JDK 11 java.base.jmod - Base Module
JDK 11 java.base.jmod is the JMOD file for JDK 11 Base module.
JDK 11 Base module compiled class files are stored in \fyicenter\jdk-11.0.1\jmods\java.base.jmod.
JDK 11 Base module compiled class files are also linked and stored in the \fyicenter\jdk-11.0.1\lib\modules JImage file.
JDK 11 Base module source code files are stored in \fyicenter\jdk-11.0.1\lib\src.zip\java.base.
You can click and view the content of each source code file in the list below.
✍: FYIcenter
⏎ java/util/concurrent/ForkJoinTask.java
/*
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*/
/*
*
*
*
*
*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package java.util.concurrent;
import java.io.Serializable;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.lang.reflect.Constructor;
import java.util.Collection;
import java.util.List;
import java.util.RandomAccess;
import java.util.concurrent.locks.ReentrantLock;
/**
* 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.
*
* <p>A "main" {@code ForkJoinTask} begins execution when it is
* explicitly submitted to a {@link ForkJoinPool}, or, if not already
* engaged in a ForkJoin computation, commenced in the {@link
* ForkJoinPool#commonPool()} via {@link #fork}, {@link #invoke}, or
* related methods. 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(ForkJoinTask...) 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.
*
* <p>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 main 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
* ideally 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. Subdividable tasks should also
* not perform blocking I/O, and should ideally access variables that
* are completely independent of those accessed by other running
* tasks. These guidelines are loosely enforced by not permitting
* checked exceptions such as {@code IOExceptions} to be
* thrown. However, computations may still encounter unchecked
* exceptions, that are rethrown to callers attempting to join
* them. These exceptions may additionally include {@link
* RejectedExecutionException} stemming from internal resource
* exhaustion, such as failure to allocate internal task
* queues. Rethrown exceptions behave in the same way as regular
* exceptions, but, when possible, contain stack traces (as displayed
* for example using {@code ex.printStackTrace()}) of both the thread
* that initiated the computation as well as the thread actually
* encountering the exception; minimally only the latter.
*
* <p>It is possible to define and use ForkJoinTasks that may block,
* but doing so requires three further considerations: (1) Completion
* of few if any <em>other</em> tasks should be dependent on a task
* that blocks on external synchronization or I/O. Event-style async
* tasks that are never joined (for example, those subclassing {@link
* CountedCompleter}) often fall into this category. (2) To minimize
* resource impact, tasks should be small; ideally performing only the
* (possibly) blocking action. (3) Unless the {@link
* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
* blocked tasks is known to be less than the pool's {@link
* ForkJoinPool#getParallelism} level, the pool cannot guarantee that
* enough threads will be available to ensure progress or good
* performance.
*
* <p>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 {@code Future}
* conventions. Method {@link #invoke} is semantically
* equivalent to {@code fork(); join()} but always attempts to begin
* execution in the current thread. The "<em>quiet</em>" forms of
* these methods do not extract results or report exceptions. These
* may be useful when a set of tasks are being executed, and you need
* to delay processing of results or exceptions until all complete.
* Method {@code invokeAll} (available in multiple versions)
* performs the most common form of parallel invocation: forking a set
* of tasks and joining them all.
*
* <p>In the most typical usages, a fork-join pair act like a call
* (fork) and return (join) from a parallel recursive function. As is
* the case with other forms of recursive calls, returns (joins)
* should be performed innermost-first. For example, {@code a.fork();
* b.fork(); b.join(); a.join();} is likely to be substantially more
* efficient than joining {@code a} before {@code b}.
*
* <p>The execution status of tasks may be queried at several levels
* of detail: {@link #isDone} is true if a task completed in any way
* (including the case where a task was cancelled without executing);
* {@link #isCompletedNormally} is true if a task completed without
* cancellation or encountering an exception; {@link #isCancelled} is
* true if the task was cancelled (in which case {@link #getException}
* returns a {@link CancellationException}); and
* {@link #isCompletedAbnormally} is true if a task was either
* cancelled or encountered an exception, in which case {@link
* #getException} will return either the encountered exception or
* {@link CancellationException}.
*
* <p>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, typically {@link
* RecursiveAction} for most computations that do not return results,
* {@link RecursiveTask} for those that do, and {@link
* CountedCompleter} for those in which completed actions trigger
* other actions. Normally, a concrete ForkJoinTask subclass declares
* fields comprising its parameters, established in a constructor, and
* then defines a {@code compute} method that somehow uses the control
* methods supplied by this base class.
*
* <p>Method {@link #join} and its variants are appropriate for use
* only when completion dependencies are acyclic; that is, the
* parallel computation can be described as a directed acyclic graph
* (DAG). Otherwise, executions may encounter a form of deadlock as
* tasks cyclically wait for each other. However, this framework
* supports other methods and techniques (for example the use of
* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
* may be of use in constructing custom subclasses for problems that
* are not statically structured as DAGs. To support such usages, a
* ForkJoinTask may be atomically <em>tagged</em> with a {@code short}
* value using {@link #setForkJoinTaskTag} or {@link
* #compareAndSetForkJoinTaskTag} and checked using {@link
* #getForkJoinTaskTag}. The ForkJoinTask implementation does not use
* these {@code protected} methods or tags for any purpose, but they
* may be of use in the construction of specialized subclasses. For
* example, parallel graph traversals can use the supplied methods to
* avoid revisiting nodes/tasks that have already been processed.
