--- jsr166/src/jsr166y/ForkJoinPool.java 2012/10/31 12:49:24 1.139
+++ jsr166/src/jsr166y/ForkJoinPool.java 2012/11/14 17:20:37 1.140
@@ -11,7 +11,6 @@ import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
-import java.util.Random;
import java.util.concurrent.AbstractExecutorService;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
@@ -19,10 +18,6 @@ import java.util.concurrent.Future;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.RunnableFuture;
import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicInteger;
-import java.util.concurrent.atomic.AtomicLong;
-import java.util.concurrent.locks.AbstractQueuedSynchronizer;
-import java.util.concurrent.locks.Condition;
/**
* An {@link ExecutorService} for running {@link ForkJoinTask}s.
@@ -47,11 +42,7 @@ import java.util.concurrent.locks.Condit
* is not explicitly submitted to a specified pool. Using the common
* pool normally reduces resource usage (its threads are slowly
* reclaimed during periods of non-use, and reinstated upon subsequent
- * use). The common pool is by default constructed with default
- * parameters, but these may be controlled by setting any or all of
- * the three properties {@code
- * java.util.concurrent.ForkJoinPool.common.{parallelism,
- * threadFactory, exceptionHandler}}.
+ * use).
*
* For applications that require separate or custom pools, a {@code
* ForkJoinPool} may be constructed with a given target parallelism
@@ -106,6 +97,16 @@ import java.util.concurrent.locks.Condit
*
*
*
+ *
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
+ * Thread.UncaughtExceptionHandler}. Upon any error in establishing
+ * these settings, default parameters are used.
+ *
*
Implementation notes: This implementation restricts the
* maximum number of running threads to 32767. Attempts to create
* pools with greater than the maximum number result in
@@ -192,21 +193,24 @@ public class ForkJoinPool extends Abstra
* WorkQueues are also used in a similar way for tasks submitted
* to the pool. We cannot mix these tasks in the same queues used
* for work-stealing (this would contaminate lifo/fifo
- * processing). Instead, we loosely associate submission queues
+ * 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 never
- * take tasks, and they are multiplexed on to a finite number of
- * shared work queues. However, classes are set up so that future
- * extensions could allow submitters to optionally help perform
- * tasks as well. 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 runState), because
- * submitters encountering a busy queue move on to try or create
- * other queues -- they block only when creating and registering
- * new queues.
+ * 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
+ * creating and registering new queues.
*
* Management
* ==========
@@ -228,11 +232,13 @@ public class ForkJoinPool extends Abstra
* and their negations (used for thresholding) to fit into 16bit
* fields.
*
- * Field "runState" contains 32 bits needed to register and
- * deregister WorkQueues, as well as to enable shutdown. It is
- * only modified under a lock (normally briefly held, but
- * occasionally protecting allocations and resizings) but even
- * when locked remains available to check consistency.
+ * Field "plock" is a form of sequence lock with a saturating
+ * shutdown bit (similarly for per-queue "qlocks"), mainly
+ * protecting updates to the workQueues array, as well as to
+ * enable shutdown. When used as a lock, it is normally only very
+ * briefly held, so is nearly always available after at most a
+ * brief spin, but we use a monitor-based backup strategy to
+ * blocking when needed.
*
* Recording WorkQueues. WorkQueues are recorded in the
* "workQueues" array that is created upon first use and expanded
@@ -241,9 +247,11 @@ public class ForkJoinPool extends Abstra
* by a lock but the array is otherwise concurrently readable, and
* accessed directly. To simplify index-based operations, the
* array size is always a power of two, and all readers must
- * tolerate null slots. Shared (submission) queues are at even
- * indices, worker queues at odd indices. Grouping them together
- * in this way simplifies and speeds up task scanning.
+ * tolerate null slots. Worker queues are at odd indices Shared
+ * (submission) queues are at even indices, up to a maximum of 64
+ * slots, to limit growth even if array needs to expand to add
+ * more workers. Grouping them together in this way simplifies and
+ * speeds up task scanning.
*
* All worker thread creation is on-demand, triggered by task
* submissions, replacement of terminated workers, and/or
@@ -304,14 +312,19 @@ public class ForkJoinPool extends Abstra
*
* 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. When a submission is added or another worker adds a
- * task to a queue that previously had fewer than two tasks, they
- * signal waiting workers (or trigger creation of new ones if
- * fewer than the given parallelism level -- see signalWork).
- * These primary signals are buttressed by signals during rescans;
- * together these cover the signals needed in cases when more
- * tasks are pushed but untaken, and improve performance compared
- * to having one thread wake up all workers.
+ * 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 is
+ * apparently empty, they signal waiting workers (or trigger
+ * creation of new ones if fewer than the given parallelism level
+ * -- see signalWork). These primary signals are buttressed by
+ * signals whenever other threads scan for work or do not have a
+ * task to process. 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.
*
* Trimming workers. To release resources after periods of lack of
* use, a worker starting to wait when the pool is quiescent will
@@ -322,8 +335,8 @@ public class ForkJoinPool extends Abstra
* periods of non-use.
*
* Shutdown and Termination. A call to shutdownNow atomically sets
- * a runState bit and then (non-atomically) sets each worker's
- * runState status, cancels all unprocessed tasks, and wakes up
+ * a plock bit and then (non-atomically) sets each worker's
+ * qlock status, cancels all unprocessed tasks, and wakes up
* all waiting workers. Detecting whether termination should
* commence after a non-abrupt shutdown() call requires more work
* and bookkeeping. We need consensus about quiescence (i.e., that
@@ -351,13 +364,13 @@ public class ForkJoinPool extends Abstra
* method tryCompensate() may create or re-activate a spare
* thread to compensate for blocked joiners until they unblock.
*
- * A third form (implemented in tryRemoveAndExec and
- * tryPollForAndExec) amounts to helping a hypothetical
- * compensator: If we can readily tell that a possible action of a
- * compensator is to steal and execute the task being joined, the
- * joining thread can do so directly, without the need for a
- * compensation thread (although at the expense of larger run-time
- * stacks, but the tradeoff is typically worthwhile).
+ * A third form (implemented in tryRemoveAndExec) amounts to
+ * helping a hypothetical compensator: If we can readily tell that
+ * a possible action of a compensator is to steal and execute the
+ * task being joined, the joining thread can do so directly,
+ * without the need for a compensation thread (although at the
+ * expense of larger run-time stacks, but the tradeoff is
+ * typically worthwhile).
*
* The ManagedBlocker extension API can't use helping so relies
* only on compensation in method awaitBlocker.
@@ -392,6 +405,12 @@ public class ForkJoinPool extends Abstra
* to find work (see MAX_HELP) and fall back to suspending the
* worker and if necessary replacing it with another.
*
+ * Helping actions for CountedCompleters are much simpler: Method
+ * helpComplete can take and execute any task with the same root
+ * as the task being waited on. However, this still entails some
+ * traversal of completer chains, so is less efficient than using
+ * CountedCompleters without explicit joins.
+ *
* It is impossible to keep exactly the target parallelism number
* of threads running at any given time. Determining the
* existence of conservatively safe helping targets, the
@@ -413,30 +432,41 @@ public class ForkJoinPool extends Abstra
* intractable) game with an opponent that may choose the worst
* (for us) active thread to stall at any time. We take several
* precautions to bound losses (and thus bound gains), mainly in
- * methods tryCompensate and awaitJoin: (1) We only try
- * compensation after attempting enough helping steps (measured
- * via counting and timing) that we have already consumed the
- * estimated cost of creating and activating a new thread. (2) We
- * allow up to 50% of threads to be blocked before initially
- * adding any others, and unless completely saturated, check that
- * some work is available for a new worker before adding. Also, we
- * create up to only 50% more threads until entering a mode that
- * only adds a thread if all others are possibly blocked. All
- * together, this means that we might be half as fast to react,
- * and create half as many threads as possible in the ideal case,
- * but present vastly fewer anomalies in all other cases compared
- * to both more aggressive and more conservative alternatives.
- *
- * Style notes: There is a lot of representation-level coupling
- * among classes ForkJoinPool, ForkJoinWorkerThread, and
- * ForkJoinTask. The fields of WorkQueue maintain data structures
- * managed by ForkJoinPool, so are directly accessed. There is
- * little point trying to reduce this, since any associated future
- * changes in representations will need to be accompanied by
- * algorithmic changes anyway. Several methods intrinsically
- * sprawl because they must accumulate sets of consistent reads of
- * volatiles held in local variables. Methods signalWork() and
- * scan() are the main bottlenecks, so are especially heavily
+ * methods tryCompensate and awaitJoin.
+ *
+ * Common Pool
+ * ===========
+ *
+ * The static commonPool 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
+ * allocation. Most bootstrapping occurs within method
+ * 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
+ * submissions are to the common pool -- if not, externalHelpJoin
+ * returns quicky (at the most helping to signal some common pool
+ * workers). These submitters would otherwise be blocked waiting
+ * for completion, so the extra effort (with liberally sprinkled
+ * task status checks) in inapplicable cases amounts to an odd
+ * form of limited spin-wait before blocking in ForkJoinTask.join.
+ *
+ * Style notes
+ * ===========
+ *
+ * There is a lot of representation-level coupling among classes
+ * ForkJoinPool, ForkJoinWorkerThread, and ForkJoinTask. The
+ * fields of WorkQueue maintain data structures managed by
+ * ForkJoinPool, so are directly accessed. There is little point
+ * trying to reduce this, since any associated future changes in
+ * representations will need to be accompanied by algorithmic
+ * changes anyway. Several methods intrinsically sprawl because
+ * they must accumulate sets of consistent reads of volatiles held
+ * in local variables. Methods signalWork() and scan() are the
+ * main bottlenecks, so are especially heavily
* micro-optimized/mangled. There are lots of inline assignments
* (of form "while ((local = field) != 0)") which are usually the
* simplest way to ensure the required read orderings (which are
@@ -444,7 +474,8 @@ public class ForkJoinPool extends Abstra
* declarations of these locals at the heads of methods or blocks.
* There are several occurrences of the unusual "do {} while
* (!cas...)" which is the simplest way to force an update of a
- * CAS'ed variable. There are also other coding oddities that help
+ * CAS'ed variable. There are also other coding oddities (including
+ * several unnecessary-looking hoisted null checks) that help
* some methods perform reasonably even when interpreted (not
* compiled).
*
@@ -507,6 +538,7 @@ public class ForkJoinPool extends Abstra
* actually do anything beyond having a unique identity.
*/
static final class EmptyTask extends ForkJoinTask {
+ private static final long serialVersionUID = -7721805057305804111L;
EmptyTask() { status = ForkJoinTask.NORMAL; } // force done
public final Void getRawResult() { return null; }
public final void setRawResult(Void x) {}
@@ -527,27 +559,31 @@ public class ForkJoinPool extends Abstra
*
* Field "top" is the index (mod array.length) of the next queue
* slot to push to or pop from. It is written only by owner thread
- * for push, or under lock for trySharedPush, and accessed by
- * other threads only after reading (volatile) base. Both top and
- * base are allowed to wrap around on overflow, but (top - base)
- * (or more commonly -(base - top) to force volatile read of base
- * before top) still estimates size.
