--- jsr166/src/jsr166y/ForkJoinTask.java 2009/07/20 21:54:51 1.8
+++ jsr166/src/jsr166y/ForkJoinTask.java 2010/05/27 16:46:48 1.48
@@ -5,55 +5,60 @@
*/
package jsr166y;
-import java.io.Serializable;
-import java.util.*;
+
import java.util.concurrent.*;
-import java.util.concurrent.atomic.*;
-import sun.misc.Unsafe;
-import java.lang.reflect.*;
+
+import java.io.Serializable;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.RandomAccess;
+import java.util.Map;
+import java.util.WeakHashMap;
/**
- * Abstract base class for tasks that run within a {@link
- * ForkJoinPool}. A ForkJoinTask is a thread-like entity that is much
+ * Abstract base class for tasks that run within a {@link ForkJoinPool}.
+ * A {@code ForkJoinTask} is a thread-like entity that is much
* lighter weight than a normal thread. Huge numbers of tasks and
* subtasks may be hosted by a small number of actual threads in a
* ForkJoinPool, at the price of some usage limitations.
*
- * A "main" ForkJoinTask begins execution when submitted to a
- * {@link ForkJoinPool}. Once started, it will usually in turn start
- * other subtasks. As indicated by the name of this class, many
- * programs using ForkJoinTasks employ only methods {@code fork}
- * and {@code join}, or derivatives such as
- * {@code invokeAll}. However, this class also provides a number
- * of other methods that can come into play in advanced usages, as
- * well as extension mechanics that allow support of new forms of
- * fork/join processing.
+ *
A "main" {@code ForkJoinTask} begins execution when submitted
+ * to a {@link ForkJoinPool}. Once started, it will usually in turn
+ * start other subtasks. As indicated by the name of this class,
+ * many programs using {@code ForkJoinTask} employ only methods
+ * {@link #fork} and {@link #join}, or derivatives such as {@link
+ * #invokeAll}. However, this class also provides a number of other
+ * methods that can come into play in advanced usages, as well as
+ * extension mechanics that allow support of new forms of fork/join
+ * processing.
*
- *
A ForkJoinTask is a lightweight form of {@link Future}. The
- * efficiency of ForkJoinTasks stems from a set of restrictions (that
- * are only partially statically enforceable) reflecting their
- * intended use as computational tasks calculating pure functions or
- * operating on purely isolated objects. The primary coordination
- * mechanisms are {@link #fork}, that arranges asynchronous execution,
- * and {@link #join}, that doesn't proceed until the task's result has
- * been computed. Computations should avoid {@code synchronized}
- * methods or blocks, and should minimize other blocking
- * synchronization apart from joining other tasks or using
- * synchronizers such as Phasers that are advertised to cooperate with
- * fork/join scheduling. Tasks should also not perform blocking IO,
- * and should ideally access variables that are completely independent
- * of those accessed by other running tasks. Minor breaches of these
- * restrictions, for example using shared output streams, may be
- * tolerable in practice, but frequent use may result in poor
- * performance, and the potential to indefinitely stall if the number
- * of threads not waiting for IO or other external synchronization
- * becomes exhausted. This usage restriction is in part enforced by
- * not permitting checked exceptions such as {@code IOExceptions}
- * to be thrown. However, computations may still encounter unchecked
- * exceptions, that are rethrown to callers attempting join
- * them. These exceptions may additionally include
- * RejectedExecutionExceptions stemming from internal resource
- * exhaustion such as failure to allocate internal task queues.
+ *
A {@code ForkJoinTask} is a lightweight form of {@link Future}.
+ * The efficiency of {@code ForkJoinTask}s stems from a set of
+ * restrictions (that are only partially statically enforceable)
+ * reflecting their intended use as computational tasks calculating
+ * pure functions or operating on purely isolated objects. The
+ * primary coordination mechanisms are {@link #fork}, that arranges
+ * asynchronous execution, and {@link #join}, that doesn't proceed
+ * until the task's result has been computed. Computations should
+ * avoid {@code synchronized} methods or blocks, and should minimize
+ * other blocking synchronization apart from joining other tasks or
+ * using synchronizers such as Phasers that are advertised to
+ * cooperate with fork/join scheduling. Tasks should also not perform
+ * blocking IO, and should ideally access variables that are
+ * completely independent of those accessed by other running
+ * tasks. Minor breaches of these restrictions, for example using
+ * shared output streams, may be tolerable in practice, but frequent
+ * use may result in poor performance, and the potential to
+ * indefinitely stall if the number of threads not waiting for IO or
+ * other external synchronization becomes exhausted. This usage
+ * restriction is in part enforced by not permitting checked
+ * exceptions such as {@code IOExceptions} to be thrown. However,
+ * computations may still encounter unchecked exceptions, that are
+ * rethrown to callers attempting to join them. These exceptions may
+ * additionally include {@link RejectedExecutionException} stemming
+ * from internal resource exhaustion, such as failure to allocate
+ * internal task queues.
*
*
The primary method for awaiting completion and extracting
* results of a task is {@link #join}, but there are several variants:
@@ -63,408 +68,301 @@ import java.lang.reflect.*;
* execute other tasks while awaiting joins, which is sometimes more
* efficient but only applies when all subtasks are known to be
* strictly tree-structured. Method {@link #invoke} is semantically
- * equivalent to {@code fork(); join()} but always attempts to
- * begin execution in the current thread. The "quiet" forms
- * of these methods do not extract results or report exceptions. These
+ * equivalent to {@code fork(); join()} but always attempts to begin
+ * execution in the current thread. The "quiet" forms of
+ * these methods do not extract results or report exceptions. These
* may be useful when a set of tasks are being executed, and you need
* to delay processing of results or exceptions until all complete.
* Method {@code invokeAll} (available in multiple versions)
* performs the most common form of parallel invocation: forking a set
* of tasks and joining them all.
*
- *
The ForkJoinTask class is not usually directly subclassed.
+ *
The execution status of tasks may be queried at several levels
+ * of detail: {@link #isDone} is true if a task completed in any way
+ * (including the case where a task was cancelled without executing);
+ * {@link #isCompletedNormally} is true if a task completed without
+ * cancellation or encountering an exception; {@link #isCancelled} is
+ * true if the task was cancelled (in which case {@link #getException}
+ * returns a {@link java.util.concurrent.CancellationException}); and
+ * {@link #isCompletedAbnormally} is true if a task was either
+ * cancelled or encountered an exception, in which case {@link
+ * #getException} will return either the encountered exception or
+ * {@link java.util.concurrent.CancellationException}.
+ *
+ *
The ForkJoinTask class is not usually directly subclassed.
* Instead, you subclass one of the abstract classes that support a
- * particular style of fork/join processing. Normally, a concrete
+ * particular style of fork/join processing, typically {@link
+ * RecursiveAction} for computations that do not return results, or
+ * {@link RecursiveTask} for those that do. Normally, a concrete
* ForkJoinTask subclass declares fields comprising its parameters,
* established in a constructor, and then defines a {@code compute}
* method that somehow uses the control methods supplied by this base
* class. While these methods have {@code public} access (to allow
- * instances of different task subclasses to call each others
+ * instances of different task subclasses to call each other's
* methods), some of them may only be called from within other
- * ForkJoinTasks. Attempts to invoke them in other contexts result in
- * exceptions or errors possibly including ClassCastException.
+ * ForkJoinTasks (as may be determined using method {@link
+ * #inForkJoinPool}). Attempts to invoke them in other contexts
+ * result in exceptions or errors, possibly including
+ * ClassCastException.
