--- jsr166/src/jsr166y/ForkJoinTask.java 2009/07/16 15:32:34 1.6
+++ jsr166/src/jsr166y/ForkJoinTask.java 2009/08/02 17:02:06 1.28
@@ -5,108 +5,125 @@
*/
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.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 fork
- * and join
, or derivatives such as
- * 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 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 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 join them. These exceptions may
+ * additionally include RejectedExecutionExceptions 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:
* The {@link Future#get} methods support interruptible and/or timed
- * waits for completion and report results using Future
+ * waits for completion and report results using {@code Future}
* conventions. Method {@link #helpJoin} enables callers to actively
* 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 fork(); join()
but always attempts to
+ * 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 invokeAll
(available in multiple versions)
+ * 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 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 compute
+ * 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 public
access (to allow
+ * class. While these methods have {@code public} access (to allow
* instances of different task subclasses to call each others
* 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 final
because their
+ *
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 protected
methods
- * exec
, setRawResult
, and
- * getRawResult
, while also introducing an abstract
+ * 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 protected
methods provided
+ * 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
+ * computations, otherwise 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
+ * parallelism cannot improve throughput. If too small, then memory
* and internal task maintenance overhead may overwhelm processing.
*
- *
ForkJoinTasks are Serializable
, which enables them
+ *
This class provides {@code adapt} methods for {@link
+ * java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
+ * may be of use when mixing execution of ForkJoinTasks with other
+ * kinds of tasks. When all tasks are of this form, consider using a
+ * pool in {@link ForkJoinPool#setAsyncMode}.
+ *
+ *
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.
+ *
+ * @since 1.7
+ * @author Doug Lea
*/
public abstract class ForkJoinTask implements Future, Serializable {
@@ -128,7 +145,7 @@ public abstract class ForkJoinTask im
* currently unused. Also value 0x80000000 is available as spare
* completion value.
*/
- volatile int status; // accessed directy by pool and workers
+ volatile int status; // accessed directly by pool and workers
static final int COMPLETION_MASK = 0xe0000000;
static final int NORMAL = 0xe0000000; // == mask
@@ -141,10 +158,10 @@ public abstract class ForkJoinTask im
/**
* 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
@@ -153,16 +170,16 @@ public abstract class ForkJoinTask im
// within-package utilities
/**
- * Get current worker thread, or null if not a worker thread
+ * Gets current worker thread, or null if not a worker thread.
*/
static ForkJoinWorkerThread getWorker() {
Thread t = Thread.currentThread();
- return ((t instanceof ForkJoinWorkerThread)?
- (ForkJoinWorkerThread)t : null);
+ return ((t instanceof ForkJoinWorkerThread) ?
+ (ForkJoinWorkerThread) t : null);
}
final boolean casStatus(int cmp, int val) {
- return _unsafe.compareAndSwapInt(this, statusOffset, cmp, val);
+ return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val);
}
/**
@@ -170,25 +187,26 @@ public abstract class ForkJoinTask im
*/
static void rethrowException(Throwable ex) {
if (ex != null)
- _unsafe.throwException(ex);
+ 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.
+ *
* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
*/
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));
+ 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(); }
+ synchronized (this) { notifyAll(); }
}
}
else
@@ -201,48 +219,48 @@ public abstract class ForkJoinTask im
*/
private void externallySetCompletion(int completion) {
int s;
- do;while ((s = status) >= 0 &&
- !casStatus(s, (s & SIGNAL_MASK) | completion));
- synchronized(this) { notifyAll(); }
+ do {} while ((s = status) >= 0 &&
+ !casStatus(s, (s & SIGNAL_MASK) | completion));
+ synchronized (this) { notifyAll(); }
}
/**
- * Sets status to indicate normal completion
+ * 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))
+ if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL))
setCompletion(NORMAL);
}
// internal waiting and notification
/**
- * Performs the actual monitor wait for awaitDone
+ * 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(); }
+ synchronized (this) { if (status >= 0) wait(); }
} catch (InterruptedException ie) {
onInterruptedWait();
}
}
/**
- * Performs the actual monitor wait for awaitDone
+ * Performs the actual timed monitor wait for awaitDone.