+ * for push, or under lock for external/shared push, and accessed
+ * by other threads only after reading (volatile) base. Both top
+ * and base are allowed to wrap around on overflow, but (top -
+ * base) (or more commonly -(base - top) to force volatile read of
+ * base before top) still estimates size. The lock ("qlock") is
+ * forced to -1 on termination, causing all further lock attempts
+ * to fail. (Note: we don't need CAS for termination state because
+ * upon pool shutdown, all shared-queues will stop being used
+ * anyway.) Nearly all lock bodies are set up so that exceptions
+ * within lock bodies are "impossible" (modulo JVM errors that
+ * would cause failure anyway.)
*
* The array slots are read and written using the emulation of
* volatiles/atomics provided by Unsafe. Insertions must in
* general use putOrderedObject as a form of releasing store to
* ensure that all writes to the task object are ordered before
- * its publication in the queue. (Although we can avoid one case
- * of this when locked in trySharedPush.) All removals entail a
- * CAS to null. The array is always a power of two. To ensure
- * safety of Unsafe array operations, all accesses perform
- * explicit null checks and implicit bounds checks via
- * power-of-two masking.
+ * its publication in the queue. All removals entail a CAS to
+ * null. The array is always a power of two. To ensure safety of
+ * Unsafe array operations, all accesses perform explicit null
+ * checks and implicit bounds checks via power-of-two masking.
*
* In addition to basic queuing support, this class contains
* fields described elsewhere to control execution. It turns out
- * to work better memory-layout-wise to include them in this
- * class rather than a separate class.
+ * to work better memory-layout-wise to include them in this class
+ * rather than a separate class.
*
* Performance on most platforms is very sensitive to placement of
* instances of both WorkQueues and their arrays -- we absolutely
@@ -563,8 +599,8 @@ public class ForkJoinPool extends Abstra
* 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 (via method growArray) by workers before
- * use. Others are allocated on first use.
+ * arrays are initialized by workers before use. Others are
+ * allocated on first use.
*/
static final class WorkQueue {
/**
@@ -587,16 +623,14 @@ public class ForkJoinPool extends Abstra
*/
static final int MAXIMUM_QUEUE_CAPACITY = 1 << 26; // 64M
- volatile long totalSteals; // cumulative number of steals
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 rescans; // remaining scans until block
- int nsteals; // top-level task executions since last idle
final int mode; // lifo, fifo, or shared
+ int nsteals; // cumulative number of steals
int poolIndex; // index of this queue in pool (or 0)
int stealHint; // index of most recent known stealer
- volatile int runState; // 1: locked, -1: terminate; else 0
+ 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
ForkJoinTask[] array; // the elements (initially unallocated)
@@ -618,75 +652,82 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns the approximate number of tasks in the queue.
- */
- final int queueSize() {
- int n = base - top; // non-owner callers must read base first
- 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.
- */
- final boolean isEmpty() {
- ForkJoinTask[] a; int m, s;
- int n = base - (s = top);
- return (n >= 0 ||
- (n == -1 &&
- ((a = array) == null ||
- (m = a.length - 1) < 0 ||
- U.getObjectVolatile
- (a, ((m & (s - 1)) << ASHIFT) + ABASE) == null)));
- }
-
- /**
* Pushes a task. Call only by owner in unshared queues.
+ * Cases needing resizing or rejection are relyaed to fullPush
+ * (that also handles shared queues).
*
* @param task the task. Caller must ensure non-null.
* @throw RejectedExecutionException if array cannot be resized
*/
final void push(ForkJoinTask task) {
- ForkJoinTask[] a; ForkJoinPool p;
- int s = top, m, n;
- if ((a = array) != null) { // ignore if queue removed
+ ForkJoinPool p; ForkJoinTask[] a;
+ int s = top, n;
+ if ((a = array) != null && a.length > (n = s + 1 - base)) {
U.putOrderedObject
- (a, (((m = a.length - 1) & s) << ASHIFT) + ABASE, task);
- if ((n = (top = s + 1) - base) <= 2) {
- if ((p = pool) != null)
- p.signalWork();
- }
- else if (n >= m)
- growArray(true);
+ (a, (((a.length - 1) & s) << ASHIFT) + ABASE, task);
+ top = s + 1;
+ if (n <= 1 && (p = pool) != null)
+ p.signalWork(this, 1);
}
+ else
+ fullPush(task, true);
}
/**
* Pushes a task if lock is free and array is either big
- * enough or can be resized to be big enough.
+ * enough or can be resized to be big enough. Note: a
+ * specialization of a common fast path of this method is in
+ * ForkJoinPool.externalPush. When called from a FJWT queue,
+ * this can fail only if the pool has been shut down or
+ * an out of memory error.
*
* @param task the task. Caller must ensure non-null.
- * @return true if submitted
+ * @param owned if true, throw RJE on failure
*/
- final boolean trySharedPush(ForkJoinTask task) {
- boolean submitted = false;
- if (runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
- ForkJoinTask[] a = array;
- int s = top;
- try {
- if ((a != null && a.length > s + 1 - base) ||
- (a = growArray(false)) != null) { // must presize
- int j = (((a.length - 1) & s) << ASHIFT) + ABASE;
- U.putObject(a, (long)j, task); // don't need "ordered"
- top = s + 1;
- submitted = true;
+ final boolean fullPush(ForkJoinTask task, boolean owned) {
+ ForkJoinPool p; ForkJoinTask[] a;
+ if (owned) {
+ if (qlock < 0) // must be shutting down
+ throw new RejectedExecutionException();
+ }
+ else if (!U.compareAndSwapInt(this, QLOCK, 0, 1))
+ return false;
+ try {
+ int s = top, oldLen, len;
+ if ((a = array) == null)
+ a = array = new ForkJoinTask[len=INITIAL_QUEUE_CAPACITY];
+ else if ((oldLen = a.length) > s + 1 - base)
+ len = oldLen;
+ else if ((len = oldLen << 1) > MAXIMUM_QUEUE_CAPACITY)
+ throw new RejectedExecutionException("Capacity exceeded");
+ else {
+ int oldMask, b;
+ ForkJoinTask[] oldA = a;
+ a = array = new ForkJoinTask[len];
+ if ((oldMask = oldLen - 1) >= 0 && s - (b = base) > 0) {
+ int mask = len - 1;
+ do {
+ ForkJoinTask x;
+ int oldj = ((b & oldMask) << ASHIFT) + ABASE;
+ int j = ((b & mask) << ASHIFT) + ABASE;
+ x = (ForkJoinTask)
+ U.getObjectVolatile(oldA, oldj);
+ if (x != null &&
+ U.compareAndSwapObject(oldA, oldj, x, null))
+ U.putObjectVolatile(a, j, x);
+ } while (++b != s);
}
- } finally {
- runState = 0; // unlock
}
+ U.putOrderedObject
+ (a, (((len - 1) & s) << ASHIFT) + ABASE, task);
+ top = s + 1;
+ } finally {
+ if (!owned)
+ qlock = 0;
}
- return submitted;
+ if ((p = pool) != null)
+ p.signalWork(this, 1);
+ return true;
}
/**
@@ -709,33 +750,6 @@ public class ForkJoinPool extends Abstra
return null;
}
- final ForkJoinTask sharedPop() {
- ForkJoinTask task = null;
- if (runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
- try {
- ForkJoinTask[] a; int m;
- if ((a = array) != null && (m = a.length - 1) >= 0) {
- for (int s; (s = top - 1) - base >= 0;) {
- long j = ((m & s) << ASHIFT) + ABASE;
- ForkJoinTask t =
- (ForkJoinTask)U.getObject(a, j);
- if (t == null)
- break;
- if (U.compareAndSwapObject(a, j, t, null)) {
- top = s;
- task = t;
- break;
- }
- }
- }
- } finally {
- runState = 0;
- }
- }
- return task;
- }
-
-
/**
* Takes a task in FIFO order if b is base of queue and a task
* can be claimed without contention. Specialized versions
@@ -773,7 +787,7 @@ public class ForkJoinPool extends Abstra
else if (base == b) {
if (b + 1 == top)
break;
- Thread.yield(); // wait for lagging update
+ Thread.yield(); // wait for lagging update (very rare)
}
}
return null;
@@ -800,6 +814,7 @@ public class ForkJoinPool extends Abstra
/**
* Pops the given task only if it is at the current top.
+ * (A shared version is available only via FJP.tryExternalUnpush)
*/
final boolean tryUnpush(ForkJoinTask t) {
ForkJoinTask[] a; int s;
@@ -813,79 +828,6 @@ public class ForkJoinPool extends Abstra
}
/**
- * Version of tryUnpush for shared queues; called by non-FJ
- * submitters after prechecking that task probably exists.
- */
- final boolean trySharedUnpush(ForkJoinTask t) {
- boolean success = false;
- if (runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
- try {
- ForkJoinTask[] a; int s;
- if ((a = array) != null && (s = top) != base &&
- U.compareAndSwapObject
- (a, (((a.length - 1) & --s) << ASHIFT) + ABASE, t, null)) {
- top = s;
- success = true;
- }
- } finally {
- runState = 0; // unlock
- }
- }
- return success;
- }
-
- /**
- * Polls the given task only if it is at the current base.
- */
- final boolean pollFor(ForkJoinTask task) {
- ForkJoinTask[] a; int b;
- if ((b = base) - top < 0 && (a = array) != null) {
- int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
- if (U.getObjectVolatile(a, j) == task && base == b &&
- U.compareAndSwapObject(a, j, task, null)) {
- base = b + 1;
- return true;
- }
- }
- return false;
- }
-
- /**
- * 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.
- *
- * @param rejectOnFailure if true, throw exception if capacity
- * exceeded (relayed ultimately to user); else return null.
- */
- final ForkJoinTask[] growArray(boolean rejectOnFailure) {
- ForkJoinTask[] oldA = array;
- int size = oldA != null ? oldA.length << 1 : INITIAL_QUEUE_CAPACITY;
- if (size <= MAXIMUM_QUEUE_CAPACITY) {
- int oldMask, t, b;
- ForkJoinTask[] a = array = new ForkJoinTask[size];
- if (oldA != null && (oldMask = oldA.length - 1) >= 0 &&
- (t = top) - (b = base) > 0) {
- int mask = size - 1;
- do {
- ForkJoinTask x;
- int oldj = ((b & oldMask) << ASHIFT) + ABASE;
- int j = ((b & mask) << ASHIFT) + ABASE;
- x = (ForkJoinTask)U.getObjectVolatile(oldA, oldj);
- if (x != null &&
- U.compareAndSwapObject(oldA, oldj, x, null))
- U.putObjectVolatile(a, j, x);
- } while (++b != t);
- }
- return a;
- }
- else if (!rejectOnFailure)
- return null;
- else
- throw new RejectedExecutionException("Queue capacity exceeded");
- }
-
- /**
* Removes and cancels all known tasks, ignoring any exceptions.
*/
final void cancelAll() {
@@ -909,6 +851,21 @@ public class ForkJoinPool extends Abstra
return seed = r ^= r << 5;
}
+ /**
+ * Provides a more accurate estimate of size than (top - base)
+ * by ordering reads and checking whether a near-empty queue
+ * has at least one unclaimed task.
+ */
+ final int queueSize() {
+ ForkJoinTask[] a; int k, s, n;
+ return ((n = base - (s = top)) < 0 &&
+ (n != -1 ||
+ ((a = array) != null && (k = a.length) > 0 &&
+ U.getObject
+ (a, (long)((((k - 1) & (s - 1)) << ASHIFT) + ABASE)) != null))) ?