*
- *
Most base support methods are {@code final} because their
- * implementations are intrinsically tied to the underlying
- * lightweight task scheduling framework, and so cannot be overridden.
- * Developers creating new basic styles of fork/join processing should
- * minimally implement {@code protected} methods
- * {@code exec}, {@code setRawResult}, and
- * {@code getRawResult}, while also introducing an abstract
- * computational method that can be implemented in its subclasses,
- * possibly relying on other {@code protected} methods provided
- * by this class.
+ *
Most base support methods are {@code final}, to prevent
+ * overriding of implementations that are intrinsically tied to the
+ * underlying lightweight task scheduling framework. Developers
+ * creating new basic styles of fork/join processing should minimally
+ * implement {@code protected} methods {@link #exec}, {@link
+ * #setRawResult}, and {@link #getRawResult}, while also introducing
+ * an abstract computational method that can be implemented in its
+ * subclasses, possibly relying on other {@code protected} methods
+ * provided by this class.
*
*
ForkJoinTasks should perform relatively small amounts of
- * computations, othewise splitting into smaller tasks. As a very
- * rough rule of thumb, a task should perform more than 100 and less
- * than 10000 basic computational steps. If tasks are too big, then
- * parellelism cannot improve throughput. If too small, then memory
- * and internal task maintenance overhead may overwhelm processing.
+ * computation. Large tasks should be split into smaller subtasks,
+ * usually via recursive decomposition. As a very rough rule of thumb,
+ * a task should perform more than 100 and less than 10000 basic
+ * computational steps. If tasks are too big, then parallelism cannot
+ * improve throughput. If too small, then memory and internal task
+ * maintenance overhead may overwhelm processing.
*
- *
ForkJoinTasks are {@code Serializable}, which enables them
- * to be used in extensions such as remote execution frameworks. It is
- * in general sensible to serialize tasks only before or after, but
- * not during execution. Serialization is not relied on during
- * execution itself.
+ *
This class provides {@code adapt} methods for {@link Runnable}
+ * and {@link Callable}, that may be of use when mixing execution of
+ * {@code ForkJoinTasks} with other kinds of tasks. When all tasks
+ * are of this form, consider using a pool in
+ * {@linkplain ForkJoinPool#setAsyncMode async mode}.
+ *
+ *
ForkJoinTasks are {@code Serializable}, which enables them to be
+ * used in extensions such as remote execution frameworks. It is
+ * sensible to serialize tasks only before or after, but not during,
+ * execution. Serialization is not relied on during execution itself.
+ *
+ * @since 1.7
+ * @author Doug Lea
*/
public abstract class ForkJoinTask implements Future, Serializable {
+ /*
+ * See the internal documentation of class ForkJoinPool for a
+ * general implementation overview. ForkJoinTasks are mainly
+ * responsible for maintaining their "status" field amidst relays
+ * to methods in ForkJoinWorkerThread and ForkJoinPool. The
+ * methods of this class are more-or-less layered into (1) basic
+ * status maintenance (2) execution and awaiting completion (3)
+ * user-level methods that additionally report results. This is
+ * sometimes hard to see because this file orders exported methods
+ * in a way that flows well in javadocs.
+ */
+
/**
* Run control status bits packed into a single int to minimize
* footprint and to ensure atomicity (via CAS). Status is
* initially zero, and takes on nonnegative values until
* completed, upon which status holds COMPLETED. CANCELLED, or
* EXCEPTIONAL, which use the top 3 bits. Tasks undergoing
- * blocking waits by other threads have SIGNAL_MASK bits set --
- * bit 15 for external (nonFJ) waits, and the rest a count of
- * waiting FJ threads. (This representation relies on
- * ForkJoinPool max thread limits). Completion of a stolen task
- * with SIGNAL_MASK bits set awakens waiter via notifyAll. Even
- * though suboptimal for some purposes, we use basic builtin
- * wait/notify to take advantage of "monitor inflation" in JVMs
- * that we would otherwise need to emulate to avoid adding further
- * per-task bookkeeping overhead. Note that bits 16-28 are
- * currently unused. Also value 0x80000000 is available as spare
- * completion value.
- */
- volatile int status; // accessed directy by pool and workers
-
- static final int COMPLETION_MASK = 0xe0000000;
- static final int NORMAL = 0xe0000000; // == mask
- static final int CANCELLED = 0xc0000000;
- static final int EXCEPTIONAL = 0xa0000000;
- static final int SIGNAL_MASK = 0x0000ffff;
- static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
- static final int EXTERNAL_SIGNAL = 0x00008000; // top bit of low word
+ * blocking waits by other threads have the SIGNAL bit set.
+ *
+ * Completion of a stolen task with SIGNAL set awakens any waiters
+ * via notifyAll. Even though suboptimal for some purposes, we use
+ * basic builtin wait/notify to take advantage of "monitor
+ * inflation" in JVMs that we would otherwise need to emulate to
+ * avoid adding further per-task bookkeeping overhead. We want
+ * these monitors to be "fat", i.e., not use biasing or thin-lock
+ * techniques, so use some odd coding idioms that tend to avoid
+ * them.
+ *
+ * Note that bits 1-28 are currently unused. Also value
+ * 0x80000000 is available as spare completion value.
+ */
+ volatile int status; // accessed directly by pool and workers
+
+ private static final int COMPLETION_MASK = 0xe0000000;
+ private static final int NORMAL = 0xe0000000; // == mask
+ private static final int CANCELLED = 0xc0000000;
+ private static final int EXCEPTIONAL = 0xa0000000;
+ private static final int SIGNAL = 0x00000001;
/**
* Table of exceptions thrown by tasks, to enable reporting by
* callers. Because exceptions are rare, we don't directly keep
- * them with task objects, but instead us a weak ref table. Note
+ * them with task objects, but instead use a weak ref table. Note
* that cancellation exceptions don't appear in the table, but are
* instead recorded as status values.
- * Todo: Use ConcurrentReferenceHashMap
+ * TODO: Use ConcurrentReferenceHashMap
*/
static final Map, Throwable> exceptionMap =
Collections.synchronizedMap
(new WeakHashMap, Throwable>());
- // within-package utilities
-
- /**
- * Get current worker thread, or null if not a worker thread
- */
- static ForkJoinWorkerThread getWorker() {
- Thread t = Thread.currentThread();
- return ((t instanceof ForkJoinWorkerThread)?
- (ForkJoinWorkerThread)t : null);
- }
-
- final boolean casStatus(int cmp, int val) {
- return _unsafe.compareAndSwapInt(this, statusOffset, cmp, val);
- }
+ // Maintaining completion status
/**
- * Workaround for not being able to rethrow unchecked exceptions.
- */
- static void rethrowException(Throwable ex) {
- if (ex != null)
- _unsafe.throwException(ex);
- }
-
- // Setting completion status
-
- /**
- * Mark completion and wake up threads waiting to join this task.
+ * Marks completion and wakes up threads waiting to join this task,
+ * also clearing signal request bits.
+ *
* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
+ * @return status on exit
*/
- final void setCompletion(int completion) {
- ForkJoinPool pool = getPool();
- if (pool != null) {
- int s; // Clear signal bits while setting completion status
- do;while ((s = status) >= 0 && !casStatus(s, completion));
-
- if ((s & SIGNAL_MASK) != 0) {
- if ((s &= INTERNAL_SIGNAL_MASK) != 0)
- pool.updateRunningCount(s);
- synchronized(this) { notifyAll(); }
- }
- }
- else
- externallySetCompletion(completion);
- }
-
- /**
- * Version of setCompletion for non-FJ threads. Leaves signal
- * bits for unblocked threads to adjust, and always notifies.