*/
private void doAwaitDone(long startTime, long nanos) {
- synchronized(this) {
+ synchronized (this) {
try {
while (status >= 0) {
- long nt = nanos - System.nanoTime() - startTime;
+ long nt = nanos - (System.nanoTime() - startTime);
if (nt <= 0)
break;
- wait(nt / 1000000, (int)(nt % 1000000));
+ wait(nt / 1000000, (int) (nt % 1000000));
}
} catch (InterruptedException ie) {
onInterruptedWait();
@@ -255,13 +273,15 @@ public abstract class ForkJoinTask im
/**
* Sets status to indicate there is joiner, then waits for join,
* surrounded with pool notifications.
+ *
* @return status upon exit
*/
- private int awaitDone(ForkJoinWorkerThread w, boolean maintainParallelism) {
- ForkJoinPool pool = w == null? null : w.pool;
+ 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 (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
if (pool == null || !pool.preJoin(this, maintainParallelism))
doAwaitDone();
if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
@@ -274,13 +294,14 @@ public abstract class ForkJoinTask im
/**
* Timed version of awaitDone
+ *
* @return status upon exit
*/
private int awaitDone(ForkJoinWorkerThread w, long nanos) {
- ForkJoinPool pool = w == null? null : w.pool;
+ ForkJoinPool pool = (w == null) ? null : w.pool;
int s;
while ((s = status) >= 0) {
- if (casStatus(s, pool == null? s|EXTERNAL_SIGNAL : s+1)) {
+ if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
long startTime = System.nanoTime();
if (pool == null || !pool.preJoin(this, false))
doAwaitDone(startTime, nanos);
@@ -297,18 +318,18 @@ public abstract class ForkJoinTask im
}
/**
- * Notify pool that thread is unblocked. Called by signalled
+ * Notifies pool that thread is unblocked. Called by signalled
* threads when woken by non-FJ threads (which is atypical).
*/
private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
int s;
- do;while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
+ 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
+ * Notifies pool to adjust counts on cancelled or timed out wait.
*/
private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
if (pool != null) {
@@ -323,7 +344,7 @@ public abstract class ForkJoinTask im
}
/**
- * Handle interruptions during waits.
+ * Handles interruptions during waits.
*/
private void onInterruptedWait() {
ForkJoinWorkerThread w = getWorker();
@@ -342,7 +363,8 @@ public abstract class ForkJoinTask im
}
/**
- * Throws the exception associated with status s;
+ * Throws the exception associated with status s.
+ *
* @throws the exception
*/
private void reportException(int s) {
@@ -355,8 +377,8 @@ public abstract class ForkJoinTask im
}
/**
- * Returns result or throws exception using j.u.c.Future conventions
- * Only call when isDone known to be true.
+ * Returns result or throws exception using j.u.c.Future conventions.
+ * Only call when {@code isDone} known to be true.
*/
private V reportFutureResult()
throws ExecutionException, InterruptedException {
@@ -375,7 +397,7 @@ public abstract class ForkJoinTask im
/**
* Returns result or throws exception using j.u.c.Future conventions
- * with timeouts
+ * with timeouts.
*/
private V reportTimedFutureResult()
throws InterruptedException, ExecutionException, TimeoutException {
@@ -396,7 +418,8 @@ public abstract class ForkJoinTask im
/**
* Calls exec, recording completion, and rethrowing exception if
- * encountered. Caller should normally check status before calling
+ * encountered. Caller should normally check status before calling.
+ *
* @return true if completed normally
*/
private boolean tryExec() {
@@ -414,14 +437,14 @@ public abstract class ForkJoinTask im
/**
* Main execution method used by worker threads. Invokes
- * base computation unless already complete
+ * base computation unless already complete.
*/
final void quietlyExec() {
if (status >= 0) {
try {
if (!exec())
return;
- } catch(Throwable rex) {
+ } catch (Throwable rex) {
setDoneExceptionally(rex);
return;
}
@@ -430,8 +453,9 @@ public abstract class ForkJoinTask im
}
/**
- * Calls exec, recording but not rethrowing exception
- * Caller should normally check status before calling
+ * Calls exec(), recording but not rethrowing exception.
+ * Caller should normally check status before calling.
+ *
* @return true if completed normally
*/
private boolean tryQuietlyInvoke() {
@@ -447,12 +471,12 @@ public abstract class ForkJoinTask im
}
/**
- * Cancel, ignoring any exceptions it throws
+ * Cancels, ignoring any exceptions it throws.
