--- jsr166/src/jsr166y/ForkJoinTask.java 2009/01/07 16:07:37 1.2 +++ jsr166/src/jsr166y/ForkJoinTask.java 2009/07/21 18:11:44 1.11 @@ -18,17 +18,17 @@ import java.lang.reflect.*; * 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
+ * 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 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
@@ -36,7 +36,7 @@ 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 +48,7 @@ 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 +58,17 @@ 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.
*
@@ -76,33 +76,33 @@ 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 including ClassCastException.
+ * 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
@@ -128,7 +128,7 @@ 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 get
in that abnormal
+ * This method differs from {@code get} in that abnormal
* completion results in RuntimeExceptions or Errors, not
* ExecutionExceptions.
*
@@ -485,26 +501,12 @@ 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
- * including ClassCastException.
+ * 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();
@@ -532,14 +535,15 @@ 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 including ClassCastException.
+ * 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;
@@ -576,14 +580,15 @@ 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 including ClassCastException.
+ * computations. 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)) {
@@ -627,6 +632,7 @@ 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.
*
@@ -683,7 +667,7 @@ public abstract class ForkJoinTaskcompleteExceptionally
.
+ * invoke {@code completeExceptionally}.
*
* @param mayInterruptIfRunning this value is ignored in the
* default implementation because tasks are not in general
@@ -697,13 +681,38 @@ 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
@@ -718,15 +727,15 @@ 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 {
@@ -738,37 +747,53 @@ 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 including ClassCastException.
+ * result in exceptions or errors possibly including ClassCastException.
+ *
* @return the computed result
*/
public final V helpJoin() {
ForkJoinWorkerThread w = (ForkJoinWorkerThread)(Thread.currentThread());
if (status < 0 || !w.unpushTask(this) || !tryExec())
- reportException(w.helpJoinTask(this));
+ reportException(busyJoin(w));
return getRawResult();
}
/**
* 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 including ClassCastException.
+ * computations. 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());
if (!w.unpushTask(this) || !tryQuietlyInvoke())
- w.helpJoinTask(this);
+ busyJoin(w);
}
}
@@ -799,8 +824,19 @@ 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
@@ -817,7 +853,8 @@ 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();
@@ -907,20 +936,23 @@ 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.
+ * 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. Attempts to invoke in other contexts result in
+ * exceptions or errors possibly including ClassCastException.
*
* @return the next task, or null if none are available
*/
@@ -929,32 +961,38 @@ public abstract class ForkJoinTasknull
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.
- *
+ * 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. 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())).
- getLocalOrStolenTask();
+ pollTask();
}
// Serialization support
@@ -965,7 +1003,7 @@ public abstract class ForkJoinTask