
- * rather than waiting, we set and clear the "parker" field of
- * WorkQueues to reduce unnecessary calls to unpark. (This
- * requires a secondary recheck to avoid missed signals.) Note
- * the unusual conventions about Thread.interrupts surrounding
- * parking and other blocking: Because interrupts are used solely
- * to alert threads to check termination, which is checked anyway
- * upon blocking, we clear status (using Thread.interrupted)
- * before any call to park, so that park does not immediately
- * return due to status being set via some other unrelated call to
- * interrupt in user code.
+ * to the wait queue. Because enqueued workers may actually be
+ * rescanning rather than waiting, we set and clear the "parker"
+ * field of WorkQueues to reduce unnecessary calls to unpark.
+ * (This requires a secondary recheck to avoid missed signals.)
+ * Note the unusual conventions about Thread.interrupts
+ * surrounding parking and other blocking: Because interrupts are
+ * used solely to alert threads to check termination, which is
+ * checked anyway upon blocking, we clear status (using
+ * Thread.interrupted) before any call to park, so that park does
+ * not immediately return due to status being set via some other
+ * unrelated call to interrupt in user code.
*
* Signalling. We create or wake up workers only when there
* appears to be at least one task they might be able to find and
- * execute. However, many other threads may notice the same task
- * and each signal to wake up a thread that might take it. So in
- * general, pools will be over-signalled. When a submission is
- * added or another worker adds a task to a queue that has fewer
- * than two tasks, they signal waiting workers (or trigger
- * creation of new ones if fewer than the given parallelism level
- * -- signalWork), and may leave a hint to the unparked worker to
- * help signal others upon wakeup). These primary signals are
- * buttressed by others (see method helpSignal) whenever other
- * threads scan for work or do not have a task to process. On
- * most platforms, signalling (unpark) overhead time is noticeably
+ * execute. When a submission is added or another worker adds a
+ * task to a queue that has fewer than two tasks, they signal
+ * waiting workers (or trigger creation of new ones if fewer than
+ * the given parallelism level -- signalWork). These primary
+ * signals are buttressed by others whenever other threads remove
+ * a task from a queue and notice that there are other tasks there
+ * as well. So in general, pools will be over-signalled. On most
+ * platforms, signalling (unpark) overhead time is noticeably
* long, and the time between signalling a thread and it actually
* making progress can be very noticeably long, so it is worth
* offloading these delays from critical paths as much as
- * possible.
+ * possible. Additionally, workers spin-down gradually, by staying
+ * alive so long as they see the ctl state changing. Similar
+ * stability-sensing techniques are also used before blocking in
+ * awaitJoin and helpComplete.
*
* Trimming workers. To release resources after periods of lack of
* use, a worker starting to wait when the pool is quiescent will
@@ -440,7 +450,7 @@ public class ForkJoinPool extends Abstra
* Common Pool
* ===========
*
- * The static commonPool always exists after static
+ * The static common pool always exists after static
* initialization. Since it (or any other created pool) need
* never be used, we minimize initial construction overhead and
* footprint to the setup of about a dozen fields, with no nested
@@ -448,8 +458,11 @@ public class ForkJoinPool extends Abstra
* fullExternalPush during the first submission to the pool.
*
* When external threads submit to the common pool, they can
- * perform some subtask processing (see externalHelpJoin and
- * related methods). We do not need to record whether these
+ * perform subtask processing (see externalHelpJoin and related
+ * methods). This caller-helps policy makes it sensible to set
+ * common pool parallelism level to one (or more) less than the
+ * total number of available cores, or even zero for pure
+ * caller-runs. We do not need to record whether external
* submissions are to the common pool -- if not, externalHelpJoin
* returns quickly (at the most helping to signal some common pool
* workers). These submitters would otherwise be blocked waiting
@@ -519,6 +532,7 @@ public class ForkJoinPool extends Abstra
*
* @param pool the pool this thread works in
* @throws NullPointerException if the pool is null
+ * @return the new worker thread
*/
public ForkJoinWorkerThread newThread(ForkJoinPool pool);
}
@@ -535,26 +549,6 @@ public class ForkJoinPool extends Abstra
}
/**
- * Per-thread records for threads that submit to pools. Currently
- * holds only pseudo-random seed / index that is used to choose
- * submission queues in method externalPush. In the future, this may
- * also incorporate a means to implement different task rejection
- * and resubmission policies.
- *
- * Seeds for submitters and workers/workQueues work in basically
- * the same way but are initialized and updated using slightly
- * different mechanics. Both are initialized using the same
- * approach as in class ThreadLocal, where successive values are
- * unlikely to collide with previous values. Seeds are then
- * randomly modified upon collisions using xorshifts, which
- * requires a non-zero seed.
- */
- static final class Submitter {
- int seed;
- Submitter(int s) { seed = s; }
- }
-
- /**
* Class for artificial tasks that are used to replace the target
* of local joins if they are removed from an interior queue slot
* in WorkQueue.tryRemoveAndExec. We don't need the proxy to
@@ -613,17 +607,8 @@ public class ForkJoinPool extends Abstra
* do not want multiple WorkQueue instances or multiple queue
* arrays sharing cache lines. (It would be best for queue objects
* and their arrays to share, but there is nothing available to
- * help arrange that). Unfortunately, because they are recorded
- * in a common array, WorkQueue instances are often moved to be
- * adjacent by garbage collectors. To reduce impact, we use field
- * padding that works OK on common platforms; this effectively
- * trades off slightly slower average field access for the sake of
- * avoiding really bad worst-case access. (Until better JVM
- * support is in place, this padding is dependent on transient
- * properties of JVM field layout rules.) We also take care in
- * allocating, sizing and resizing the array. Non-shared queue
- * arrays are initialized by workers before use. Others are
- * allocated on first use.
+ * help arrange that). The @Contended annotation alerts JVMs to
+ * try to keep instances apart.
*/
static final class WorkQueue {
/**
@@ -649,13 +634,12 @@ public class ForkJoinPool extends Abstra
// Heuristic padding to ameliorate unfortunate memory placements
volatile long pad00, pad01, pad02, pad03, pad04, pad05, pad06;
- int seed; // for random scanning; initialize nonzero
volatile int eventCount; // encoded inactivation count; < 0 if inactive
int nextWait; // encoded record of next event waiter
- int hint; // steal or signal hint (index)
- int poolIndex; // index of this queue in pool (or 0)
- final int mode; // 0: lifo, > 0: fifo, < 0: shared
int nsteals; // number of steals
+ int hint; // steal index hint
+ short poolIndex; // index of this queue in pool
+ final short mode; // 0: lifo, > 0: fifo, < 0: shared
volatile int qlock; // 1: locked, -1: terminate; else 0
volatile int base; // index of next slot for poll
int top; // index of next slot for push
@@ -673,8 +657,8 @@ public class ForkJoinPool extends Abstra
int seed) {
this.pool = pool;
this.owner = owner;
- this.mode = mode;
- this.seed = seed;
+ this.mode = (short)mode;
+ this.hint = seed; // store initial seed for runWorker
// Place indices in the center of array (that is not yet allocated)
base = top = INITIAL_QUEUE_CAPACITY >>> 1;
}
@@ -687,7 +671,7 @@ public class ForkJoinPool extends Abstra
return (n >= 0) ? 0 : -n; // ignore transient negative
}
- /**
+ /**
* Provides a more accurate estimate of whether this queue has
* any tasks than does queueSize, by checking whether a
* near-empty queue has at least one unclaimed task.
@@ -708,24 +692,22 @@ public class ForkJoinPool extends Abstra
* shared-queue version is embedded in method externalPush.)
*
* @param task the task. Caller must ensure non-null.
- * @throw RejectedExecutionException if array cannot be resized
+ * @throws RejectedExecutionException if array cannot be resized
*/
final void push(ForkJoinTask> task) {
ForkJoinTask>[] a; ForkJoinPool p;
- int s = top, m, n;
+ int s = top, n;
if ((a = array) != null) { // ignore if queue removed
- int j = (((m = a.length - 1) & s) << ASHIFT) + ABASE;
- U.putOrderedObject(a, j, task);
- if ((n = (top = s + 1) - base) <= 2) {
- if ((p = pool) != null)
- p.signalWork(this);
- }
+ int m = a.length - 1;
+ U.putOrderedObject(a, ((m & s) << ASHIFT) + ABASE, task);
+ if ((n = (top = s + 1) - base) <= 2)
+ (p = pool).signalWork(p.workQueues, this);
else if (n >= m)
growArray();
}
}
- /**
+ /**
* Initializes or doubles the capacity of array. Call either
* by owner or with lock held -- it is OK for base, but not
* top, to move while resizings are in progress.
@@ -783,9 +765,8 @@ public class ForkJoinPool extends Abstra
if ((a = array) != null) {
int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
if ((t = (ForkJoinTask>)U.getObjectVolatile(a, j)) != null &&
- base == b &&
- U.compareAndSwapObject(a, j, t, null)) {
- base = b + 1;
+ base == b && U.compareAndSwapObject(a, j, t, null)) {
+ U.putOrderedInt(this, QBASE, b + 1);
return t;
}
}
@@ -801,9 +782,8 @@ public class ForkJoinPool extends Abstra
int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
t = (ForkJoinTask>)U.getObjectVolatile(a, j);
if (t != null) {
- if (base == b &&
- U.compareAndSwapObject(a, j, t, null)) {
- base = b + 1;
+ if (U.compareAndSwapObject(a, j, t, null)) {
+ U.putOrderedInt(this, QBASE, b + 1);
return t;
}
}
@@ -860,63 +840,62 @@ public class ForkJoinPool extends Abstra
ForkJoinTask.cancelIgnoringExceptions(t);
}
- /**
- * Computes next value for random probes. Scans don't require
- * a very high quality generator, but also not a crummy one.
- * Marsaglia xor-shift is cheap and works well enough. Note:
- * This is manually inlined in its usages in ForkJoinPool to
- * avoid writes inside busy scan loops.
- */
- final int nextSeed() {
- int r = seed;
- r ^= r << 13;
- r ^= r >>> 17;
- return seed = r ^= r << 5;
- }
-
// Specialized execution methods
/**
- * Pops and runs tasks until empty.
- */
- private void popAndExecAll() {
- // A bit faster than repeated pop calls
- ForkJoinTask>[] a; int m, s; long j; ForkJoinTask> t;
- while ((a = array) != null && (m = a.length - 1) >= 0 &&
- (s = top - 1) - base >= 0 &&
- (t = ((ForkJoinTask>)
- U.getObject(a, j = ((m & s) << ASHIFT) + ABASE)))
- != null) {
- if (U.compareAndSwapObject(a, j, t, null)) {
- top = s;
- t.doExec();
- }
- }
- }
-
- /**
* Polls and runs tasks until empty.
*/
- private void pollAndExecAll() {
+ final void pollAndExecAll() {
for (ForkJoinTask> t; (t = poll()) != null;)
t.doExec();
}
/**
+ * Executes a top-level task and any local tasks remaining
+ * after execution.
+ */
+ final void runTask(ForkJoinTask> task) {
+ if ((currentSteal = task) != null) {
+ task.doExec();
+ ForkJoinTask>[] a = array;
+ int md = mode;
+ ++nsteals;
+ currentSteal = null;
+ if (md != 0)
+ pollAndExecAll();
+ else if (a != null) {
+ int s, m = a.length - 1;
+ while ((s = top - 1) - base >= 0) {
+ long i = ((m & s) << ASHIFT) + ABASE;
+ ForkJoinTask> t = (ForkJoinTask>)U.getObject(a, i);
+ if (t == null)
+ break;
+ if (U.compareAndSwapObject(a, i, t, null)) {
+ top = s;
+ t.doExec();
+ }
+ }
+ }
+ }
+ }
+
+ /**
* If present, removes from queue and executes the given task,
* or any other cancelled task. Returns (true) on any CAS
* or consistency check failure so caller can retry.