*/
final void cancelIgnoringExceptions() {
try {
cancel(false);
- } catch(Throwable ignore) {
+ } catch (Throwable ignore) {
}
}
@@ -464,7 +488,7 @@ public abstract class ForkJoinTask im
ForkJoinTask> t;
while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null)
t.quietlyExec();
- return (s >= 0)? awaitDone(w, false) : s; // block if no work
+ return (s >= 0) ? awaitDone(w, false) : s; // block if no work
}
// public methods
@@ -474,16 +498,21 @@ public abstract class ForkJoinTask im
* 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.
+ * computations (as may be determined using method {@link
+ * #inForkJoinPool}). Attempts to invoke in other contexts result
+ * in exceptions or errors, possibly including 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 get
in that abnormal
+ * This method differs from {@code get} in that abnormal
* completion results in RuntimeExceptions or Errors, not
* ExecutionExceptions.
*
@@ -499,8 +528,9 @@ public abstract class ForkJoinTask im
/**
* 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.
+ * exception) if the underlying computation did so
* @return the computed result
*/
public final V invoke() {
@@ -511,15 +541,17 @@ public abstract class ForkJoinTask im
}
/**
- * Forks both tasks, returning when 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
+ * Forks the given tasks, returning when {@code isDone} holds for
+ * each task or an exception is encountered. This method may be
+ * invoked only from within ForkJoinTask computations (as may be
+ * determined using method {@link #inForkJoinPool}). 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.
+ *
+ * @param t1 the first task
+ * @param t2 the second task
+ * @throws NullPointerException if any task is null
+ * @throws RuntimeException or Error if a task did so
*/
public static void invokeAll(ForkJoinTask>t1, ForkJoinTask> t2) {
t2.fork();
@@ -528,14 +560,21 @@ public abstract class ForkJoinTask im
}
/**
- * Forks the given tasks, returning when 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 exception is encountered. If any task
+ * encounters an exception, others may be, but are not guaranteed
+ * to be, cancelled. This method may be invoked only from within
+ * ForkJoinTask computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including
+ * ClassCastException.
+ *
+ * Overloadings of this method exist for the special cases
+ * of one to four arguments.
+ *
+ * @param tasks the tasks
+ * @throws NullPointerException if tasks or any element are null
+ * @throws RuntimeException or Error if any task did so
*/
public static void invokeAll(ForkJoinTask>... tasks) {
Throwable ex = null;
@@ -571,23 +610,28 @@ public abstract class ForkJoinTask im
}
/**
- * Forks all tasks in the collection, returning when
- * 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 collection, returning when {@code
+ * isDone} holds for each task or an exception is encountered. If
+ * any task encounters an exception, others may be, but are not
+ * guaranteed to be, cancelled. This method may be invoked only
+ * from within ForkJoinTask computations (as may be determined
+ * using method {@link #inForkJoinPool}). Attempts to invoke in
+ * other contexts result in exceptions or errors, possibly
+ * including 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.
- */
- public static void invokeAll(Collection extends ForkJoinTask>> tasks) {
- if (!(tasks instanceof List)) {
- invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()]));
- return;
+ * @return the tasks argument, to simplify usage
+ * @throws NullPointerException if tasks or any element are null
+ * @throws RuntimeException or Error if any task did so
+ */
+ public static > Collection invokeAll(Collection tasks) {
+ if (!(tasks instanceof List>)) {
+ invokeAll(tasks.toArray(new ForkJoinTask>[tasks.size()]));
+ return tasks;
}
+ @SuppressWarnings("unchecked")
List extends ForkJoinTask>> ts =
- (List extends ForkJoinTask>>)tasks;
+ (List extends ForkJoinTask>>) tasks;
Throwable ex = null;
int last = ts.size() - 1;
for (int i = last; i >= 0; --i) {
@@ -618,20 +662,23 @@ public abstract class ForkJoinTask im
}
if (ex != null)
rethrowException(ex);
+ return tasks;
}
/**
- * Returns true if the computation performed by this task has
- * completed (or has been cancelled).
- * @return true if this computation has completed
+ * Returns {@code true} if the computation performed by this task
+ * has completed (or has been cancelled).
+ *
+ * @return {@code true} if this computation has completed
*/
public final boolean isDone() {
return status < 0;
}
/**
- * Returns true if this task was cancelled.
- * @return true if this task was cancelled
+ * Returns {@code true} if this task was cancelled.