- */
- private void externallySetCompletion(int completion) {
+ private int setCompletion(int completion) {
int s;
- do;while ((s = status) >= 0 &&
- !casStatus(s, (s & SIGNAL_MASK) | completion));
- synchronized(this) { notifyAll(); }
- }
-
- /**
- * Sets status to indicate normal completion
- */
- final void setNormalCompletion() {
- // Try typical fast case -- single CAS, no signal, not already done.
- // Manually expand casStatus to improve chances of inlining it
- if (!_unsafe.compareAndSwapInt(this, statusOffset, 0, NORMAL))
- setCompletion(NORMAL);
- }
-
- // internal waiting and notification
-
- /**
- * Performs the actual monitor wait for awaitDone
- */
- private void doAwaitDone() {
- // Minimize lock bias and in/de-flation effects by maximizing
- // chances of waiting inside sync
- try {
- while (status >= 0)
- synchronized(this) { if (status >= 0) wait(); }
- } catch (InterruptedException ie) {
- onInterruptedWait();
- }
- }
-
- /**
- * Performs the actual monitor wait for awaitDone
- */
- private void doAwaitDone(long startTime, long nanos) {
- synchronized(this) {
- try {
- while (status >= 0) {
- long nt = nanos - System.nanoTime() - startTime;
- if (nt <= 0)
- break;
- wait(nt / 1000000, (int)(nt % 1000000));
- }
- } catch (InterruptedException ie) {
- onInterruptedWait();
+ while ((s = status) >= 0) {
+ if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
+ if ((s & SIGNAL) != 0)
+ synchronized (this) { notifyAll(); }
+ return completion;
}
}
+ return s;
}
- // Awaiting completion
-
/**
- * Sets status to indicate there is joiner, then waits for join,
- * surrounded with pool notifications.
- * @return status upon exit
+ * Record exception and set exceptional completion
+ * @return status on exit
*/
- private int awaitDone(ForkJoinWorkerThread w, boolean maintainParallelism) {
- ForkJoinPool pool = w == null? null : w.pool;
- int s;
- while ((s = status) >= 0) {
- if (casStatus(s, pool == null? s|EXTERNAL_SIGNAL : s+1)) {
- if (pool == null || !pool.preJoin(this, maintainParallelism))
- doAwaitDone();
- if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
- adjustPoolCountsOnUnblock(pool);
- break;
- }
- }
- return s;
+ private int setExceptionalCompletion(Throwable rex) {
+ exceptionMap.put(this, rex);
+ return setCompletion(EXCEPTIONAL);
}
/**
- * Timed version of awaitDone
- * @return status upon exit
+ * Blocks a worker thread until completion. Called only by pool.
*/
- private int awaitDone(ForkJoinWorkerThread w, long nanos) {
- ForkJoinPool pool = w == null? null : w.pool;
+ final void internalAwaitDone() {
int s;
while ((s = status) >= 0) {
- if (casStatus(s, pool == null? s|EXTERNAL_SIGNAL : s+1)) {
- long startTime = System.nanoTime();
- if (pool == null || !pool.preJoin(this, false))
- doAwaitDone(startTime, nanos);
- if ((s = status) >= 0) {
- adjustPoolCountsOnCancelledWait(pool);
- s = status;
+ synchronized(this) {
+ if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
+ do {
+ try {
+ wait();
+ } catch (InterruptedException ie) {
+ cancelIfTerminating();
+ }
+ } while (status >= 0);
+ break;
}
- if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0)
- adjustPoolCountsOnUnblock(pool);
- break;
}
}
- return s;
}
/**
- * Notify pool that thread is unblocked. Called by signalled
- * threads when woken by non-FJ threads (which is atypical).
+ * Blocks a non-worker-thread until completion.
+ * @return status on exit
*/
- private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
+ private int externalAwaitDone() {
int s;
- do;while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
- if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
- pool.updateRunningCount(s);
- }
-
- /**
- * Notify pool to adjust counts on cancelled or timed out wait
- */
- private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
- if (pool != null) {
- int s;
- while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) {
- if (casStatus(s, s - 1)) {
- pool.updateRunningCount(1);
+ while ((s = status) >= 0) {
+ synchronized(this) {
+ if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
+ boolean interrupted = false;
+ do {
+ try {
+ wait();
+ } catch (InterruptedException ie) {
+ interrupted = true;
+ }
+ } while ((s = status) >= 0);
+ if (interrupted)
+ Thread.currentThread().interrupt();
break;
}
}
}
+ return s;
}
/**
- * Handle interruptions during waits.
- */
- private void onInterruptedWait() {
- ForkJoinWorkerThread w = getWorker();
- if (w == null)
- Thread.currentThread().interrupt(); // re-interrupt
- else if (w.isTerminating())
- cancelIgnoringExceptions();
- // else if FJworker, ignore interrupt
- }
-
- // Recording and reporting exceptions
-
- private void setDoneExceptionally(Throwable rex) {
- exceptionMap.put(this, rex);
- setCompletion(EXCEPTIONAL);
- }
-
- /**
- * Throws the exception associated with status s;
- * @throws the exception
- */
- private void reportException(int s) {
- if ((s &= COMPLETION_MASK) < NORMAL) {
- if (s == CANCELLED)
- throw new CancellationException();
- else
- rethrowException(exceptionMap.get(this));
- }
- }
-
- /**
- * Returns result or throws exception using j.u.c.Future conventions
- * Only call when isDone known to be true.
- */
- private V reportFutureResult()
- throws ExecutionException, InterruptedException {
- int s = status & COMPLETION_MASK;
- if (s < NORMAL) {
- Throwable ex;
- if (s == CANCELLED)
- throw new CancellationException();
- if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
- throw new ExecutionException(ex);
- if (Thread.interrupted())
- throw new InterruptedException();
- }
- return getRawResult();
- }
-
- /**
- * Returns result or throws exception using j.u.c.Future conventions
- * with timeouts
+ * Unless done, calls exec and records status if completed, but
+ * doesn't wait for completion otherwise.
*/
- private V reportTimedFutureResult()
- throws InterruptedException, ExecutionException, TimeoutException {
- Throwable ex;
- int s = status & COMPLETION_MASK;
- if (s == NORMAL)
- return getRawResult();
- if (s == CANCELLED)
- throw new CancellationException();
- if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
- throw new ExecutionException(ex);
- if (Thread.interrupted())
- throw new InterruptedException();
- throw new TimeoutException();
- }
-
- // internal execution methods
-
- /**
- * Calls exec, recording completion, and rethrowing exception if
- * encountered. Caller should normally check status before calling
- * @return true if completed normally
- */
- private boolean tryExec() {
- try { // try block must contain only call to exec
- if (!exec())
- return false;
+ final void tryExec() {
+ try {
+ if (status < 0 || !exec())
+ return;
} catch (Throwable rex) {
- setDoneExceptionally(rex);
- rethrowException(rex);
- return false; // not reached
+ setExceptionalCompletion(rex);
+ return;
}
- setNormalCompletion();
- return true;
+ setCompletion(NORMAL); // must be outside try block
}
/**
- * Main execution method used by worker threads. Invokes
- * base computation unless already complete
+ * If not done and this task is next in worker queue, runs it,
+ * else waits for it.