+ -n : 0;
+ }
+
// Specialized execution methods
/**
@@ -938,16 +895,14 @@ public class ForkJoinPool extends Abstra
}
/**
- * If present, removes from queue and executes the given task, or
- * any other cancelled task. Returns (true) immediately on any CAS
+ * 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 0 if no progress can be made, else positive
- * (this unusual convention simplifies use with tryHelpStealer.)
+ * @return false if no progress can be made, else true;
*/
- final int tryRemoveAndExec(ForkJoinTask task) {
- int stat = 1;
- boolean removed = false, empty = true;
+ final boolean tryRemoveAndExec(ForkJoinTask task) {
+ boolean stat = true, removed = false, empty = true;
ForkJoinTask[] a; int m, s, b, n;
if ((a = array) != null && (m = a.length - 1) >= 0 &&
(n = (s = top) - (b = base)) > 0) {
@@ -977,7 +932,7 @@ public class ForkJoinPool extends Abstra
}
if (--n == 0) {
if (!empty && base == b)
- stat = 0;
+ stat = false;
break;
}
}
@@ -988,42 +943,32 @@ public class ForkJoinPool extends Abstra
}
/**
- * Version of shared pop that takes top element only if it
- * its root is the given CountedCompleter.
+ * Polls for and executes the given task or any other task in
+ * its CountedCompleter computation
*/
- final CountedCompleter sharedPopCC(CountedCompleter root) {
- CountedCompleter task = null;
- if (runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
- try {
- ForkJoinTask[] a; int m;
- if ((a = array) != null && (m = a.length - 1) >= 0) {
- outer:for (int s; (s = top - 1) - base >= 0;) {
- long j = ((m & s) << ASHIFT) + ABASE;
- ForkJoinTask t =
- (ForkJoinTask)U.getObject(a, j);
- if (t == null || !(t instanceof CountedCompleter))
- break;
- CountedCompleter cc = (CountedCompleter)t;
- for (CountedCompleter q = cc, p;;) {
- if (q == root) {
- if (U.compareAndSwapObject(a, j, cc, null)) {
- top = s;
- task = cc;
- break outer;
- }
- break;
- }
- if ((p = q.completer) == null)
- break outer;
- q = p;
- }
+ final boolean pollAndExecCC(ForkJoinTask root) {
+ ForkJoinTask[] a; int b; Object o;
+ outer: while ((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();
+ return true;
}
+ else
+ break; // restart
}
- } finally {
- runState = 0;
+ if ((r = r.completer) == null)
+ break outer; // not part of root computation
}
}
- return task;
+ return false;
}
/**
@@ -1032,16 +977,19 @@ public class ForkJoinPool extends Abstra
*/
final void runTask(ForkJoinTask t) {
if (t != null) {
- currentSteal = t;
- t.doExec();
+ (currentSteal = t).doExec();
+ currentSteal = null;
+ if (++nsteals < 0) { // spill on overflow
+ ForkJoinPool p;
+ if ((p = pool) != null)
+ p.collectStealCount(this);
+ }
if (top != base) { // process remaining local tasks
if (mode == 0)
popAndExecAll();
else
pollAndExecAll();
}
- ++nsteals;
- currentSteal = null;
}
}
@@ -1051,8 +999,7 @@ public class ForkJoinPool extends Abstra
final void runSubtask(ForkJoinTask t) {
if (t != null) {
ForkJoinTask ps = currentSteal;
- currentSteal = t;
- t.doExec();
+ (currentSteal = t).doExec();
currentSteal = ps;
}
}
@@ -1087,7 +1034,7 @@ public class ForkJoinPool extends Abstra
// Unsafe mechanics
private static final sun.misc.Unsafe U;
- private static final long RUNSTATE;
+ private static final long QLOCK;
private static final int ABASE;
private static final int ASHIFT;
static {
@@ -1096,8 +1043,8 @@ public class ForkJoinPool extends Abstra
U = getUnsafe();
Class k = WorkQueue.class;
Class ak = ForkJoinTask[].class;
- RUNSTATE = U.objectFieldOffset
- (k.getDeclaredField("runState"));
+ QLOCK = U.objectFieldOffset
+ (k.getDeclaredField("qlock"));
ABASE = U.arrayBaseOffset(ak);
s = U.arrayIndexScale(ak);
} catch (Exception e) {
@@ -1112,7 +1059,7 @@ 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 doSubmit. In the future, this may
+ * submission queues in method externalPush. In the future, this may
* also incorporate a means to implement different task rejection
* and resubmission policies.
*
@@ -1120,23 +1067,18 @@ public class ForkJoinPool extends Abstra
* 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. This is done during
- * registration for workers, but requires a separate AtomicInteger
- * for submitters. Seeds are then randomly modified upon
- * collisions using xorshifts, which requires a non-zero seed.
+ * 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 = nextSubmitterSeed.getAndAdd(SEED_INCREMENT);
- seed = (s == 0) ? 1 : s; // ensure non-zero
- }
+ Submitter(int s) { seed = s; }
}
- /** ThreadLocal class for Submitters */
- static final class ThreadSubmitter extends ThreadLocal {
- public Submitter initialValue() { return new Submitter(); }
- }
+ /** Property prefix for constructing common pool */
+ private static final String propPrefix =
+ "java.util.concurrent.ForkJoinPool.common.";
// static fields (initialized in static initializer below)
@@ -1147,66 +1089,67 @@ public class ForkJoinPool extends Abstra
public static final ForkJoinWorkerThreadFactory
defaultForkJoinWorkerThreadFactory;
- /** Property prefix for constructing common pool */
- private static final String propPrefix =
- "java.util.concurrent.ForkJoinPool.common.";
-
/**
* Common (static) pool. Non-null for public use unless a static
- * construction exception, but internal usages must null-check on
- * use.
+ * construction exception, but internal usages null-check on use
+ * to paranoically avoid potential initialization circularities
+ * as well as to simplify generated code.
*/
static final ForkJoinPool commonPool;
/**
- * Common pool parallelism. Must equal commonPool.parallelism.
+ * Permission required for callers of methods that may start or
+ * kill threads.
*/
- static final int commonPoolParallelism;
+ private static final RuntimePermission modifyThreadPermission;
/**
- * Generator for assigning sequence numbers as pool names.
+ * 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.
+ * Lazily initialized on first submission (but null-checked
+ * in other contexts to avoid unnecessary initialization).
*/
- private static final AtomicInteger poolNumberGenerator;
+ static final ThreadLocal submitters;
/**
- * Generator for initial hashes/seeds for submitters. Accessed by
- * Submitter class constructor.
+ * Common pool parallelism. Must equal commonPool.parallelism.
*/
- static final AtomicInteger nextSubmitterSeed;
+ static final int commonPoolParallelism;
/**
- * Permission required for callers of methods that may start or
- * kill threads.
+ * Sequence number for creating workerNamePrefix.
*/
- private static final RuntimePermission modifyThreadPermission;
+ private static int poolNumberSequence;
/**
- * 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.
+ * Return the next sequence number. We don't expect this to
+ * ever contend so use simple builtin sync.
*/
- private static final ThreadSubmitter submitters;
+ private static final synchronized int nextPoolId() {
+ return ++poolNumberSequence;
+ }
// static constants
/**
- * Initial timeout value (in nanoseconds) for the thread triggering
- * quiescence to park waiting for new work. On timeout, the thread
- * will instead try to shrink the number of workers.
+ * Initial timeout value (in nanoseconds) for the thread
+ * triggering quiescence to park waiting for new work. On timeout,
+ * the thread will instead try to shrink the number of
+ * workers. The value should be large enough to avoid overly
+ * aggressive shrinkage during most transient stalls (long GCs
+ * etc).
*/
- private static final long IDLE_TIMEOUT = 1000L * 1000L * 1000L; // 1sec
+ private static final long IDLE_TIMEOUT = 2000L * 1000L * 1000L; // 2sec
/**
* Timeout value when there are more threads than parallelism level
*/
- private static final long FAST_IDLE_TIMEOUT = 100L * 1000L * 1000L;
+ private static final long FAST_IDLE_TIMEOUT = 200L * 1000L * 1000L;
/**
* The maximum stolen->joining link depth allowed in method
- * tryHelpStealer. Must be a power of two. This value also
- * controls the maximum number of times to try to help join a task
- * without any apparent progress or change in pool state before
- * giving up and blocking (see awaitJoin). Depths for legitimate
+ * tryHelpStealer. Must be a power of two. Depths for legitimate
* chains are unbounded, but we use a fixed constant to avoid
* (otherwise unchecked) cycles and to bound staleness of
* traversal parameters at the expense of sometimes blocking when
@@ -1215,16 +1158,6 @@ public class ForkJoinPool extends Abstra
private static final int MAX_HELP = 64;
/**
- * Secondary time-based bound (in nanosecs) for helping attempts
- * before trying compensated blocking in awaitJoin. Used in
- * conjunction with MAX_HELP to reduce variance due to different
- * polling rates associated with different helping options. The
- * value should roughly approximate the time required to create
- * and/or activate a worker thread.
- */
- private static final long COMPENSATION_DELAY = 1L << 18; // ~0.25 millisec
-
- /**
* Increment for seed generators. See class ThreadLocal for
* explanation.
*/
@@ -1258,14 +1191,14 @@ public class ForkJoinPool extends Abstra
* scan for them to avoid queuing races. Note however that
* eventCount updates lag releases so usage requires care.
*
- * Field runState is an int packed with:
+ * Field plock is an int packed with:
* SHUTDOWN: true if shutdown is enabled (1 bit)
- * SEQ: a sequence number updated upon (de)registering workers (30 bits)
- * INIT: set true after workQueues array construction (1 bit)
+ * SEQ: a sequence lock, with PL_LOCK bit set if locked (30 bits)
+ * SIGNAL: set when threads may be waiting on the lock (1 bit)
*
* The sequence number enables simple consistency checks:
* Staleness of read-only operations on the workQueues array can
- * be checked by comparing runState before vs after the reads.
+ * be checked by comparing plock before vs after the reads.
*/
// bit positions/shifts for fields
@@ -1277,7 +1210,8 @@ public class ForkJoinPool extends Abstra
// bounds
private static final int SMASK = 0xffff; // short bits
private static final int MAX_CAP = 0x7fff; // max #workers - 1
- private static final int SQMASK = 0xfffe; // even short bits
+ private static final int EVENMASK = 0xfffe; // even short bits
+ private static final int SQMASK = 0x007e; // max 64 (even) slots
private static final int SHORT_SIGN = 1 << 15;
private static final int INT_SIGN = 1 << 31;
@@ -1302,8 +1236,11 @@ public class ForkJoinPool extends Abstra
private static final int E_MASK = 0x7fffffff; // no STOP_BIT
private static final int E_SEQ = 1 << EC_SHIFT;
- // runState bits
+ // plock bits
private static final int SHUTDOWN = 1 << 31;
+ private static final int PL_LOCK = 2;
+ private static final int PL_SIGNAL = 1;
+ private static final int PL_SPINS = 1 << 8;
// access mode for WorkQueue
static final int LIFO_QUEUE = 0;
@@ -1318,45 +1255,43 @@ public class ForkJoinPool extends Abstra
* declaration order and may differ across JVMs, but the following
* empirically works OK on current JVMs.