*
- * @return false if no progress can be made, else true;
+ * @return false if no progress can be made, else true
*/
final boolean tryRemoveAndExec(ForkJoinTask> task) {
- boolean stat = true, removed = false, empty = true;
+ boolean stat;
ForkJoinTask>[] a; int m, s, b, n;
- if ((a = array) != null && (m = a.length - 1) >= 0 &&
+ if (task != null && (a = array) != null && (m = a.length - 1) >= 0 &&
(n = (s = top) - (b = base)) > 0) {
+ boolean removed = false, empty = true;
+ stat = true;
for (ForkJoinTask> t;;) { // traverse from s to b
- int j = ((--s & m) << ASHIFT) + ABASE;
- t = (ForkJoinTask>)U.getObjectVolatile(a, j);
+ long j = ((--s & m) << ASHIFT) + ABASE;
+ t = (ForkJoinTask>)U.getObject(a, j);
if (t == null) // inconsistent length
break;
else if (t == task) {
@@ -944,69 +923,95 @@ public class ForkJoinPool extends Abstra
break;
}
}
+ if (removed)
+ task.doExec();
}
- if (removed)
- task.doExec();
+ else
+ stat = false;
return stat;
}
/**
- * Polls for and executes the given task or any other task in
- * its CountedCompleter computation
+ * Tries to poll for and execute the given task or any other
+ * task in its CountedCompleter computation.
*/
- final boolean pollAndExecCC(ForkJoinTask> root) {
- ForkJoinTask>[] a; int b; Object o;
- outer: while ((b = base) - top < 0 && (a = array) != null) {
+ final boolean pollAndExecCC(CountedCompleter> root) {
+ ForkJoinTask>[] a; int b; Object o; CountedCompleter> t, r;
+ if ((b = base) - top < 0 && (a = array) != null) {
long j = (((a.length - 1) & b) << ASHIFT) + ABASE;
- if ((o = U.getObject(a, j)) == null ||
- !(o instanceof CountedCompleter))
- break;
- for (CountedCompleter> t = (CountedCompleter>)o, r = t;;) {
- if (r == root) {
- if (base == b &&
- U.compareAndSwapObject(a, j, t, null)) {
- base = b + 1;
- t.doExec();
+ if ((o = U.getObjectVolatile(a, j)) == null)
+ return true; // retry
+ if (o instanceof CountedCompleter) {
+ for (t = (CountedCompleter>)o, r = t;;) {
+ if (r == root) {
+ if (base == b &&
+ U.compareAndSwapObject(a, j, t, null)) {
+ U.putOrderedInt(this, QBASE, b + 1);
+ t.doExec();
+ }
return true;
}
- else
- break; // restart
+ else if ((r = r.completer) == null)
+ break; // not part of root computation
}
- if ((r = r.completer) == null)
- break outer; // not part of root computation
}
}
return false;
}
/**
- * Executes a top-level task and any local tasks remaining
- * after execution.
+ * Tries to pop and execute the given task or any other task
+ * in its CountedCompleter computation.
*/
- final void runTask(ForkJoinTask> t) {
- if (t != null) {
- (currentSteal = t).doExec();
- currentSteal = null;
- if (base - top < 0) { // process remaining local tasks
- if (mode == 0)
- popAndExecAll();
- else
- pollAndExecAll();
+ final boolean externalPopAndExecCC(CountedCompleter> root) {
+ ForkJoinTask>[] a; int s; Object o; CountedCompleter> t, r;
+ if (base - (s = top) < 0 && (a = array) != null) {
+ long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE;
+ if ((o = U.getObject(a, j)) instanceof CountedCompleter) {
+ for (t = (CountedCompleter>)o, r = t;;) {
+ if (r == root) {
+ if (U.compareAndSwapInt(this, QLOCK, 0, 1)) {
+ if (top == s && array == a &&
+ U.compareAndSwapObject(a, j, t, null)) {
+ top = s - 1;
+ qlock = 0;
+ t.doExec();
+ }
+ else
+ qlock = 0;
+ }
+ return true;
+ }
+ else if ((r = r.completer) == null)
+ break;
+ }
}
- ++nsteals;
- hint = -1;
}
+ return false;
}
/**
- * Executes a non-top-level (stolen) task.
+ * Internal version
*/
- final void runSubtask(ForkJoinTask> t) {
- if (t != null) {
- ForkJoinTask> ps = currentSteal;
- (currentSteal = t).doExec();
- currentSteal = ps;
+ final boolean internalPopAndExecCC(CountedCompleter> root) {
+ ForkJoinTask>[] a; int s; Object o; CountedCompleter> t, r;
+ if (base - (s = top) < 0 && (a = array) != null) {
+ long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE;
+ if ((o = U.getObject(a, j)) instanceof CountedCompleter) {
+ for (t = (CountedCompleter>)o, r = t;;) {
+ if (r == root) {
+ if (U.compareAndSwapObject(a, j, t, null)) {
+ top = s - 1;
+ t.doExec();
+ }
+ return true;
+ }
+ else if ((r = r.completer) == null)
+ break;
+ }
+ }
}
+ return false;
}
/**
@@ -1021,56 +1026,35 @@ public class ForkJoinPool extends Abstra
s != Thread.State.TIMED_WAITING);
}
- /**
- * If this owned and is not already interrupted, try to
- * interrupt and/or unpark, ignoring exceptions.
- */
- final void interruptOwner() {
- Thread wt, p;
- if ((wt = owner) != null && !wt.isInterrupted()) {
- try {
- wt.interrupt();
- } catch (SecurityException ignore) {
- }
- }
- if ((p = parker) != null)
- U.unpark(p);
- }
-
// Unsafe mechanics
private static final sun.misc.Unsafe U;
+ private static final long QBASE;
private static final long QLOCK;
private static final int ABASE;
private static final int ASHIFT;
static {
- int s;
try {
U = getUnsafe();
Class> k = WorkQueue.class;
Class> ak = ForkJoinTask[].class;
+ QBASE = U.objectFieldOffset
+ (k.getDeclaredField("base"));
QLOCK = U.objectFieldOffset
(k.getDeclaredField("qlock"));
ABASE = U.arrayBaseOffset(ak);
- s = U.arrayIndexScale(ak);
+ int scale = U.arrayIndexScale(ak);
+ if ((scale & (scale - 1)) != 0)
+ throw new Error("data type scale not a power of two");
+ ASHIFT = 31 - Integer.numberOfLeadingZeros(scale);
} catch (Exception e) {
throw new Error(e);
}
- if ((s & (s-1)) != 0)
- throw new Error("data type scale not a power of two");
- ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
}
}
// static fields (initialized in static initializer below)
/**
- * Creates a new ForkJoinWorkerThread. This factory is used unless
- * overridden in ForkJoinPool constructors.
- */
- public static final ForkJoinWorkerThreadFactory
- defaultForkJoinWorkerThreadFactory;
-
- /**
* Per-thread submission bookkeeping. Shared across all pools
* to reduce ThreadLocal pollution and because random motion
* to avoid contention in one pool is likely to hold for others.
@@ -1080,6 +1064,13 @@ public class ForkJoinPool extends Abstra
static final ThreadLocal submitters;
/**
+ * Creates a new ForkJoinWorkerThread. This factory is used unless
+ * overridden in ForkJoinPool constructors.
+ */
+ public static final ForkJoinWorkerThreadFactory
+ defaultForkJoinWorkerThreadFactory;
+
+ /**
* Permission required for callers of methods that may start or
* kill threads.
*/
@@ -1091,12 +1082,15 @@ public class ForkJoinPool extends Abstra
* to paranoically avoid potential initialization circularities
* as well as to simplify generated code.
*/
- static final ForkJoinPool commonPool;
+ static final ForkJoinPool common;
/**
- * Common pool parallelism. Must equal commonPool.parallelism.
+ * Common pool parallelism. To allow simpler use and management
+ * when common pool threads are disabled, we allow the underlying
+ * common.parallelism field to be zero, but in that case still report
+ * parallelism as 1 to reflect resulting caller-runs mechanics.
*/
- static final int commonPoolParallelism;
+ static final int commonParallelism;
/**
* Sequence number for creating workerNamePrefix.
@@ -1104,8 +1098,8 @@ public class ForkJoinPool extends Abstra
private static int poolNumberSequence;
/**
- * Return the next sequence number. We don't expect this to
- * ever contend so use simple builtin sync.
+ * Returns the next sequence number. We don't expect this to
+ * ever contend, so use simple builtin sync.
*/
private static final synchronized int nextPoolId() {
return ++poolNumberSequence;
@@ -1129,6 +1123,11 @@ public class ForkJoinPool extends Abstra
private static final long FAST_IDLE_TIMEOUT = 200L * 1000L * 1000L;
/**
+ * Tolerance for idle timeouts, to cope with timer undershoots
+ */
+ private static final long TIMEOUT_SLOP = 2000000L;
+
+ /**
* The maximum stolen->joining link depth allowed in method
* tryHelpStealer. Must be a power of two. Depths for legitimate
* chains are unbounded, but we use a fixed constant to avoid
@@ -1144,7 +1143,7 @@ public class ForkJoinPool extends Abstra
*/
private static final int SEED_INCREMENT = 0x61c88647;
- /**
+ /*
* Bits and masks for control variables
*
* Field ctl is a long packed with:
@@ -1228,64 +1227,40 @@ public class ForkJoinPool extends Abstra
static final int FIFO_QUEUE = 1;
static final int SHARED_QUEUE = -1;
- // bounds for #steps in scan loop -- must be power 2 minus 1
- private static final int MIN_SCAN = 0x1ff; // cover estimation slop
- private static final int MAX_SCAN = 0x1ffff; // 4 * max workers
-
- // Instance fields
-
- /*
- * Field layout of this class tends to matter more than one would
- * like. Runtime layout order is only loosely related to
- * declaration order and may differ across JVMs, but the following
- * empirically works OK on current JVMs.
- */
-
// Heuristic padding to ameliorate unfortunate memory placements
volatile long pad00, pad01, pad02, pad03, pad04, pad05, pad06;
+ // Instance fields
volatile long stealCount; // collects worker counts
volatile long ctl; // main pool control
volatile int plock; // shutdown status and seqLock
volatile int indexSeed; // worker/submitter index seed
- final int config; // mode and parallelism level
+ final short parallelism; // parallelism level
+ final short mode; // LIFO/FIFO
WorkQueue[] workQueues; // main registry
final ForkJoinWorkerThreadFactory factory;
- final Thread.UncaughtExceptionHandler ueh; // per-worker UEH
+ final UncaughtExceptionHandler ueh; // per-worker UEH
final String workerNamePrefix; // to create worker name string
volatile Object pad10, pad11, pad12, pad13, pad14, pad15, pad16, pad17;
volatile Object pad18, pad19, pad1a, pad1b;
- /*
+ /**
* Acquires the plock lock to protect worker array and related
* updates. This method is called only if an initial CAS on plock
- * fails. This acts as a spinLock for normal cases, but falls back
+ * fails. This acts as a spinlock for normal cases, but falls back
* to builtin monitor to block when (rarely) needed. This would be
* a terrible idea for a highly contended lock, but works fine as
- * a more conservative alternative to a pure spinlock. See
- * internal ConcurrentHashMap documentation for further
- * explanation of nearly the same construction.
+ * a more conservative alternative to a pure spinlock.
*/
private int acquirePlock() {
- int spins = PL_SPINS, r = 0, ps, nps;
+ int spins = PL_SPINS, ps, nps;
for (;;) {
if (((ps = plock) & PL_LOCK) == 0 &&
U.compareAndSwapInt(this, PLOCK, ps, nps = ps + PL_LOCK))
return nps;
- else if (r == 0) { // randomize spins if possible
- Thread t = Thread.currentThread(); WorkQueue w; Submitter z;
- if ((t instanceof ForkJoinWorkerThread) &&
- (w = ((ForkJoinWorkerThread)t).workQueue) != null)
- r = w.seed;
- else if ((z = submitters.get()) != null)
- r = z.seed;
- else
- r = 1;
- }
else if (spins >= 0) {
- r ^= r << 1; r ^= r >>> 3; r ^= r << 10; // xorshift
- if (r >= 0)
+ if (ThreadLocalRandom.current().nextInt() >= 0)
--spins;
}
else if (U.compareAndSwapInt(this, PLOCK, ps, ps | PL_SIGNAL)) {
@@ -1317,48 +1292,15 @@ public class ForkJoinPool extends Abstra
}
/**
- * Performs secondary initialization, called when plock is zero.