* (Method names for tagging are bulky in part to encourage definition
* of methods that reflect their usage patterns.)
*
* <p>Most base support methods are {@code final}, to prevent
* overriding of implementations that are intrinsically tied to the
* underlying lightweight task scheduling framework. Developers
* creating new basic styles of fork/join processing should minimally
* implement {@code protected} methods {@link #exec}, {@link
* #setRawResult}, and {@link #getRawResult}, while also introducing
* an abstract computational method that can be implemented in its
* subclasses, possibly relying on other {@code protected} methods
* provided by this class.
*
* <p>ForkJoinTasks should perform relatively small amounts of
* computation. Large tasks should be split into smaller subtasks,
* usually via recursive decomposition. As a very rough rule of thumb,
* a task should perform more than 100 and less than 10000 basic
* computational steps, and should avoid indefinite looping. If tasks
* are too big, then parallelism cannot improve throughput. If too
* small, then memory and internal task maintenance overhead may
* overwhelm processing.
*
* <p>This class provides {@code adapt} methods for {@link Runnable}
* and {@link Callable}, that may be of use when mixing execution of
* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
* of this form, consider using a pool constructed in <em>asyncMode</em>.
*
* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
* used in extensions such as remote execution frameworks. It is
* sensible to serialize tasks only before or after, but not during,
* execution. Serialization is not relied on during execution itself.
*
* @since 1.7
* @author Doug Lea
*/
public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
/*
* See the internal documentation of class ForkJoinPool for a
* general implementation overview. ForkJoinTasks are mainly
* responsible for maintaining their "status" field amidst relays
* to methods in ForkJoinWorkerThread and ForkJoinPool.
*
* The methods of this class are more-or-less layered into
* (1) basic status maintenance
* (2) execution and awaiting completion
* (3) user-level methods that additionally report results.
* This is sometimes hard to see because this file orders exported
* methods in a way that flows well in javadocs.
*/
/**
* The status field holds run control status bits packed into a
* single int to ensure atomicity. Status is initially zero, and
* takes on nonnegative values until completed, upon which it
* holds (sign bit) DONE, possibly with ABNORMAL (cancelled or
* exceptional) and THROWN (in which case an exception has been
* stored). Tasks with dependent blocked waiting joiners have the
* SIGNAL bit set. Completion of a task with SIGNAL set awakens
* any waiters via notifyAll. (Waiters also help signal others
* upon completion.)
*
* These control bits occupy only (some of) the upper half (16
* bits) of status field. The lower bits are used for user-defined
* tags.
*/
volatile int status; // accessed directly by pool and workers
private static final int DONE = 1 << 31; // must be negative
private static final int ABNORMAL = 1 << 18; // set atomically with DONE
private static final int THROWN = 1 << 17; // set atomically with ABNORMAL
private static final int SIGNAL = 1 << 16; // true if joiner waiting
private static final int SMASK = 0xffff; // short bits for tags
static boolean isExceptionalStatus(int s) { // needed by subclasses
return (s & THROWN) != 0;
}
/**
* Sets DONE status and wakes up threads waiting to join this task.
*
* @return status on exit
*/
private int setDone() {
int s;
if (((s = (int)STATUS.getAndBitwiseOr(this, DONE)) & SIGNAL) != 0)
synchronized (this) { notifyAll(); }
return s | DONE;
}
/**
* Marks cancelled or exceptional completion unless already done.
*
* @param completion must be DONE | ABNORMAL, ORed with THROWN if exceptional
* @return status on exit
*/
private int abnormalCompletion(int completion) {
for (int s, ns;;) {
if ((s = status) < 0)
return s;
else if (STATUS.weakCompareAndSet(this, s, ns = s | completion)) {
if ((s & SIGNAL) != 0)
synchronized (this) { notifyAll(); }
return ns;
}
}
}
/**
* Primary execution method for stolen tasks. Unless done, calls
* exec and records status if completed, but doesn't wait for
* completion otherwise.
*
* @return status on exit from this method
*/
final int doExec() {
int s; boolean completed;
if ((s = status) >= 0) {
try {
completed = exec();
} catch (Throwable rex) {
completed = false;
s = setExceptionalCompletion(rex);
}
if (completed)
s = setDone();
}
return s;
}
/**
* If not done, sets SIGNAL status and performs Object.wait(timeout).
* This task may or may not be done on exit. Ignores interrupts.
*
* @param timeout using Object.wait conventions.
*/
final void internalWait(long timeout) {
if ((int)STATUS.getAndBitwiseOr(this, SIGNAL) >= 0) {
synchronized (this) {
if (status >= 0)
try { wait(timeout); } catch (InterruptedException ie) { }
else
notifyAll();
}
}
}
/**
* Blocks a non-worker-thread until completion.
* @return status upon completion
*/
private int externalAwaitDone() {
int s = tryExternalHelp();
if (s >= 0 && (s = (int)STATUS.getAndBitwiseOr(this, SIGNAL)) >= 0) {
boolean interrupted = false;
synchronized (this) {
for (;;) {
if ((s = status) >= 0) {
try {
wait(0L);
} catch (InterruptedException ie) {
interrupted = true;
}
}
else {
notifyAll();
break;
}
}
}
if (interrupted)
Thread.currentThread().interrupt();
}
return s;
}
/**
* Blocks a non-worker-thread until completion or interruption.