*/
-
volatile long stealCount; // collects worker counts
volatile long ctl; // main pool control
final int parallelism; // parallelism level
final int localMode; // per-worker scheduling mode
- volatile int nextWorkerNumber; // to create worker name string
- final int submitMask; // submit queue index bound
- int nextSeed; // for initializing worker seeds
- volatile int mainLock; // spinlock for array updates
- volatile int runState; // shutdown status and seq
+ volatile int indexSeed; // worker/submitter index seed
+ volatile int plock; // shutdown status and seqLock
WorkQueue[] workQueues; // main registry
final ForkJoinWorkerThreadFactory factory; // factory for new workers
final Thread.UncaughtExceptionHandler ueh; // per-worker UEH
final String workerNamePrefix; // to create worker name string
/*
- * Mechanics for main lock protecting worker array updates. Uses
- * the same strategy as ConcurrentHashMap bins -- a spinLock for
- * normal cases, but falling back to builtin lock when (rarely)
- * needed. See internal ConcurrentHashMap documentation for
- * explanation.
- */
-
- static final int LOCK_WAITING = 2; // bit to indicate need for signal
- static final int MAX_LOCK_SPINS = 1 << 8;
-
- private void tryAwaitMainLock() {
- int spins = MAX_LOCK_SPINS, r = 0, h;
- while (((h = mainLock) & 1) != 0) {
- if (r == 0)
+ * 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
+ * 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.
+ */
+ private int acquirePlock() {
+ int spins = PL_SPINS, r = 0, ps, nps;
+ for (;;) {
+ if (((ps = plock) & PL_LOCK) == 0 &&
+ U.compareAndSwapInt(this, PLOCK, ps, nps = ps + PL_LOCK))
+ return nps;
+ else if (r == 0)
r = ThreadLocalRandom.current().nextInt(); // randomize spins
else if (spins >= 0) {
r ^= r << 1; r ^= r >>> 3; r ^= r << 10; // xorshift
if (r >= 0)
--spins;
}
- else if (U.compareAndSwapInt(this, MAINLOCK, h, h | LOCK_WAITING)) {
- synchronized (this) {
- if ((mainLock & LOCK_WAITING) != 0) {
+ else if (U.compareAndSwapInt(this, PLOCK, ps, ps | PL_SIGNAL)) {
+ synchronized(this) {
+ if ((plock & PL_SIGNAL) != 0) {
try {
wait();
} catch (InterruptedException ie) {
@@ -1367,44 +1302,22 @@ public class ForkJoinPool extends Abstra
}
}
else
- notifyAll(); // possibly won race vs signaller
+ notifyAll();
}
- break;
}
}
}
- // Creating, registering, and deregistering workers
-
/**
- * Tries to create and start a worker
+ * Unlocks and signals any thread waiting for plock. Called only
+ * when CAS of seq value for unlock fails.
*/
- private void addWorker() {
- Throwable ex = null;
- ForkJoinWorkerThread wt = null;
- try {
- if ((wt = factory.newThread(this)) != null) {
- wt.start();
- return;
- }
- } catch (Throwable e) {
- ex = e;
- }
- deregisterWorker(wt, ex); // adjust counts etc on failure
+ private void releasePlock(int ps) {
+ plock = ps;
+ synchronized(this) { notifyAll(); }
}
- /**
- * Callback from ForkJoinWorkerThread constructor to assign a
- * public name. This must be separate from registerWorker because
- * it is called during the "super" constructor call in
- * ForkJoinWorkerThread.
- */
- final String nextWorkerName() {
- int n;
- do {} while (!U.compareAndSwapInt(this, NEXTWORKERNUMBER,
- n = nextWorkerNumber, ++n));
- return workerNamePrefix.concat(Integer.toString(n));
- }
+ // Registering and deregistering workers
/**
* Callback from ForkJoinWorkerThread constructor to establish its
@@ -1416,20 +1329,23 @@ public class ForkJoinPool extends Abstra
* @param w the worker's queue
*/
final void registerWorker(WorkQueue w) {
- while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
- tryAwaitMainLock();
+ int s, ps; // generate a rarely colliding candidate index seed
+ do {} while (!U.compareAndSwapInt(this, INDEXSEED,
+ s = indexSeed, s += SEED_INCREMENT) ||
+ s == 0); // skip 0
+ if (((ps = plock) & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
try {
WorkQueue[] ws;
- if ((ws = workQueues) == null)
- ws = workQueues = new WorkQueue[submitMask + 1];
- if (w != null) {
- int rs, n = ws.length, m = n - 1;
- int s = nextSeed += SEED_INCREMENT; // rarely-colliding sequence
- w.seed = (s == 0) ? 1 : s; // ensure non-zero seed
+ if (w != null && (ws = workQueues) != null) {
+ w.seed = s;
+ int n = ws.length, m = n - 1;
int r = (s << 1) | 1; // use odd-numbered indices
if (ws[r &= m] != null) { // collision
int probes = 0; // step by approx half size
- int step = (n <= 4) ? 2 : ((n >>> 1) & SQMASK) + 2;
+ int step = (n <= 4) ? 2 : ((n >>> 1) & EVENMASK) + 2;
while (ws[r = (r + step) & m] != null) {
if (++probes >= n) {
workQueues = ws = Arrays.copyOf(ws, n <<= 1);
@@ -1439,45 +1355,41 @@ public class ForkJoinPool extends Abstra
}
}
w.eventCount = w.poolIndex = r; // establish before recording
- ws[r] = w; // also update seq
- runState = ((rs = runState) & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN);
+ ws[r] = w;
}
} finally {
- if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
- mainLock = 0;
- synchronized (this) { notifyAll(); };
- }
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
}
}
/**
* Final callback from terminating worker, as well as upon failure
- * to construct or start a worker in addWorker. Removes record of
- * worker from array, and adjusts counts. If pool is shutting
- * down, tries to complete termination.
+ * to construct or start a worker. Removes record of worker from
+ * array, and adjusts counts. If pool is shutting down, tries to
+ * complete termination.
*
- * @param wt the worker thread or null if addWorker 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) {
- w.runState = -1; // ensure runState is set
- long steals = w.totalSteals + w.nsteals, sc;
- do {} while (!U.compareAndSwapLong(this, STEALCOUNT,
- sc = stealCount, sc + steals));
- int idx = w.poolIndex;
- while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
- tryAwaitMainLock();
+ int ps;
+ collectStealCount(w);
+ w.qlock = -1; // ensure set
+ if (((ps = plock) & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
try {
+ int idx = w.poolIndex;
WorkQueue[] ws = workQueues;
if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w)
ws[idx] = null;
} finally {
- if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
- mainLock = 0;
- synchronized (this) { notifyAll(); };
- }
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
}
}
@@ -1490,7 +1402,7 @@ public class ForkJoinPool extends Abstra
if (!tryTerminate(false, false) && w != null) {
w.cancelAll(); // cancel remaining tasks
if (w.array != null) // suppress signal if never ran
- signalWork(); // wake up or create replacement
+ signalWork(null, 1); // wake up or create replacement
if (ex == null) // help clean refs on way out
ForkJoinTask.helpExpungeStaleExceptions();
}
@@ -1499,139 +1411,114 @@ public class ForkJoinPool extends Abstra
ForkJoinTask.rethrow(ex);
}
+ /**
+ * Collect worker steal count into total. Called on termination
+ * and upon int overflow of local count. (There is a possible race
+ * in the latter case vs any caller of getStealCount, which can
+ * make its results less accurate than usual.)
+ */
+ final void collectStealCount(WorkQueue w) {
+ if (w != null) {
+ long sc;
+ int ns = w.nsteals;
+ w.nsteals = 0; // handle overflow
+ long steals = (ns >= 0) ? ns : 1L + (long)(Integer.MAX_VALUE);
+ do {} while (!U.compareAndSwapLong(this, STEALCOUNT,
+ sc = stealCount, sc + steals));
+ }
+ }
+
// Submissions
/**
* Unless shutting down, adds the given task to a submission queue
* at submitter's current queue index (modulo submission
- * range). If no queue exists at the index, one is created. If
- * the queue is busy, another index is randomly chosen. The
- * submitMask bounds the effective number of queues to the
- * (nearest power of two for) parallelism level.
+ * range). Only the most common path is directly handled in this
+ * method. All others are relayed to fullExternalPush.
*
* @param task the task. Caller must ensure non-null.
*/
- private void doSubmit(ForkJoinTask task) {
- Submitter s = submitters.get();
- for (int r = s.seed, m = submitMask;;) {
- WorkQueue[] ws; WorkQueue q;
- int k = r & m & SQMASK; // use only even indices
- if (runState < 0)
- throw new RejectedExecutionException(); // shutting down
- else if ((ws = workQueues) == null || ws.length <= k) {
- while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
- tryAwaitMainLock();
- try {
- if (workQueues == null)
- workQueues = new WorkQueue[submitMask + 1];
- } finally {
- if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
- mainLock = 0;
- synchronized (this) { notifyAll(); };
- }
- }
- }
- else if ((q = ws[k]) == null) { // create new queue
- WorkQueue nq = new WorkQueue(this, null, SHARED_QUEUE);
- while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
- tryAwaitMainLock();
- try {
- int rs = runState; // to update seq
- if (ws == workQueues && ws[k] == null) {
- ws[k] = nq;
- runState = ((rs & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN));
- }
- } finally {
- if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
- mainLock = 0;
- synchronized (this) { notifyAll(); };
- }
- }
- }
- else if (q.trySharedPush(task)) {
- signalWork();
+ 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 &&
+ U.compareAndSwapInt(q, QLOCK, 0, 1)) { // lock
+ int s = q.top, n;
+ if ((a = q.array) != null && a.length > (n = s + 1 - q.base)) {
+ U.putObject(a, (long)(((a.length - 1) & s) << ASHIFT) + ABASE,
+ task);
+ q.top = s + 1; // push on to deque
+ q.qlock = 0;
+ if (n <= 1)
+ signalWork(q, 1);
return;
}
- else if (m > 1) { // move to a different index
- r ^= r << 13; // same xorshift as WorkQueues
- r ^= r >>> 17;
- s.seed = r ^= r << 5;
- }
- else
- Thread.yield(); // yield if no alternatives
+ q.qlock = 0;
}
+ fullExternalPush(task);
}
/**
- * Submits the given (non-null) task to the common pool, if possible.
- */
- static void submitToCommonPool(ForkJoinTask task) {
- ForkJoinPool p;
- if ((p = commonPool) == null)
- throw new RejectedExecutionException("Common Pool Unavailable");
- p.doSubmit(task);
- }
-
- /**
- * Returns true if the given task was submitted to common pool
- * and has not yet commenced execution, and is available for
- * removal according to execution policies; if so removing the
- * submission from the pool.