- * Creates workQueue array and sets plock to a valid value. The
- * lock body must be exception-free (so no try/finally) so we
- * optimistically allocate new array outside the lock and throw
- * away if (very rarely) not needed. (A similar tactic is used in
- * fullExternalPush.) Because the plock seq value can eventually
- * wrap around zero, this method harmlessly fails to reinitialize
- * if workQueues exists, while still advancing plock.
- *
- * Additonally tries to create the first worker.
- */
- private void initWorkers() {
- WorkQueue[] ws, nws; int ps;
- int p = config & SMASK; // find power of two table size
- int n = (p > 1) ? p - 1 : 1; // ensure at least 2 slots
- n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16;
- n = (n + 1) << 1;
- if ((ws = workQueues) == null || ws.length == 0)
- nws = new WorkQueue[n];
- else
- nws = null;
- if (((ps = plock) & PL_LOCK) != 0 ||
- !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
- ps = acquirePlock();
- if (((ws = workQueues) == null || ws.length == 0) && nws != null)
- workQueues = nws;
- int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
- if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
- releasePlock(nps);
- tryAddWorker();
- }
-
- /**
- * Tries to create and start one worker. Adjusts counts etc on
- * failure.
+ * Tries to create and start one worker if fewer than target
+ * parallelism level exist. Adjusts counts etc on failure.
*/
private void tryAddWorker() {
- long c; int u;
+ long c; int u, e;
while ((u = (int)((c = ctl) >>> 32)) < 0 &&
- (u & SHORT_SIGN) != 0 && (int)c == 0) {
- long nc = (long)(((u + UTC_UNIT) & UTC_MASK) |
- ((u + UAC_UNIT) & UAC_MASK)) << 32;
+ (u & SHORT_SIGN) != 0 && (e = (int)c) >= 0) {
+ long nc = ((long)(((u + UTC_UNIT) & UTC_MASK) |
+ ((u + UAC_UNIT) & UAC_MASK)) << 32) | (long)e;
if (U.compareAndSwapLong(this, CTL, c, nc)) {
ForkJoinWorkerThreadFactory fac;
Throwable ex = null;
@@ -1369,8 +1311,8 @@ public class ForkJoinPool extends Abstra
wt.start();
break;
}
- } catch (Throwable e) {
- ex = e;
+ } catch (Throwable rex) {
+ ex = rex;
}
deregisterWorker(wt, ex);
break;
@@ -1391,14 +1333,14 @@ public class ForkJoinPool extends Abstra
* @return the worker's queue
*/
final WorkQueue registerWorker(ForkJoinWorkerThread wt) {
- Thread.UncaughtExceptionHandler handler; WorkQueue[] ws; int s, ps;
+ UncaughtExceptionHandler handler; WorkQueue[] ws; int s, ps;
wt.setDaemon(true);
if ((handler = ueh) != null)
wt.setUncaughtExceptionHandler(handler);
do {} while (!U.compareAndSwapInt(this, INDEXSEED, s = indexSeed,
s += SEED_INCREMENT) ||
s == 0); // skip 0
- WorkQueue w = new WorkQueue(this, wt, config >>> 16, s);
+ WorkQueue w = new WorkQueue(this, wt, mode, s);
if (((ps = plock) & PL_LOCK) != 0 ||
!U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
ps = acquirePlock();
@@ -1418,14 +1360,15 @@ public class ForkJoinPool extends Abstra
}
}
}
- w.eventCount = w.poolIndex = r; // volatile write orders
+ w.poolIndex = (short)r;
+ w.eventCount = r; // volatile write orders
ws[r] = w;
}
} finally {
if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
releasePlock(nps);
}
- wt.setName(workerNamePrefix.concat(Integer.toString(w.poolIndex)));
+ wt.setName(workerNamePrefix.concat(Integer.toString(w.poolIndex >>> 1)));
return w;
}
@@ -1435,17 +1378,16 @@ public class ForkJoinPool extends Abstra
* array, and adjusts counts. If pool is shutting down, tries to
* complete termination.
*
- * @param wt the worker thread or null if construction failed
+ * @param wt the worker thread, or null if construction failed
* @param ex the exception causing failure, or null if none
*/
final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
WorkQueue w = null;
if (wt != null && (w = wt.workQueue) != null) {
- int ps;
+ int ps; long sc;
w.qlock = -1; // ensure set
- long ns = w.nsteals, sc; // collect steal count
- do {} while (!U.compareAndSwapLong(this, STEALCOUNT,
- sc = stealCount, sc + ns));
+ do {} while(!U.compareAndSwapLong(this, STEALCOUNT, sc = stealCount,
+ sc + w.nsteals));
if (((ps = plock) & PL_LOCK) != 0 ||
!U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
ps = acquirePlock();
@@ -1461,27 +1403,68 @@ public class ForkJoinPool extends Abstra
}
}
- long c; // adjust ctl counts
+ long c; // adjust ctl counts
do {} while (!U.compareAndSwapLong
(this, CTL, c = ctl, (((c - AC_UNIT) & AC_MASK) |
((c - TC_UNIT) & TC_MASK) |
(c & ~(AC_MASK|TC_MASK)))));
- if (!tryTerminate(false, false) && w != null) {
- w.cancelAll(); // cancel remaining tasks
- if (w.array != null) // suppress signal if never ran
- tryAddWorker(); // create replacement
- if (ex == null) // help clean refs on way out
- ForkJoinTask.helpExpungeStaleExceptions();
+ if (!tryTerminate(false, false) && w != null && w.array != null) {
+ w.cancelAll(); // cancel remaining tasks
+ WorkQueue[] ws; WorkQueue v; Thread p; int u, i, e;
+ while ((u = (int)((c = ctl) >>> 32)) < 0 && (e = (int)c) >= 0) {
+ if (e > 0) { // activate or create replacement
+ if ((ws = workQueues) == null ||
+ (i = e & SMASK) >= ws.length ||
+ (v = ws[i]) == null)
+ break;
+ long nc = (((long)(v.nextWait & E_MASK)) |
+ ((long)(u + UAC_UNIT) << 32));
+ if (v.eventCount != (e | INT_SIGN))
+ break;
+ if (U.compareAndSwapLong(this, CTL, c, nc)) {
+ v.eventCount = (e + E_SEQ) & E_MASK;
+ if ((p = v.parker) != null)
+ U.unpark(p);
+ break;
+ }
+ }
+ else {
+ if ((short)u < 0)
+ tryAddWorker();
+ break;
+ }
+ }
}
-
- if (ex != null) // rethrow
+ if (ex == null) // help clean refs on way out
+ ForkJoinTask.helpExpungeStaleExceptions();
+ else // rethrow
ForkJoinTask.rethrow(ex);
}
// Submissions
/**
+ * Per-thread records for threads that submit to pools. Currently
+ * holds only pseudo-random seed / index that is used to choose
+ * submission queues in method externalPush. In the future, this may
+ * also incorporate a means to implement different task rejection
+ * and resubmission policies.
+ *
+ * Seeds for submitters and workers/workQueues work in basically
+ * the same way but are initialized and updated using slightly
+ * different mechanics. Both are initialized using the same
+ * approach as in class ThreadLocal, where successive values are
+ * unlikely to collide with previous values. Seeds are then
+ * randomly modified upon collisions using xorshifts, which
+ * requires a non-zero seed.
+ */
+ static final class Submitter {
+ int seed;
+ Submitter(int s) { seed = s; }
+ }
+
+ /**
* Unless shutting down, adds the given task to a submission queue
* at submitter's current queue index (modulo submission
* range). Only the most common path is directly handled in this
@@ -1490,19 +1473,21 @@ public class ForkJoinPool extends Abstra
* @param task the task. Caller must ensure non-null.
*/
final void externalPush(ForkJoinTask> task) {
- WorkQueue[] ws; WorkQueue q; Submitter z; int m; ForkJoinTask>[] a;
- if ((z = submitters.get()) != null && plock > 0 &&
- (ws = workQueues) != null && (m = (ws.length - 1)) >= 0 &&
- (q = ws[m & z.seed & SQMASK]) != null &&
+ Submitter z = submitters.get();
+ WorkQueue q; int r, m, s, n, am; ForkJoinTask>[] a;
+ int ps = plock;
+ WorkQueue[] ws = workQueues;
+ if (z != null && ps > 0 && ws != null && (m = (ws.length - 1)) >= 0 &&
+ (q = ws[m & (r = z.seed) & SQMASK]) != null && r != 0 &&
U.compareAndSwapInt(q, QLOCK, 0, 1)) { // lock
- int b = q.base, s = q.top, n, an;
- if ((a = q.array) != null && (an = a.length) > (n = s + 1 - b)) {
- int j = (((an - 1) & s) << ASHIFT) + ABASE;
+ if ((a = q.array) != null &&
+ (am = a.length - 1) > (n = (s = q.top) - q.base)) {
+ int j = ((am & s) << ASHIFT) + ABASE;
U.putOrderedObject(a, j, task);
q.top = s + 1; // push on to deque
q.qlock = 0;
- if (n <= 2)
- signalWork(q);
+ if (n <= 1)
+ signalWork(ws, q);
return;
}
q.qlock = 0;
@@ -1513,13 +1498,19 @@ public class ForkJoinPool extends Abstra
/**
* Full version of externalPush. This method is called, among
* other times, upon the first submission of the first task to the
- * pool, so must perform secondary initialization (via
- * initWorkers). It also detects first submission by an external
- * thread by looking up its ThreadLocal, and creates a new shared
- * queue if the one at index if empty or contended. The plock lock
- * body must be exception-free (so no try/finally) so we
- * optimistically allocate new queues outside the lock and throw
- * them away if (very rarely) not needed.
+ * pool, so must perform secondary initialization. It also
+ * detects first submission by an external thread by looking up
+ * its ThreadLocal, and creates a new shared queue if the one at
+ * index if empty or contended. The plock lock body must be
+ * exception-free (so no try/finally) so we optimistically
+ * allocate new queues outside the lock and throw them away if
+ * (very rarely) not needed.
+ *
+ * Secondary initialization occurs when plock is zero, to create
+ * workQueue array and set plock to a valid value. This lock body
+ * must also be exception-free. Because the plock seq value can
+ * eventually wrap around zero, this method harmlessly fails to
+ * reinitialize if workQueues exists, while still advancing plock.
*/
private void fullExternalPush(ForkJoinTask> task) {
int r = 0; // random index seed
@@ -1530,17 +1521,31 @@ public class ForkJoinPool extends Abstra
r += SEED_INCREMENT) && r != 0)
submitters.set(z = new Submitter(r));
}
- else if (r == 0) { // move to a different index
+ else if (r == 0) { // move to a different index
r = z.seed;
- r ^= r << 13; // same xorshift as WorkQueues
+ r ^= r << 13; // same xorshift as WorkQueues
r ^= r >>> 17;
- z.seed = r ^ (r << 5);
+ z.seed = r ^= (r << 5);
}
- else if ((ps = plock) < 0)
+ if ((ps = plock) < 0)
throw new RejectedExecutionException();
else if (ps == 0 || (ws = workQueues) == null ||
- (m = ws.length - 1) < 0)
- initWorkers();
+ (m = ws.length - 1) < 0) { // initialize workQueues
+ int p = parallelism; // find power of two table size
+ int n = (p > 1) ? p - 1 : 1; // ensure at least 2 slots
+ n |= n >>> 1; n |= n >>> 2; n |= n >>> 4;
+ n |= n >>> 8; n |= n >>> 16; n = (n + 1) << 1;
+ WorkQueue[] nws = ((ws = workQueues) == null || ws.length == 0 ?
