--- jsr166/src/jsr166y/ForkJoinTask.java 2009/07/26 05:55:34 1.20
+++ jsr166/src/jsr166y/ForkJoinTask.java 2009/08/02 11:54:31 1.27
@@ -16,8 +16,8 @@ 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.
@@ -25,12 +25,11 @@ import java.util.WeakHashMap;
*
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.
+ * 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
@@ -77,7 +76,9 @@ import java.util.WeakHashMap;
*
*
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
@@ -94,8 +95,8 @@ import java.util.WeakHashMap;
* 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
+ * {@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.
@@ -107,6 +108,12 @@ import java.util.WeakHashMap;
* parallelism cannot improve throughput. If too small, then memory
* and internal task maintenance overhead may overwhelm processing.
*
+ *
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
@@ -248,7 +255,7 @@ public abstract class ForkJoinTask im
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));
@@ -493,7 +500,7 @@ public abstract class ForkJoinTask im
* #inForkJoinPool}). Attempts to invoke in other contexts result
* in exceptions or errors, possibly including ClassCastException.
*
- * @return this
, to simplify usage.
+ * @return {@code this}, to simplify usage.
*/
public final ForkJoinTask fork() {
((ForkJoinWorkerThread) Thread.currentThread())
@@ -532,17 +539,17 @@ public abstract class ForkJoinTask im
}
/**
- * Forks both tasks, returning when {@code isDone} holds for
- * both of them or an exception is encountered. This method may be
+ * 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();
@@ -551,15 +558,19 @@ public abstract class ForkJoinTask im
}
/**
- * 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
+ * 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.
*
- * @param tasks the array of tasks
+ * 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
*/
@@ -597,13 +608,14 @@ public abstract class ForkJoinTask im
}
/**
- * 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 (as
- * may be determined using method {@link
- * #inForkJoinPool}). Attempts to invoke in other contexts result
- * 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
* @return the tasks argument, to simplify usage
@@ -652,19 +664,19 @@ public abstract class ForkJoinTask im
}
/**
- * Returns true if the computation performed by this task has
- * completed (or has been cancelled).
+ * Returns {@code true} if the computation performed by this task
+ * has completed (or has been cancelled).
*
- * @return true if this computation has completed
+ * @return {@code true} if this computation has completed
*/
public final boolean isDone() {
return status < 0;
}
/**
- * Returns true if this task was cancelled.
+ * Returns {@code true} if this task was cancelled.
*
- * @return true if this task was cancelled
+ * @return {@code true} if this task was cancelled
*/
public final boolean isCancelled() {
return (status & COMPLETION_MASK) == CANCELLED;
@@ -673,13 +685,13 @@ public abstract class ForkJoinTask im
/**
* Asserts that the results of this task's computation will not be
* 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
+ * 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 {@code isCancelled} will report true, whether
- * {@code 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
@@ -689,13 +701,13 @@ public abstract class ForkJoinTask im
* 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
*
- * @return true if this task is now cancelled
+ * @return {@code true} if this task is now cancelled
*/
public boolean cancel(boolean mayInterruptIfRunning) {
setCompletion(CANCELLED);
@@ -703,9 +715,9 @@ public abstract class ForkJoinTask im
}
/**
- * Returns true if this task threw an exception or was cancelled.
+ * Returns {@code true} if this task threw an exception or was cancelled.
*
- * @return 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;
@@ -716,7 +728,7 @@ public abstract class ForkJoinTask im
* 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;
@@ -733,7 +745,7 @@ 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.
*
@@ -753,7 +765,7 @@ 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.
*
@@ -778,9 +790,10 @@ 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();
}
@@ -852,7 +865,11 @@ 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())
@@ -866,7 +883,7 @@ public abstract class ForkJoinTask im
* 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() {
@@ -879,7 +896,8 @@ public abstract class ForkJoinTask im
* Returns the pool hosting the current task execution, or null
* if this task is executing outside of any ForkJoinPool.