*/
private int externalInterruptibleAwaitDone() throws InterruptedException {
int s = tryExternalHelp();
if (s >= 0 && (s = (int)STATUS.getAndBitwiseOr(this, SIGNAL)) >= 0) {
synchronized (this) {
for (;;) {
if ((s = status) >= 0)
wait(0L);
else {
notifyAll();
break;
}
}
}
}
else if (Thread.interrupted())
throw new InterruptedException();
return s;
}
/**
* Tries to help with tasks allowed for external callers.
*
* @return current status
*/
private int tryExternalHelp() {
int s;
return ((s = status) < 0 ? s:
(this instanceof CountedCompleter) ?
ForkJoinPool.common.externalHelpComplete(
(CountedCompleter<?>)this, 0) :
ForkJoinPool.common.tryExternalUnpush(this) ?
doExec() : 0);
}
/**
* Implementation for join, get, quietlyJoin. Directly handles
* only cases of already-completed, external wait, and
* unfork+exec. Others are relayed to ForkJoinPool.awaitJoin.
*
* @return status upon completion
*/
private int doJoin() {
int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
return (s = status) < 0 ? s :
((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
(w = (wt = (ForkJoinWorkerThread)t).workQueue).
tryUnpush(this) && (s = doExec()) < 0 ? s :
wt.pool.awaitJoin(w, this, 0L) :
externalAwaitDone();
}
/**
* Implementation for invoke, quietlyInvoke.
*
* @return status upon completion
*/
private int doInvoke() {
int s; Thread t; ForkJoinWorkerThread wt;
return (s = doExec()) < 0 ? s :
((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
(wt = (ForkJoinWorkerThread)t).pool.
awaitJoin(wt.workQueue, this, 0L) :
externalAwaitDone();
}
// Exception table support
/**
* Hash 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 use a weak ref table. Note
* that cancellation exceptions don't appear in the table, but are
* instead recorded as status values.
*
* The exception table has a fixed capacity.
*/
private static final ExceptionNode[] exceptionTable
= new ExceptionNode[32];
/** Lock protecting access to exceptionTable. */
private static final ReentrantLock exceptionTableLock
= new ReentrantLock();
/** Reference queue of stale exceptionally completed tasks. */
private static final ReferenceQueue<ForkJoinTask<?>> exceptionTableRefQueue
= new ReferenceQueue<>();
/**
* Key-value nodes for exception table. The chained hash table
* uses identity comparisons, full locking, and weak references
* for keys. The table has a fixed capacity because it only
* maintains task exceptions long enough for joiners to access
* them, so should never become very large for sustained
* periods. However, since we do not know when the last joiner
* completes, we must use weak references and expunge them. We do
* so on each operation (hence full locking). Also, some thread in
* any ForkJoinPool will call helpExpungeStaleExceptions when its
* pool becomes isQuiescent.
*/
static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> {
final Throwable ex;
ExceptionNode next;
final long thrower; // use id not ref to avoid weak cycles
final int hashCode; // store task hashCode before weak ref disappears
ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next,
ReferenceQueue<ForkJoinTask<?>> exceptionTableRefQueue) {
super(task, exceptionTableRefQueue);
this.ex = ex;
this.next = next;
this.thrower = Thread.currentThread().getId();
this.hashCode = System.identityHashCode(task);
}
}
/**
* Records exception and sets status.
*
* @return status on exit
*/
final int recordExceptionalCompletion(Throwable ex) {
int s;
if ((s = status) >= 0) {
int h = System.identityHashCode(this);
final ReentrantLock lock = exceptionTableLock;
lock.lock();
try {
expungeStaleExceptions();
ExceptionNode[] t = exceptionTable;
int i = h & (t.length - 1);
for (ExceptionNode e = t[i]; ; e = e.next) {
if (e == null) {
t[i] = new ExceptionNode(this, ex, t[i],
exceptionTableRefQueue);
break;
}
if (e.get() == this) // already present
break;
}
} finally {
lock.unlock();
}
s = abnormalCompletion(DONE | ABNORMAL | THROWN);
}
return s;
}
/**
* Records exception and possibly propagates.
*
* @return status on exit
*/
private int setExceptionalCompletion(Throwable ex) {
int s = recordExceptionalCompletion(ex);
if ((s & THROWN) != 0)
internalPropagateException(ex);
return s;
}
/**
* Hook for exception propagation support for tasks with completers.
*/
void internalPropagateException(Throwable ex) {
}
/**
* Cancels, ignoring any exceptions thrown by cancel. Used during
* worker and pool shutdown. Cancel is spec'ed not to throw any
* exceptions, but if it does anyway, we have no recourse during
* shutdown, so guard against this case.
*/
static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
if (t != null && t.status >= 0) {
try {
t.cancel(false);
} catch (Throwable ignore) {
}
}
}
/**
* Removes exception node and clears status.
*/
private void clearExceptionalCompletion() {
int h = System.identityHashCode(this);
final ReentrantLock lock = exceptionTableLock;
lock.lock();
try {
ExceptionNode[] t = exceptionTable;
int i = h & (t.length - 1);
ExceptionNode e = t[i];
ExceptionNode pred = null;
while (e != null) {
ExceptionNode next = e.next;
if (e.get() == this) {
if (pred == null)
t[i] = next;
else
pred.next = next;
break;
}
pred = e;
e = next;
}
expungeStaleExceptions();
status = 0;
} finally {
lock.unlock();
}
}
/**
* Returns a rethrowable exception for this task, if available.