+ * @return status on exit
*/
- final void quietlyExec() {
- if (status >= 0) {
- try {
- if (!exec())
- return;
- } catch(Throwable rex) {
- setDoneExceptionally(rex);
- return;
+ private int waitingJoin() {
+ int s = status;
+ if (s < 0)
+ return s;
+ Thread t = Thread.currentThread();
+ if (t instanceof ForkJoinWorkerThread) {
+ ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
+ if (w.unpushTask(this)) {
+ boolean completed;
+ try {
+ completed = exec();
+ } catch (Throwable rex) {
+ return setExceptionalCompletion(rex);
+ }
+ if (completed)
+ return setCompletion(NORMAL);
}
- setNormalCompletion();
+ return w.pool.awaitJoin(this);
}
+ else
+ return externalAwaitDone();
}
/**
- * Calls exec, recording but not rethrowing exception
- * Caller should normally check status before calling
- * @return true if completed normally
+ * Unless done, calls exec and records status if completed, or
+ * waits for completion otherwise.
+ * @return status on exit
*/
- private boolean tryQuietlyInvoke() {
+ private int waitingInvoke() {
+ int s = status;
+ if (s < 0)
+ return s;
+ boolean completed;
try {
- if (!exec())
- return false;
+ completed = exec();
} catch (Throwable rex) {
- setDoneExceptionally(rex);
- return false;
+ return setExceptionalCompletion(rex);
}
- setNormalCompletion();
- return true;
+ if (completed)
+ return setCompletion(NORMAL);
+ return waitingJoin();
}
/**
- * Cancel, ignoring any exceptions it throws
+ * If this task is next in worker queue, runs it, else processes other
+ * tasks until complete.
+ * @return status on exit
*/
- final void cancelIgnoringExceptions() {
- try {
- cancel(false);
- } catch(Throwable ignore) {
+ private int busyJoin() {
+ int s = status;
+ if (s < 0)
+ return s;
+ ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
+ if (w.unpushTask(this)) {
+ boolean completed;
+ try {
+ completed = exec();
+ } catch (Throwable rex) {
+ return setExceptionalCompletion(rex);
+ }
+ if (completed)
+ return setCompletion(NORMAL);
}
+ return w.execWhileJoining(this);
}
/**
- * Main implementation of helpJoin
+ * Returns result or throws exception associated with given status.
+ * @param s the status
*/
- private int busyJoin(ForkJoinWorkerThread w) {
- int s;
- ForkJoinTask t;
- while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null)
- t.quietlyExec();
- return (s >= 0)? awaitDone(w, false) : s; // block if no work
+ private V reportResult(int s) {
+ Throwable ex;
+ if (s < NORMAL && (ex = getException()) != null)
+ UNSAFE.throwException(ex);
+ return getRawResult();
}
// public methods
@@ -472,70 +370,93 @@ public abstract class ForkJoinTask im
/**
* Arranges to asynchronously execute this task. While it is not
* necessarily enforced, it is a usage error to fork a task more
- * than once unless it has completed and been reinitialized. This
- * method may be invoked only from within ForkJoinTask
- * computations. Attempts to invoke in other contexts result in
- * exceptions or errors possibly including ClassCastException.
+ * than once unless it has completed and been reinitialized.
+ * Subsequent modifications to the state of this task or any data
+ * it operates on are not necessarily consistently observable by
+ * any thread other than the one executing it unless preceded by a
+ * call to {@link #join} or related methods, or a call to {@link
+ * #isDone} returning {@code true}.
+ *
+ * This method may be invoked only from within {@code
+ * ForkJoinTask} computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including {@code
+ * ClassCastException}.
+ *
+ * @return {@code this}, to simplify usage
*/
- public final void fork() {
- ((ForkJoinWorkerThread)(Thread.currentThread())).pushTask(this);
+ public final ForkJoinTask fork() {
+ ((ForkJoinWorkerThread) Thread.currentThread())
+ .pushTask(this);
+ return this;
}
/**
- * Returns the result of the computation when it is ready.
- * This method differs from {@code get} in that abnormal
- * completion results in RuntimeExceptions or Errors, not
- * ExecutionExceptions.
+ * Returns the result of the computation when it {@link #isDone is done}.
+ * This method differs from {@link #get()} in that
+ * abnormal completion results in {@code RuntimeException} or
+ * {@code Error}, not {@code ExecutionException}.
*
* @return the computed result
*/
public final V join() {
- ForkJoinWorkerThread w = getWorker();
- if (w == null || status < 0 || !w.unpushTask(this) || !tryExec())
- reportException(awaitDone(w, true));
- return getRawResult();
+ return reportResult(waitingJoin());
}
/**
* Commences performing this task, awaits its completion if
- * necessary, and return its result.
- * @throws Throwable (a RuntimeException, Error, or unchecked
- * exception) if the underlying computation did so.
+ * necessary, and return its result, or throws an (unchecked)
+ * exception if the underlying computation did so.
+ *
* @return the computed result
*/
public final V invoke() {
- if (status >= 0 && tryExec())
- return getRawResult();
- else
- return join();
+ return reportResult(waitingInvoke());
}
/**
- * Forks both tasks, returning when {@code isDone} holds for
- * both of them or an exception is encountered. This method may be
- * invoked only from within ForkJoinTask computations. Attempts to
- * invoke in other contexts result in exceptions or errors
- * possibly including ClassCastException.
- * @param t1 one task
- * @param t2 the other task
- * @throws NullPointerException if t1 or t2 are null
- * @throws RuntimeException or Error if either task did so.
+ * Forks the given tasks, returning when {@code isDone} holds for
+ * each task or an (unchecked) exception is encountered, in which
+ * case the exception is rethrown. If either task encounters an
+ * exception, the other one may be, but is not guaranteed to be,
+ * cancelled. If both tasks throw an exception, then this method
+ * throws one of them. The individual status of each task may be
+ * checked using {@link #getException()} and related methods.
+ *
+ * This method may be invoked only from within {@code
+ * ForkJoinTask} computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including {@code
+ * ClassCastException}.
+ *
+ * @param t1 the first task
+ * @param t2 the second task
+ * @throws NullPointerException if any task is null
*/
- public static void invokeAll(ForkJoinTaskt1, ForkJoinTask t2) {
+ public static void invokeAll(ForkJoinTask t1, ForkJoinTask t2) {
t2.fork();
t1.invoke();
t2.join();
}
/**
- * Forks the given tasks, returning when {@code isDone} holds
- * for all of them. If any task encounters an exception, others
- * may be cancelled. This method may be invoked only from within
- * ForkJoinTask computations. Attempts to invoke in other contexts
- * result in exceptions or errors possibly including ClassCastException.
- * @param tasks the array of tasks
- * @throws NullPointerException if tasks or any element are null.
- * @throws RuntimeException or Error if any task did so.
+ * Forks the given tasks, returning when {@code isDone} holds for
+ * each task or an (unchecked) exception is encountered, in which
+ * case the exception is rethrown. If any task encounters an
+ * exception, others may be, but are not guaranteed to be,
+ * cancelled. If more than one task encounters an exception, then
+ * this method throws any one of these exceptions. The individual
+ * status of each task may be checked using {@link #getException()}
+ * and related methods.
+ *
+ *
This method may be invoked only from within {@code
+ * ForkJoinTask} computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including {@code
+ * ClassCastException}.