*
- * @return the pool, or null if none
+ * @see #inForkJoinPool
+ * @return the pool, or {@code null} if none
*/
public static ForkJoinPool getPool() {
Thread t = Thread.currentThread();
@@ -910,7 +928,7 @@ public abstract class ForkJoinTask im
* result in exceptions or errors, possibly including
* ClassCastException.
*
- * @return true if unforked
+ * @return {@code true} if unforked
*/
public boolean tryUnfork() {
return ((ForkJoinWorkerThread) Thread.currentThread())
@@ -921,8 +939,11 @@ public abstract class ForkJoinTask im
* 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() {
@@ -938,8 +959,11 @@ public abstract class ForkJoinTask im
* 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() {
@@ -950,13 +974,13 @@ public abstract class ForkJoinTask im
// 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();
@@ -975,26 +999,29 @@ 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
+ * {@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 (as may be determined using method {@link
- * #inForkJoinPool}). 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())
@@ -1011,7 +1038,7 @@ public abstract class ForkJoinTask im
* 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())
@@ -1032,51 +1059,104 @@ public abstract class ForkJoinTask im
* 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();
}
- // adaptors
+ /**
+ * 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 run
+ * Returns a new ForkJoinTask that performs the {@code run}
* method of the given Runnable as its action, and returns a null
- * result upon join
.
+ * result upon {@code join}.
*
* @param runnable the runnable action
* @return the task
*/
- public static ForkJoinTask adapt(Runnable runnable) {
- return new ForkJoinPool.AdaptedRunnable(runnable, null);
+ public static ForkJoinTask> adapt(Runnable runnable) {
+ return new AdaptedRunnable(runnable, null);
}
/**
- * Returns a new ForkJoinTask that performs the run
+ * Returns a new ForkJoinTask that performs the {@code run}
* method of the given Runnable as its action, and returns the
- * given result upon join
.
+ * 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 ForkJoinPool.AdaptedRunnable(runnable, result);
+ return new AdaptedRunnable(runnable, result);
}
/**
- * Returns a new ForkJoinTask that performs the call
+ * Returns a new ForkJoinTask that performs the {@code call}
* method of the given Callable as its action, and returns its
- * result upon join
, translating any checked
- * exceptions encountered into RuntimeException.
+ * 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 callable) {
- return new ForkJoinPool.AdaptedCallable(callable);
+ public static ForkJoinTask adapt(Callable extends T> callable) {
+ return new AdaptedCallable(callable);
}
// Serialization support
@@ -1087,7 +1167,7 @@ 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)
@@ -1111,16 +1191,43 @@ public abstract class ForkJoinTask im
setDoneExceptionally((Throwable) ex);
}
- // Unsafe mechanics for jsr166y 3rd party package.
+ // 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 sun.misc.Unsafe.getUnsafe();
} catch (SecurityException se) {
try {
return java.security.AccessController.doPrivileged
- (new java.security.PrivilegedExceptionAction() {
+ (new java.security
+ .PrivilegedExceptionAction() {
public sun.misc.Unsafe run() throws Exception {
- return getUnsafeByReflection();
+ 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 new RuntimeException("Could not initialize intrinsics",
@@ -1128,28 +1235,4 @@ public abstract class ForkJoinTask im
}
}
}
-
- private static sun.misc.Unsafe getUnsafeByReflection()
- throws NoSuchFieldException, IllegalAccessException {
- java.lang.reflect.Field f =
- sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
- f.setAccessible(true);
- return (sun.misc.Unsafe) f.get(null);
- }
-
- private static long fieldOffset(String fieldName, Class> klazz) {
- try {
- return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName));
- } catch (NoSuchFieldException e) {
- // Convert Exception to Error
- NoSuchFieldError error = new NoSuchFieldError(fieldName);
- error.initCause(e);
- throw error;
- }
- }
-
- private static final sun.misc.Unsafe UNSAFE = getUnsafe();
- private static final long statusOffset =
- fieldOffset("status", ForkJoinTask.class);
-
}