* To provide accurate stack traces, if the exception was not
* thrown by the current thread, we try to create a new exception
* of the same type as the one thrown, but with the recorded
* exception as its cause. If there is no such constructor, we
* instead try to use a no-arg constructor, followed by initCause,
* to the same effect. If none of these apply, or any fail due to
* other exceptions, we return the recorded exception, which is
* still correct, although it may contain a misleading stack
* trace.
*
* @return the exception, or null if none
*/
private Throwable getThrowableException() {
int h = System.identityHashCode(this);
ExceptionNode e;
final ReentrantLock lock = exceptionTableLock;
lock.lock();
try {
expungeStaleExceptions();
ExceptionNode[] t = exceptionTable;
e = t[h & (t.length - 1)];
while (e != null && e.get() != this)
e = e.next;
} finally {
lock.unlock();
}
Throwable ex;
if (e == null || (ex = e.ex) == null)
return null;
if (e.thrower != Thread.currentThread().getId()) {
try {
Constructor<?> noArgCtor = null;
// public ctors only
for (Constructor<?> c : ex.getClass().getConstructors()) {
Class<?>[] ps = c.getParameterTypes();
if (ps.length == 0)
noArgCtor = c;
else if (ps.length == 1 && ps[0] == Throwable.class)
return (Throwable)c.newInstance(ex);
}
if (noArgCtor != null) {
Throwable wx = (Throwable)noArgCtor.newInstance();
wx.initCause(ex);
return wx;
}
} catch (Exception ignore) {
}
}
return ex;
}
/**
* Polls stale refs and removes them. Call only while holding lock.
*/
private static void expungeStaleExceptions() {
for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
if (x instanceof ExceptionNode) {
ExceptionNode[] t = exceptionTable;
int i = ((ExceptionNode)x).hashCode & (t.length - 1);
ExceptionNode e = t[i];
ExceptionNode pred = null;
while (e != null) {
ExceptionNode next = e.next;
if (e == x) {
if (pred == null)
t[i] = next;
else
pred.next = next;
break;
}
pred = e;
e = next;
}
}
}
}
/**
* If lock is available, polls stale refs and removes them.
* Called from ForkJoinPool when pools become quiescent.
*/
static final void helpExpungeStaleExceptions() {
final ReentrantLock lock = exceptionTableLock;
if (lock.tryLock()) {
try {
expungeStaleExceptions();
} finally {
lock.unlock();
}
}
}
/**
* A version of "sneaky throw" to relay exceptions.
*/
static void rethrow(Throwable ex) {
ForkJoinTask.<RuntimeException>uncheckedThrow(ex);
}
/**
* The sneaky part of sneaky throw, relying on generics
* limitations to evade compiler complaints about rethrowing
* unchecked exceptions.
*/
@SuppressWarnings("unchecked") static <T extends Throwable>
void uncheckedThrow(Throwable t) throws T {
if (t != null)
throw (T)t; // rely on vacuous cast
else
throw new Error("Unknown Exception");
}
/**
* Throws exception, if any, associated with the given status.
*/
private void reportException(int s) {
rethrow((s & THROWN) != 0 ? getThrowableException() :
new CancellationException());
}
// public methods
/**
* Arranges to asynchronously execute this task in the pool the
* current task is running in, if applicable, or using the {@link
* ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}. While
* it is not necessarily enforced, it is a usage error to fork a
* task more than once unless it has completed and been
* reinitialized. Subsequent modifications to the state of this
* task or any data it operates on are not necessarily
* consistently observable by any thread other than the one
* executing it unless preceded by a call to {@link #join} or
* related methods, or a call to {@link #isDone} returning {@code
* true}.
*
* @return {@code this}, to simplify usage
*/
public final ForkJoinTask<V> fork() {
Thread t;
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
((ForkJoinWorkerThread)t).workQueue.push(this);
else
ForkJoinPool.common.externalPush(this);
return this;
}
/**
* Returns the result of the computation when it
* {@linkplain #isDone is done}.
* This method differs from {@link #get()} in that abnormal
* completion results in {@code RuntimeException} or {@code Error},
* not {@code ExecutionException}, and that interrupts of the
* calling thread do <em>not</em> cause the method to abruptly
* return by throwing {@code InterruptedException}.
*
* @return the computed result
*/
public final V join() {
int s;
if (((s = doJoin()) & ABNORMAL) != 0)
reportException(s);
return getRawResult();
}
/**
* Commences performing this task, awaits its completion if
* necessary, and returns its result, or throws an (unchecked)
* {@code RuntimeException} or {@code Error} if the underlying
* computation did so.
*
* @return the computed result
*/
public final V invoke() {
int s;
if (((s = doInvoke()) & ABNORMAL) != 0)
reportException(s);
return getRawResult();
}
/**
* Forks the given tasks, returning when {@code isDone} holds for
* each task or an (unchecked) exception is encountered, in which
* case the exception is rethrown. If more than one task
* encounters an exception, then this method throws any one of
* these exceptions. If any task encounters an exception, the
* other may be cancelled. However, the execution status of
* individual tasks is not guaranteed upon exceptional return. The
* status of each task may be obtained using {@link
* #getException()} and related methods to check if they have been
* cancelled, completed normally or exceptionally, or left
* unprocessed.