- *
- * @param task the task
- * @return true if successful
- */
- static boolean tryUnsubmitFromCommonPool(ForkJoinTask task) {
- // If not oversaturating platform, peek, looking for task and
- // eligibility before using trySharedUnpush to actually take
- // it under lock
- ForkJoinPool p; WorkQueue[] ws; WorkQueue w, q;
- ForkJoinTask[] a; int ac, s, m;
- if ((p = commonPool) != null && (ws = p.workQueues) != null) {
- int k = submitters.get().seed & p.submitMask & SQMASK;
- if ((m = ws.length - 1) >= k && (q = ws[k]) != null &&
- (ac = (int)(p.ctl >> AC_SHIFT)) <= 0) {
- if (ac == 0) { // double check if all workers active
- for (int i = 1; i <= m; i += 2) {
- if ((w = ws[i]) != null && w.parker != null) {
- ac = -1;
- break;
- }
- }
- }
- return (ac < 0 && (a = q.array) != null &&
- (s = q.top - 1) - q.base >= 0 &&
- s >= 0 && s < a.length &&
- a[s] == task &&
- q.trySharedUnpush(task));
+ * 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: creating
+ * workQueue array and setting plock to a valid value. 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 lock bodies must be
+ * exception-free (so no try/finally) so we optimistically
+ * allocate new queues/arrays outside the locks and throw them
+ * away if (very rarely) not needed. Note that the plock seq value
+ * can eventually wrap around zero, but if so harmlessly fails to
+ * reinitialize.
+ */
+ private void fullExternalPush(ForkJoinTask task) {
+ for (Submitter z = null;;) {
+ WorkQueue[] ws; WorkQueue q; int ps, m, r, s;
+ if ((ps = plock) < 0)
+ throw new RejectedExecutionException();
+ else if ((ws = workQueues) == null || (m = ws.length - 1) < 0) {
+ int n = parallelism - 1; n |= n >>> 1; n |= n >>> 2;
+ n |= n >>> 4; n |= n >>> 8; n |= n >>> 16;
+ WorkQueue[] nws = new WorkQueue[(n + 1) << 1]; // power of two
+ if ((ps & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ if ((ws = workQueues) == null)
+ workQueues = nws;
+ int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
+ }
+ else if (z == null && (z = submitters.get()) == null) {
+ if (U.compareAndSwapInt(this, INDEXSEED,
+ s = indexSeed, s += SEED_INCREMENT) &&
+ s != 0) // skip 0
+ submitters.set(z = new Submitter(s));
}
- }
- return false;
- }
-
- /**
- * Tries to pop and run a task within same computation from common pool
- */
- static void popAndExecCCFromCommonPool(CountedCompleter cc) {
- ForkJoinPool p; WorkQueue[] ws; WorkQueue q, w; int m, ac;
- CountedCompleter par, task;
- if ((p = commonPool) != null && (ws = p.workQueues) != null) {
- while ((par = cc.completer) != null) // find root
- cc = par;
- int k = submitters.get().seed & p.submitMask & SQMASK;
- if ((m = ws.length - 1) >= k && (q = ws[k]) != null &&
- (ac = (int)(p.ctl >> AC_SHIFT)) <= 0) {
- if (ac == 0) {
- for (int i = 1; i <= m; i += 2) {
- if ((w = ws[i]) != null && w.parker != null) {
- ac = -1;
- break;
- }
- }
+ else {
+ int k = (r = z.seed) & m & SQMASK;
+ if ((q = ws[k]) == null && (ps & PL_LOCK) == 0) {
+ (q = new WorkQueue(this, null, SHARED_QUEUE)).poolIndex = k;
+ if (((ps = plock) & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ WorkQueue w = null;
+ if ((ws = workQueues) != null && k < ws.length &&
+ (w = ws[k]) == null)
+ ws[k] = q;
+ else
+ q = w;
+ int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
}
- if (ac < 0 && q.top - q.base > 0 &&
- (task = q.sharedPopCC(cc)) != null)
- task.exec();
+ if (q != null && q.qlock == 0 && q.fullPush(task, false))
+ return;
+ r ^= r << 13; // same xorshift as WorkQueues
+ r ^= r >>> 17;
+ z.seed = r ^= r << 5; // move to a different index
}
}
}
@@ -1647,32 +1534,56 @@ public class ForkJoinPool extends Abstra
}
/**
- * Tries to create one or activate one or more workers if too few are active.
- */
- final void signalWork() {
- long c; int u;
- while ((u = (int)((c = ctl) >>> 32)) < 0) { // too few active
- WorkQueue[] ws = workQueues; int e, i; WorkQueue w; Thread p;
- if ((e = (int)c) > 0) { // at least one waiting
- if (ws != null && (i = e & SMASK) < ws.length &&
+ * Tries to create (at most one) or activate (possibly several)
+ * workers if too few are active. On contention failure, continues
+ * until at least one worker is signalled or the given queue is
+ * empty or all workers are active.
+ *
+ * @param q if non-null, the queue holding tasks to be signalled
+ * @param signals the target number of signals.
+ */
+ final void signalWork(WorkQueue q, int signals) {
+ long c; int e, u, i; 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.eventCount = (e + E_SEQ) & E_MASK;
if ((p = w.parker) != null)
- U.unpark(p); // activate and release
- break;
+ U.unpark(p);
+ if (--signals <= 0)
+ break;
}
+ else
+ signals = 1;
+ if ((q != null && q.queueSize() == 0))
+ break;
}
else
break;
}
- else if (e == 0 && (u & SHORT_SIGN) != 0) { // too few total
+ else if (e == 0 && (u & SHORT_SIGN) != 0) {
long nc = (long)(((u + UTC_UNIT) & UTC_MASK) |
((u + UAC_UNIT) & UAC_MASK)) << 32;
if (U.compareAndSwapLong(this, CTL, c, nc)) {
- addWorker();
+ ForkJoinWorkerThread wt = null;
+ Throwable ex = null;
+ boolean started = false;
+ try {
+ ForkJoinWorkerThreadFactory fac;
+ if ((fac = factory) != null &&
+ (wt = fac.newThread(this)) != null) {
+ wt.start();
+ started = true;
+ }
+ } catch (Throwable rex) {
+ ex = rex;
+ }
+ if (!started)
+ deregisterWorker(wt, ex); // adjust counts on failure
break;
}
}
@@ -1687,8 +1598,9 @@ public class ForkJoinPool extends Abstra
* Top-level runloop for workers, called by ForkJoinWorkerThread.run.
*/
final void runWorker(WorkQueue w) {
- w.growArray(false); // initialize queue array in this thread
- do { w.runTask(scan(w)); } while (w.runState >= 0);
+ // initialize queue array in this thread
+ w.array = new ForkJoinTask[WorkQueue.INITIAL_QUEUE_CAPACITY];
+ do { w.runTask(scan(w)); } while (w.qlock >= 0);
}
/**
@@ -1704,108 +1616,80 @@ public class ForkJoinPool extends Abstra
* relative prime, checking each at least once). 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. On failure to find a task, we
+ * 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 trtry 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 a complete sweep, try to release a waiting worker. If
- * the scan terminated because the worker is inactivated, then the
- * released worker will often be the calling worker, and it can
- * succeed obtaining a task on the next call. Or maybe it is
- * another worker, but with same net effect. Releasing in other
- * cases as well ensures that we have enough workers running.
- *
* * 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 inactive, and the caller has run a task since the
- * last empty scan, return (to allow rescan) unless others are
- * also inactivated. Field WorkQueue.rescans counts down on each
- * scan to ensure eventual inactivation and blocking.
- *
- * * If already enqueued and none of the above apply, park
- * awaiting signal,
+ * * If already enqueued and none of the above apply, possibly
+ * (with 1/2 probablility) park awaiting signal, else lingering to
+ * help scan and signal.
*
* @param w the worker (via its WorkQueue)
* @return a task or null if none found
*/
private final ForkJoinTask scan(WorkQueue w) {
- WorkQueue[] ws; // first update random seed
+ WorkQueue[] ws; WorkQueue q; // first update random seed
int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
- int rs = runState, m; // volatile read order matters
+ int ps = plock, m; // volatile read order matters
if ((ws = workQueues) != null && (m = ws.length - 1) > 0) {
- int ec = w.eventCount; // ec is negative if inactive
- int step = (r >>> 16) | 1; // relative prime
- for (int j = (m + 1) << 2; ; r += step) {
- WorkQueue q; ForkJoinTask t; ForkJoinTask[] a; int b;
+ int ec = w.eventCount; // ec is negative if inactive
+ int step = (r >>> 16) | 1; // relatively prime
+ for (int j = (m + 1) << 2; ; --j, r += step) {
+ ForkJoinTask t; ForkJoinTask[] a; int b, n;
if ((q = ws[r & m]) != null && (b = q.base) - q.top < 0 &&
- (a = q.array) != null) { // probably nonempty
+ (a = q.array) != null) { // probably nonempty
int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
t = (ForkJoinTask)U.getObjectVolatile(a, i);
if (q.base == b && ec >= 0 && t != null &&
U.compareAndSwapObject(a, i, t, null)) {
- if (q.top - (q.base = b + 1) > 0)
- signalWork(); // help pushes signal
- return t;
- }
- else if (ec < 0 || j <= m) {
- rs = 0; // mark scan as imcomplete
- break; // caller can retry after release
+ if ((n = q.top - (q.base = b + 1)) > 0)
+ signalWork(q, n);
+ return t; // taken
+ }
+ if (j < m || (ec < 0 && (ec = w.eventCount) < 0)) {
+ if ((n = q.queueSize() - 1) > 0)
+ signalWork(q, n);
+ break; // let caller retry after signal
}
}
- if (--j < 0)
- break;
- }
-
- long c = ctl; int e = (int)c, a = (int)(c >> AC_SHIFT), nr, ns;
- if (e < 0) // decode ctl on empty scan
- w.runState = -1; // pool is terminating
- else if (rs == 0 || rs != runState) { // incomplete scan
- WorkQueue v; Thread p; // try to release a waiter
- if (e > 0 && a < 0 && w.eventCount == ec &&
- (v = ws[e & m]) != null && v.eventCount == (e | INT_SIGN)) {
- long nc = ((long)(v.nextWait & E_MASK) |
- ((c + AC_UNIT) & (AC_MASK|TC_MASK)));
- if (ctl == c && U.compareAndSwapLong(this, CTL, c, nc)) {
- v.eventCount = (e + E_SEQ) & E_MASK;
- if ((p = v.parker) != null)
- U.unpark(p);
+ else if (j < 0) { // end of scan
+ long c = ctl; int e;
+ if (plock != ps) // incomplete sweep
+ break;
+ if ((e = (int)c) < 0) // pool is terminating
+ w.qlock = -1;
+ else if (ec >= 0) { // try to enqueue/inactivate
+ long nc = ((long)ec |
+ ((c - AC_UNIT) & (AC_MASK|TC_MASK)));
+ w.nextWait = e;
+ w.eventCount = ec | INT_SIGN; // mark as inactive
+ if (ctl != c ||
+ !U.compareAndSwapLong(this, CTL, c, nc))
+ w.eventCount = ec; // unmark on CAS failure
+ else if ((int)(c >> AC_SHIFT) == 1 - parallelism)
+ idleAwaitWork(w, nc, c); // quiescent
+ }
+ else if (w.seed >= 0 && w.eventCount < 0) {
+ 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 (ec >= 0) { // try to enqueue/inactivate
- long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
- w.nextWait = e;
- w.eventCount = ec | INT_SIGN; // mark as inactive
- if (ctl != c || !U.compareAndSwapLong(this, CTL, c, nc))
- w.eventCount = ec; // unmark on CAS failure
- else {
- if ((ns = w.nsteals) != 0) {
- w.nsteals = 0; // set rescans if ran task
- w.rescans = (a > 0) ? 0 : a + parallelism;
- w.totalSteals += ns;
- }
- if (a == 1 - parallelism) // quiescent
- idleAwaitWork(w, nc, c);
- }
- }
- else if (w.eventCount < 0) { // already queued
- int ac = a + parallelism;
- if ((nr = w.rescans) > 0) // continue rescanning
- w.rescans = (ac < nr) ? ac : nr - 1;
- else if (((w.seed >>> 16) & ac) == 0) { // randomize park
- Thread.interrupted(); // clear status
- Thread wt = Thread.currentThread();
- 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);
+ break;
}
}
}
@@ -1825,8 +1709,9 @@ public class ForkJoinPool extends Abstra
* @param prevCtl the ctl value to restore if thread is terminated
*/
private void idleAwaitWork(WorkQueue w, long currentCtl, long prevCtl) {
- if (w.eventCount < 0 && !tryTerminate(false, false) &&
- (int)prevCtl != 0 && !hasQueuedSubmissions() && ctl == currentCtl) {
+ if (w.eventCount < 0 &&
+ (this == commonPool || !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
@@ -1844,7 +1729,7 @@ public class ForkJoinPool extends Abstra
if (deadline - System.nanoTime() <= 0L &&
U.compareAndSwapLong(this, CTL, currentCtl, prevCtl)) {
w.eventCount = (w.eventCount + E_SEQ) | E_MASK;
- w.runState = -1; // shrink
+ w.qlock = -1; // shrink
break;
}
}
@@ -1852,6 +1737,31 @@ public class ForkJoinPool extends Abstra
}
/**
+ * Scans through queues looking for work while joining a task;
+ * if any are present, signals.