+ new WorkQueue[n] : null);
+ if (((ps = plock) & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ if (((ws = workQueues) == null || ws.length == 0) && nws != null)
+ workQueues = nws;
+ int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
+ }
else if ((q = ws[k = r & m & SQMASK]) != null) {
if (q.qlock == 0 && U.compareAndSwapInt(q, QLOCK, 0, 1)) {
ForkJoinTask>[] a = q.array;
@@ -1558,7 +1563,7 @@ public class ForkJoinPool extends Abstra
q.qlock = 0; // unlock
}
if (submitted) {
- signalWork(q);
+ signalWork(ws, q);
return;
}
}
@@ -1566,6 +1571,7 @@ public class ForkJoinPool extends Abstra
}
else if (((ps = plock) & PL_LOCK) == 0) { // create new queue
q = new WorkQueue(this, null, SHARED_QUEUE, r);
+ q.poolIndex = (short)k;
if (((ps = plock) & PL_LOCK) != 0 ||
!U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
ps = acquirePlock();
@@ -1576,7 +1582,7 @@ public class ForkJoinPool extends Abstra
releasePlock(nps);
}
else
- r = 0; // try elsewhere while lock held
+ r = 0;
}
}
@@ -1587,41 +1593,42 @@ public class ForkJoinPool extends Abstra
*/
final void incrementActiveCount() {
long c;
- do {} while (!U.compareAndSwapLong(this, CTL, c = ctl, c + AC_UNIT));
+ do {} while (!U.compareAndSwapLong
+ (this, CTL, c = ctl, ((c & ~AC_MASK) |
+ ((c & AC_MASK) + AC_UNIT))));
}
/**
* Tries to create or activate a worker if too few are active.
*
- * @param q the (non-null) queue holding tasks to be signalled
+ * @param ws the worker array to use to find signallees
+ * @param q if non-null, the queue holding tasks to be processed
*/
- final void signalWork(WorkQueue q) {
- int hint = q.poolIndex;
- long c; int e, u, i, n; WorkQueue[] ws; WorkQueue w; Thread p;
- while ((u = (int)((c = ctl) >>> 32)) < 0) {
- if ((e = (int)c) > 0) {
- if ((ws = workQueues) != null && ws.length > (i = e & SMASK) &&
- (w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) {
- long nc = (((long)(w.nextWait & E_MASK)) |
- ((long)(u + UAC_UNIT) << 32));
- if (U.compareAndSwapLong(this, CTL, c, nc)) {
- w.hint = hint;
- w.eventCount = (e + E_SEQ) & E_MASK;
- if ((p = w.parker) != null)
- U.unpark(p);
- break;
- }
- if (q.top - q.base <= 0)
- break;
- }
- else
- break;
- }
- else {
+ final void signalWork(WorkQueue[] ws, WorkQueue q) {
+ for (;;) {
+ long c; int e, u, i; WorkQueue w; Thread p;
+ if ((u = (int)((c = ctl) >>> 32)) >= 0)
+ break;
+ if ((e = (int)c) <= 0) {
if ((short)u < 0)
tryAddWorker();
break;
}
+ if (ws == null || ws.length <= (i = e & SMASK) ||
+ (w = ws[i]) == null)
+ break;
+ long nc = (((long)(w.nextWait & E_MASK)) |
+ ((long)(u + UAC_UNIT)) << 32);
+ int ne = (e + E_SEQ) & E_MASK;
+ if (w.eventCount == (e | INT_SIGN) &&
+ U.compareAndSwapLong(this, CTL, c, nc)) {
+ w.eventCount = ne;
+ if ((p = w.parker) != null)
+ U.unpark(p);
+ break;
+ }
+ if (q != null && q.base >= q.top)
+ break;
}
}
@@ -1632,186 +1639,154 @@ public class ForkJoinPool extends Abstra
*/
final void runWorker(WorkQueue w) {
w.growArray(); // allocate queue
- do { w.runTask(scan(w)); } while (w.qlock >= 0);
+ for (int r = w.hint; scan(w, r) == 0; ) {
+ r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // xorshift
+ }
}
/**
- * Scans for and, if found, returns one task, else possibly
+ * Scans for and, if found, runs one task, else possibly
* inactivates the worker. This method operates on single reads of
* volatile state and is designed to be re-invoked continuously,
* in part because it returns upon detecting inconsistencies,
* contention, or state changes that indicate possible success on
* re-invocation.
*
- * The scan searches for tasks across queues (starting at a random
- * index, and relying on registerWorker to irregularly scatter
- * them within array to avoid bias), checking each at least twice.
- * The scan terminates upon either finding a non-empty queue, or
- * completing the sweep. If the worker is not inactivated, it
- * takes and returns a task from this queue. Otherwise, if not
- * activated, it signals workers (that may include itself) and
- * returns so caller can retry. Also returns for true if the
- * worker array may have changed during an empty scan. On failure
- * to find a task, we take one of the following actions, after
- * which the caller will retry calling this method unless
- * terminated.
- *
- * * If pool is terminating, terminate the worker.
- *
- * * If not already enqueued, try to inactivate and enqueue the
- * worker on wait queue. Or, if inactivating has caused the pool
- * to be quiescent, relay to idleAwaitWork to check for
- * termination and possibly shrink pool.
- *
- * * If already enqueued and none of the above apply, possibly
- * (with 1/2 probability) park awaiting signal, else lingering to
- * help scan and signal.
+ * The scan searches for tasks across queues starting at a random
+ * index, checking each at least twice. The scan terminates upon
+ * either finding a non-empty queue, or completing the sweep. If
+ * the worker is not inactivated, it takes and runs a task from
+ * this queue. Otherwise, if not activated, it tries to activate
+ * itself or some other worker by signalling. On failure to find a
+ * task, returns (for retry) if pool state may have changed during
+ * an empty scan, or tries to inactivate if active, else possibly
+ * blocks or terminates via method awaitWork.
*
* @param w the worker (via its WorkQueue)
- * @return a task or null if none found
+ * @param r a random seed
+ * @return worker qlock status if would have waited, else 0
*/
- private final ForkJoinTask> scan(WorkQueue w) {
+ private final int scan(WorkQueue w, int r) {
WorkQueue[] ws; int m;
- int ps = plock; // read plock before ws
- if (w != null && (ws = workQueues) != null && (m = ws.length - 1) >= 0) {
- int ec = w.eventCount; // ec is negative if inactive
- int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
- int j = ((m + m + 1) | MIN_SCAN) & MAX_SCAN;
- do {
- WorkQueue q; ForkJoinTask>[] a; int b;
- if ((q = ws[(r + j) & m]) != null && (b = q.base) - q.top < 0 &&
- (a = q.array) != null) { // probably nonempty
- int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
- ForkJoinTask> t = (ForkJoinTask>)
- U.getObjectVolatile(a, i);
- if (q.base == b && ec >= 0 && t != null &&
- U.compareAndSwapObject(a, i, t, null)) {
- if ((q.base = b + 1) - q.top < 0)
- signalWork(q);
- return t; // taken
- }
- else if ((ec < 0 || j < m) && (int)(ctl >> AC_SHIFT) <= 0) {
- w.hint = (r + j) & m; // help signal below
- break; // cannot take
- }
- }
- } while (--j >= 0);
-
- long c, sc; int e, ns, h;
- if ((h = w.hint) < 0) {
- if ((ns = w.nsteals) != 0) {
- if (U.compareAndSwapLong(this, STEALCOUNT,
- sc = stealCount, sc + ns))
- w.nsteals = 0; // collect steals
- }
- else if (plock != ps) // consistency check
- ; // skip
- else if ((e = (int)(c = ctl)) < 0)
- w.qlock = -1; // pool is terminating
- else if (ec >= 0) { // try to enqueue/inactivate
- long nc = ((long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK)));
- w.nextWait = e; // link and mark inactive
- w.eventCount = ec | INT_SIGN;
- if (ctl != c || !U.compareAndSwapLong(this, CTL, c, nc))
- w.eventCount = ec; // unmark on CAS failure
- else if ((int)(c >> AC_SHIFT) == 1 - (config & SMASK))
- idleAwaitWork(w, nc, c);
+ long c = ctl; // for consistency check
+ if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 && w != null) {
+ for (int j = m + m + 1, ec = w.eventCount;;) {
+ WorkQueue q; int b, e; ForkJoinTask>[] a; ForkJoinTask> t;
+ if ((q = ws[(r - j) & m]) != null &&
+ (b = q.base) - q.top < 0 && (a = q.array) != null) {
+ long i = (((a.length - 1) & b) << ASHIFT) + ABASE;
+ if ((t = ((ForkJoinTask>)
+ U.getObjectVolatile(a, i))) != null) {
+ if (ec < 0)
+ helpRelease(c, ws, w, q, b);
+ else if (q.base == b &&
+ U.compareAndSwapObject(a, i, t, null)) {
+ U.putOrderedInt(q, QBASE, b + 1);
+ if ((b + 1) - q.top < 0)
+ signalWork(ws, q);
+ w.runTask(t);
+ }
+ }
+ break;
}
- else if (w.eventCount < 0) { // block
- Thread wt = Thread.currentThread();
- Thread.interrupted(); // clear status
- U.putObject(wt, PARKBLOCKER, this);
- w.parker = wt; // emulate LockSupport.park
- if (w.eventCount < 0) // recheck
- U.park(false, 0L);
- w.parker = null;
- U.putObject(wt, PARKBLOCKER, null);
+ else if (--j < 0) {
+ if ((ec | (e = (int)c)) < 0) // inactive or terminating
+ return awaitWork(w, c, ec);
+ else if (ctl == c) { // try to inactivate and enqueue
+ long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
+ w.nextWait = e;
+ w.eventCount = ec | INT_SIGN;
+ if (!U.compareAndSwapLong(this, CTL, c, nc))
+ w.eventCount = ec; // back out
+ }
+ break;
}
}
- if (h >= 0 || (h = w.hint) >= 0) { // signal others before retry
- w.hint = -1; // reset
- helpSignal(null, h, true);
- }
}
- return null;
+ return 0;
}
/**
- * If inactivating worker w has caused the pool to become
- * quiescent, checks for pool termination, and, so long as this is
- * not the only worker, waits for event for up to a given
- * duration. On timeout, if ctl has not changed, terminates the
- * worker, which will in turn wake up another worker to possibly
- * repeat this process.
+ * A continuation of scan(), possibly blocking or terminating
+ * worker w. Returns without blocking if pool state has apparently
+ * changed since last invocation. Also, if inactivating w has
+ * caused the pool to become quiescent, checks for pool
+ * termination, and, so long as this is not the only worker, waits
+ * for event for up to a given duration. On timeout, if ctl has
+ * not changed, terminates the worker, which will in turn wake up
+ * another worker to possibly repeat this process.
*
* @param w the calling worker
- * @param currentCtl the ctl value triggering possible quiescence
- * @param prevCtl the ctl value to restore if thread is terminated
+ * @param c the ctl value on entry to scan
+ * @param ec the worker's eventCount on entry to scan
*/
- private void idleAwaitWork(WorkQueue w, long currentCtl, long prevCtl) {
- if (w != null && w.eventCount < 0 &&
- !tryTerminate(false, false) && (int)prevCtl != 0) {
- int dc = -(short)(currentCtl >>> TC_SHIFT);
- long parkTime = dc < 0 ? FAST_IDLE_TIMEOUT: (dc + 1) * IDLE_TIMEOUT;
- long deadline = System.nanoTime() + parkTime - 100000L; // 1ms slop
- Thread wt = Thread.currentThread();
- while (ctl == currentCtl) {
- Thread.interrupted(); // timed variant of version in scan()
- U.putObject(wt, PARKBLOCKER, this);
- w.parker = wt;
- if (ctl == currentCtl)
- U.park(false, parkTime);
- w.parker = null;
- U.putObject(wt, PARKBLOCKER, null);
- if (ctl != currentCtl)
- break;
- if (deadline - System.nanoTime() <= 0L &&
- U.compareAndSwapLong(this, CTL, currentCtl, prevCtl)) {
- w.eventCount = (w.eventCount + E_SEQ) | E_MASK;
- w.qlock = -1; // shrink
- break;
+ private final int awaitWork(WorkQueue w, long c, int ec) {
+ int stat, ns; long parkTime, deadline;
+ if ((stat = w.qlock) >= 0 && w.eventCount == ec && ctl == c &&
+ !Thread.interrupted()) {
+ int e = (int)c;
+ int u = (int)(c >>> 32);
+ int d = (u >> UAC_SHIFT) + parallelism; // active count
+
+ if (e < 0 || (d <= 0 && tryTerminate(false, false)))
+ stat = w.qlock = -1; // pool is terminating
+ else if ((ns = w.nsteals) != 0) { // collect steals and retry
+ long sc;
+ w.nsteals = 0;
+ do {} while(!U.compareAndSwapLong(this, STEALCOUNT,
+ sc = stealCount, sc + ns));
+ }
+ else {
+ long pc = ((d > 0 || ec != (e | INT_SIGN)) ? 0L :
+ ((long)(w.nextWait & E_MASK)) | // ctl to restore
+ ((long)(u + UAC_UNIT)) << 32);
+ if (pc != 0L) { // timed wait if last waiter
+ int dc = -(short)(c >>> TC_SHIFT);
+ parkTime = (dc < 0 ? FAST_IDLE_TIMEOUT:
+ (dc + 1) * IDLE_TIMEOUT);
+ deadline = System.nanoTime() + parkTime - TIMEOUT_SLOP;
+ }
+ else
+ parkTime = deadline = 0L;
+ if (w.eventCount == ec && ctl == c) {
+ Thread wt = Thread.currentThread();
+ U.putObject(wt, PARKBLOCKER, this);
+ w.parker = wt; // emulate LockSupport.park
+ if (w.eventCount == ec && ctl == c)
+ U.park(false, parkTime); // must recheck before park
+ w.parker = null;
+ U.putObject(wt, PARKBLOCKER, null);
+ if (parkTime != 0L && ctl == c &&
+ deadline - System.nanoTime() <= 0L &&
+ U.compareAndSwapLong(this, CTL, c, pc))
+ stat = w.qlock = -1; // shrink pool
}
}
}
+ return stat;
}
/**
- * Scans through queues looking for work (optionally, while
- * joining a task); if any present, signals. May return early if
- * more signalling is detectably unneeded.