*
* @param t1 the first task
* @param t2 the second task
* @throws NullPointerException if any task is null
*/
public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
int s1, s2;
t2.fork();
if (((s1 = t1.doInvoke()) & ABNORMAL) != 0)
t1.reportException(s1);
if (((s2 = t2.doJoin()) & ABNORMAL) != 0)
t2.reportException(s2);
}
/**
* Forks the given tasks, returning when {@code isDone} holds for
* each task or an (unchecked) exception is encountered, in which
* case the exception is rethrown. If more than one task
* encounters an exception, then this method throws any one of
* these exceptions. If any task encounters an exception, others
* may be cancelled. However, the execution status of individual
* tasks is not guaranteed upon exceptional return. The status of
* each task may be obtained using {@link #getException()} and
* related methods to check if they have been cancelled, completed
* normally or exceptionally, or left unprocessed.
*
* @param tasks the tasks
* @throws NullPointerException if any task is null
*/
public static void invokeAll(ForkJoinTask<?>... tasks) {
Throwable ex = null;
int last = tasks.length - 1;
for (int i = last; i >= 0; --i) {
ForkJoinTask<?> t = tasks[i];
if (t == null) {
if (ex == null)
ex = new NullPointerException();
}
else if (i != 0)
t.fork();
else if ((t.doInvoke() & ABNORMAL) != 0 && ex == null)
ex = t.getException();
}
for (int i = 1; i <= last; ++i) {
ForkJoinTask<?> t = tasks[i];
if (t != null) {
if (ex != null)
t.cancel(false);
else if ((t.doJoin() & ABNORMAL) != 0)
ex = t.getException();
}
}
if (ex != null)
rethrow(ex);
}
/**
* Forks all tasks in the specified collection, returning when
* {@code isDone} holds for each task or an (unchecked) exception
* is encountered, in which case the exception is rethrown. If
* more than one task encounters an exception, then this method
* throws any one of these exceptions. If any task encounters an
* exception, others may be cancelled. However, the execution
* status of individual tasks is not guaranteed upon exceptional
* return. The status of each task may be obtained using {@link
* #getException()} and related methods to check if they have been
* cancelled, completed normally or exceptionally, or left
* unprocessed.
*
* @param tasks the collection of tasks
* @param <T> the type of the values returned from the tasks
* @return the tasks argument, to simplify usage
* @throws NullPointerException if tasks or any element are null
*/
public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
invokeAll(tasks.toArray(new ForkJoinTask<?>[0]));
return tasks;
}
@SuppressWarnings("unchecked")
List<? extends ForkJoinTask<?>> ts =
(List<? extends ForkJoinTask<?>>) tasks;
Throwable ex = null;
int last = ts.size() - 1;
for (int i = last; i >= 0; --i) {
ForkJoinTask<?> t = ts.get(i);
if (t == null) {
if (ex == null)
ex = new NullPointerException();
}
else if (i != 0)
t.fork();
else if ((t.doInvoke() & ABNORMAL) != 0 && ex == null)
ex = t.getException();
}
for (int i = 1; i <= last; ++i) {
ForkJoinTask<?> t = ts.get(i);
if (t != null) {
if (ex != null)
t.cancel(false);
else if ((t.doJoin() & ABNORMAL) != 0)
ex = t.getException();
}
}
if (ex != null)
rethrow(ex);
return tasks;
}
/**
* Attempts to cancel execution of this task. This attempt will
* fail if the task has already completed or could not be
* cancelled for some other reason. If successful, and this task
* has not started when {@code cancel} is called, execution of
* this task is suppressed. After this method returns
* successfully, unless there is an intervening call to {@link
* #reinitialize}, subsequent calls to {@link #isCancelled},
* {@link #isDone}, and {@code cancel} will return {@code true}
* and calls to {@link #join} and related methods will result in
* {@code CancellationException}.
*
* <p>This method may be overridden in subclasses, but if so, must
* still ensure that these properties hold. In particular, the
* {@code cancel} method itself must not throw exceptions.
*
* <p>This method is designed to be invoked by <em>other</em>
* tasks. To terminate the current task, you can just return or
* throw an unchecked exception from its computation method, or
* invoke {@link #completeExceptionally(Throwable)}.
*
* @param mayInterruptIfRunning this value has no effect in the
* default implementation because interrupts are not used to
* control cancellation.
*
* @return {@code true} if this task is now cancelled
*/
public boolean cancel(boolean mayInterruptIfRunning) {
int s = abnormalCompletion(DONE | ABNORMAL);
return (s & (ABNORMAL | THROWN)) == ABNORMAL;
}
public final boolean isDone() {
return status < 0;
}
public final boolean isCancelled() {
return (status & (ABNORMAL | THROWN)) == ABNORMAL;
}
/**
* 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 & ABNORMAL) != 0;
}
/**
* Returns {@code true} if this task completed without throwing an
* exception and was not cancelled.
*
* @return {@code true} if this task completed without throwing an
* exception and was not cancelled
*/
public final boolean isCompletedNormally() {
return (status & (DONE | ABNORMAL)) == DONE;
}
/**
* Returns the exception thrown by the base computation, or a
* {@code CancellationException} if cancelled, or {@code null} if
* none or if the method has not yet completed.