+ *
+ * @return {@code true} if this task was cancelled
*/
public final boolean isCancelled() {
return (status & COMPLETION_MASK) == CANCELLED;
@@ -639,30 +686,30 @@ public abstract class ForkJoinTask im
/**
* 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, isCancelled
- * will report true, and join
will result in a
- * CancellationException
being thrown. Otherwise, when
+ * used. If a cancellation occurs before attempting to execute this
+ * task, execution will be suppressed, {@link #isCancelled}
+ * will report true, and {@link #join} will result in a
+ * {@code CancellationException} being thrown. Otherwise, when
* cancellation races with completion, there are no guarantees
- * about whether isCancelled
will report true, whether
- * join
will return normally or via an exception, or
- * whether these behaviors will remain consistent upon repeated
+ * about whether {@code isCancelled} will report {@code true},
+ * whether {@code join} will return normally or via an exception,
+ * or whether these behaviors will remain consistent upon repeated
* invocation.
*
* 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.
*
- *
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 completeExceptionally
.
+ * invoke {@link #completeExceptionally}.
*
* @param mayInterruptIfRunning this value is ignored in the
* default implementation because tasks are not in general
- * cancelled via interruption.
+ * 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);
@@ -670,8 +717,9 @@ 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
+ * 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;
@@ -681,7 +729,8 @@ public abstract class ForkJoinTask im
* 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
+ *
+ * @return the exception, or {@code null} if none
*/
public final Throwable getException() {
int s = status & COMPLETION_MASK;
@@ -695,11 +744,11 @@ public abstract class ForkJoinTask im
/**
* Completes this task abnormally, and if not already aborted or
* cancelled, causes it to throw the given exception upon
- * join
and related operations. This method may be used
+ * {@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
- * overridable, but overridden versions must invoke super
+ * 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
@@ -708,26 +757,26 @@ public abstract class ForkJoinTask im
*/
public void completeExceptionally(Throwable ex) {
setDoneExceptionally((ex instanceof RuntimeException) ||
- (ex instanceof Error)? ex :
+ (ex instanceof Error) ? ex :
new RuntimeException(ex));
}
/**
* Completes this task, and if not already aborted or cancelled,
- * returning a null
result upon join
and related
+ * returning a {@code null} result upon {@code join} and related
* 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
- * overridable, but overridden versions must invoke super
+ * 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) {
+ } catch (Throwable rex) {
setDoneExceptionally(rex);
return;
}
@@ -743,26 +792,30 @@ public abstract class ForkJoinTask im
public final V get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException {
+ long nanos = unit.toNanos(timeout);
ForkJoinWorkerThread w = getWorker();
if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
- awaitDone(w, unit.toNanos(timeout));
+ awaitDone(w, nanos);
return reportTimedFutureResult();
}
/**
* Possibly executes other tasks until this task is ready, then
* returns the result of the computation. This method may be more
- * efficient than join
, but is only applicable when
- * there are no potemtial dependencies between continuation of the
+ * 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
- * ForkJoinTask computations. Attempts to invoke in other contexts
- * resul!t in exceptions or errors possibly including ClassCastException.
+ * ForkJoinTask computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including
+ * ClassCastException.
+ *
* @return the computed result
*/
public final V helpJoin() {
- ForkJoinWorkerThread w = (ForkJoinWorkerThread)(Thread.currentThread());
+ ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
if (status < 0 || !w.unpushTask(this) || !tryExec())
reportException(busyJoin(w));
return getRawResult();
@@ -771,13 +824,14 @@ public abstract class ForkJoinTask im
/**
* 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.
+ * computations (as may be determined using method {@link
+ * #inForkJoinPool}). Attempts to invoke in other contexts result
+ * in exceptions or errors, possibly including ClassCastException.
*/
public final void quietlyHelpJoin() {
if (status >= 0) {
ForkJoinWorkerThread w =
- (ForkJoinWorkerThread)(Thread.currentThread());
+ (ForkJoinWorkerThread) Thread.currentThread();
if (!w.unpushTask(this) || !tryQuietlyInvoke())
busyJoin(w);
}
@@ -813,21 +867,25 @@ public abstract class ForkJoinTask im
* 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.
+ * joined, instead executing them until all are processed. This
+ * method may be invoked only from within ForkJoinTask
+ * computations (as may be determined using method {@link
+ * #inForkJoinPool}). Attempts to invoke in other contexts result
+ * in exceptions or errors, possibly including ClassCastException.
*/
public static void helpQuiesce() {
- ((ForkJoinWorkerThread)(Thread.currentThread())).