- *
- * @param task if non-null, return early if done
- * @param origin an index to start scan
- * @param once if only the origin should be checked
- */
- private void helpSignal(ForkJoinTask> task, int origin, boolean once) {
- WorkQueue[] ws; WorkQueue w; Thread p; long c; int m, u, e, i, s;
- if ((u = (int)(ctl >>> 32)) < 0 && (u >> UAC_SHIFT) < 0 &&
- (ws = workQueues) != null && (m = ws.length - 1) >= 0) {
- outer: for (int k = origin, j = once ? 0 : m; j >= 0; --j) {
- WorkQueue q = ws[k++ & m];
- for (int n = m;;) { // limit to at most m signals
- if (task != null && task.status < 0)
- break outer;
- if (q == null ||
- ((s = (task == null ? -1 : 0) - q.base + q.top) <= n &&
- (n = s) <= 0))
- break;
- if ((u = (int)((c = ctl) >>> 32)) >= 0 ||
- (e = (int)c) <= 0 || m < (i = e & SMASK) ||
- (w = ws[i]) == null)
- break outer;
- long nc = (((long)(w.nextWait & E_MASK)) |
- ((long)(u + UAC_UNIT) << 32));
- if (w.eventCount == (e | INT_SIGN) &&
- U.compareAndSwapLong(this, CTL, c, nc)) {
- w.eventCount = (e + E_SEQ) & E_MASK;
- if ((p = w.parker) != null)
- U.unpark(p);
- if (--n <= 0)
- break;
- }
- }
+ * Possibly releases (signals) a worker. Called only from scan()
+ * when a worker with apparently inactive status finds a non-empty
+ * queue. This requires revalidating all of the associated state
+ * from caller.
+ */
+ private final void helpRelease(long c, WorkQueue[] ws, WorkQueue w,
+ WorkQueue q, int b) {
+ WorkQueue v; int e, i; Thread p;
+ if (w != null && w.eventCount < 0 && (e = (int)c) > 0 &&
+ ws != null && ws.length > (i = e & SMASK) &&
+ (v = ws[i]) != null && ctl == c) {
+ long nc = (((long)(v.nextWait & E_MASK)) |
+ ((long)((int)(c >>> 32) + UAC_UNIT)) << 32);
+ int ne = (e + E_SEQ) & E_MASK;
+ if (q != null && q.base == b && w.eventCount < 0 &&
+ v.eventCount == (e | INT_SIGN) &&
+ U.compareAndSwapLong(this, CTL, c, nc)) {
+ v.eventCount = ne;
+ if ((p = v.parker) != null)
+ U.unpark(p);
}
}
}
@@ -1836,7 +1811,8 @@ public class ForkJoinPool extends Abstra
*/
private int tryHelpStealer(WorkQueue joiner, ForkJoinTask> task) {
int stat = 0, steps = 0; // bound to avoid cycles
- if (joiner != null && task != null) { // hoist null checks
+ if (task != null && joiner != null &&
+ joiner.base - joiner.top >= 0) { // hoist checks
restart: for (;;) {
ForkJoinTask> subtask = task; // current target
for (WorkQueue j = joiner, v;;) { // v is stealer of subtask
@@ -1863,7 +1839,7 @@ public class ForkJoinPool extends Abstra
}
}
for (;;) { // help stealer or descend to its stealer
- ForkJoinTask[] a; int b;
+ ForkJoinTask[] a; int b;
if (subtask.status < 0) // surround probes with
continue restart; // consistency checks
if ((b = v.base) - v.top < 0 && (a = v.array) != null) {
@@ -1874,13 +1850,23 @@ public class ForkJoinPool extends Abstra
v.currentSteal != subtask)
continue restart; // stale
stat = 1; // apparent progress
- if (t != null && v.base == b &&
- U.compareAndSwapObject(a, i, t, null)) {
- v.base = b + 1; // help stealer
- joiner.runSubtask(t);
+ if (v.base == b) {
+ if (t == null)
+ break restart;
+ if (U.compareAndSwapObject(a, i, t, null)) {
+ U.putOrderedInt(v, QBASE, b + 1);
+ ForkJoinTask> ps = joiner.currentSteal;
+ int jt = joiner.top;
+ do {
+ joiner.currentSteal = t;
+ t.doExec(); // clear local tasks too
+ } while (task.status >= 0 &&
+ joiner.top != jt &&
+ (t = joiner.pop()) != null);
+ joiner.currentSteal = ps;
+ break restart;
+ }
}
- else if (v.base == b && ++steps == MAX_HELP)
- break restart; // v apparently stalled
}
else { // empty -- try to descend
ForkJoinTask> next = v.currentJoin;
@@ -1907,28 +1893,33 @@ public class ForkJoinPool extends Abstra
* and run tasks within the target's computation.
*
* @param task the task to join
- * @param mode if shared, exit upon completing any task
- * if all workers are active
- *
*/
- private int helpComplete(ForkJoinTask> task, int mode) {
- WorkQueue[] ws; WorkQueue q; int m, n, s, u;
- if (task != null && (ws = workQueues) != null &&
- (m = ws.length - 1) >= 0) {
- for (int j = 1, origin = j;;) {
+ private int helpComplete(WorkQueue joiner, CountedCompleter> task) {
+ WorkQueue[] ws; int m;
+ int s = 0;
+ if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 &&
+ joiner != null && task != null) {
+ int j = joiner.poolIndex;
+ int scans = m + m + 1;
+ long c = 0L; // for stability check
+ for (int k = scans; ; j += 2) {
+ WorkQueue q;
if ((s = task.status) < 0)
- return s;
- if ((q = ws[j & m]) != null && q.pollAndExecCC(task)) {
- origin = j;
- if (mode == SHARED_QUEUE &&
- ((u = (int)(ctl >>> 32)) >= 0 || (u >> UAC_SHIFT) >= 0))
+ break;
+ else if (joiner.internalPopAndExecCC(task))
+ k = scans;
+ else if ((s = task.status) < 0)
+ break;
+ else if ((q = ws[j & m]) != null && q.pollAndExecCC(task))
+ k = scans;
+ else if (--k < 0) {
+ if (c == (c = ctl))
break;
+ k = scans;
}
- else if ((j = (j + 2) & m) == origin)
- break;
}
}
- return 0;
+ return s;
}
/**
@@ -1937,17 +1928,22 @@ public class ForkJoinPool extends Abstra
* for blocking. Fails on contention or termination. Otherwise,
* adds a new thread if no idle workers are available and pool
* may become starved.
+ *
+ * @param c the assumed ctl value
*/
- final boolean tryCompensate() {
- int pc = config & SMASK, e, i, tc; long c;
- WorkQueue[] ws; WorkQueue w; Thread p;
- if ((ws = workQueues) != null && (e = (int)(c = ctl)) >= 0) {
- if (e != 0 && (i = e & SMASK) < ws.length &&
- (w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) {
+ final boolean tryCompensate(long c) {
+ WorkQueue[] ws = workQueues;
+ int pc = parallelism, e = (int)c, m, tc;
+ if (ws != null && (m = ws.length - 1) >= 0 && e >= 0 && ctl == c) {
+ WorkQueue w = ws[e & m];
+ if (e != 0 && w != null) {
+ Thread p;
long nc = ((long)(w.nextWait & E_MASK) |
(c & (AC_MASK|TC_MASK)));
- if (U.compareAndSwapLong(this, CTL, c, nc)) {
- w.eventCount = (e + E_SEQ) & E_MASK;
+ int ne = (e + E_SEQ) & E_MASK;
+ if (w.eventCount == (e | INT_SIGN) &&
+ U.compareAndSwapLong(this, CTL, c, nc)) {
+ w.eventCount = ne;
if ((p = w.parker) != null)
U.unpark(p);
return true; // replace with idle worker
@@ -1990,23 +1986,20 @@ public class ForkJoinPool extends Abstra
*/
final int awaitJoin(WorkQueue joiner, ForkJoinTask> task) {
int s = 0;
- if (joiner != null && task != null && (s = task.status) >= 0) {
+ if (task != null && (s = task.status) >= 0 && joiner != null) {
ForkJoinTask> prevJoin = joiner.currentJoin;
joiner.currentJoin = task;
- do {} while ((s = task.status) >= 0 && !joiner.isEmpty() &&
- joiner.tryRemoveAndExec(task)); // process local tasks
- if (s >= 0 && (s = task.status) >= 0) {
- helpSignal(task, joiner.poolIndex, false);
- if ((s = task.status) >= 0 &&
- (task instanceof CountedCompleter))
- s = helpComplete(task, LIFO_QUEUE);
- }
+ do {} while (joiner.tryRemoveAndExec(task) && // process local tasks
+ (s = task.status) >= 0);
+ if (s >= 0 && (task instanceof CountedCompleter))
+ s = helpComplete(joiner, (CountedCompleter>)task);
+ long cc = 0; // for stability checks
while (s >= 0 && (s = task.status) >= 0) {
- if ((!joiner.isEmpty() || // try helping
- (s = tryHelpStealer(joiner, task)) == 0) &&
+ if ((s = tryHelpStealer(joiner, task)) == 0 &&
(s = task.status) >= 0) {
- helpSignal(task, joiner.poolIndex, false);
- if ((s = task.status) >= 0 && tryCompensate()) {
+ if (!tryCompensate(cc))
+ cc = ctl;
+ else {
if (task.trySetSignal() && (s = task.status) >= 0) {
synchronized (task) {
if (task.status >= 0) {
@@ -2019,9 +2012,11 @@ public class ForkJoinPool extends Abstra
task.notifyAll();
}
}
- long c; // re-activate
+ long c; // reactivate
do {} while (!U.compareAndSwapLong
- (this, CTL, c = ctl, c + AC_UNIT));
+ (this, CTL, c = ctl,
+ ((c & ~AC_MASK) |
+ ((c & AC_MASK) + AC_UNIT))));
}
}
}
@@ -2043,15 +2038,11 @@ public class ForkJoinPool extends Abstra
if (joiner != null && task != null && (s = task.status) >= 0) {
ForkJoinTask> prevJoin = joiner.currentJoin;
joiner.currentJoin = task;
- do {} while ((s = task.status) >= 0 && !joiner.isEmpty() &&
- joiner.tryRemoveAndExec(task));
- if (s >= 0 && (s = task.status) >= 0) {
- helpSignal(task, joiner.poolIndex, false);
- if ((s = task.status) >= 0 &&
- (task instanceof CountedCompleter))
- s = helpComplete(task, LIFO_QUEUE);
- }
- if (s >= 0 && joiner.isEmpty()) {
+ do {} while (joiner.tryRemoveAndExec(task) && // process local tasks
+ (s = task.status) >= 0);
+ if (s >= 0) {
+ if (task instanceof CountedCompleter)
+ helpComplete(joiner, (CountedCompleter>)task);
do {} while (task.status >= 0 &&
tryHelpStealer(joiner, task) > 0);
}
@@ -2061,29 +2052,22 @@ public class ForkJoinPool extends Abstra
/**
* Returns a (probably) non-empty steal queue, if one is found
- * during a random, then cyclic scan, else null. This method must
- * be retried by caller if, by the time it tries to use the queue,
- * it is empty.