+ *
+ * @param task to return early if done
+ * @param origin an index to start scan
+ */
+ final int helpSignal(ForkJoinTask task, int origin) {
+ WorkQueue[] ws; WorkQueue q; int m, n, s;
+ if (task != null && (ws = workQueues) != null &&
+ (m = ws.length - 1) >= 0) {
+ for (int i = 0; i <= m; ++i) {
+ if ((s = task.status) < 0)
+ return s;
+ if ((q = ws[(i + origin) & m]) != null &&
+ (n = q.queueSize()) > 0) {
+ signalWork(q, n);
+ if ((int)(ctl >> AC_SHIFT) >= 0)
+ break;
+ }
+ }
+ }
+ return 0;
+ }
+
+ /**
* Tries to locate and execute tasks for a stealer of the given
* task, or in turn one of its stealers, Traces currentSteal ->
* currentJoin links looking for a thread working on a descendant
@@ -1938,88 +1848,77 @@ public class ForkJoinPool extends Abstra
}
/**
- * If task is at base of some steal queue, steals and executes it.
+ * Analog of tryHelpStealer for CountedCompleters. Tries to steal
+ * 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
*
- * @param joiner the joining worker
- * @param task the task
*/
- private void tryPollForAndExec(WorkQueue joiner, ForkJoinTask task) {
- WorkQueue[] ws;
- if ((ws = workQueues) != null) {
- for (int j = 1; j < ws.length && task.status >= 0; j += 2) {
- WorkQueue q = ws[j];
- if (q != null && q.pollFor(task)) {
- joiner.runSubtask(task);
- break;
+ private int helpComplete(ForkJoinTask task, int mode) {
+ WorkQueue[] ws; WorkQueue q; int m, n, s;
+ if (task != null && (ws = workQueues) != null &&
+ (m = ws.length - 1) >= 0) {
+ for (int j = 1, origin = j;;) {
+ if ((s = task.status) < 0)
+ return s;
+ if ((q = ws[j & m]) != null && q.pollAndExecCC(task)) {
+ origin = j;
+ if (mode == SHARED_QUEUE && (int)(ctl >> AC_SHIFT) >= 0)
+ break;
}
+ else if ((j = (j + 2) & m) == origin)
+ break;
}
}
+ return 0;
}
/**
* Tries to decrement active count (sometimes implicitly) and
* possibly release or create a compensating worker in preparation
* for blocking. Fails on contention or termination. Otherwise,
- * adds a new thread if no idle workers are available and either
- * pool would become completely starved or: (at least half
- * starved, and fewer than 50% spares exist, and there is at least
- * one task apparently available). Even though the availability
- * check requires a full scan, it is worthwhile in reducing false
- * alarms.
- *
- * @param task if non-null, a task being waited for
- * @param blocker if non-null, a blocker being waited for
- * @return true if the caller can block, else should recheck and retry
+ * adds a new thread if no idle workers are available and pool
+ * may become starved.
*/
- final boolean tryCompensate(ForkJoinTask task, ManagedBlocker blocker) {
- int pc = parallelism, e;
- long c = ctl;
- WorkQueue[] ws = workQueues;
- if ((e = (int)c) >= 0 && ws != null) {
- int u, a, ac, hc;
- int tc = (short)((u = (int)(c >>> 32)) >>> UTC_SHIFT) + pc;
- boolean replace = false;
- if ((a = u >> UAC_SHIFT) <= 0) {
- if ((ac = a + pc) <= 1)
- replace = true;
- else if ((e > 0 || (task != null &&
- ac <= (hc = pc >>> 1) && tc < pc + hc))) {
- WorkQueue w;
- for (int j = 0; j < ws.length; ++j) {
- if ((w = ws[j]) != null && !w.isEmpty()) {
- replace = true;
- break; // in compensation range and tasks available
- }
- }
+ final boolean tryCompensate() {
+ int pc = parallelism, e, u, i, tc; long c;
+ WorkQueue[] ws; WorkQueue w; Thread p;
+ if ((e = (int)(c = ctl)) >= 0 && (ws = workQueues) != null) {
+ if (e != 0 && (i = e & SMASK) < ws.length &&
+ (w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) {
+ 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;
+ if ((p = w.parker) != null)
+ U.unpark(p);
+ return true; // replace with idle worker
}
}
- if ((task == null || task.status >= 0) && // recheck need to block
- (blocker == null || !blocker.isReleasable()) && ctl == c) {
- if (!replace) { // no compensation
- long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
- if (U.compareAndSwapLong(this, CTL, c, nc))
- return true;
- }
- else if (e != 0) { // release an idle worker
- WorkQueue w; Thread p; int i;
- if ((i = e & SMASK) < ws.length && (w = ws[i]) != null) {
- long nc = ((long)(w.nextWait & E_MASK) |
- (c & (AC_MASK|TC_MASK)));
- 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);
+ else if ((short)((u = (int)(c >>> 32)) >>> UTC_SHIFT) >= 0 &&
+ (u >> UAC_SHIFT) + pc > 1) {
+ long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
+ if (U.compareAndSwapLong(this, CTL, c, nc))
+ return true; // no compensation
+ }
+ else if ((tc = u + pc) < MAX_CAP) {
+ long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
+ if (U.compareAndSwapLong(this, CTL, c, nc)) {
+ Throwable ex = null;
+ ForkJoinWorkerThread wt = null;
+ try {
+ ForkJoinWorkerThreadFactory fac;
+ if ((fac = factory) != null &&
+ (wt = fac.newThread(this)) != null) {
+ wt.start();
return true;
}
+ } catch (Throwable rex) {
+ ex = rex;
}
- }
- else if (tc < MAX_CAP) { // create replacement
- long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
- if (U.compareAndSwapLong(this, CTL, c, nc)) {
- addWorker();
- return true;
- }
+ deregisterWorker(wt, ex); // adjust counts etc
}
}
}
@@ -2034,48 +1933,39 @@ public class ForkJoinPool extends Abstra
* @return task status on exit
*/
final int awaitJoin(WorkQueue joiner, ForkJoinTask task) {
- int s;
- if ((s = task.status) >= 0) {
+ int s = 0;
+ if (joiner != null && task != null && (s = task.status) >= 0) {
ForkJoinTask prevJoin = joiner.currentJoin;
joiner.currentJoin = task;
- long startTime = 0L;
- for (int k = 0;;) {
- if ((s = (joiner.isEmpty() ? // try to help
- tryHelpStealer(joiner, task) :
- joiner.tryRemoveAndExec(task))) == 0 &&
- (s = task.status) >= 0) {
- if (k == 0) {
- startTime = System.nanoTime();
- tryPollForAndExec(joiner, task); // check uncommon case
- }
- else if ((k & (MAX_HELP - 1)) == 0 &&
- System.nanoTime() - startTime >=
- COMPENSATION_DELAY &&
- tryCompensate(task, null)) {
- if (task.trySetSignal()) {
- synchronized (task) {
- if (task.status >= 0) {
- try { // see ForkJoinTask
- task.wait(); // for explanation
- } catch (InterruptedException ie) {
- }
+ do {} while ((s = task.status) >= 0 &&
+ joiner.queueSize() > 0 &&
+ joiner.tryRemoveAndExec(task)); // process local tasks
+ if (s >= 0 && (s = task.status) >= 0 &&
+ (s = helpSignal(task, joiner.poolIndex)) >= 0 &&
+ (task instanceof CountedCompleter))
+ s = helpComplete(task, LIFO_QUEUE);
+ while (s >= 0 && (s = task.status) >= 0) {
+ if ((joiner.queueSize() > 0 || // try helping
+ (s = tryHelpStealer(joiner, task)) == 0) &&
+ (s = task.status) >= 0 && tryCompensate()) {
+ if (task.trySetSignal() && (s = task.status) >= 0) {
+ synchronized (task) {
+ if (task.status >= 0) {
+ try { // see ForkJoinTask
+ task.wait(); // for explanation
+ } catch (InterruptedException ie) {
}
- else
- task.notifyAll();
}
+ else
+ task.notifyAll();
}
- long c; // re-activate
- do {} while (!U.compareAndSwapLong
- (this, CTL, c = ctl, c + AC_UNIT));
}
+ long c; // re-activate
+ do {} while (!U.compareAndSwapLong
+ (this, CTL, c = ctl, c + AC_UNIT));
}
- if (s < 0 || (s = task.status) < 0) {
- joiner.currentJoin = prevJoin;
- break;
- }
- else if ((k++ & (MAX_HELP - 1)) == MAX_HELP >>> 1)
- Thread.yield(); // for politeness
}
+ joiner.currentJoin = prevJoin;
}
return s;
}
@@ -2087,16 +1977,25 @@ public class ForkJoinPool extends Abstra
*
* @param joiner the joining worker
* @param task the task
- * @return task status on exit
*/
- final int helpJoinOnce(WorkQueue joiner, ForkJoinTask task) {
+ final void helpJoinOnce(WorkQueue joiner, ForkJoinTask task) {
int s;
- while ((s = task.status) >= 0 &&
- (joiner.isEmpty() ?