+ *
+ * @param tasks the tasks
+ * @throws NullPointerException if any task is null
*/
public static void invokeAll(ForkJoinTask... tasks) {
Throwable ex = null;
@@ -548,46 +469,52 @@ public abstract class ForkJoinTask im
}
else if (i != 0)
t.fork();
- else {
- t.quietlyInvoke();
- if (ex == null)
- ex = t.getException();
- }
+ else if (t.waitingInvoke() < NORMAL && ex == null)
+ ex = t.getException();
}
for (int i = 1; i <= last; ++i) {
ForkJoinTask t = tasks[i];
if (t != null) {
if (ex != null)
t.cancel(false);
- else {
- t.quietlyJoin();
- if (ex == null)
- ex = t.getException();
- }
+ else if (t.waitingJoin() < NORMAL && ex == null)
+ ex = t.getException();
}
}
if (ex != null)
- rethrowException(ex);
+ UNSAFE.throwException(ex);
}
/**
- * Forks all tasks in the collection, returning when
- * {@code isDone} holds for all of them. If any task
- * encounters an exception, others may be cancelled. This method
- * may be invoked only from within ForkJoinTask
- * computations. Attempts to invoke in other contexts resul!t in
- * exceptions or errors possibly including ClassCastException.
+ * Forks all tasks in the specified collection, returning when
+ * {@code isDone} holds for each task or an (unchecked) exception
+ * is encountered. If any task encounters an exception, others
+ * may be, but are not guaranteed to be, cancelled. If more than
+ * one task encounters an exception, then this method throws any
+ * one of these exceptions. The individual status of each task
+ * may be checked using {@link #getException()} and related
+ * methods. The behavior of this operation is undefined if the
+ * specified collection is modified while the operation is in
+ * progress.
+ *
+ * This method may be invoked only from within {@code
+ * ForkJoinTask} computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including {@code
+ * ClassCastException}.
+ *
* @param tasks the collection of tasks
- * @throws NullPointerException if tasks or any element are null.
- * @throws RuntimeException or Error if any task did so.
+ * @return the tasks argument, to simplify usage
+ * @throws NullPointerException if tasks or any element are null
*/
- public static void invokeAll(Collection> tasks) {
- if (!(tasks instanceof List)) {
- invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()]));
- return;
+ public static > Collection invokeAll(Collection tasks) {
+ if (!(tasks instanceof RandomAccess) || !(tasks instanceof List)) {
+ invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()]));
+ return tasks;
}
+ @SuppressWarnings("unchecked")
List> ts =
- (List>)tasks;
+ (List>) tasks;
Throwable ex = null;
int last = ts.size() - 1;
for (int i = last; i >= 0; --i) {
@@ -598,71 +525,46 @@ public abstract class ForkJoinTask im
}
else if (i != 0)
t.fork();
- else {
- t.quietlyInvoke();
- if (ex == null)
- ex = t.getException();
- }
+ else if (t.waitingInvoke() < NORMAL && ex == null)
+ ex = t.getException();
}
for (int i = 1; i <= last; ++i) {
ForkJoinTask t = ts.get(i);
if (t != null) {
if (ex != null)
t.cancel(false);
- else {
- t.quietlyJoin();
- if (ex == null)
- ex = t.getException();
- }
+ else if (t.waitingJoin() < NORMAL && ex == null)
+ ex = t.getException();
}
}
if (ex != null)
- rethrowException(ex);
- }
-
- /**
- * Returns true if the computation performed by this task has
- * completed (or has been cancelled).
- * @return true if this computation has completed
- */
- public final boolean isDone() {
- return status < 0;
+ UNSAFE.throwException(ex);
+ return tasks;
}
/**
- * Returns true if this task was cancelled.
- * @return true if this task was cancelled
- */
- public final boolean isCancelled() {
- return (status & COMPLETION_MASK) == CANCELLED;
- }
-
- /**
- * Asserts that the results of this task's computation will not be
- * used. If a cancellation occurs before atempting to execute this
- * task, then execution will be suppressed, {@code isCancelled}
- * will report true, and {@code join} will result in a
- * {@code CancellationException} being thrown. Otherwise, when
- * cancellation races with completion, there are no guarantees
- * about whether {@code isCancelled} will report true, whether
- * {@code join} will return normally or via an exception, or
- * whether these behaviors will remain consistent upon repeated
- * invocation.
+ * Attempts to cancel execution of this task. This attempt will
+ * fail if the task has already completed, has already been
+ * cancelled, or could not be cancelled for some other reason. If
+ * successful, and this task has not started when cancel is
+ * called, execution of this task is suppressed, {@link
+ * #isCancelled} will report true, and {@link #join} will result
+ * in a {@code CancellationException} being thrown.
*
* This method may be overridden in subclasses, but if so, must
* still ensure that these minimal properties hold. In particular,
- * the cancel method itself must not throw exceptions.
+ * the {@code cancel} method itself must not throw exceptions.
*
- *
This method is designed to be invoked by other
+ *
This method is designed to be invoked by other
* tasks. To terminate the current task, you can just return or
* throw an unchecked exception from its computation method, or
- * invoke {@code completeExceptionally}.
+ * invoke {@link #completeExceptionally}.
*
* @param mayInterruptIfRunning this value is ignored in the
- * default implementation because tasks are not in general
- * cancelled via interruption.
+ * default implementation because tasks are not
+ * cancelled via interruption
*
- * @return true if this task is now cancelled
+ * @return {@code true} if this task is now cancelled
*/
public boolean cancel(boolean mayInterruptIfRunning) {
setCompletion(CANCELLED);
@@ -670,26 +572,70 @@ public abstract class ForkJoinTask im
}
/**
- * Returns true if this task threw an exception or was cancelled
- * @return true if this task threw an exception or was cancelled
+ * Cancels, ignoring any exceptions it throws. Used during worker
+ * and pool shutdown.
+ */
+ final void cancelIgnoringExceptions() {
+ try {
+ cancel(false);
+ } catch (Throwable ignore) {
+ }
+ }
+
+ /**
+ * Cancels ignoring exceptions if worker is terminating
+ */
+ private void cancelIfTerminating() {
+ Thread t = Thread.currentThread();
+ if ((t instanceof ForkJoinWorkerThread) &&
+ ((ForkJoinWorkerThread) t).isTerminating()) {
+ try {
+ cancel(false);
+ } catch (Throwable ignore) {
+ }
+ }
+ }
+
+ public final boolean isDone() {
+ return status < 0;
+ }
+
+ public final boolean isCancelled() {
+ return (status & COMPLETION_MASK) == CANCELLED;
+ }
+
+ /**
+ * Returns {@code true} if this task threw an exception or was cancelled.
+ *
+ * @return {@code true} if this task threw an exception or was cancelled
*/
public final boolean isCompletedAbnormally() {
return (status & COMPLETION_MASK) < NORMAL;
}
/**
+ * Returns {@code true} if this task completed without throwing an
+ * exception and was not cancelled.
+ *
+ * @return {@code true} if this task completed without throwing an
+ * exception and was not cancelled
+ */
+ public final boolean isCompletedNormally() {
+ return (status & COMPLETION_MASK) == NORMAL;
+ }
+
+ /**
* Returns the exception thrown by the base computation, or a
- * CancellationException if cancelled, or null if none or if the
- * method has not yet completed.
- * @return the exception, or null if none
+ * {@code CancellationException} if cancelled, or {@code null} if
+ * none or if the method has not yet completed.
+ *
+ * @return the exception, or {@code null} if none
*/
public final Throwable getException() {
int s = status & COMPLETION_MASK;
- if (s >= NORMAL)
- return null;
- if (s == CANCELLED)
- return new CancellationException();
- return exceptionMap.get(this);
+ return ((s >= NORMAL) ? null :
+ (s == CANCELLED) ? new CancellationException() :
+ exceptionMap.get(this));
}
/**
@@ -698,18 +644,18 @@ public abstract class ForkJoinTask im
* {@code join} and related operations. This method may be used
* to induce exceptions in asynchronous tasks, or to force
* completion of tasks that would not otherwise complete. Its use
- * in other situations is likely to be wrong. This method is
+ * in other situations is discouraged. This method is
* overridable, but overridden versions must invoke {@code super}
* implementation to maintain guarantees.