- helpQuiescePool();
+ ((ForkJoinWorkerThread) Thread.currentThread())
+ .helpQuiescePool();
}
/**
* Resets the internal bookkeeping state of this task, allowing a
- * subsequent fork
. This method allows repeated reuse of
+ * subsequent {@code fork}. This method allows repeated reuse of
* 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
+ * discouraged. This method may be useful when executing
* pre-constructed trees of subtasks in loops.
*/
public void reinitialize() {
@@ -838,13 +896,26 @@ 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;
}
/**
@@ -854,52 +925,64 @@ public abstract class ForkJoinTask im
* 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
+ * ForkJoinTask computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including
+ * ClassCastException.
+ *
+ * @return {@code true} if unforked
*/
public boolean tryUnfork() {
- return ((ForkJoinWorkerThread)(Thread.currentThread())).unpushTask(this);
+ return ((ForkJoinWorkerThread) Thread.currentThread())
+ .unpushTask(this);
}
/**
* Returns an estimate of the number of tasks that have been
* forked by the current worker thread but not yet executed. This
* value may be useful for heuristic decisions about whether to
- * fork other tasks.
+ * fork other tasks. This method may be invoked only from within
+ * ForkJoinTask computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including
+ * 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
* usages of ForkJoinTasks, at steady state, each worker should
* aim to maintain a small constant surplus (for example, 3) of
* tasks, and to process computations locally if this threshold is
- * exceeded.
+ * exceeded. This method may be invoked only from within
+ * ForkJoinTask computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including
+ * 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 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();
@@ -918,27 +1001,33 @@ 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
- * complete
to become joinable. It may throw exceptions
+ * {@link #complete} to become joinable. It may throw exceptions
* to indicate abnormal exit.
- * @return true if completed normally
+ *
+ * @return {@code true} if completed normally
* @throws Error or RuntimeException if encountered during computation
*/
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
+ * ForkJoinTask computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including
+ * 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();
}
/**
@@ -946,34 +1035,130 @@ public abstract class ForkJoinTask im
* 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
+ * within ForkJoinTask computations (as may be determined using
+ * method {@link #inForkJoinPool}). Attempts to invoke in other
+ * contexts result in exceptions or errors, possibly including
* 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> pollNextLocalTask() {
- return ((ForkJoinWorkerThread)(Thread.currentThread())).pollLocalTask();
+ return ((ForkJoinWorkerThread) Thread.currentThread())
+ .pollLocalTask();
}
-
+
/**
* Unschedules and returns, without executing, the next task
* 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
- * 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
+ * ForkJoinTask computations (as may be determined using method
+ * {@link #inForkJoinPool}). Attempts to invoke in other contexts
+ * result in exceptions or errors, possibly including
* 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 extends T> callable;
+ T result;
+ AdaptedCallable(Callable extends T> 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 ForkJoinTask that performs the {@code run}
+ * method of the given Runnable as its action, and returns a null
+ * result upon {@code join}.
+ *
+ * @param runnable the runnable action
+ * @return the task
+ */
+ public static ForkJoinTask> adapt(Runnable runnable) {
+ return new AdaptedRunnable(runnable, null);
+ }
+
+ /**
+ * Returns a new ForkJoinTask that performs the {@code run}
+ * method of the given Runnable as its action, and returns the
+ * given result upon {@code 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 ForkJoinTask that performs the {@code call}
+ * method of the given Callable as its action, and returns its
+ * result upon {@code join}, translating any checked
+ * exceptions encountered into {@code RuntimeException}.
+ *
+ * @param callable the callable action
+ * @return the task
+ */
+ public static ForkJoinTask adapt(Callable extends T> callable) {
+ return new AdaptedCallable(callable);
}
// Serialization support
@@ -984,7 +1169,7 @@ public abstract class ForkJoinTask im
* Save 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)
@@ -995,6 +1180,7 @@ public abstract class ForkJoinTask im
/**
* Reconstitute the instance from a stream.
+ *
* @param s the stream
*/
private void readObject(java.io.ObjectInputStream s)
@@ -1004,49 +1190,51 @@ public abstract class ForkJoinTask im
status |= EXTERNAL_SIGNAL; // conservatively set external signal
Object ex = s.readObject();
if (ex != null)
- setDoneExceptionally((Throwable)ex);
+ setDoneExceptionally((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.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 Unsafe.getUnsafe();
+ 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);
- }
- }
-
}