- tryHelpStealer(joiner, task) :
- joiner.tryRemoveAndExec(task)) != 0)
- ;
- return s;
+ if (joiner != null && task != null && (s = task.status) >= 0) {
+ ForkJoinTask prevJoin = joiner.currentJoin;
+ joiner.currentJoin = task;
+ do {} while ((s = task.status) >= 0 &&
+ joiner.queueSize() > 0 &&
+ joiner.tryRemoveAndExec(task));
+ if (s >= 0 && (s = task.status) >= 0 &&
+ (s = helpSignal(task, joiner.poolIndex)) >= 0 &&
+ (task instanceof CountedCompleter))
+ s = helpComplete(task, LIFO_QUEUE);
+ if (s >= 0 && joiner.queueSize() == 0) {
+ do {} while (task.status >= 0 &&
+ tryHelpStealer(joiner, task) > 0);
+ }
+ joiner.currentJoin = prevJoin;
+ }
}
/**
@@ -2104,21 +2003,20 @@ public class ForkJoinPool extends Abstra
* 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(WorkQueue w) {
- // Similar to loop in scan(), but ignoring submissions
- int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
+ private WorkQueue findNonEmptyStealQueue(int r) {
int step = (r >>> 16) | 1;
for (WorkQueue[] ws;;) {
- int rs = runState, m;
+ int ps = plock, m;
if ((ws = workQueues) == null || (m = ws.length - 1) < 1)
return null;
for (int j = (m + 1) << 2; ; r += step) {
WorkQueue q = ws[((r << 1) | 1) & m];
- if (q != null && !q.isEmpty())
+ if (q != null && q.queueSize() > 0)
return q;
else if (--j < 0) {
- if (runState == rs)
+ if (plock == ps)
return null;
break;
}
@@ -2137,7 +2035,8 @@ public class ForkJoinPool extends Abstra
ForkJoinTask localTask; // exhaust local queue
while ((localTask = w.nextLocalTask()) != null)
localTask.doExec();
- WorkQueue q = findNonEmptyStealQueue(w);
+ // Similar to loop in scan(), but ignoring submissions
+ WorkQueue q = findNonEmptyStealQueue(w.nextSeed());
if (q != null) {
ForkJoinTask t; int b;
if (!active) { // re-establish active count
@@ -2168,30 +2067,6 @@ public class ForkJoinPool extends Abstra
}
/**
- * Restricted version of helpQuiescePool for non-FJ callers
- */
- static void externalHelpQuiescePool() {
- ForkJoinPool p; WorkQueue[] ws; WorkQueue q, sq;
- ForkJoinTask[] a; int b;
- ForkJoinTask t = null;
- int k = submitters.get().seed & SQMASK;
- if ((p = commonPool) != null &&
- (ws = p.workQueues) != null &&
- ws.length > (k &= p.submitMask) &&
- (q = ws[k]) != null) {
- while (q.top - q.base > 0) {
- if ((t = q.sharedPop()) != null)
- break;
- }
- if (t == null && (sq = p.findNonEmptyStealQueue(q)) != null &&
- (b = sq.base) - sq.top < 0)
- t = sq.pollAt(b);
- if (t != null)
- t.doExec();
- }
- }
-
- /**
* Gets and removes a local or stolen task for the given worker.
*
* @return a task, if available
@@ -2201,7 +2076,7 @@ public class ForkJoinPool extends Abstra
WorkQueue q; int b;
if ((t = w.nextLocalTask()) != null)
return t;
- if ((q = findNonEmptyStealQueue(w)) == null)
+ if ((q = findNonEmptyStealQueue(w.nextSeed())) == null)
return null;
if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
return t;
@@ -2209,31 +2084,64 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns the approximate (non-atomic) number of idle threads per
- * active thread to offset steal queue size for method
- * ForkJoinTask.getSurplusQueuedTaskCount().
- */
- final int idlePerActive() {
- // Approximate at powers of two for small values, saturate past 4
- int p = parallelism;
- int a = p + (int)(ctl >> AC_SHIFT);
- return (a > (p >>>= 1) ? 0 :
- a > (p >>>= 1) ? 1 :
- a > (p >>>= 1) ? 2 :
- a > (p >>>= 1) ? 4 :
- 8);
- }
-
- /**
- * Returns approximate submission queue length for the given caller
- */
- static int getEstimatedSubmitterQueueLength() {
- ForkJoinPool p; WorkQueue[] ws; WorkQueue q;
- int k = submitters.get().seed & SQMASK;
- return ((p = commonPool) != null && (ws = p.workQueues) != null &&
- ws.length > (k &= p.submitMask) &&
- (q = ws[k]) != null) ?
- q.queueSize() : 0;
+ * Returns a cheap heuristic guide for task partitioning when
+ * programmers, frameworks, tools, or languages have little or no
+ * idea about task granularity. In essence by offering this
+ * method, we ask users only about tradeoffs in overhead vs
+ * expected throughput and its variance, rather than how finely to
+ * partition tasks.
+ *
+ * In a steady state strict (tree-structured) computation, each
+ * thread makes available for stealing enough tasks for other
+ * threads to remain active. Inductively, if all threads play by
+ * the same rules, each thread should make available only a
+ * constant number of tasks.
+ *
+ * The minimum useful constant is just 1. But using a value of 1
+ * would require immediate replenishment upon each steal to
+ * maintain enough tasks, which is infeasible. Further,
+ * partitionings/granularities of offered tasks should minimize
+ * steal rates, which in general means that threads nearer the top
+ * of computation tree should generate more than those nearer the
+ * bottom. In perfect steady state, each thread is at
+ * approximately the same level of computation tree. However,
+ * producing extra tasks amortizes the uncertainty of progress and
+ * diffusion assumptions.
+ *
+ * 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
+ * value to compare with the results of this call to guide
+ * decisions, but recommend values such as 3.
+ *
+ * When all threads are active, it is on average OK to estimate
+ * surplus strictly locally. In steady-state, if one thread is
+ * maintaining say 2 surplus tasks, then so are others. So we can
+ * just use estimated queue length. However, this strategy alone
+ * leads to serious mis-estimates in some non-steady-state
+ * conditions (ramp-up, ramp-down, other stalls). We can detect
+ * many of these by further considering the number of "idle"
+ * threads, that are known to have zero queued tasks, so
+ * compensate by a factor of (#idle/#active) threads.
+ *
+ * Note: The approximation of #busy workers as #active workers is
+ * not very good under current signalling scheme, and should be
+ * improved.
+ */
+ static int getSurplusQueuedTaskCount() {
+ Thread t; ForkJoinWorkerThread wt; ForkJoinPool pool; WorkQueue q;
+ if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) {
+ int b = (q = (wt = (ForkJoinWorkerThread)t).workQueue).base;
+ int p = (pool = wt.pool).parallelism;
+ int a = (int)(pool.ctl >> AC_SHIFT) + p;
+ return q.top - b - (a > (p >>>= 1) ? 0 :
+ a > (p >>>= 1) ? 1 :
+ a > (p >>>= 1) ? 2 :
+ a > (p >>>= 1) ? 4 :
+ 8);
+ }
+ return 0;
}
// Termination
@@ -2253,6 +2161,8 @@ 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
+ return false;
for (long c;;) {
if (((c = ctl) & STOP_BIT) != 0) { // already terminating
if ((short)(c >>> TC_SHIFT) == -parallelism) {
@@ -2262,19 +2172,16 @@ public class ForkJoinPool extends Abstra
}
return true;
}
- if (runState >= 0) { // not yet enabled
+ if (plock >= 0) { // not yet enabled
+ int ps;
if (!enable)
return false;
- while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
- tryAwaitMainLock();
- try {
- runState |= SHUTDOWN;
- } finally {
- if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
- mainLock = 0;
- synchronized (this) { notifyAll(); };
- }
- }
+ 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) != -parallelism ||
@@ -2297,7 +2204,7 @@ public class ForkJoinPool extends Abstra
int n = ws.length;
for (int i = 0; i < n; ++i) {
if ((w = ws[i]) != null) {
- w.runState = -1;
+ w.qlock = -1;
if (pass > 0) {
w.cancelAll();
if (pass > 1)
@@ -2316,7 +2223,7 @@ public class ForkJoinPool extends Abstra
if (w.eventCount == (e | INT_SIGN) &&
U.compareAndSwapLong(this, CTL, cc, nc)) {
w.eventCount = (e + E_SEQ) & E_MASK;
- w.runState = -1;
+ w.qlock = -1;
if ((p = w.parker) != null)
U.unpark(p);
}
@@ -2327,6 +2234,142 @@ public class ForkJoinPool extends Abstra
}
}
+ // external operations on common pool
+
+ /**
+ * Returns common pool queue for a thread that has submitted at
+ * least one task.
+ */
+ static WorkQueue commonSubmitterQueue() {
+ ForkJoinPool p; WorkQueue[] ws; int m; Submitter z;
+ return ((z = submitters.get()) != null &&
+ (p = commonPool) != null &&
+ (ws = p.workQueues) != null &&
+ (m = ws.length - 1) >= 0) ?
+ ws[m & z.seed & SQMASK] : null;
+ }
+
+ /**
+ * 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; long j;
+ if ((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 &&
+ U.getObjectVolatile
+ (a, j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE) == 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;
+ }
+ q.qlock = 0;
+ }
+ return false;
+ }
+
+ /**
+ * 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; 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 || (int)(ctl >> AC_SHIFT) >= 0)
+ break;
+ if (task == null) {
+ if (helpSignal(root, q.poolIndex) >= 0)
+ helpComplete(root, SHARED_QUEUE);
+ break;
+ }
+ }
+ }
+ }
+
+ /**
+ * 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; long j;
+ if (t != null && t.status >= 0 &&
+ (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) {
+ if ((s = q.top) != q.base &&
+ U.getObjectVolatile
+ (a, j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE) == 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);
+ }
+ }
+ }
+
+ /**
+ * Restricted version of helpQuiescePool for external callers
+ */
+ static void externalHelpQuiescePool() {
+ ForkJoinPool p; ForkJoinTask t; WorkQueue q; int b;
+ int r = ThreadLocalRandom.current().nextInt();
+ if ((p = commonPool) != null &&
+ (q = p.findNonEmptyStealQueue(r)) != null &&
+ (b = q.base) - q.top < 0 &&
+ (t = q.pollAt(b)) != null)
+ t.doExec();
+ }
+
// Exported methods
// Constructors
@@ -2404,34 +2447,26 @@ public class ForkJoinPool extends Abstra
this.localMode = asyncMode ? FIFO_QUEUE : LIFO_QUEUE;
long np = (long)(-parallelism); // offset ctl counts
this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
- // Use nearest power 2 for workQueues size. See Hackers Delight sec 3.2.
- int n = parallelism - 1;
- n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16;
- this.submitMask = ((n + 1) << 1) - 1;
- int pn = poolNumberGenerator.incrementAndGet();
+ int pn = nextPoolId();
StringBuilder sb = new StringBuilder("ForkJoinPool-");
sb.append(Integer.toString(pn));
sb.append("-worker-");
this.workerNamePrefix = sb.toString();
- this.runState = 1; // set init flag
}
/**
* Constructor for common pool, suitable only for static initialization.
* Basically the same as above, but uses smallest possible initial footprint.