*
- * @param ex the exception to throw. If this exception is
- * not a RuntimeException or Error, the actual exception thrown
- * will be a RuntimeException with cause ex.
+ * @param ex the exception to throw. If this exception is not a
+ * {@code RuntimeException} or {@code Error}, the actual exception
+ * thrown will be a {@code RuntimeException} with cause {@code ex}.
*/
public void completeExceptionally(Throwable ex) {
- setDoneExceptionally((ex instanceof RuntimeException) ||
- (ex instanceof Error)? ex :
- new RuntimeException(ex));
+ setExceptionalCompletion((ex instanceof RuntimeException) ||
+ (ex instanceof Error) ? ex :
+ new RuntimeException(ex));
}
/**
@@ -718,69 +664,146 @@ public abstract class ForkJoinTask im
* operations. This method may be used to provide results for
* asynchronous tasks, or to provide alternative handling for
* tasks that would not otherwise complete normally. Its use in
- * other situations is likely to be wrong. This method is
+ * other situations is discouraged. This method is
* overridable, but overridden versions must invoke {@code super}
* implementation to maintain guarantees.
*
- * @param value the result value for this task.
+ * @param value the result value for this task
*/
public void complete(V value) {
try {
setRawResult(value);
- } catch(Throwable rex) {
- setDoneExceptionally(rex);
+ } catch (Throwable rex) {
+ setExceptionalCompletion(rex);
return;
}
- setNormalCompletion();
+ setCompletion(NORMAL);
}
public final V get() throws InterruptedException, ExecutionException {
- ForkJoinWorkerThread w = getWorker();
- if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
- awaitDone(w, true);
- return reportFutureResult();
+ int s = waitingJoin() & COMPLETION_MASK;
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ if (s < NORMAL) {
+ Throwable ex;
+ if (s == CANCELLED)
+ throw new CancellationException();
+ if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
+ throw new ExecutionException(ex);
+ }
+ return getRawResult();
}
public final V get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException {
- ForkJoinWorkerThread w = getWorker();
- if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
- awaitDone(w, unit.toNanos(timeout));
- return reportTimedFutureResult();
+ Thread t = Thread.currentThread();
+ ForkJoinPool pool;
+ if (t instanceof ForkJoinWorkerThread) {
+ ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
+ if (status >= 0 && w.unpushTask(this))
+ tryExec();
+ pool = w.pool;
+ }
+ else
+ pool = null;
+ /*
+ * Timed wait loop intermixes cases for fj (pool != null) and
+ * non FJ threads. For FJ, decrement pool count but don't try
+ * for replacement; increment count on completion. For non-FJ,
+ * deal with interrupts. This is messy, but a little less so
+ * than is splitting the FJ and nonFJ cases.
+ */
+ boolean interrupted = false;
+ boolean dec = false; // true if pool count decremented
+ for (;;) {
+ if (Thread.interrupted() && pool == null) {
+ interrupted = true;
+ break;
+ }
+ int s = status;
+ if (s < 0)
+ break;
+ if (UNSAFE.compareAndSwapInt(this, statusOffset,
+ s, s | SIGNAL)) {
+ long startTime = System.nanoTime();
+ long nanos = unit.toNanos(timeout);
+ long nt; // wait time
+ while (status >= 0 &&
+ (nt = nanos - (System.nanoTime() - startTime)) > 0) {
+ if (pool != null && !dec)
+ dec = pool.tryDecrementRunningCount();
+ else {
+ long ms = nt / 1000000;
+ int ns = (int) (nt % 1000000);
+ try {
+ synchronized(this) {
+ if (status >= 0)
+ wait(ms, ns);
+ }
+ } catch (InterruptedException ie) {
+ if (pool != null)
+ cancelIfTerminating();
+ else {
+ interrupted = true;
+ break;
+ }
+ }
+ }
+ }
+ break;
+ }
+ }
+ if (pool != null && dec)
+ pool.updateRunningCount(1);
+ if (interrupted)
+ throw new InterruptedException();
+ int es = status & COMPLETION_MASK;
+ if (es != NORMAL) {
+ Throwable ex;
+ if (es == CANCELLED)
+ throw new CancellationException();
+ if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
+ throw new ExecutionException(ex);
+ throw new TimeoutException();
+ }
+ return getRawResult();
}
/**
- * Possibly executes other tasks until this task is ready, then
- * returns the result of the computation. This method may be more
- * efficient than {@code join}, but is only applicable when
- * there are no potemtial dependencies between continuation of the
- * current task and that of any other task that might be executed
- * while helping. (This usually holds for pure divide-and-conquer
- * tasks). This method may be invoked only from within
- * ForkJoinTask computations. Attempts to invoke in other contexts
- * resul!t in exceptions or errors possibly including ClassCastException.
+ * Possibly executes other tasks until this task {@link #isDone is
+ * done}, then returns the result of the computation. This method
+ * may be more efficient than {@code join}, but is only applicable
+ * when there are no potential dependencies between continuation
+ * of the current task and that of any other task that might be
+ * executed while helping. (This usually holds for pure
+ * divide-and-conquer tasks).
+ *
+ * This method may be invoked only from within {@code
+ * ForkJoinTask} computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including {@code
+ * ClassCastException}.
+ *
* @return the computed result
*/
public final V helpJoin() {
- ForkJoinWorkerThread w = (ForkJoinWorkerThread)(Thread.currentThread());
- if (status < 0 || !w.unpushTask(this) || !tryExec())
- reportException(busyJoin(w));
- return getRawResult();
+ return reportResult(busyJoin());
}
/**
- * Possibly executes other tasks until this task is ready. This
- * method may be invoked only from within ForkJoinTask
- * computations. Attempts to invoke in other contexts resul!t in
- * exceptions or errors possibly including ClassCastException.
+ * Possibly executes other tasks until this task {@link #isDone is
+ * done}. This method may be useful when processing collections
+ * of tasks when some have been cancelled or otherwise known to
+ * have aborted.
+ *
+ *
This method may be invoked only from within {@code
+ * ForkJoinTask} computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including {@code
+ * ClassCastException}.
*/
public final void quietlyHelpJoin() {
- if (status >= 0) {
- ForkJoinWorkerThread w =
- (ForkJoinWorkerThread)(Thread.currentThread());
- if (!w.unpushTask(this) || !tryQuietlyInvoke())
- busyJoin(w);
- }
+ busyJoin();
}
/**
@@ -790,11 +813,7 @@ public abstract class ForkJoinTask im
* known to have aborted.
*/
public final void quietlyJoin() {
- if (status >= 0) {
- ForkJoinWorkerThread w = getWorker();
- if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
- awaitDone(w, true);
- }
+ waitingJoin();
}
/**
@@ -805,19 +824,25 @@ public abstract class ForkJoinTask im
* known to have aborted.
*/
public final void quietlyInvoke() {
- if (status >= 0 && !tryQuietlyInvoke())
- quietlyJoin();
+ waitingInvoke();
}
/**
* Possibly executes tasks until the pool hosting the current task
- * {@link ForkJoinPool#isQuiescent}. This method may be of use in
- * designs in which many tasks are forked, but none are explicitly
- * joined, instead executing them until all are processed.