- * @param r a (random) seed for scanning
- */
- private WorkQueue findNonEmptyStealQueue(int r) {
- for (WorkQueue[] ws;;) {
- int ps = plock, m, n;
- if ((ws = workQueues) == null || (m = ws.length - 1) < 1)
- return null;
- for (int j = (m + 1) << 2; ;) {
- WorkQueue q = ws[(((r + j) << 1) | 1) & m];
- if (q != null && (n = q.base - q.top) < 0) {
- if (n < -1)
- signalWork(q);
- return q;
- }
- else if (--j < 0) {
- if (plock == ps)
- return null;
- break;
+ * during a scan, else null. This method must be retried by
+ * caller if, by the time it tries to use the queue, it is empty.
+ */
+ private WorkQueue findNonEmptyStealQueue() {
+ int r = ThreadLocalRandom.current().nextInt();
+ for (;;) {
+ int ps = plock, m; WorkQueue[] ws; WorkQueue q;
+ if ((ws = workQueues) != null && (m = ws.length - 1) >= 0) {
+ for (int j = (m + 1) << 2; j >= 0; --j) {
+ if ((q = ws[(((r - j) << 1) | 1) & m]) != null &&
+ q.base - q.top < 0)
+ return q;
}
}
+ if (plock == ps)
+ return null;
}
}
@@ -2094,38 +2078,36 @@ public class ForkJoinPool extends Abstra
* find tasks either.
*/
final void helpQuiescePool(WorkQueue w) {
+ ForkJoinTask> ps = w.currentSteal;
for (boolean active = true;;) {
- ForkJoinTask> localTask; // exhaust local queue
- while ((localTask = w.nextLocalTask()) != null)
- localTask.doExec();
- // Similar to loop in scan(), but ignoring submissions
- WorkQueue q = findNonEmptyStealQueue(w.nextSeed());
- if (q != null) {
- ForkJoinTask> t; int b;
+ long c; WorkQueue q; ForkJoinTask> t; int b;
+ while ((t = w.nextLocalTask()) != null)
+ t.doExec();
+ if ((q = findNonEmptyStealQueue()) != null) {
if (!active) { // re-establish active count
- long c;
active = true;
do {} while (!U.compareAndSwapLong
- (this, CTL, c = ctl, c + AC_UNIT));
+ (this, CTL, c = ctl,
+ ((c & ~AC_MASK) |
+ ((c & AC_MASK) + AC_UNIT))));
+ }
+ if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null) {
+ (w.currentSteal = t).doExec();
+ w.currentSteal = ps;
}
- if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
- w.runSubtask(t);
}
- else {
- long c;
- if (active) { // decrement active count without queuing
+ else if (active) { // decrement active count without queuing
+ long nc = ((c = ctl) & ~AC_MASK) | ((c & AC_MASK) - AC_UNIT);
+ if ((int)(nc >> AC_SHIFT) + parallelism == 0)
+ break; // bypass decrement-then-increment
+ if (U.compareAndSwapLong(this, CTL, c, nc))
active = false;
- do {} while (!U.compareAndSwapLong
- (this, CTL, c = ctl, c -= AC_UNIT));
- }
- else
- c = ctl; // re-increment on exit
- if ((int)(c >> AC_SHIFT) + (config & SMASK) == 0) {
- do {} while (!U.compareAndSwapLong
- (this, CTL, c = ctl, c + AC_UNIT));
- break;
- }
}
+ else if ((int)((c = ctl) >> AC_SHIFT) + parallelism <= 0 &&
+ U.compareAndSwapLong
+ (this, CTL, c, ((c & ~AC_MASK) |
+ ((c & AC_MASK) + AC_UNIT))))
+ break;
}
}
@@ -2139,7 +2121,7 @@ public class ForkJoinPool extends Abstra
WorkQueue q; int b;
if ((t = w.nextLocalTask()) != null)
return t;
- if ((q = findNonEmptyStealQueue(w.nextSeed())) == null)
+ if ((q = findNonEmptyStealQueue()) == null)
return null;
if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
return t;
@@ -2171,7 +2153,7 @@ public class ForkJoinPool extends Abstra
* producing extra tasks amortizes the uncertainty of progress and
* diffusion assumptions.
*
- * So, users will want to use values larger, but not much larger
+ * So, users will want to use values larger (but not much larger)
* than 1 to both smooth over transient shortages and hedge
* against uneven progress; as traded off against the cost of
* extra task overhead. We leave the user to pick a threshold
@@ -2195,7 +2177,7 @@ public class ForkJoinPool extends Abstra
static int getSurplusQueuedTaskCount() {
Thread t; ForkJoinWorkerThread wt; ForkJoinPool pool; WorkQueue q;
if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) {
- int p = (pool = (wt = (ForkJoinWorkerThread)t).pool).config & SMASK;
+ int p = (pool = (wt = (ForkJoinWorkerThread)t).pool).parallelism;
int n = (q = wt.workQueue).top - q.base;
int a = (int)(pool.ctl >> AC_SHIFT) + p;
return n - (a > (p >>>= 1) ? 0 :
@@ -2224,61 +2206,69 @@ public class ForkJoinPool extends Abstra
* @return true if now terminating or terminated
*/
private boolean tryTerminate(boolean now, boolean enable) {
- if (this == commonPool) // cannot shut down
+ int ps;
+ if (this == common) // cannot shut down
return false;
+ if ((ps = plock) >= 0) { // enable by setting plock
+ if (!enable)
+ return false;
+ if ((ps & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ int nps = ((ps + PL_LOCK) & ~SHUTDOWN) | SHUTDOWN;
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
+ }
for (long c;;) {
- if (((c = ctl) & STOP_BIT) != 0) { // already terminating
- if ((short)(c >>> TC_SHIFT) == -(config & SMASK)) {
+ if (((c = ctl) & STOP_BIT) != 0) { // already terminating
+ if ((short)(c >>> TC_SHIFT) + parallelism <= 0) {
synchronized (this) {
- notifyAll(); // signal when 0 workers
+ notifyAll(); // signal when 0 workers
}
}
return true;
}
- if (plock >= 0) { // not yet enabled
- int ps;
- if (!enable)
- return false;
- if (((ps = plock) & PL_LOCK) != 0 ||
- !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
- ps = acquirePlock();
- int nps = SHUTDOWN;
- if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
- releasePlock(nps);
- }
- if (!now) { // check if idle & no tasks
- if ((int)(c >> AC_SHIFT) != -(config & SMASK) ||
- hasQueuedSubmissions())
+ if (!now) { // check if idle & no tasks
+ WorkQueue[] ws; WorkQueue w;
+ if ((int)(c >> AC_SHIFT) + parallelism > 0)
return false;
- // Check for unqueued inactive workers. One pass suffices.
- WorkQueue[] ws = workQueues; WorkQueue w;
- if (ws != null) {
- for (int i = 1; i < ws.length; i += 2) {
- if ((w = ws[i]) != null && w.eventCount >= 0)
+ if ((ws = workQueues) != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ if ((w = ws[i]) != null &&
+ (!w.isEmpty() ||
+ ((i & 1) != 0 && w.eventCount >= 0))) {
+ signalWork(ws, w);
return false;
+ }
}
}
}
if (U.compareAndSwapLong(this, CTL, c, c | STOP_BIT)) {
for (int pass = 0; pass < 3; ++pass) {
- WorkQueue[] ws = workQueues;
- if (ws != null) {
- WorkQueue w;
+ WorkQueue[] ws; WorkQueue w; Thread wt;
+ if ((ws = workQueues) != null) {
int n = ws.length;
for (int i = 0; i < n; ++i) {
if ((w = ws[i]) != null) {
w.qlock = -1;
if (pass > 0) {
w.cancelAll();
- if (pass > 1)
- w.interruptOwner();
+ if (pass > 1 && (wt = w.owner) != null) {
+ if (!wt.isInterrupted()) {
+ try {
+ wt.interrupt();
+ } catch (Throwable ignore) {
+ }
+ }
+ U.unpark(wt);
+ }
}
}
}
// Wake up workers parked on event queue
int i, e; long cc; Thread p;
while ((e = (int)(cc = ctl) & E_MASK) != 0 &&
- (i = e & SMASK) < n &&
+ (i = e & SMASK) < n && i >= 0 &&
(w = ws[i]) != null) {
long nc = ((long)(w.nextWait & E_MASK) |
((cc + AC_UNIT) & AC_MASK) |
@@ -2304,9 +2294,9 @@ public class ForkJoinPool extends Abstra
* least one task.
*/
static WorkQueue commonSubmitterQueue() {
- ForkJoinPool p; WorkQueue[] ws; int m; Submitter z;
+ Submitter z; ForkJoinPool p; WorkQueue[] ws; int m, r;
return ((z = submitters.get()) != null &&
- (p = commonPool) != null &&
+ (p = common) != null &&
(ws = p.workQueues) != null &&
(m = ws.length - 1) >= 0) ?
ws[m & z.seed & SQMASK] : null;
@@ -2315,127 +2305,57 @@ public class ForkJoinPool extends Abstra
/**
* Tries to pop the given task from submitter's queue in common pool.
*/
- static boolean tryExternalUnpush(ForkJoinTask> t) {
- ForkJoinPool p; WorkQueue[] ws; WorkQueue q; Submitter z;
- ForkJoinTask>[] a; int m, s;
- if (t != null &&
- (z = submitters.get()) != null &&
- (p = commonPool) != null &&
- (ws = p.workQueues) != null &&
- (m = ws.length - 1) >= 0 &&
- (q = ws[m & z.seed & SQMASK]) != null &&
- (s = q.top) != q.base &&
- (a = q.array) != null) {
+ final boolean tryExternalUnpush(ForkJoinTask> task) {
+ WorkQueue joiner; ForkJoinTask>[] a; int m, s;
+ Submitter z = submitters.get();
+ WorkQueue[] ws = workQueues;
+ boolean popped = false;
+ if (z != null && ws != null && (m = ws.length - 1) >= 0 &&
+ (joiner = ws[z.seed & m & SQMASK]) != null &&
+ joiner.base != (s = joiner.top) &&
+ (a = joiner.array) != null) {
long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE;
- if (U.getObject(a, j) == t &&
- U.compareAndSwapInt(q, QLOCK, 0, 1)) {
- if (q.array == a && q.top == s && // recheck
- U.compareAndSwapObject(a, j, t, null)) {
- q.top = s - 1;
- q.qlock = 0;
- return true;
+ if (U.getObject(a, j) == task &&
+ U.compareAndSwapInt(joiner, QLOCK, 0, 1)) {
+ if (joiner.top == s && joiner.array == a &&
+ U.compareAndSwapObject(a, j, task, null)) {
+ joiner.top = s - 1;
+ popped = true;
}
- q.qlock = 0;
+ joiner.qlock = 0;
}
}
- return false;
+ return popped;
}
- /**
- * Tries to pop and run local tasks within the same computation
- * as the given root. On failure, tries to help complete from
- * other queues via helpComplete.