*
* @return the exception, or {@code null} if none
*/
public final Throwable getException() {
int s = status;
return ((s & ABNORMAL) == 0 ? null :
(s & THROWN) == 0 ? new CancellationException() :
getThrowableException());
}
/**
* Completes this task abnormally, and if not already aborted or
* cancelled, causes it to throw the given exception upon
* {@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 discouraged. This method is
* overridable, but overridden versions must invoke {@code super}
* implementation to maintain guarantees.
*
* @param ex the exception to throw. If this exception is not a
* {@code RuntimeException} or {@code Error}, the actual exception
* thrown will be a {@code RuntimeException} with cause {@code ex}.
*/
public void completeExceptionally(Throwable ex) {
setExceptionalCompletion((ex instanceof RuntimeException) ||
(ex instanceof Error) ? ex :
new RuntimeException(ex));
}
/**
* Completes this task, and if not already aborted or cancelled,
* returning the given value as the result of subsequent
* invocations of {@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
* discouraged. This method is overridable, but overridden
* versions must invoke {@code super} implementation to maintain
* guarantees.
*
* @param value the result value for this task
*/
public void complete(V value) {
try {
setRawResult(value);
} catch (Throwable rex) {
setExceptionalCompletion(rex);
return;
}
setDone();
}
/**
* Completes this task normally without setting a value. The most
* recent value established by {@link #setRawResult} (or {@code
* null} by default) will be returned as the result of subsequent
* invocations of {@code join} and related operations.
*
* @since 1.8
*/
public final void quietlyComplete() {
setDone();
}
/**
* Waits if necessary for the computation to complete, and then
* retrieves its result.
*
* @return the computed result
* @throws CancellationException if the computation was cancelled
* @throws ExecutionException if the computation threw an
* exception
* @throws InterruptedException if the current thread is not a
* member of a ForkJoinPool and was interrupted while waiting
*/
public final V get() throws InterruptedException, ExecutionException {
int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
doJoin() : externalInterruptibleAwaitDone();
if ((s & THROWN) != 0)
throw new ExecutionException(getThrowableException());
else if ((s & ABNORMAL) != 0)
throw new CancellationException();
else
return getRawResult();
}
/**
* Waits if necessary for at most the given time for the computation
* to complete, and then retrieves its result, if available.
*
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
* @return the computed result
* @throws CancellationException if the computation was cancelled
* @throws ExecutionException if the computation threw an
* exception
* @throws InterruptedException if the current thread is not a
* member of a ForkJoinPool and was interrupted while waiting
* @throws TimeoutException if the wait timed out
*/
public final V get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException {
int s;
long nanos = unit.toNanos(timeout);
if (Thread.interrupted())
throw new InterruptedException();
if ((s = status) >= 0 && nanos > 0L) {
long d = System.nanoTime() + nanos;
long deadline = (d == 0L) ? 1L : d; // avoid 0
Thread t = Thread.currentThread();
if (t instanceof ForkJoinWorkerThread) {
ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
s = wt.pool.awaitJoin(wt.workQueue, this, deadline);
}
else if ((s = ((this instanceof CountedCompleter) ?
ForkJoinPool.common.externalHelpComplete(
(CountedCompleter<?>)this, 0) :
ForkJoinPool.common.tryExternalUnpush(this) ?
doExec() : 0)) >= 0) {
long ns, ms; // measure in nanosecs, but wait in millisecs
while ((s = status) >= 0 &&
(ns = deadline - System.nanoTime()) > 0L) {
if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
(s = (int)STATUS.getAndBitwiseOr(this, SIGNAL)) >= 0) {
synchronized (this) {
if (status >= 0)
wait(ms); // OK to throw InterruptedException
else
notifyAll();
}
}
}
}
}
if (s >= 0)
throw new TimeoutException();
else if ((s & THROWN) != 0)
throw new ExecutionException(getThrowableException());
else if ((s & ABNORMAL) != 0)
throw new CancellationException();
else
return getRawResult();
}
/**
* Joins this task, without returning its result or throwing its
* exception. This method may be useful when processing
* collections of tasks when some have been cancelled or otherwise
* known to have aborted.
*/
public final void quietlyJoin() {
doJoin();
}
/**
* Commences performing this task and awaits its completion if
* necessary, without returning its result or throwing its
* exception.
*/
public final void quietlyInvoke() {
doInvoke();
}
/**
* Possibly executes tasks until the pool hosting the current task
* {@linkplain ForkJoinPool#isQuiescent is quiescent}. This
* method may be of use in designs in which many tasks are forked,
* but none are explicitly joined, instead executing them until
* all are processed.
*/
public static void helpQuiesce() {
Thread t;
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
wt.pool.helpQuiescePool(wt.workQueue);
}
else
ForkJoinPool.quiesceCommonPool();
}
/**
* Resets the internal bookkeeping state of this task, allowing a
* 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.
* This method may be useful when executing
* pre-constructed trees of subtasks in loops.
*
* <p>Upon completion of this method, {@code isDone()} reports
* {@code false}, and {@code getException()} reports {@code
* null}. However, the value returned by {@code getRawResult} is
* unaffected. To clear this value, you can invoke {@code
* setRawResult(null)}.