+ * {@link ForkJoinPool#isQuiescent is quiescent}. This method may
+ * be of use in designs in which many tasks are forked, but none
+ * are explicitly joined, instead executing them until all are
+ * processed.
+ *
+ * This method may be invoked only from within {@code
+ * ForkJoinTask} computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including {@code
+ * ClassCastException}.
*/
public static void helpQuiesce() {
- ((ForkJoinWorkerThread)(Thread.currentThread())).
- helpQuiescePool();
+ ((ForkJoinWorkerThread) Thread.currentThread())
+ .helpQuiescePool();
}
/**
@@ -826,8 +851,8 @@ public abstract class ForkJoinTask im
* this task, but only if reuse occurs when this task has either
* never been forked, or has been forked, then completed and all
* outstanding joins of this task have also completed. Effects
- * under any other usage conditions are not guaranteed, and are
- * almost surely wrong. This method may be useful when executing
+ * under any other usage conditions are not guaranteed.
+ * This method may be useful when executing
* pre-constructed trees of subtasks in loops.
*/
public void reinitialize() {
@@ -838,13 +863,26 @@ public abstract class ForkJoinTask im
/**
* Returns the pool hosting the current task execution, or null
- * if this task is executing outside of any pool.
- * @return the pool, or null if none.
+ * if this task is executing outside of any ForkJoinPool.
+ *
+ * @see #inForkJoinPool
+ * @return the pool, or {@code null} if none
*/
public static ForkJoinPool getPool() {
Thread t = Thread.currentThread();
- return ((t instanceof ForkJoinWorkerThread)?
- ((ForkJoinWorkerThread)t).pool : null);
+ return (t instanceof ForkJoinWorkerThread) ?
+ ((ForkJoinWorkerThread) t).pool : null;
+ }
+
+ /**
+ * Returns {@code true} if the current thread is executing as a
+ * ForkJoinPool computation.
+ *
+ * @return {@code true} if the current thread is executing as a
+ * ForkJoinPool computation, or false otherwise
+ */
+ public static boolean inForkJoinPool() {
+ return Thread.currentThread() instanceof ForkJoinWorkerThread;
}
/**
@@ -853,13 +891,19 @@ public abstract class ForkJoinTask im
* by the current thread, and has not commenced executing in
* another thread. This method may be useful when arranging
* alternative local processing of tasks that could have been, but
- * were not, stolen. This method may be invoked only from within
- * ForkJoinTask computations. Attempts to invoke in other contexts
- * result in exceptions or errors possibly including ClassCastException.
- * @return true if unforked
+ * were not, stolen.
+ *
+ * This method may be invoked only from within {@code
+ * ForkJoinTask} computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including {@code
+ * ClassCastException}.
+ *
+ * @return {@code true} if unforked
*/
public boolean tryUnfork() {
- return ((ForkJoinWorkerThread)(Thread.currentThread())).unpushTask(this);
+ return ((ForkJoinWorkerThread) Thread.currentThread())
+ .unpushTask(this);
}
/**
@@ -867,15 +911,22 @@ public abstract class ForkJoinTask im
* forked by the current worker thread but not yet executed. This
* value may be useful for heuristic decisions about whether to
* fork other tasks.
+ *
+ * This method may be invoked only from within {@code
+ * ForkJoinTask} computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including {@code
+ * ClassCastException}.
+ *
* @return the number of tasks
*/
public static int getQueuedTaskCount() {
- return ((ForkJoinWorkerThread)(Thread.currentThread())).
- getQueueSize();
+ return ((ForkJoinWorkerThread) Thread.currentThread())
+ .getQueueSize();
}
/**
- * Returns a estimate of how many more locally queued tasks are
+ * Returns an estimate of how many more locally queued tasks are
* held by the current worker thread than there are other worker
* threads that might steal them. This value may be useful for
* heuristic decisions about whether to fork other tasks. In many
@@ -883,23 +934,30 @@ public abstract class ForkJoinTask im
* aim to maintain a small constant surplus (for example, 3) of
* tasks, and to process computations locally if this threshold is
* exceeded.
+ *
+ * This method may be invoked only from within {@code
+ * ForkJoinTask} computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including {@code
+ * ClassCastException}.
+ *
* @return the surplus number of tasks, which may be negative
*/
public static int getSurplusQueuedTaskCount() {
- return ((ForkJoinWorkerThread)(Thread.currentThread()))
+ return ((ForkJoinWorkerThread) Thread.currentThread())
.getEstimatedSurplusTaskCount();
}
// Extension methods
/**
- * Returns the result that would be returned by {@code join},
- * even if this task completed abnormally, or null if this task is
- * not known to have been completed. This method is designed to
- * aid debugging, as well as to support extensions. Its use in any
- * other context is discouraged.
+ * Returns the result that would be returned by {@link #join}, even
+ * if this task completed abnormally, or {@code null} if this task
+ * is not known to have been completed. This method is designed
+ * to aid debugging, as well as to support extensions. Its use in
+ * any other context is discouraged.
*
- * @return the result, or null if not completed.
+ * @return the result, or {@code null} if not completed
*/
public abstract V getRawResult();
@@ -918,42 +976,53 @@ public abstract class ForkJoinTask im
* called otherwise. The return value controls whether this task
* is considered to be done normally. It may return false in
* asynchronous actions that require explicit invocations of
- * {@code complete} to become joinable. It may throw exceptions
- * to indicate abnormal exit.
- * @return true if completed normally
- * @throws Error or RuntimeException if encountered during computation
+ * {@link #complete} to become joinable. It may also throw an
+ * (unchecked) exception to indicate abnormal exit.
+ *
+ * @return {@code true} if completed normally
*/
protected abstract boolean exec();
/**
- * Returns, but does not unschedule or execute, the task queued by
- * the current thread but not yet executed, if one is
+ * Returns, but does not unschedule or execute, a task queued by
+ * the current thread but not yet executed, if one is immediately
* available. There is no guarantee that this task will actually
- * be polled or executed next. This method is designed primarily
- * to support extensions, and is unlikely to be useful otherwise.
- * This method may be invoked only from within ForkJoinTask
- * computations. Attempts to invoke in other contexts result in
- * exceptions or errors possibly including ClassCastException.
+ * be polled or executed next. Conversely, this method may return
+ * null even if a task exists but cannot be accessed without
+ * contention with other threads. This method is designed
+ * primarily to support extensions, and is unlikely to be useful
+ * otherwise.
+ *
+ * This method may be invoked only from within {@code
+ * ForkJoinTask} computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including {@code
+ * ClassCastException}.
*
- * @return the next task, or null if none are available
+ * @return the next task, or {@code null} if none are available
*/
protected static ForkJoinTask peekNextLocalTask() {
- return ((ForkJoinWorkerThread)(Thread.currentThread())).peekTask();
+ return ((ForkJoinWorkerThread) Thread.currentThread())
+ .peekTask();
}
/**
* Unschedules and returns, without executing, the next task
* queued by the current thread but not yet executed. This method
* is designed primarily to support extensions, and is unlikely to
- * be useful otherwise. This method may be invoked only from
- * within ForkJoinTask computations. Attempts to invoke in other
- * contexts result in exceptions or errors possibly including
- * ClassCastException.
+ * be useful otherwise.
*
- * @return the next task, or null if none are available
+ *
This method may be invoked only from within {@code
+ * ForkJoinTask} computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including {@code
+ * ClassCastException}.