- */
- private void externalHelpComplete(WorkQueue q, ForkJoinTask> root) {
- ForkJoinTask>[] a; int m;
- if (q != null && (a = q.array) != null && (m = (a.length - 1)) >= 0 &&
- root != null && root.status >= 0) {
- for (;;) {
- int s, u; Object o; CountedCompleter> task = null;
- if ((s = q.top) - q.base > 0) {
- long j = ((m & (s - 1)) << ASHIFT) + ABASE;
- if ((o = U.getObject(a, j)) != null &&
- (o instanceof CountedCompleter)) {
- CountedCompleter> t = (CountedCompleter>)o, r = t;
- do {
- if (r == root) {
- if (U.compareAndSwapInt(q, QLOCK, 0, 1)) {
- if (q.array == a && q.top == s &&
- U.compareAndSwapObject(a, j, t, null)) {
- q.top = s - 1;
- task = t;
- }
- q.qlock = 0;
- }
- break;
- }
- } while ((r = r.completer) != null);
- }
- }
- if (task != null)
- task.doExec();
- if (root.status < 0 ||
- (u = (int)(ctl >>> 32)) >= 0 || (u >> UAC_SHIFT) >= 0)
+ final int externalHelpComplete(CountedCompleter> task) {
+ WorkQueue joiner; int m, j;
+ Submitter z = submitters.get();
+ WorkQueue[] ws = workQueues;
+ int s = 0;
+ if (z != null && ws != null && (m = ws.length - 1) >= 0 &&
+ (joiner = ws[(j = z.seed) & m & SQMASK]) != null && task != null) {
+ int scans = m + m + 1;
+ long c = 0L; // for stability check
+ j |= 1; // poll odd queues
+ for (int k = scans; ; j += 2) {
+ WorkQueue q;
+ if ((s = task.status) < 0)
break;
- if (task == null) {
- helpSignal(root, q.poolIndex, false);
- if (root.status >= 0)
- helpComplete(root, SHARED_QUEUE);
+ else if (joiner.externalPopAndExecCC(task))
+ k = scans;
+ else if ((s = task.status) < 0)
break;
+ else if ((q = ws[j & m]) != null && q.pollAndExecCC(task))
+ k = scans;
+ else if (--k < 0) {
+ if (c == (c = ctl))
+ break;
+ k = scans;
}
}
}
- }
-
- /**
- * Tries to help execute or signal availability of the given task
- * from submitter's queue in common pool.
- */
- static void externalHelpJoin(ForkJoinTask> t) {
- // Some hard-to-avoid overlap with tryExternalUnpush
- ForkJoinPool p; WorkQueue[] ws; WorkQueue q, w; Submitter z;
- ForkJoinTask>[] a; int m, s, n;
- if (t != null &&
- (z = submitters.get()) != null &&
- (p = commonPool) != null &&
- (ws = p.workQueues) != null &&
- (m = ws.length - 1) >= 0 &&
- (q = ws[m & z.seed & SQMASK]) != null &&
- (a = q.array) != null) {
- int am = a.length - 1;
- if ((s = q.top) != q.base) {
- long j = ((am & (s - 1)) << ASHIFT) + ABASE;
- if (U.getObject(a, j) == t &&
- U.compareAndSwapInt(q, QLOCK, 0, 1)) {
- if (q.array == a && q.top == s &&
- U.compareAndSwapObject(a, j, t, null)) {
- q.top = s - 1;
- q.qlock = 0;
- t.doExec();
- }
- else
- q.qlock = 0;
- }
- }
- if (t.status >= 0) {
- if (t instanceof CountedCompleter)
- p.externalHelpComplete(q, t);
- else
- p.helpSignal(t, q.poolIndex, false);
- }
- }
- }
-
- /**
- * Restricted version of helpQuiescePool for external callers
- */
- static void externalHelpQuiescePool() {
- ForkJoinPool p; ForkJoinTask> t; WorkQueue q; int b;
- if ((p = commonPool) != null &&
- (q = p.findNonEmptyStealQueue(1)) != null &&
- (b = q.base) - q.top < 0 &&
- (t = q.pollAt(b)) != null)
- t.doExec();
+ return s;
}
// Exported methods
@@ -2454,7 +2374,7 @@ public class ForkJoinPool extends Abstra
* java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool() {
- this(Runtime.getRuntime().availableProcessors(),
+ this(Math.min(MAX_CAP, Runtime.getRuntime().availableProcessors()),
defaultForkJoinWorkerThreadFactory, null, false);
}
@@ -2502,47 +2422,64 @@ public class ForkJoinPool extends Abstra
*/
public ForkJoinPool(int parallelism,
ForkJoinWorkerThreadFactory factory,
- Thread.UncaughtExceptionHandler handler,
+ UncaughtExceptionHandler handler,
boolean asyncMode) {
+ this(checkParallelism(parallelism),
+ checkFactory(factory),
+ handler,
+ (asyncMode ? FIFO_QUEUE : LIFO_QUEUE),
+ "ForkJoinPool-" + nextPoolId() + "-worker-");
checkPermission();
- if (factory == null)
- throw new NullPointerException();
+ }
+
+ private static int checkParallelism(int parallelism) {
if (parallelism <= 0 || parallelism > MAX_CAP)
throw new IllegalArgumentException();
- this.factory = factory;
- this.ueh = handler;
- this.config = parallelism | (asyncMode ? (FIFO_QUEUE << 16) : 0);
- long np = (long)(-parallelism); // offset ctl counts
- this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
- int pn = nextPoolId();
- StringBuilder sb = new StringBuilder("ForkJoinPool-");
- sb.append(Integer.toString(pn));
- sb.append("-worker-");
- this.workerNamePrefix = sb.toString();
+ return parallelism;
+ }
+
+ private static ForkJoinWorkerThreadFactory checkFactory
+ (ForkJoinWorkerThreadFactory factory) {
+ if (factory == null)
+ throw new NullPointerException();
+ return factory;
}
/**
- * Constructor for common pool, suitable only for static initialization.
- * Basically the same as above, but uses smallest possible initial footprint.
- */
- ForkJoinPool(int parallelism, long ctl,
- ForkJoinWorkerThreadFactory factory,
- Thread.UncaughtExceptionHandler handler) {
- this.config = parallelism;
- this.ctl = ctl;
+ * Creates a {@code ForkJoinPool} with the given parameters, without
+ * any security checks or parameter validation. Invoked directly by
+ * makeCommonPool.
+ */
+ private ForkJoinPool(int parallelism,
+ ForkJoinWorkerThreadFactory factory,
+ UncaughtExceptionHandler handler,
+ int mode,
+ String workerNamePrefix) {
+ this.workerNamePrefix = workerNamePrefix;
this.factory = factory;
this.ueh = handler;
- this.workerNamePrefix = "ForkJoinPool.commonPool-worker-";
+ this.mode = (short)mode;
+ this.parallelism = (short)parallelism;
+ long np = (long)(-parallelism); // offset ctl counts
+ this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
}
/**
- * Returns the common pool instance.
+ * Returns the common pool instance. This pool is statically
+ * constructed; its run state is unaffected by attempts to {@link
+ * #shutdown} or {@link #shutdownNow}. However this pool and any
+ * ongoing processing are automatically terminated upon program
+ * {@link System#exit}. Any program that relies on asynchronous
+ * task processing to complete before program termination should
+ * invoke {@code commonPool().}{@link #awaitQuiescence awaitQuiescence},
+ * before exit.
*
* @return the common pool instance
+ * @since 1.8
*/
public static ForkJoinPool commonPool() {
- // assert commonPool != null : "static init error";
- return commonPool;
+ // assert common != null : "static init error";
+ return common;
}
// Execution methods
@@ -2598,7 +2535,7 @@ public class ForkJoinPool extends Abstra
if (task instanceof ForkJoinTask>) // avoid re-wrap
job = (ForkJoinTask>) task;
else
- job = new ForkJoinTask.AdaptedRunnableAction(task);
+ job = new ForkJoinTask.RunnableExecuteAction(task);
externalPush(job);
}
@@ -2665,27 +2602,23 @@ public class ForkJoinPool extends Abstra
// In previous versions of this class, this method constructed
// a task to run ForkJoinTask.invokeAll, but now external
// invocation of multiple tasks is at least as efficient.
- List> fs = new ArrayList>(tasks.size());
- // Workaround needed because method wasn't declared with
- // wildcards in return type but should have been.
- @SuppressWarnings({"unchecked", "rawtypes"})
- List> futures = (List>) (List) fs;
+ ArrayList> futures = new ArrayList>(tasks.size());
boolean done = false;
try {
for (Callable t : tasks) {
ForkJoinTask f = new ForkJoinTask.AdaptedCallable(t);
+ futures.add(f);
externalPush(f);
- fs.add(f);
}
- for (ForkJoinTask f : fs)
- f.quietlyJoin();
+ for (int i = 0, size = futures.size(); i < size; i++)
+ ((ForkJoinTask>)futures.get(i)).quietlyJoin();
done = true;
return futures;
} finally {
if (!done)
- for (ForkJoinTask f : fs)
- f.cancel(false);
+ for (int i = 0, size = futures.size(); i < size; i++)
+ futures.get(i).cancel(false);
}
}
@@ -2704,7 +2637,7 @@ public class ForkJoinPool extends Abstra
*
* @return the handler, or {@code null} if none
*/
- public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
+ public UncaughtExceptionHandler getUncaughtExceptionHandler() {
return ueh;
}
@@ -2714,16 +2647,18 @@ public class ForkJoinPool extends Abstra
* @return the targeted parallelism level of this pool
*/
public int getParallelism() {
- return config & SMASK;
+ int par;
+ return ((par = parallelism) > 0) ? par : 1;
}
/**
* Returns the targeted parallelism level of the common pool.
*
* @return the targeted parallelism level of the common pool
+ * @since 1.8
*/
public static int getCommonPoolParallelism() {
- return commonPoolParallelism;
+ return commonParallelism;
}
/**
@@ -2735,7 +2670,7 @@ public class ForkJoinPool extends Abstra
* @return the number of worker threads
*/
public int getPoolSize() {
- return (config & SMASK) + (short)(ctl >>> TC_SHIFT);
+ return parallelism + (short)(ctl >>> TC_SHIFT);
}
/**
@@ -2745,7 +2680,7 @@ public class ForkJoinPool extends Abstra
* @return {@code true} if this pool uses async mode
*/
public boolean getAsyncMode() {
- return (config >>> 16) == FIFO_QUEUE;
+ return mode == FIFO_QUEUE;
}
/**
@@ -2776,7 +2711,7 @@ public class ForkJoinPool extends Abstra
* @return the number of active threads
*/
public int getActiveThreadCount() {
- int r = (config & SMASK) + (int)(ctl >> AC_SHIFT);
+ int r = parallelism + (int)(ctl >> AC_SHIFT);
return (r <= 0) ? 0 : r; // suppress momentarily negative values
}
@@ -2792,7 +2727,7 @@ public class ForkJoinPool extends Abstra
* @return {@code true} if all threads are currently idle
*/
public boolean isQuiescent() {
- return (int)(ctl >> AC_SHIFT) + (config & SMASK) == 0;
+ return parallelism + (int)(ctl >> AC_SHIFT) <= 0;
}
/**
@@ -2955,7 +2890,7 @@ public class ForkJoinPool extends Abstra
}
}
}
- int pc = (config & SMASK);
+ int pc = parallelism;
int tc = pc + (short)(c >>> TC_SHIFT);
int ac = pc + (int)(c >> AC_SHIFT);
if (ac < 0) // ignore transient negative
@@ -2981,7 +2916,7 @@ public class ForkJoinPool extends Abstra
* Possibly initiates an orderly shutdown in which previously
* submitted tasks are executed, but no new tasks will be
* accepted. Invocation has no effect on execution state if this
- * is the {@link #commonPool}, and no additional effect if
+ * is the {@link #commonPool()}, and 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.
