--- jsr166/src/jsr166y/ForkJoinTask.java 2009/01/12 17:16:18 1.4 +++ jsr166/src/jsr166y/ForkJoinTask.java 2009/07/25 15:50:57 1.18 @@ -5,12 +5,15 @@ */ 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 @@ -22,9 +25,9 @@ import java.lang.reflect.*; *
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
+ * 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.
@@ -36,7 +39,7 @@ import java.lang.reflect.*;
* 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
+ * 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
@@ -48,7 +51,7 @@ import java.lang.reflect.*;
* 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
+ * 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
@@ -58,17 +61,17 @@ import java.lang.reflect.*;
*
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.
*
@@ -76,37 +79,42 @@ import java.lang.reflect.*;
* Instead, you subclass one of the abstract classes that support a
* particular style of fork/join processing. 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
+ * {@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 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
+ *
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 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 this
, to simplify usage.
*/
- public final void fork() {
- ((ForkJoinWorkerThread)(Thread.currentThread())).pushTask(this);
+ public final ForkJoinTaskget
in that abnormal
+ * This method differs from {@code get} in that abnormal
* completion results in RuntimeExceptions or Errors, not
* ExecutionExceptions.
*
@@ -499,8 +519,9 @@ public abstract class ForkJoinTaskisDone
holds for
+ * 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
+ * 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.
+ * @throws RuntimeException or Error if either task did so
*/
public static void invokeAll(ForkJoinTask>t1, ForkJoinTask> t2) {
t2.fork();
@@ -528,14 +551,17 @@ public abstract class ForkJoinTaskisDone
holds
+ * 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.
+ * 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 array of tasks
- * @throws NullPointerException if tasks or any element are null.
- * @throws RuntimeException or Error if any task did so.
+ * @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;
@@ -572,22 +598,25 @@ public abstract class ForkJoinTaskisDone
holds for all of them. If any task
+ * {@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.
+ * 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.
+ * @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()]));
+ if (!(tasks instanceof List>)) {
+ invokeAll(tasks.toArray(new ForkJoinTask>[tasks.size()]));
return;
}
+ @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) {
@@ -623,6 +652,7 @@ public abstract class ForkJoinTaskisCancelled
- * 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, 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 isCancelled
will report true, whether
- * join
will return normally or via an exception, or
+ * 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.
*
@@ -656,11 +687,11 @@ public abstract class ForkJoinTaskcompleteExceptionally
.
+ * invoke {@code 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
*/
@@ -670,7 +701,8 @@ public abstract class ForkJoinTaskjoin
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
+ * overridable, but overridden versions must invoke {@code super}
* implementation to maintain guarantees.
*
* @param ex the exception to throw. If this exception is
@@ -708,26 +741,26 @@ public abstract class ForkJoinTasknull
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
+ * 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;
}
@@ -752,17 +785,20 @@ public abstract class ForkJoinTaskjoin
, 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 +807,14 @@ public abstract class ForkJoinTaskfork
. 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
@@ -838,13 +875,25 @@ public abstract class ForkJoinTaskjoin
,
+ * 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.
*
- * @return the result, or null if not completed.
+ * @return the result, or null if not completed
*/
public abstract V getRawResult();
@@ -918,63 +973,108 @@ public abstract class ForkJoinTaskcomplete
to become joinable. It may throw exceptions
+ * {@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
*/
protected abstract boolean exec();
/**
- * Returns, but does not unschedule or execute, the task most
- * recently forked by the current thread but not yet executed, if
- * one is 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.
+ * Returns, but does not unschedule or execute, the task queued by
+ * the current thread but not yet executed, if one is
+ * 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 (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
*/
protected static ForkJoinTask> peekNextLocalTask() {
- return ((ForkJoinWorkerThread)(Thread.currentThread())).peekTask();
+ return ((ForkJoinWorkerThread) Thread.currentThread())
+ .peekTask();
}
/**
- * Unschedules and returns, without executing, the task most
- * recently forked 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.
+ * 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 (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
*/
protected static ForkJoinTask> pollNextLocalTask() {
- return ((ForkJoinWorkerThread)(Thread.currentThread())).popTask();
+ return ((ForkJoinWorkerThread) Thread.currentThread())
+ .pollLocalTask();
}
/**
- * Unschedules and returns, without executing, the task most
- * recently forked 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 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.
+ * 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
+ * {@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 (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
*/
protected static ForkJoinTask> pollTask() {
- return ((ForkJoinWorkerThread)(Thread.currentThread())).
- pollTask();
+ return ((ForkJoinWorkerThread) Thread.currentThread())
+ .pollTask();
+ }
+
+ // adaptors
+
+ /**
+ * Returns a new ForkJoinTask that performs the run
+ * method of the given Runnable as its action, and returns a null
+ * result upon join
.
+ *
+ * @param runnable the runnable action
+ * @return the task
+ */
+ public static ForkJoinTaskrun
+ * method of the given Runnable as its action, and returns the
+ * given result upon join
.
+ *
+ * @param runnable the runnable action
+ * @param result the result upon completion
+ * @return the task
+ */
+ public static call
+ * method of the given Callable as its action, and returns its
+ * result upon join
, translating any checked
+ * exceptions encountered into RuntimeException
.
+ *
+ * @param callable the callable action
+ * @return the task
+ */
+ public static