+ *
+ * @return the next task, or {@code null} if none are available
*/
protected static ForkJoinTask pollNextLocalTask() {
- return ((ForkJoinWorkerThread)(Thread.currentThread())).pollLocalTask();
+ return ((ForkJoinWorkerThread) Thread.currentThread())
+ .pollLocalTask();
}
/**
@@ -961,19 +1030,115 @@ public abstract class ForkJoinTask im
* queued by the current thread but not yet executed, if one is
* available, or if not available, a task that was forked by some
* other thread, if available. Availability may be transient, so a
- * {@code null} result does not necessarily imply quiecence
+ * {@code null} result does not necessarily imply quiescence
* of the pool this task is operating in. This method is designed
* primarily to support extensions, and is unlikely to be useful
- * otherwise. This method may be invoked only from within
- * ForkJoinTask computations. Attempts to invoke in other contexts
- * result in exceptions or errors possibly including
- * ClassCastException.
+ * otherwise.
+ *
+ * This method may be invoked only from within {@code
+ * ForkJoinTask} computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including {@code
+ * ClassCastException}.
*
- * @return a task, or null if none are available
+ * @return a task, or {@code null} if none are available
*/
protected static ForkJoinTask pollTask() {
- return ((ForkJoinWorkerThread)(Thread.currentThread())).
- pollTask();
+ return ((ForkJoinWorkerThread) Thread.currentThread())
+ .pollTask();
+ }
+
+ /**
+ * Adaptor for Runnables. This implements RunnableFuture
+ * to be compliant with AbstractExecutorService constraints
+ * when used in ForkJoinPool.
+ */
+ static final class AdaptedRunnable extends ForkJoinTask
+ implements RunnableFuture {
+ final Runnable runnable;
+ final T resultOnCompletion;
+ T result;
+ AdaptedRunnable(Runnable runnable, T result) {
+ if (runnable == null) throw new NullPointerException();
+ this.runnable = runnable;
+ this.resultOnCompletion = result;
+ }
+ public T getRawResult() { return result; }
+ public void setRawResult(T v) { result = v; }
+ public boolean exec() {
+ runnable.run();
+ result = resultOnCompletion;
+ return true;
+ }
+ public void run() { invoke(); }
+ private static final long serialVersionUID = 5232453952276885070L;
+ }
+
+ /**
+ * Adaptor for Callables
+ */
+ static final class AdaptedCallable extends ForkJoinTask
+ implements RunnableFuture {
+ final Callable callable;
+ T result;
+ AdaptedCallable(Callable callable) {
+ if (callable == null) throw new NullPointerException();
+ this.callable = callable;
+ }
+ public T getRawResult() { return result; }
+ public void setRawResult(T v) { result = v; }
+ public boolean exec() {
+ try {
+ result = callable.call();
+ return true;
+ } catch (Error err) {
+ throw err;
+ } catch (RuntimeException rex) {
+ throw rex;
+ } catch (Exception ex) {
+ throw new RuntimeException(ex);
+ }
+ }
+ public void run() { invoke(); }
+ private static final long serialVersionUID = 2838392045355241008L;
+ }
+
+ /**
+ * Returns a new {@code ForkJoinTask} that performs the {@code run}
+ * method of the given {@code Runnable} as its action, and returns
+ * a null result upon {@link #join}.
+ *
+ * @param runnable the runnable action
+ * @return the task
+ */
+ public static ForkJoinTask adapt(Runnable runnable) {
+ return new AdaptedRunnable(runnable, null);
+ }
+
+ /**
+ * Returns a new {@code ForkJoinTask} that performs the {@code run}
+ * method of the given {@code Runnable} as its action, and returns
+ * the given result upon {@link #join}.
+ *
+ * @param runnable the runnable action
+ * @param result the result upon completion
+ * @return the task
+ */
+ public static ForkJoinTask adapt(Runnable runnable, T result) {
+ return new AdaptedRunnable(runnable, result);
+ }
+
+ /**
+ * Returns a new {@code ForkJoinTask} that performs the {@code call}
+ * method of the given {@code Callable} as its action, and returns
+ * its result upon {@link #join}, translating any checked exceptions
+ * encountered into {@code RuntimeException}.
+ *
+ * @param callable the callable action
+ * @return the task
+ */
+ public static ForkJoinTask adapt(Callable callable) {
+ return new AdaptedCallable(callable);
}
// Serialization support
@@ -981,10 +1146,10 @@ public abstract class ForkJoinTask im
private static final long serialVersionUID = -7721805057305804111L;
/**
- * Save the state to a stream.
+ * Saves the state to a stream.
*
* @serialData the current run status and the exception thrown
- * during execution, or null if none.
+ * during execution, or {@code null} if none
* @param s the stream
*/
private void writeObject(java.io.ObjectOutputStream s)
@@ -994,59 +1159,61 @@ public abstract class ForkJoinTask im
}
/**
- * Reconstitute the instance from a stream.
+ * Reconstitutes the instance from a stream.
+ *
* @param s the stream
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
- status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
- status |= EXTERNAL_SIGNAL; // conservatively set external signal
+ status |= SIGNAL; // conservatively set external signal
Object ex = s.readObject();
if (ex != null)
- setDoneExceptionally((Throwable)ex);
+ setExceptionalCompletion((Throwable) ex);
}
- // Temporary Unsafe mechanics for preliminary release
- private static Unsafe getUnsafe() throws Throwable {
+ // Unsafe mechanics
+
+ private static final sun.misc.Unsafe UNSAFE = getUnsafe();
+ private static final long statusOffset =
+ objectFieldOffset("status", ForkJoinTask.class);
+
+ private static long objectFieldOffset(String field, Class klazz) {
try {
- return Unsafe.getUnsafe();
+ return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
+ } catch (NoSuchFieldException e) {
+ // Convert Exception to corresponding Error
+ NoSuchFieldError error = new NoSuchFieldError(field);
+ error.initCause(e);
+ throw error;
+ }
+ }
+
+ /**
+ * Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package.
+ * Replace with a simple call to Unsafe.getUnsafe when integrating
+ * into a jdk.
+ *
+ * @return a sun.misc.Unsafe
+ */
+ private static sun.misc.Unsafe getUnsafe() {
+ try {
+ return sun.misc.Unsafe.getUnsafe();
} catch (SecurityException se) {
try {
return java.security.AccessController.doPrivileged
- (new java.security.PrivilegedExceptionAction() {
- public Unsafe run() throws Exception {
- return getUnsafePrivileged();
+ (new java.security
+ .PrivilegedExceptionAction() {
+ public sun.misc.Unsafe run() throws Exception {
+ java.lang.reflect.Field f = sun.misc
+ .Unsafe.class.getDeclaredField("theUnsafe");
+ f.setAccessible(true);
+ return (sun.misc.Unsafe) f.get(null);
}});
} catch (java.security.PrivilegedActionException e) {
- throw e.getCause();
+ throw new RuntimeException("Could not initialize intrinsics",
+ e.getCause());
}
}
}
-
- private static Unsafe getUnsafePrivileged()
- throws NoSuchFieldException, IllegalAccessException {
- Field f = Unsafe.class.getDeclaredField("theUnsafe");
- f.setAccessible(true);
- return (Unsafe) f.get(null);
- }
-
- private static long fieldOffset(String fieldName)
- throws NoSuchFieldException {
- return _unsafe.objectFieldOffset
- (ForkJoinTask.class.getDeclaredField(fieldName));
- }
-
- static final Unsafe _unsafe;
- static final long statusOffset;
-
- static {
- try {
- _unsafe = getUnsafe();
- statusOffset = fieldOffset("status");
- } catch (Throwable e) {
- throw new RuntimeException("Could not initialize intrinsics", e);
- }
- }
-
}