@@ -2999,7 +2934,7 @@ public class ForkJoinPool extends Abstra
/**
* Possibly attempts to cancel and/or stop all tasks, and reject
* all subsequently submitted tasks. Invocation has no effect on
- * execution state if this is the {@link #commonPool}, and no
+ * execution state if this is the {@link #commonPool()}, and no
* additional effect if already shut down. Otherwise, tasks that
* are in the process of being submitted or executed concurrently
* during the course of this method may or may not be
@@ -3028,7 +2963,7 @@ public class ForkJoinPool extends Abstra
public boolean isTerminated() {
long c = ctl;
return ((c & STOP_BIT) != 0L &&
- (short)(c >>> TC_SHIFT) == -(config & SMASK));
+ (short)(c >>> TC_SHIFT) + parallelism <= 0);
}
/**
@@ -3036,7 +2971,7 @@ public class ForkJoinPool extends Abstra
* commenced but not yet completed. This method may be useful for
* debugging. A return of {@code true} reported a sufficient
* period after shutdown may indicate that submitted tasks have
- * ignored or suppressed interruption, or are waiting for IO,
+ * ignored or suppressed interruption, or are waiting for I/O,
* causing this executor not to properly terminate. (See the
* advisory notes for class {@link ForkJoinTask} stating that
* tasks should not normally entail blocking operations. But if
@@ -3047,7 +2982,7 @@ public class ForkJoinPool extends Abstra
public boolean isTerminating() {
long c = ctl;
return ((c & STOP_BIT) != 0L &&
- (short)(c >>> TC_SHIFT) != -(config & SMASK));
+ (short)(c >>> TC_SHIFT) + parallelism > 0);
}
/**
@@ -3062,9 +2997,10 @@ public class ForkJoinPool extends Abstra
/**
* Blocks until all tasks have completed execution after a
* shutdown request, or the timeout occurs, or the current thread
- * is interrupted, whichever happens first. Note that the {@link
- * #commonPool()} never terminates until program shutdown so
- * this method will always time out.
+ * is interrupted, whichever happens first. Because the {@link
+ * #commonPool()} never terminates until program shutdown, when
+ * applied to the common pool, this method is equivalent to {@link
+ * #awaitQuiescence(long, TimeUnit)} but always returns {@code false}.
*
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
@@ -3074,22 +3010,82 @@ public class ForkJoinPool extends Abstra
*/
public boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException {
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ if (this == common) {
+ awaitQuiescence(timeout, unit);
+ return false;
+ }
long nanos = unit.toNanos(timeout);
if (isTerminated())
return true;
- long startTime = System.nanoTime();
- boolean terminated = false;
+ if (nanos <= 0L)
+ return false;
+ long deadline = System.nanoTime() + nanos;
synchronized (this) {
- for (long waitTime = nanos, millis = 0L;;) {
- if (terminated = isTerminated() ||
- waitTime <= 0L ||
- (millis = unit.toMillis(waitTime)) <= 0L)
+ for (;;) {
+ if (isTerminated())
+ return true;
+ if (nanos <= 0L)
+ return false;
+ long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
+ wait(millis > 0L ? millis : 1L);
+ nanos = deadline - System.nanoTime();
+ }
+ }
+ }
+
+ /**
+ * If called by a ForkJoinTask operating in this pool, equivalent
+ * in effect to {@link ForkJoinTask#helpQuiesce}. Otherwise,
+ * waits and/or attempts to assist performing tasks until this
+ * pool {@link #isQuiescent} or the indicated timeout elapses.
+ *
+ * @param timeout the maximum time to wait
+ * @param unit the time unit of the timeout argument
+ * @return {@code true} if quiescent; {@code false} if the
+ * timeout elapsed.
+ */
+ public boolean awaitQuiescence(long timeout, TimeUnit unit) {
+ long nanos = unit.toNanos(timeout);
+ ForkJoinWorkerThread wt;
+ Thread thread = Thread.currentThread();
+ if ((thread instanceof ForkJoinWorkerThread) &&
+ (wt = (ForkJoinWorkerThread)thread).pool == this) {
+ helpQuiescePool(wt.workQueue);
+ return true;
+ }
+ long startTime = System.nanoTime();
+ WorkQueue[] ws;
+ int r = 0, m;
+ boolean found = true;
+ while (!isQuiescent() && (ws = workQueues) != null &&
+ (m = ws.length - 1) >= 0) {
+ if (!found) {
+ if ((System.nanoTime() - startTime) > nanos)
+ return false;
+ Thread.yield(); // cannot block
+ }
+ found = false;
+ for (int j = (m + 1) << 2; j >= 0; --j) {
+ ForkJoinTask> t; WorkQueue q; int b;
+ if ((q = ws[r++ & m]) != null && (b = q.base) - q.top < 0) {
+ found = true;
+ if ((t = q.pollAt(b)) != null)
+ t.doExec();
break;
- wait(millis);
- waitTime = nanos - (System.nanoTime() - startTime);
+ }
}
}
- return terminated;
+ return true;
+ }
+
+ /**
+ * Waits and/or attempts to assist performing tasks indefinitely
+ * until the {@link #commonPool()} {@link #isQuiescent}.
+ */
+ static void quiesceCommonPool() {
+ common.awaitQuiescence(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
}
/**
@@ -3101,9 +3097,9 @@ public class ForkJoinPool extends Abstra
* not necessary. Method {@code block} blocks the current thread
* if necessary (perhaps internally invoking {@code isReleasable}
* before actually blocking). These actions are performed by any
- * thread invoking {@link ForkJoinPool#managedBlock}. The
- * unusual methods in this API accommodate synchronizers that may,
- * but don't usually, block for long periods. Similarly, they
+ * thread invoking {@link ForkJoinPool#managedBlock(ManagedBlocker)}.
+ * The unusual methods in this API accommodate synchronizers that
+ * may, but don't usually, block for long periods. Similarly, they
* allow more efficient internal handling of cases in which
* additional workers may be, but usually are not, needed to
* ensure sufficient parallelism. Toward this end,
@@ -3161,6 +3157,7 @@ public class ForkJoinPool extends Abstra
/**
* Returns {@code true} if blocking is unnecessary.
+ * @return {@code true} if blocking is unnecessary
*/
boolean isReleasable();
}
@@ -3190,21 +3187,8 @@ public class ForkJoinPool extends Abstra
Thread t = Thread.currentThread();
if (t instanceof ForkJoinWorkerThread) {
ForkJoinPool p = ((ForkJoinWorkerThread)t).pool;
- while (!blocker.isReleasable()) { // variant of helpSignal
- WorkQueue[] ws; WorkQueue q; int m, u;
- if ((ws = p.workQueues) != null && (m = ws.length - 1) >= 0) {
- for (int i = 0; i <= m; ++i) {
- if (blocker.isReleasable())
- return;
- if ((q = ws[i]) != null && q.base - q.top < 0) {
- p.signalWork(q);
- if ((u = (int)(p.ctl >>> 32)) >= 0 ||
- (u >> UAC_SHIFT) >= 0)
- break;
- }
- }
- }
- if (p.tryCompensate()) {
+ while (!blocker.isReleasable()) {
+ if (p.tryCompensate(p.ctl)) {
try {
do {} while (!blocker.isReleasable() &&
!blocker.block());
@@ -3242,10 +3226,11 @@ public class ForkJoinPool extends Abstra
private static final long STEALCOUNT;
private static final long PLOCK;
private static final long INDEXSEED;
+ private static final long QBASE;
private static final long QLOCK;
static {
- int s; // initialize field offsets for CAS etc
+ // initialize field offsets for CAS etc
try {
U = getUnsafe();
Class> k = ForkJoinPool.class;
@@ -3261,58 +3246,66 @@ public class ForkJoinPool extends Abstra
PARKBLOCKER = U.objectFieldOffset
(tk.getDeclaredField("parkBlocker"));
Class> wk = WorkQueue.class;
+ QBASE = U.objectFieldOffset
+ (wk.getDeclaredField("base"));
QLOCK = U.objectFieldOffset
(wk.getDeclaredField("qlock"));
Class> ak = ForkJoinTask[].class;
ABASE = U.arrayBaseOffset(ak);
- s = U.arrayIndexScale(ak);
- ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
+ int scale = U.arrayIndexScale(ak);
+ if ((scale & (scale - 1)) != 0)
+ throw new Error("data type scale not a power of two");
+ ASHIFT = 31 - Integer.numberOfLeadingZeros(scale);
} catch (Exception e) {
throw new Error(e);
}
- if ((s & (s-1)) != 0)
- throw new Error("data type scale not a power of two");
submitters = new ThreadLocal();
- ForkJoinWorkerThreadFactory fac = defaultForkJoinWorkerThreadFactory =
+ defaultForkJoinWorkerThreadFactory =
new DefaultForkJoinWorkerThreadFactory();
modifyThreadPermission = new RuntimePermission("modifyThread");
- /*
- * Establish common pool parameters. For extra caution,
- * computations to set up common pool state are here; the
- * constructor just assigns these values to fields.
- */
+ common = java.security.AccessController.doPrivileged
+ (new java.security.PrivilegedAction() {
+ public ForkJoinPool run() { return makeCommonPool(); }});
+ int par = common.parallelism; // report 1 even if threads disabled
+ commonParallelism = par > 0 ? par : 1;
+ }
- int par = 0;
- Thread.UncaughtExceptionHandler handler = null;
- try { // TBD: limit or report ignored exceptions?
+ /**
+ * Creates and returns the common pool, respecting user settings
+ * specified via system properties.
+ */
+ private static ForkJoinPool makeCommonPool() {
+ int parallelism = -1;
+ ForkJoinWorkerThreadFactory factory
+ = defaultForkJoinWorkerThreadFactory;
+ UncaughtExceptionHandler handler = null;
+ try { // ignore exceptions in accesing/parsing properties
String pp = System.getProperty
("java.util.concurrent.ForkJoinPool.common.parallelism");
- String hp = System.getProperty
- ("java.util.concurrent.ForkJoinPool.common.exceptionHandler");
String fp = System.getProperty
("java.util.concurrent.ForkJoinPool.common.threadFactory");
+ String hp = System.getProperty
+ ("java.util.concurrent.ForkJoinPool.common.exceptionHandler");
+ if (pp != null)
+ parallelism = Integer.parseInt(pp);
if (fp != null)
- fac = ((ForkJoinWorkerThreadFactory)ClassLoader.
- getSystemClassLoader().loadClass(fp).newInstance());
+ factory = ((ForkJoinWorkerThreadFactory)ClassLoader.
+ getSystemClassLoader().loadClass(fp).newInstance());
if (hp != null)
- handler = ((Thread.UncaughtExceptionHandler)ClassLoader.
+ handler = ((UncaughtExceptionHandler)ClassLoader.
getSystemClassLoader().loadClass(hp).newInstance());
- if (pp != null)
- par = Integer.parseInt(pp);
} catch (Exception ignore) {
}
- if (par <= 0)
- par = Runtime.getRuntime().availableProcessors();
- if (par > MAX_CAP)
- par = MAX_CAP;
- commonPoolParallelism = par;
- long np = (long)(-par); // precompute initial ctl value
- long ct = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
-
- commonPool = new ForkJoinPool(par, ct, fac, handler);
+ if (parallelism < 0 && // default 1 less than #cores
+ (parallelism = Runtime.getRuntime().availableProcessors() - 1) < 0)
+ parallelism = 0;
+ if (parallelism > MAX_CAP)
+ parallelism = MAX_CAP;
+ return new ForkJoinPool(parallelism, factory, handler, LIFO_QUEUE,
+ "ForkJoinPool.commonPool-worker-");
}
/**
@@ -3325,22 +3318,23 @@ public class ForkJoinPool extends Abstra
private static sun.misc.Unsafe getUnsafe() {
try {
return sun.misc.Unsafe.getUnsafe();
- } catch (SecurityException se) {
- try {
- return java.security.AccessController.doPrivileged
- (new java.security
- .PrivilegedExceptionAction() {
- public sun.misc.Unsafe run() throws Exception {
- java.lang.reflect.Field f = sun.misc
- .Unsafe.class.getDeclaredField("theUnsafe");
- f.setAccessible(true);
- return (sun.misc.Unsafe) f.get(null);
- }});
- } catch (java.security.PrivilegedActionException e) {
- throw new RuntimeException("Could not initialize intrinsics",
- e.getCause());
- }
+ } catch (SecurityException tryReflectionInstead) {}
+ try {
+ return java.security.AccessController.doPrivileged
+ (new java.security.PrivilegedExceptionAction() {
+ public sun.misc.Unsafe run() throws Exception {
+ Class k = sun.misc.Unsafe.class;
+ for (java.lang.reflect.Field f : k.getDeclaredFields()) {
+ f.setAccessible(true);
+ Object x = f.get(null);
+ if (k.isInstance(x))
+ return k.cast(x);
+ }
+ throw new NoSuchFieldError("the Unsafe");
+ }});
+ } catch (java.security.PrivilegedActionException e) {
+ throw new RuntimeException("Could not initialize intrinsics",
+ e.getCause());
}
}
-
}