*/
public void reinitialize() {
if ((status & THROWN) != 0)
clearExceptionalCompletion();
else
status = 0;
}
/**
* Returns the pool hosting the current thread, or {@code null}
* if the current thread is executing outside of any ForkJoinPool.
*
* <p>This method returns {@code null} if and only if {@link
* #inForkJoinPool} returns {@code false}.
*
* @return the pool, or {@code null} if none
*/
public static ForkJoinPool getPool() {
Thread t = Thread.currentThread();
return (t instanceof ForkJoinWorkerThread) ?
((ForkJoinWorkerThread) t).pool : null;
}
/**
* Returns {@code true} if the current thread is a {@link
* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
*
* @return {@code true} if the current thread is a {@link
* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
* or {@code false} otherwise
*/
public static boolean inForkJoinPool() {
return Thread.currentThread() instanceof ForkJoinWorkerThread;
}
/**
* Tries to unschedule this task for execution. This method will
* typically (but is not guaranteed to) succeed if this task is
* the most recently forked task by the current thread, and has
* not commenced executing in another thread. This method may be
* useful when arranging alternative local processing of tasks
* that could have been, but were not, stolen.
*
* @return {@code true} if unforked
*/
public boolean tryUnfork() {
Thread t;
return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) :
ForkJoinPool.common.tryExternalUnpush(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.
*
* @return the number of tasks
*/
public static int getQueuedTaskCount() {
Thread t; ForkJoinPool.WorkQueue q;
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
q = ((ForkJoinWorkerThread)t).workQueue;
else
q = ForkJoinPool.commonSubmitterQueue();
return (q == null) ? 0 : q.queueSize();
}
/**
* 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, or zero if this thread is not
* operating in a ForkJoinPool. 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.
*
* @return the surplus number of tasks, which may be negative
*/
public static int getSurplusQueuedTaskCount() {
return ForkJoinPool.getSurplusQueuedTaskCount();
}
// Extension methods
/**
* 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 {@code null} if not completed
*/
public abstract V getRawResult();
/**
* Forces the given value to be returned as a result. This method
* is designed to support extensions, and should not in general be
* called otherwise.
*
* @param value the value
*/
protected abstract void setRawResult(V value);
/**
* Immediately performs the base action of this task and returns
* true if, upon return from this method, this task is guaranteed
* to have completed normally. This method may return false
* otherwise, to indicate that this task is not necessarily
* complete (or is not known to be complete), for example in
* asynchronous actions that require explicit invocations of
* completion methods. This method may also throw an (unchecked)
* exception to indicate abnormal exit. This method is designed to
* support extensions, and should not in general be called
* otherwise.
*
* @return {@code true} if this task is known to have completed normally
*/
protected abstract boolean exec();
/**
* 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. 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.
*
* @return the next task, or {@code null} if none are available
*/
protected static ForkJoinTask<?> peekNextLocalTask() {
Thread t; ForkJoinPool.WorkQueue q;
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
q = ((ForkJoinWorkerThread)t).workQueue;
else
q = ForkJoinPool.commonSubmitterQueue();
return (q == null) ? null : q.peek();
}
/**
* Unschedules and returns, without executing, the next task
* queued by the current thread but not yet executed, if the
* current thread is operating in a ForkJoinPool. This method is
* designed primarily to support extensions, and is unlikely to be
* useful otherwise.
*
* @return the next task, or {@code null} if none are available
*/
protected static ForkJoinTask<?> pollNextLocalTask() {
Thread t;
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
((ForkJoinWorkerThread)t).workQueue.nextLocalTask() :
null;
}
/**
* If the current thread is operating in a ForkJoinPool,
* 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.
*
* @return a task, or {@code null} if none are available
*/
protected static ForkJoinTask<?> pollTask() {
Thread t; ForkJoinWorkerThread wt;
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
(wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) :
null;
}
/**
* If the current thread is operating in a ForkJoinPool,
* unschedules and returns, without executing, a task externally
* submitted to the pool, if one is available. Availability may be
* transient, so a {@code null} result does not necessarily imply
* quiescence of the pool. This method is designed primarily to
* support extensions, and is unlikely to be useful otherwise.
*
* @return a task, or {@code null} if none are available
* @since 9
*/
protected static ForkJoinTask<?> pollSubmission() {
Thread t;
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
((ForkJoinWorkerThread)t).pool.pollSubmission() : null;
}
// tag operations
/**
* Returns the tag for this task.
*
* @return the tag for this task
* @since 1.8
*/
public final short getForkJoinTaskTag() {
return (short)status;
}
/**
* Atomically sets the tag value for this task and returns the old value.
*
* @param newValue the new tag value
* @return the previous value of the tag
* @since 1.8
*/
public final short setForkJoinTaskTag(short newValue) {
for (int s;;) {
if (STATUS.weakCompareAndSet(this, s = status,
(s & ~SMASK) | (newValue & SMASK)))
return (short)s;
}
}
/**
* Atomically conditionally sets the tag value for this task.
* Among other applications, tags can be used as visit markers
* in tasks operating on graphs, as in methods that check: {@code
* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
* before processing, otherwise exiting because the node has
* already been visited.
*
* @param expect the expected tag value
* @param update the new tag value
* @return {@code true} if successful; i.e., the current value was
* equal to {@code expect} and was changed to {@code update}.