*/
- ForkJoinPool(int parallelism, int submitMask,
+ ForkJoinPool(int parallelism, long ctl,
ForkJoinWorkerThreadFactory factory,
Thread.UncaughtExceptionHandler handler) {
+ this.parallelism = parallelism;
+ this.ctl = ctl;
this.factory = factory;
this.ueh = handler;
- this.submitMask = submitMask;
- this.parallelism = parallelism;
- long np = (long)(-parallelism);
- this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
this.localMode = LIFO_QUEUE;
this.workerNamePrefix = "ForkJoinPool.commonPool-worker-";
- this.runState = 1;
}
/**
@@ -2440,10 +2475,7 @@ public class ForkJoinPool extends Abstra
* @return the common pool instance
*/
public static ForkJoinPool commonPool() {
- ForkJoinPool p;
- if ((p = commonPool) == null)
- throw new Error("Common Pool Unavailable");
- return p;
+ return commonPool; // cannot be null (if so, a static init error)
}
// Execution methods
@@ -2467,7 +2499,7 @@ public class ForkJoinPool extends Abstra
public T invoke(ForkJoinTask task) {
if (task == null)
throw new NullPointerException();
- doSubmit(task);
+ externalPush(task);
return task.join();
}
@@ -2482,7 +2514,7 @@ public class ForkJoinPool extends Abstra
public void execute(ForkJoinTask task) {
if (task == null)
throw new NullPointerException();
- doSubmit(task);
+ externalPush(task);
}
// AbstractExecutorService methods
@@ -2500,7 +2532,7 @@ public class ForkJoinPool extends Abstra
job = (ForkJoinTask) task;
else
job = new ForkJoinTask.AdaptedRunnableAction(task);
- doSubmit(job);
+ externalPush(job);
}
/**
@@ -2515,7 +2547,7 @@ public class ForkJoinPool extends Abstra
public ForkJoinTask submit(ForkJoinTask task) {
if (task == null)
throw new NullPointerException();
- doSubmit(task);
+ externalPush(task);
return task;
}
@@ -2526,7 +2558,7 @@ public class ForkJoinPool extends Abstra
*/
public ForkJoinTask submit(Callable task) {
ForkJoinTask job = new ForkJoinTask.AdaptedCallable(task);
- doSubmit(job);
+ externalPush(job);
return job;
}
@@ -2537,7 +2569,7 @@ public class ForkJoinPool extends Abstra
*/
public ForkJoinTask submit(Runnable task, T result) {
ForkJoinTask job = new ForkJoinTask.AdaptedRunnable(task, result);
- doSubmit(job);
+ externalPush(job);
return job;
}
@@ -2554,7 +2586,7 @@ public class ForkJoinPool extends Abstra
job = (ForkJoinTask) task;
else
job = new ForkJoinTask.AdaptedRunnableAction(task);
- doSubmit(job);
+ externalPush(job);
return job;
}
@@ -2576,7 +2608,7 @@ public class ForkJoinPool extends Abstra
try {
for (Callable t : tasks) {
ForkJoinTask f = new ForkJoinTask.AdaptedCallable(t);
- doSubmit(f);
+ externalPush(f);
fs.add(f);
}
for (ForkJoinTask f : fs)
@@ -2713,7 +2745,7 @@ public class ForkJoinPool extends Abstra
if ((ws = workQueues) != null) {
for (int i = 1; i < ws.length; i += 2) {
if ((w = ws[i]) != null)
- count += w.totalSteals;
+ count += w.nsteals;
}
}
return count;
@@ -2770,7 +2802,7 @@ public class ForkJoinPool extends Abstra
WorkQueue[] ws; WorkQueue w;
if ((ws = workQueues) != null) {
for (int i = 0; i < ws.length; i += 2) {
- if ((w = ws[i]) != null && !w.isEmpty())
+ if ((w = ws[i]) != null && w.queueSize() != 0)
return true;
}
}
@@ -2849,7 +2881,7 @@ public class ForkJoinPool extends Abstra
qs += size;
else {
qt += size;
- st += w.totalSteals;
+ st += w.nsteals;
if (w.isApparentlyUnblocked())
++rc;
}
@@ -2865,7 +2897,7 @@ public class ForkJoinPool extends Abstra
if ((c & STOP_BIT) != 0)
level = (tc == 0) ? "Terminated" : "Terminating";
else
- level = runState < 0 ? "Shutting down" : "Running";
+ level = plock < 0 ? "Shutting down" : "Running";
return super.toString() +
"[" + level +
", parallelism = " + pc +
@@ -2894,8 +2926,7 @@ public class ForkJoinPool extends Abstra
*/
public void shutdown() {
checkPermission();
- if (this != commonPool)
- tryTerminate(false, true);
+ tryTerminate(false, true);
}
/**
@@ -2918,8 +2949,7 @@ public class ForkJoinPool extends Abstra
*/
public List shutdownNow() {
checkPermission();
- if (this != commonPool)
- tryTerminate(true, true);
+ tryTerminate(true, true);
return Collections.emptyList();
}
@@ -2959,13 +2989,15 @@ public class ForkJoinPool extends Abstra
* @return {@code true} if this pool has been shut down
*/
public boolean isShutdown() {
- return runState < 0;
+ return plock < 0;
}
/**
- * Blocks until all tasks have completed execution after a shutdown
- * request, or the timeout occurs, or the current thread is
- * interrupted, whichever happens first.
+ * 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.
*
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
@@ -3089,19 +3121,36 @@ public class ForkJoinPool extends Abstra
public static void managedBlock(ManagedBlocker blocker)
throws InterruptedException {
Thread t = Thread.currentThread();
- ForkJoinPool p = ((t instanceof ForkJoinWorkerThread) ?
- ((ForkJoinWorkerThread)t).pool : null);
- while (!blocker.isReleasable()) {
- if (p == null || p.tryCompensate(null, blocker)) {
- try {
- do {} while (!blocker.isReleasable() && !blocker.block());
- } finally {
- if (p != null)
+ if (t instanceof ForkJoinWorkerThread) {
+ ForkJoinPool p = ((ForkJoinWorkerThread)t).pool;
+ while (!blocker.isReleasable()) { // variant of helpSignal
+ WorkQueue[] ws; WorkQueue q; int m, n;
+ 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 && (n = q.queueSize()) > 0) {
+ p.signalWork(q, n);
+ if ((int)(p.ctl >> AC_SHIFT) >= 0)
+ break;
+ }
+ }
+ }
+ if (p.tryCompensate()) {
+ try {
+ do {} while (!blocker.isReleasable() &&
+ !blocker.block());
+ } finally {
p.incrementActiveCount();
+ }
+ break;
}
- break;
}
}
+ else {
+ do {} while (!blocker.isReleasable() &&
+ !blocker.block());
+ }
}
// AbstractExecutorService overrides. These rely on undocumented
@@ -3122,33 +3171,52 @@ public class ForkJoinPool extends Abstra
private static final long PARKBLOCKER;
private static final int ABASE;
private static final int ASHIFT;
- private static final long NEXTWORKERNUMBER;
private static final long STEALCOUNT;
- private static final long MAINLOCK;
+ private static final long PLOCK;
+ private static final long INDEXSEED;
+ private static final long QLOCK;
static {
- poolNumberGenerator = new AtomicInteger();
- nextSubmitterSeed = new AtomicInteger(0x55555555);
- modifyThreadPermission = new RuntimePermission("modifyThread");
- defaultForkJoinWorkerThreadFactory =
- new DefaultForkJoinWorkerThreadFactory();
- submitters = new ThreadSubmitter();
- int s;
+ // Establish common pool parameters
+ // TBD: limit or report ignored exceptions?
+
+ int par = 0;
+ ForkJoinWorkerThreadFactory fac = null;
+ Thread.UncaughtExceptionHandler handler = null;
+ try {
+ String pp = System.getProperty(propPrefix + "parallelism");
+ String hp = System.getProperty(propPrefix + "exceptionHandler");
+ String fp = System.getProperty(propPrefix + "threadFactory");
+ if (fp != null)
+ fac = ((ForkJoinWorkerThreadFactory)ClassLoader.
+ getSystemClassLoader().loadClass(fp).newInstance());
+ if (hp != null)
+ handler = ((Thread.UncaughtExceptionHandler)ClassLoader.
+ getSystemClassLoader().loadClass(hp).newInstance());
+ if (pp != null)
+ par = Integer.parseInt(pp);
+ } catch(Exception ignore) {
+ }
+
+ int s; // initialize field offsets for CAS etc
try {
U = getUnsafe();
Class k = ForkJoinPool.class;
- Class ak = ForkJoinTask[].class;
CTL = U.objectFieldOffset
(k.getDeclaredField("ctl"));
- NEXTWORKERNUMBER = U.objectFieldOffset
- (k.getDeclaredField("nextWorkerNumber"));
STEALCOUNT = U.objectFieldOffset
(k.getDeclaredField("stealCount"));
- MAINLOCK = U.objectFieldOffset
- (k.getDeclaredField("mainLock"));
+ PLOCK = U.objectFieldOffset
+ (k.getDeclaredField("plock"));
+ INDEXSEED = U.objectFieldOffset
+ (k.getDeclaredField("indexSeed"));
Class tk = Thread.class;
PARKBLOCKER = U.objectFieldOffset
(tk.getDeclaredField("parkBlocker"));
+ Class wk = WorkQueue.class;
+ QLOCK = U.objectFieldOffset
+ (wk.getDeclaredField("qlock"));
+ Class ak = ForkJoinTask[].class;
ABASE = U.arrayBaseOffset(ak);
s = U.arrayIndexScale(ak);
ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
@@ -3157,31 +3225,27 @@ public class ForkJoinPool extends Abstra
}
if ((s & (s-1)) != 0)
throw new Error("data type scale not a power of two");
- try { // Establish common pool
- String pp = System.getProperty(propPrefix + "parallelism");
- String fp = System.getProperty(propPrefix + "threadFactory");
- String up = System.getProperty(propPrefix + "exceptionHandler");
- ForkJoinWorkerThreadFactory fac = (fp == null) ?
- defaultForkJoinWorkerThreadFactory :
- ((ForkJoinWorkerThreadFactory)ClassLoader.
- getSystemClassLoader().loadClass(fp).newInstance());
- Thread.UncaughtExceptionHandler ueh = (up == null) ? null :
- ((Thread.UncaughtExceptionHandler)ClassLoader.
- getSystemClassLoader().loadClass(up).newInstance());
- int par;
- if ((pp == null || (par = Integer.parseInt(pp)) <= 0))
- par = Runtime.getRuntime().availableProcessors();
- if (par > MAX_CAP)
- par = MAX_CAP;
- commonPoolParallelism = par;
- int n = par - 1; // precompute submit mask
- n |= n >>> 1; n |= n >>> 2; n |= n >>> 4;
- n |= n >>> 8; n |= n >>> 16;
- int mask = ((n + 1) << 1) - 1;
- commonPool = new ForkJoinPool(par, mask, fac, ueh);
- } catch (Exception e) {
- throw new Error(e);
- }
+
+ /*
+ * For extra caution, computations to set up pool state are
+ * here; the constructor just assigns these values to fields.
+ */
+ ForkJoinWorkerThreadFactory defaultFac =
+ defaultForkJoinWorkerThreadFactory =
+ new DefaultForkJoinWorkerThreadFactory();
+ if (fac == null)
+ fac = defaultFac;
+ if (par <= 0)
+ par = Runtime.getRuntime().availableProcessors();
+ if (par > MAX_CAP)
+ par = MAX_CAP;
+ long np = (long)(-par); // precompute initial ctl value
+ long ct = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
+
+ commonPoolParallelism = par;
+ commonPool = new ForkJoinPool(par, ct, fac, handler);
+ modifyThreadPermission = new RuntimePermission("modifyThread");
+ submitters = new ThreadLocal();
}
/**