* @since 1.8
*/
public final boolean compareAndSetForkJoinTaskTag(short expect, short update) {
for (int s;;) {
if ((short)(s = status) != expect)
return false;
if (STATUS.weakCompareAndSet(this, s,
(s & ~SMASK) | (update & SMASK)))
return true;
}
}
/**
* Adapter for Runnables. This implements RunnableFuture
* to be compliant with AbstractExecutorService constraints
* when used in ForkJoinPool.
*/
static final class AdaptedRunnable<T> extends ForkJoinTask<T>
implements RunnableFuture<T> {
final Runnable runnable;
T result;
AdaptedRunnable(Runnable runnable, T result) {
if (runnable == null) throw new NullPointerException();
this.runnable = runnable;
this.result = result; // OK to set this even before completion
}
public final T getRawResult() { return result; }
public final void setRawResult(T v) { result = v; }
public final boolean exec() { runnable.run(); return true; }
public final void run() { invoke(); }
public String toString() {
return super.toString() + "[Wrapped task = " + runnable + "]";
}
private static final long serialVersionUID = 5232453952276885070L;
}
/**
* Adapter for Runnables without results.
*/
static final class AdaptedRunnableAction extends ForkJoinTask<Void>
implements RunnableFuture<Void> {
final Runnable runnable;
AdaptedRunnableAction(Runnable runnable) {
if (runnable == null) throw new NullPointerException();
this.runnable = runnable;
}
public final Void getRawResult() { return null; }
public final void setRawResult(Void v) { }
public final boolean exec() { runnable.run(); return true; }
public final void run() { invoke(); }
public String toString() {
return super.toString() + "[Wrapped task = " + runnable + "]";
}
private static final long serialVersionUID = 5232453952276885070L;
}
/**
* Adapter for Runnables in which failure forces worker exception.
*/
static final class RunnableExecuteAction extends ForkJoinTask<Void> {
final Runnable runnable;
RunnableExecuteAction(Runnable runnable) {
if (runnable == null) throw new NullPointerException();
this.runnable = runnable;
}
public final Void getRawResult() { return null; }
public final void setRawResult(Void v) { }
public final boolean exec() { runnable.run(); return true; }
void internalPropagateException(Throwable ex) {
rethrow(ex); // rethrow outside exec() catches.
}
private static final long serialVersionUID = 5232453952276885070L;
}
/**
* Adapter for Callables.
*/
static final class AdaptedCallable<T> extends ForkJoinTask<T>
implements RunnableFuture<T> {
final Callable<? extends T> callable;
T result;
AdaptedCallable(Callable<? extends T> callable) {
if (callable == null) throw new NullPointerException();
this.callable = callable;
}
public final T getRawResult() { return result; }
public final void setRawResult(T v) { result = v; }
public final boolean exec() {
try {
result = callable.call();
return true;
} catch (RuntimeException rex) {
throw rex;
} catch (Exception ex) {
throw new RuntimeException(ex);
}
}
public final void run() { invoke(); }
public String toString() {
return super.toString() + "[Wrapped task = " + callable + "]";
}
private static final long serialVersionUID = 2838392045355241008L;
}
/**
* Returns a new {@code ForkJoinTask} that performs the {@code run}
* method of the given {@code Runnable} as its action, and returns
* a null result upon {@link #join}.
*
* @param runnable the runnable action
* @return the task
*/
public static ForkJoinTask<?> adapt(Runnable runnable) {
return new AdaptedRunnableAction(runnable);
}
/**
* Returns a new {@code ForkJoinTask} that performs the {@code run}
* method of the given {@code Runnable} as its action, and returns
* the given result upon {@link #join}.
*
* @param runnable the runnable action
* @param result the result upon completion
* @param <T> the type of the result
* @return the task
*/
public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
return new AdaptedRunnable<T>(runnable, result);
}
/**
* Returns a new {@code ForkJoinTask} that performs the {@code call}
* method of the given {@code Callable} as its action, and returns
* its result upon {@link #join}, translating any checked exceptions
* encountered into {@code RuntimeException}.
*
* @param callable the callable action
* @param <T> the type of the callable's result
* @return the task
*/
public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
return new AdaptedCallable<T>(callable);
}
// Serialization support
private static final long serialVersionUID = -7721805057305804111L;
/**
* Saves this task to a stream (that is, serializes it).
*
* @param s the stream
* @throws java.io.IOException if an I/O error occurs
* @serialData the current run status and the exception thrown
* during execution, or {@code null} if none
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
s.defaultWriteObject();
s.writeObject(getException());
}
/**
* Reconstitutes this task from a stream (that is, deserializes it).
* @param s the stream
* @throws ClassNotFoundException if the class of a serialized object
* could not be found
* @throws java.io.IOException if an I/O error occurs
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
Object ex = s.readObject();
if (ex != null)
setExceptionalCompletion((Throwable)ex);
}
// VarHandle mechanics
private static final VarHandle STATUS;
static {
try {
MethodHandles.Lookup l = MethodHandles.lookup();
STATUS = l.findVarHandle(ForkJoinTask.class, "status", int.class);
} catch (ReflectiveOperationException e) {
throw new ExceptionInInitializerError(e);
}
}
}
⏎ java/util/concurrent/ForkJoinTask.java
Or download all of them as a single archive file:
File name: java.base-11.0.1-src.zip File size: 8740354 bytes Release date: 2018-11-04 Download
2020-05-29, 205255👍, 0💬
Related Topics: