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1861 lines
73 KiB
Java
1861 lines
73 KiB
Java
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* This file is available under and governed by the GNU General Public
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* License version 2 only, as published by the Free Software Foundation.
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* However, the following notice accompanied the original version of this
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* file:
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*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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*/
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package java.util.concurrent;
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import java.io.Serializable;
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import java.lang.reflect.Constructor;
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import java.util.Collection;
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import java.util.List;
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import java.util.Objects;
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import java.util.RandomAccess;
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import java.util.concurrent.locks.LockSupport;
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import jdk.internal.misc.Unsafe;
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/**
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* Abstract base class for tasks that run within a {@link ForkJoinPool}.
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* A {@code ForkJoinTask} is a thread-like entity that is much
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* lighter weight than a normal thread. Huge numbers of tasks and
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* subtasks may be hosted by a small number of actual threads in a
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* ForkJoinPool, at the price of some usage limitations.
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*
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* <p>A "main" {@code ForkJoinTask} begins execution when it is
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* explicitly submitted to a {@link ForkJoinPool}, or, if not already
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* engaged in a ForkJoin computation, commenced in the {@link
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* ForkJoinPool#commonPool()} via {@link #fork}, {@link #invoke}, or
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* related methods. Once started, it will usually in turn start other
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* subtasks. As indicated by the name of this class, many programs
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* using {@code ForkJoinTask} employ only methods {@link #fork} and
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* {@link #join}, or derivatives such as {@link
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* #invokeAll(ForkJoinTask...) invokeAll}. However, this class also
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* provides a number of other methods that can come into play in
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* advanced usages, as well as extension mechanics that allow support
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* of new forms of fork/join processing.
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*
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* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
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* The efficiency of {@code ForkJoinTask}s stems from a set of
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* restrictions (that are only partially statically enforceable)
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* reflecting their main use as computational tasks calculating pure
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* functions or operating on purely isolated objects. The primary
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* coordination mechanisms are {@link #fork}, that arranges
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* asynchronous execution, and {@link #join}, that doesn't proceed
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* until the task's result has been computed. Computations should
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* ideally avoid {@code synchronized} methods or blocks, and should
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* minimize other blocking synchronization apart from joining other
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* tasks or using synchronizers such as Phasers that are advertised to
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* cooperate with fork/join scheduling. Subdividable tasks should also
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* not perform blocking I/O, and should ideally access variables that
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* are completely independent of those accessed by other running
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* tasks. These guidelines are loosely enforced by not permitting
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* checked exceptions such as {@code IOExceptions} to be
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* thrown. However, computations may still encounter unchecked
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* exceptions, that are rethrown to callers attempting to join
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* them. These exceptions may additionally include {@link
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* RejectedExecutionException} stemming from internal resource
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* exhaustion, such as failure to allocate internal task
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* queues. Rethrown exceptions behave in the same way as regular
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* exceptions, but, when possible, contain stack traces (as displayed
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* for example using {@code ex.printStackTrace()}) of both the thread
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* that initiated the computation as well as the thread actually
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* encountering the exception; minimally only the latter.
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*
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* <p>It is possible to define and use ForkJoinTasks that may block,
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* but doing so requires three further considerations: (1) Completion
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* of few if any <em>other</em> tasks should be dependent on a task
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* that blocks on external synchronization or I/O. Event-style async
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* tasks that are never joined (for example, those subclassing {@link
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* CountedCompleter}) often fall into this category. (2) To minimize
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* resource impact, tasks should be small; ideally performing only the
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* (possibly) blocking action. (3) Unless the {@link
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* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
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* blocked tasks is known to be less than the pool's {@link
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* ForkJoinPool#getParallelism} level, the pool cannot guarantee that
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* enough threads will be available to ensure progress or good
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* performance.
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*
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* <p>The primary method for awaiting completion and extracting
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* results of a task is {@link #join}, but there are several variants:
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* The {@link Future#get} methods support interruptible and/or timed
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* waits for completion and report results using {@code Future}
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* conventions. Method {@link #invoke} is semantically
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* equivalent to {@code fork(); join()} but always attempts to begin
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* execution in the current thread. The "<em>quiet</em>" forms of
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* these methods do not extract results or report exceptions. These
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* may be useful when a set of tasks are being executed, and you need
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* to delay processing of results or exceptions until all complete.
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* Method {@code invokeAll} (available in multiple versions)
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* performs the most common form of parallel invocation: forking a set
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* of tasks and joining them all.
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*
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* <p>In the most typical usages, a fork-join pair act like a call
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* (fork) and return (join) from a parallel recursive function. As is
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* the case with other forms of recursive calls, returns (joins)
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* should be performed innermost-first. For example, {@code a.fork();
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* b.fork(); b.join(); a.join();} is likely to be substantially more
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* efficient than joining {@code a} before {@code b}.
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*
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* <p>The execution status of tasks may be queried at several levels
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* of detail: {@link #isDone} is true if a task completed in any way
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* (including the case where a task was cancelled without executing);
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* {@link #isCompletedNormally} is true if a task completed without
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* cancellation or encountering an exception; {@link #isCancelled} is
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* true if the task was cancelled (in which case {@link #getException}
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* returns a {@link CancellationException}); and
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* {@link #isCompletedAbnormally} is true if a task was either
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* cancelled or encountered an exception, in which case {@link
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* #getException} will return either the encountered exception or
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* {@link CancellationException}.
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*
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* <p>The ForkJoinTask class is not usually directly subclassed.
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* Instead, you subclass one of the abstract classes that support a
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* particular style of fork/join processing, typically {@link
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* RecursiveAction} for most computations that do not return results,
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* {@link RecursiveTask} for those that do, and {@link
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* CountedCompleter} for those in which completed actions trigger
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* other actions. Normally, a concrete ForkJoinTask subclass declares
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* fields comprising its parameters, established in a constructor, and
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* then defines a {@code compute} method that somehow uses the control
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* methods supplied by this base class.
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*
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* <p>Method {@link #join} and its variants are appropriate for use
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* only when completion dependencies are acyclic; that is, the
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* parallel computation can be described as a directed acyclic graph
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* (DAG). Otherwise, executions may encounter a form of deadlock as
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* tasks cyclically wait for each other. However, this framework
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* supports other methods and techniques (for example the use of
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* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
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* may be of use in constructing custom subclasses for problems that
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* are not statically structured as DAGs. To support such usages, a
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* ForkJoinTask may be atomically <em>tagged</em> with a {@code short}
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* value using {@link #setForkJoinTaskTag} or {@link
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* #compareAndSetForkJoinTaskTag} and checked using {@link
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* #getForkJoinTaskTag}. The ForkJoinTask implementation does not use
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* these {@code protected} methods or tags for any purpose, but they
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* may be of use in the construction of specialized subclasses. For
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* example, parallel graph traversals can use the supplied methods to
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* avoid revisiting nodes/tasks that have already been processed.
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* (Method names for tagging are bulky in part to encourage definition
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* of methods that reflect their usage patterns.)
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*
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* <p>Most base support methods are {@code final}, to prevent
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* overriding of implementations that are intrinsically tied to the
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* underlying lightweight task scheduling framework. Developers
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* creating new basic styles of fork/join processing should minimally
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* implement {@code protected} methods {@link #exec}, {@link
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* #setRawResult}, and {@link #getRawResult}, while also introducing
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* an abstract computational method that can be implemented in its
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* subclasses, possibly relying on other {@code protected} methods
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* provided by this class.
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*
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* <p>ForkJoinTasks should perform relatively small amounts of
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* computation. Large tasks should be split into smaller subtasks,
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* usually via recursive decomposition. As a very rough rule of thumb,
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* a task should perform more than 100 and less than 10000 basic
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* computational steps, and should avoid indefinite looping. If tasks
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* are too big, then parallelism cannot improve throughput. If too
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* small, then memory and internal task maintenance overhead may
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* overwhelm processing.
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*
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* <p>This class provides {@code adapt} methods for {@link Runnable}
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* and {@link Callable}, that may be of use when mixing execution of
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* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
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* of this form, consider using a pool constructed in <em>asyncMode</em>.
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*
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* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
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* used in extensions such as remote execution frameworks. It is
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* sensible to serialize tasks only before or after, but not during,
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* execution. Serialization is not relied on during execution itself.
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*
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* @param <V> the type of the result of the task
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*
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* @since 1.7
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* @author Doug Lea
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*/
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public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
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/*
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* See the internal documentation of class ForkJoinPool for a
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* general implementation overview. ForkJoinTasks are mainly
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* responsible for maintaining their "status" field amidst relays
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* to methods in ForkJoinWorkerThread and ForkJoinPool, along with
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* recording and reporting exceptions. The status field mainly
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* holds bits recording completion status. Note that there is no
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* status bit representing "running", recording whether incomplete
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* tasks are queued vs executing. However these cases can be
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* distinguished in subclasses of InterruptibleTask that adds this
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* capability by recording the running thread. Cancellation is
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* recorded in status bits (ABNORMAL but not THROWN), but reported
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* in joining methods by throwing an exception. Other exceptions
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* of completed (THROWN) tasks are recorded in the "aux" field,
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* but are reconstructed (in getException) to produce more useful
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* stack traces when reported. Sentinels for interruptions or
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* timeouts while waiting for completion are not recorded as
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* status bits but are included in return values of methods in
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* which they occur.
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*
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* The methods of this class are more-or-less layered into
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* (1) basic status maintenance
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* (2) execution and awaiting completion
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* (3) user-level methods that additionally report results.
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* (4) Subclasses for adaptors and internal usages
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* This is sometimes hard to see because this file orders exported
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* methods in a way that flows well in javadocs.
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*/
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/**
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* Nodes for threads waiting for completion, or holding a thrown
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* exception (never both). Waiting threads prepend nodes
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* Treiber-stack-style. Signallers detach and unpark
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* waiters. Cancelled waiters try to unsplice.
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*/
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static final class Aux {
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Thread thread; // thrower or waiter
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final Throwable ex;
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Aux next; // accessed only via memory-acquire chains
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Aux(Thread thread, Throwable ex) {
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this.thread = thread;
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this.ex = ex;
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}
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final boolean casNext(Aux c, Aux v) { // used only in cancellation
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return U.compareAndSetReference(this, NEXT, c, v);
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}
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private static final Unsafe U;
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private static final long NEXT;
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static {
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U = Unsafe.getUnsafe();
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NEXT = U.objectFieldOffset(Aux.class, "next");
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}
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}
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/*
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* The status field holds bits packed into a single int to ensure
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* atomicity. Status is initially zero, and takes on nonnegative
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* values until completed, upon which it holds (sign bit) DONE,
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* possibly with ABNORMAL (cancelled or exceptional) and THROWN
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* (in which case an exception has been stored). A value of
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* ABNORMAL without DONE signifies an interrupted wait. These
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* control bits occupy only (some of) the upper half (16 bits) of
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* status field. The lower bits are used for user-defined tags.
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*/
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static final int DONE = 1 << 31; // must be negative
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static final int ABNORMAL = 1 << 16;
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static final int THROWN = 1 << 17;
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static final int HAVE_EXCEPTION = DONE | ABNORMAL | THROWN;
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static final int MARKER = 1 << 30; // utility marker
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static final int SMASK = 0xffff; // short bits for tags
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static final int UNCOMPENSATE = 1 << 16; // helpJoin sentinel
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// Fields
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/** @serial */
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volatile int status; // accessed directly by pool and workers
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private transient volatile Aux aux; // either waiters or thrown Exception
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// Support for atomic operations
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private static final Unsafe U;
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private static final long STATUS;
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private static final long AUX;
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private int getAndBitwiseOrStatus(int v) {
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return U.getAndBitwiseOrInt(this, STATUS, v);
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}
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private boolean casStatus(int c, int v) {
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return U.compareAndSetInt(this, STATUS, c, v);
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}
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// Support for waiting and signalling
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private boolean casAux(Aux c, Aux v) {
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return U.compareAndSetReference(this, AUX, c, v);
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}
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private Aux compareAndExchangeAux(Aux c, Aux v) {
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return (Aux)U.compareAndExchangeReference(this, AUX, c, v);
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}
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/** Removes and unparks waiters */
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private void signalWaiters() {
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for (Aux a = aux;;) {
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if (a == null || a.ex != null)
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break;
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if (a == (a = compareAndExchangeAux(a, null))) {
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do { // detach entire list
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LockSupport.unpark(a.thread);
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} while ((a = a.next) != null);
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break;
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}
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}
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}
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/**
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* Sets DONE status and wakes up threads waiting to join this task.
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*/
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private void setDone() {
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getAndBitwiseOrStatus(DONE);
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signalWaiters();
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}
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/**
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* Sets ABNORMAL DONE status unless already done, and wakes up threads
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* waiting to join this task.
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* @return previous status
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*/
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final int trySetCancelled() {
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int s;
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for (;;) {
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if ((s = status) < 0)
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break;
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if (casStatus(s, s | (DONE | ABNORMAL))) {
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signalWaiters();
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break;
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}
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}
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return s;
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}
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/**
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* Records exception and sets ABNORMAL THROWN DONE status unless
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* already done, and wakes up threads waiting to join this task.
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* If losing a race with setDone or trySetCancelled, the exception
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* may be recorded but not reported.
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*
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* @return true if set
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*/
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final boolean trySetThrown(Throwable ex) {
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int s;
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boolean set = false, installed = false;
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if ((s = status) >= 0) {
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Aux a, p = null, h = new Aux(Thread.currentThread(), ex);
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do {
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if (!installed && ((a = aux) == null || a.ex == null) &&
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(installed = casAux(a, h)))
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p = a; // list of waiters replaced by h
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if (installed && (set = casStatus(s, s | HAVE_EXCEPTION)))
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break;
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} while ((s = status) >= 0);
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for (; p != null; p = p.next)
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LockSupport.unpark(p.thread);
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}
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return set;
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}
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/**
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* Overridable action on setting exception
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*/
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void onAuxExceptionSet(Throwable ex) {
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}
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/**
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* Tries to set exception, if so invoking onAuxExceptionSet
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*/
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final void trySetException(Throwable ex) {
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if (trySetThrown(ex))
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onAuxExceptionSet(ex);
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}
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/*
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* Waits for signal, interrupt, timeout, or pool termination.
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*
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* @param pool if nonnull, the pool of ForkJoinWorkerThread caller
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* @param compensation result from a helping method
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* @param interruptible if wait is interruptible
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* @param deadline if nonzero, timeout deadline
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* @return ABNORMAL if interrupted, 0 on timeout, else status on exit
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*/
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private int awaitDone(ForkJoinPool pool, int compensation,
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boolean interruptible, long deadline) {
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int s;
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if ((s = status) >= 0) {
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Aux node = null;
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try { // spinwait if out of memory
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node = new Aux(Thread.currentThread(), null);
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} catch (OutOfMemoryError ex) {
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}
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boolean queued = false;
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for (Aux a;;) { // try to install node
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if ((s = status) < 0)
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break;
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else if (node == null)
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Thread.onSpinWait();
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else if (((a = aux) == null || a.ex == null) &&
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(queued = casAux(node.next = a, node)))
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break;
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}
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if (queued) { // await signal or interrupt
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LockSupport.setCurrentBlocker(this);
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int interrupts = 0; // < 0 : throw; > 0 : re-interrupt
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for (;;) {
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if ((s = status) < 0)
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break;
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else if (interrupts < 0) {
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s = ABNORMAL; // interrupted and not done
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break;
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}
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else if (Thread.interrupted()) {
|
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if (!ForkJoinPool.poolIsStopping(pool))
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interrupts = interruptible ? -1 : 1;
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else {
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interrupts = 1; // re-assert if cleared
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try {
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cancel(true);
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} catch (Throwable ignore) {
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}
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}
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}
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else if (deadline != 0L) {
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long ns;
|
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if ((ns = deadline - System.nanoTime()) <= 0) {
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s = 0;
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break;
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}
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LockSupport.parkNanos(ns);
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}
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else
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LockSupport.park();
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}
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node.thread = null; // help clean aux; raciness OK
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clean: for (Aux a;;) { // remove node if still present
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if ((a = aux) == null || a.ex != null)
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break;
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for (Aux prev = null;;) {
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Aux next = a.next;
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if (a == node) {
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if (prev != null)
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prev.casNext(prev, next);
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else if (casAux(a, next))
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break clean;
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break; // check for failed or stale CAS
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}
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prev = a;
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if ((a = next) == null)
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break clean; // not found
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}
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}
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LockSupport.setCurrentBlocker(null);
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if (interrupts > 0)
|
|
Thread.currentThread().interrupt();
|
|
}
|
|
}
|
|
if (compensation == UNCOMPENSATE && pool != null)
|
|
pool.uncompensate();
|
|
return s;
|
|
}
|
|
|
|
/**
|
|
* Tries applicable helping steps while joining this task,
|
|
* otherwise invokes blocking version of awaitDone. Called only
|
|
* when pre-checked not to be done, and pre-screened for
|
|
* interrupts and timeouts, if applicable.
|
|
*
|
|
* @param interruptible if wait is interruptible
|
|
* @param deadline if nonzero, timeout deadline
|
|
* @return ABNORMAL if interrupted, else status on exit
|
|
*/
|
|
private int awaitDone(boolean interruptible, long deadline) {
|
|
ForkJoinWorkerThread wt; ForkJoinPool p; ForkJoinPool.WorkQueue q;
|
|
Thread t; boolean internal; int s;
|
|
if (internal =
|
|
(t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
|
|
p = (wt = (ForkJoinWorkerThread)t).pool;
|
|
q = wt.workQueue;
|
|
}
|
|
else
|
|
q = ForkJoinPool.externalQueue(p = ForkJoinPool.common);
|
|
return (((s = (p == null) ? 0 :
|
|
((this instanceof CountedCompleter) ?
|
|
p.helpComplete(this, q, internal) :
|
|
(this instanceof InterruptibleTask) && !internal ? status :
|
|
p.helpJoin(this, q, internal))) < 0)) ? s :
|
|
awaitDone(internal ? p : null, s, interruptible, deadline);
|
|
}
|
|
|
|
/**
|
|
* Runs a task body: Unless done, calls exec and records status if
|
|
* completed, but doesn't wait for completion otherwise.
|
|
*/
|
|
final void doExec() {
|
|
if (status >= 0) {
|
|
boolean completed = false;
|
|
try {
|
|
completed = exec();
|
|
} catch (Throwable rex) {
|
|
trySetException(rex);
|
|
}
|
|
if (completed)
|
|
setDone();
|
|
}
|
|
}
|
|
|
|
// Reporting Exceptions
|
|
|
|
/**
|
|
* 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.
|
|
*
|
|
* @param asExecutionException true if wrap as ExecutionException
|
|
* @return the exception, or null if none
|
|
*/
|
|
private Throwable getException(boolean asExecutionException) {
|
|
int s; Throwable ex; Aux a;
|
|
if ((s = status) >= 0 || (s & ABNORMAL) == 0)
|
|
return null;
|
|
else if ((s & THROWN) == 0 || (a = aux) == null || (ex = a.ex) == null) {
|
|
ex = new CancellationException();
|
|
if (!asExecutionException || !(this instanceof InterruptibleTask))
|
|
return ex; // else wrap below
|
|
}
|
|
else if (a.thread != Thread.currentThread()) {
|
|
try {
|
|
Constructor<?> noArgCtor = null, oneArgCtor = null;
|
|
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) {
|
|
oneArgCtor = c;
|
|
break;
|
|
}
|
|
}
|
|
if (oneArgCtor != null)
|
|
ex = (Throwable)oneArgCtor.newInstance(ex);
|
|
else if (noArgCtor != null) {
|
|
Throwable rx = (Throwable)noArgCtor.newInstance();
|
|
rx.initCause(ex);
|
|
ex = rx;
|
|
}
|
|
} catch (Exception ignore) {
|
|
}
|
|
}
|
|
return (asExecutionException) ? new ExecutionException(ex) : ex;
|
|
}
|
|
|
|
/**
|
|
* Throws thrown exception, or CancellationException if none
|
|
* recorded.
|
|
*/
|
|
private void reportException(boolean asExecutionException) {
|
|
ForkJoinTask.<RuntimeException>
|
|
uncheckedThrow(getException(asExecutionException));
|
|
}
|
|
|
|
/**
|
|
* A version of "sneaky throw" to relay exceptions in other
|
|
* contexts.
|
|
*/
|
|
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. If argument null, throws
|
|
* CancellationException.
|
|
*/
|
|
@SuppressWarnings("unchecked") static <T extends Throwable>
|
|
void uncheckedThrow(Throwable t) throws T {
|
|
if (t == null)
|
|
t = new CancellationException();
|
|
throw (T)t; // rely on vacuous cast
|
|
}
|
|
|
|
// Utilities shared among ForkJoinTask, ForkJoinPool
|
|
|
|
/**
|
|
* Sets MARKER bit, returning nonzero if previously set
|
|
*/
|
|
final int setForkJoinTaskStatusMarkerBit() {
|
|
return getAndBitwiseOrStatus(MARKER) & MARKER;
|
|
}
|
|
|
|
/**
|
|
* Returns nonzero if MARKER bit set.
|
|
*/
|
|
final int getForkJoinTaskStatusMarkerBit() {
|
|
return status & MARKER;
|
|
}
|
|
|
|
// public methods
|
|
|
|
/**
|
|
* Constructor for subclasses to call.
|
|
*/
|
|
public ForkJoinTask() {}
|
|
|
|
/**
|
|
* 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; ForkJoinWorkerThread wt;
|
|
ForkJoinPool p; ForkJoinPool.WorkQueue q; boolean internal;
|
|
if (internal =
|
|
(t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
|
|
q = (wt = (ForkJoinWorkerThread)t).workQueue;
|
|
p = wt.pool;
|
|
}
|
|
else
|
|
q = (p = ForkJoinPool.common).externalSubmissionQueue();
|
|
q.push(this, p, internal);
|
|
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 = status) < 0 ? s : awaitDone(false, 0L)) & ABNORMAL) != 0)
|
|
reportException(false);
|
|
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() {
|
|
doExec();
|
|
return join();
|
|
}
|
|
|
|
/**
|
|
* 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;
|
|
if (t1 == null || t2 == null)
|
|
throw new NullPointerException();
|
|
t2.fork();
|
|
t1.doExec();
|
|
if ((((s1 = t1.status) < 0 ? s1 :
|
|
t1.awaitDone(false, 0L)) & ABNORMAL) != 0) {
|
|
t2.cancel(false);
|
|
t1.reportException(false);
|
|
}
|
|
else if ((((s2 = t2.status) < 0 ? s2 :
|
|
t2.awaitDone(false, 0L)) & ABNORMAL) != 0)
|
|
t2.reportException(false);
|
|
}
|
|
|
|
/**
|
|
* 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; int s;
|
|
if ((t = tasks[i]) == null) {
|
|
ex = new NullPointerException();
|
|
break;
|
|
}
|
|
if (i == 0) {
|
|
t.doExec();
|
|
if ((((s = t.status) < 0 ? s :
|
|
t.awaitDone(false, 0L)) & ABNORMAL) != 0)
|
|
ex = t.getException(false);
|
|
break;
|
|
}
|
|
t.fork();
|
|
}
|
|
if (ex == null) {
|
|
for (int i = 1; i <= last; ++i) {
|
|
ForkJoinTask<?> t; int s;
|
|
if ((t = tasks[i]) != null &&
|
|
((((s = t.status) < 0 ? s :
|
|
t.awaitDone(false, 0L)) & ABNORMAL) != 0) &&
|
|
(ex = t.getException(false)) != null)
|
|
break;
|
|
}
|
|
}
|
|
if (ex != null) {
|
|
for (int i = 1; i <= last; ++i) {
|
|
ForkJoinTask<?> t;
|
|
if ((t = tasks[i]) != null)
|
|
t.cancel(false);
|
|
}
|
|
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; // nearly same as array version
|
|
for (int i = last; i >= 0; --i) {
|
|
ForkJoinTask<?> t; int s;
|
|
if ((t = ts.get(i)) == null) {
|
|
ex = new NullPointerException();
|
|
break;
|
|
}
|
|
if (i == 0) {
|
|
t.doExec();
|
|
if ((((s = t.status) < 0 ? s :
|
|
t.awaitDone(false, 0L)) & ABNORMAL) != 0)
|
|
ex = t.getException(false);
|
|
break;
|
|
}
|
|
t.fork();
|
|
}
|
|
if (ex == null) {
|
|
for (int i = 1; i <= last; ++i) {
|
|
ForkJoinTask<?> t; int s;
|
|
if ((t = ts.get(i)) != null &&
|
|
((((s = t.status) < 0 ? s :
|
|
t.awaitDone(false, 0L)) & ABNORMAL) != 0) &&
|
|
(ex = t.getException(false)) != null)
|
|
break;
|
|
}
|
|
}
|
|
if (ex != null) {
|
|
for (int i = 1; i <= last; ++i) {
|
|
ForkJoinTask<?> t;
|
|
if ((t = ts.get(i)) != null)
|
|
t.cancel(false);
|
|
}
|
|
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 = trySetCancelled();
|
|
return (s >= 0 || (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;
|
|
}
|
|
|
|
/**
|
|
* @since 19
|
|
*/
|
|
@Override
|
|
public State state() {
|
|
int s = status;
|
|
return (s >= 0) ? State.RUNNING :
|
|
((s & (DONE | ABNORMAL)) == DONE) ? State.SUCCESS:
|
|
((s & (ABNORMAL | THROWN)) == (ABNORMAL | THROWN)) ? State.FAILED :
|
|
State.CANCELLED;
|
|
}
|
|
|
|
/**
|
|
* @since 19
|
|
*/
|
|
@Override
|
|
public V resultNow() {
|
|
int s = status;
|
|
if ((s & DONE) == 0)
|
|
throw new IllegalStateException("Task has not completed");
|
|
if ((s & ABNORMAL) != 0) {
|
|
if ((s & THROWN) != 0)
|
|
throw new IllegalStateException("Task completed with exception");
|
|
else
|
|
throw new IllegalStateException("Task was cancelled");
|
|
}
|
|
return getRawResult();
|
|
}
|
|
|
|
/**
|
|
* @since 19
|
|
*/
|
|
@Override
|
|
public Throwable exceptionNow() {
|
|
Throwable ex;
|
|
if ((status & HAVE_EXCEPTION) != HAVE_EXCEPTION ||
|
|
(ex = getException(false)) == null)
|
|
throw new IllegalStateException();
|
|
return ex;
|
|
}
|
|
|
|
/**
|
|
* 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() {
|
|
return getException(false);
|
|
}
|
|
|
|
/**
|
|
* 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) {
|
|
trySetException((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) {
|
|
trySetException(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 stat = status;
|
|
int s = ((stat < 0) ? stat :
|
|
(Thread.interrupted()) ? ABNORMAL :
|
|
awaitDone(true, 0L));
|
|
if (s == ABNORMAL)
|
|
throw new InterruptedException();
|
|
else if ((s & ABNORMAL) != 0)
|
|
reportException(true);
|
|
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 {
|
|
long nanos = unit.toNanos(timeout);
|
|
int stat = status;
|
|
int s = ((stat < 0) ? stat :
|
|
(Thread.interrupted()) ? ABNORMAL :
|
|
(nanos <= 0L) ? 0 :
|
|
awaitDone(true, (System.nanoTime() + nanos) | 1L));
|
|
if (s == ABNORMAL)
|
|
throw new InterruptedException();
|
|
else if (s >= 0)
|
|
throw new TimeoutException();
|
|
else if ((s & ABNORMAL) != 0)
|
|
reportException(true);
|
|
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() {
|
|
if (status >= 0)
|
|
awaitDone(false, 0L);
|
|
}
|
|
|
|
/**
|
|
* Commences performing this task and awaits its completion if
|
|
* necessary, without returning its result or throwing its
|
|
* exception.
|
|
*/
|
|
public final void quietlyInvoke() {
|
|
doExec();
|
|
if (status >= 0)
|
|
awaitDone(false, 0L);
|
|
}
|
|
|
|
/**
|
|
* Tries to join this task, returning true if it completed
|
|
* (possibly exceptionally) before the given timeout elapsed and
|
|
* the current thread has not been interrupted.
|
|
*
|
|
* @param timeout the maximum time to wait
|
|
* @param unit the time unit of the timeout argument
|
|
* @return true if this task completed
|
|
* @throws InterruptedException if the current thread was
|
|
* interrupted while waiting
|
|
* @since 19
|
|
*/
|
|
public final boolean quietlyJoin(long timeout, TimeUnit unit)
|
|
throws InterruptedException {
|
|
long nanos = unit.toNanos(timeout);
|
|
int stat = status;
|
|
int s = ((stat < 0) ? stat :
|
|
(Thread.interrupted()) ? ABNORMAL :
|
|
(nanos <= 0L) ? 0 :
|
|
awaitDone(true, (System.nanoTime() + nanos) | 1L));
|
|
if (s == ABNORMAL)
|
|
throw new InterruptedException();
|
|
return (s < 0);
|
|
}
|
|
|
|
/**
|
|
* Tries to join this task, returning true if it completed
|
|
* (possibly exceptionally) before the given timeout elapsed.
|
|
*
|
|
* @param timeout the maximum time to wait
|
|
* @param unit the time unit of the timeout argument
|
|
* @return true if this task completed
|
|
* @since 19
|
|
*/
|
|
public final boolean quietlyJoinUninterruptibly(long timeout,
|
|
TimeUnit unit) {
|
|
int s;
|
|
long nanos = unit.toNanos(timeout);
|
|
if ((s = status) >= 0 && nanos > 0L)
|
|
s = awaitDone(false, (System.nanoTime() + nanos) | 1L);
|
|
return (s < 0);
|
|
}
|
|
|
|
/**
|
|
* Utility for possibly-timed ForkJoinPool.invokeAll
|
|
*/
|
|
final void quietlyJoinPoolInvokeAllTask(long deadline)
|
|
throws InterruptedException {
|
|
int s;
|
|
if ((s = status) >= 0) {
|
|
if (Thread.interrupted())
|
|
s = ABNORMAL;
|
|
else if (deadline == 0L || deadline - System.nanoTime() > 0L)
|
|
s = awaitDone(true, deadline);
|
|
if (s == ABNORMAL)
|
|
throw new InterruptedException();
|
|
else if (s >= 0)
|
|
cancel(true);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* 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() {
|
|
ForkJoinPool.helpQuiescePool(null, Long.MAX_VALUE, false);
|
|
}
|
|
|
|
/**
|
|
* 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() {
|
|
aux = null;
|
|
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;
|
|
return (((t = Thread.currentThread()) 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; ForkJoinPool.WorkQueue q; boolean internal;
|
|
if (internal =
|
|
(t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
|
|
q = ((ForkJoinWorkerThread)t).workQueue;
|
|
else
|
|
q = ForkJoinPool.commonQueue();
|
|
return (q != null && q.tryUnpush(this, internal));
|
|
}
|
|
|
|
/**
|
|
* 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.commonQueue();
|
|
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. 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.commonQueue();
|
|
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 w;
|
|
return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
|
|
(w = (ForkJoinWorkerThread)t).pool.nextTaskFor(w.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 (casStatus(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 (casStatus(s, (s & ~SMASK) | (update & SMASK)))
|
|
return true;
|
|
}
|
|
}
|
|
|
|
// Factory methods for adaptors below
|
|
|
|
/**
|
|
* 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);
|
|
}
|
|
|
|
/**
|
|
* 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}. Additionally,
|
|
* invocations of {@code cancel} with {@code mayInterruptIfRunning
|
|
* true} will attempt to interrupt the thread performing the task.
|
|
*
|
|
* @param callable the callable action
|
|
* @param <T> the type of the callable's result
|
|
* @return the task
|
|
*
|
|
* @since 19
|
|
*/
|
|
public static <T> ForkJoinTask<T> adaptInterruptible(Callable<? extends T> callable) {
|
|
return new AdaptedInterruptibleCallable<T>(callable);
|
|
}
|
|
|
|
/**
|
|
* 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}, translating any checked exceptions
|
|
* encountered into {@code RuntimeException}. Additionally,
|
|
* invocations of {@code cancel} with {@code mayInterruptIfRunning
|
|
* true} will attempt to interrupt the thread performing the task.
|
|
*
|
|
* @param runnable the runnable action
|
|
* @param result the result upon completion
|
|
* @param <T> the type of the result
|
|
* @return the task
|
|
*
|
|
* @since 22
|
|
*/
|
|
public static <T> ForkJoinTask<T> adaptInterruptible(Runnable runnable, T result) {
|
|
return new AdaptedInterruptibleRunnable<T>(runnable, result);
|
|
}
|
|
|
|
/**
|
|
* Returns a new {@code ForkJoinTask} that performs the {@code
|
|
* run} method of the given {@code Runnable} as its action, and
|
|
* returns null upon {@link #join}, translating any checked
|
|
* exceptions encountered into {@code RuntimeException}.
|
|
* Additionally, invocations of {@code cancel} with {@code
|
|
* mayInterruptIfRunning true} will attempt to interrupt the
|
|
* thread performing the task.
|
|
*
|
|
* @param runnable the runnable action
|
|
* @return the task
|
|
*
|
|
* @since 22
|
|
*/
|
|
public static ForkJoinTask<?> adaptInterruptible(Runnable runnable) {
|
|
return new AdaptedInterruptibleRunnable<Void>(runnable, null);
|
|
}
|
|
|
|
// 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 {
|
|
Aux a;
|
|
s.defaultWriteObject();
|
|
s.writeObject((a = aux) == null ? null : a.ex);
|
|
}
|
|
|
|
/**
|
|
* 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)
|
|
aux = new Aux(Thread.currentThread(), (Throwable)ex);
|
|
}
|
|
|
|
static {
|
|
U = Unsafe.getUnsafe();
|
|
STATUS = U.objectFieldOffset(ForkJoinTask.class, "status");
|
|
AUX = U.objectFieldOffset(ForkJoinTask.class, "aux");
|
|
Class<?> dep1 = LockSupport.class; // ensure loaded
|
|
Class<?> dep2 = Aux.class;
|
|
}
|
|
|
|
// Special subclasses for adaptors and internal tasks
|
|
|
|
/**
|
|
* 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> {
|
|
@SuppressWarnings("serial") // Conditionally serializable
|
|
final Runnable runnable;
|
|
@SuppressWarnings("serial") // Conditionally serializable
|
|
T result;
|
|
AdaptedRunnable(Runnable runnable, T result) {
|
|
Objects.requireNonNull(runnable);
|
|
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> {
|
|
@SuppressWarnings("serial") // Conditionally serializable
|
|
final Runnable runnable;
|
|
AdaptedRunnableAction(Runnable runnable) {
|
|
Objects.requireNonNull(runnable);
|
|
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 Callables.
|
|
*/
|
|
static final class AdaptedCallable<T> extends ForkJoinTask<T>
|
|
implements RunnableFuture<T> {
|
|
@SuppressWarnings("serial") // Conditionally serializable
|
|
final Callable<? extends T> callable;
|
|
@SuppressWarnings("serial") // Conditionally serializable
|
|
T result;
|
|
AdaptedCallable(Callable<? extends T> callable) {
|
|
Objects.requireNonNull(callable);
|
|
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;
|
|
}
|
|
|
|
/**
|
|
* Tasks with semantics conforming to ExecutorService conventions.
|
|
* Tasks are interruptible when cancelled, including cases of
|
|
* cancellation upon pool termination. In addition to recording
|
|
* the running thread to enable interrupt in cancel(true), the
|
|
* task checks for termination before executing the compute
|
|
* method, to cover shutdown races in which the task has not yet
|
|
* been cancelled on entry and might not otherwise be cancelled by
|
|
* others.
|
|
*/
|
|
abstract static class InterruptibleTask<T> extends ForkJoinTask<T>
|
|
implements RunnableFuture<T> {
|
|
transient volatile Thread runner;
|
|
abstract T compute() throws Exception;
|
|
public final boolean exec() {
|
|
Thread.interrupted();
|
|
Thread t = runner = Thread.currentThread();
|
|
try {
|
|
if ((t instanceof ForkJoinWorkerThread) &&
|
|
ForkJoinPool.poolIsStopping(((ForkJoinWorkerThread)t).pool))
|
|
cancel(true);
|
|
else {
|
|
try {
|
|
if (status >= 0)
|
|
setRawResult(compute());
|
|
} catch (Exception ex) {
|
|
trySetException(ex);
|
|
}
|
|
}
|
|
} finally {
|
|
runner = null;
|
|
}
|
|
return true;
|
|
}
|
|
public boolean cancel(boolean mayInterruptIfRunning) {
|
|
Thread t;
|
|
if (trySetCancelled() >= 0) {
|
|
if (mayInterruptIfRunning && (t = runner) != null) {
|
|
try {
|
|
t.interrupt();
|
|
} catch (Throwable ignore) {
|
|
}
|
|
}
|
|
return true;
|
|
}
|
|
return isCancelled();
|
|
}
|
|
public final void run() { quietlyInvoke(); }
|
|
Object adaptee() { return null; } // for printing and diagnostics
|
|
public String toString() {
|
|
Object a = adaptee();
|
|
String s = super.toString();
|
|
return ((a == null) ? s :
|
|
(s + "[Wrapped task = " + a.toString() + "]"));
|
|
}
|
|
private static final long serialVersionUID = 2838392045355241008L;
|
|
}
|
|
|
|
/**
|
|
* Adapter for Callable-based interruptible tasks.
|
|
*/
|
|
static final class AdaptedInterruptibleCallable<T> extends InterruptibleTask<T> {
|
|
@SuppressWarnings("serial") // Conditionally serializable
|
|
final Callable<? extends T> callable;
|
|
@SuppressWarnings("serial") // Conditionally serializable
|
|
T result;
|
|
AdaptedInterruptibleCallable(Callable<? extends T> callable) {
|
|
Objects.requireNonNull(callable);
|
|
this.callable = callable;
|
|
}
|
|
public final T getRawResult() { return result; }
|
|
public final void setRawResult(T v) { result = v; }
|
|
final T compute() throws Exception { return callable.call(); }
|
|
final Object adaptee() { return callable; }
|
|
private static final long serialVersionUID = 2838392045355241008L;
|
|
}
|
|
|
|
/**
|
|
* Adapter for Runnable-based interruptible tasks.
|
|
*/
|
|
static final class AdaptedInterruptibleRunnable<T> extends InterruptibleTask<T> {
|
|
@SuppressWarnings("serial") // Conditionally serializable
|
|
final Runnable runnable;
|
|
@SuppressWarnings("serial") // Conditionally serializable
|
|
final T result;
|
|
AdaptedInterruptibleRunnable(Runnable runnable, T result) {
|
|
Objects.requireNonNull(runnable);
|
|
this.runnable = runnable;
|
|
this.result = result;
|
|
}
|
|
public final T getRawResult() { return result; }
|
|
public final void setRawResult(T v) { }
|
|
final T compute() { runnable.run(); return result; }
|
|
final Object adaptee() { return runnable; }
|
|
private static final long serialVersionUID = 2838392045355241008L;
|
|
}
|
|
|
|
/**
|
|
* Adapter for Runnables in which failure forces worker exception.
|
|
*/
|
|
static final class RunnableExecuteAction extends InterruptibleTask<Void> {
|
|
@SuppressWarnings("serial") // Conditionally serializable
|
|
final Runnable runnable;
|
|
RunnableExecuteAction(Runnable runnable) {
|
|
Objects.requireNonNull(runnable);
|
|
this.runnable = runnable;
|
|
}
|
|
public final Void getRawResult() { return null; }
|
|
public final void setRawResult(Void v) { }
|
|
final Void compute() { runnable.run(); return null; }
|
|
final Object adaptee() { return runnable; }
|
|
void onAuxExceptionSet(Throwable ex) { // if a handler, invoke it
|
|
Thread t; java.lang.Thread.UncaughtExceptionHandler h;
|
|
if ((h = ((t = Thread.currentThread()).
|
|
getUncaughtExceptionHandler())) != null) {
|
|
try {
|
|
h.uncaughtException(t, ex);
|
|
} catch (Throwable ignore) {
|
|
}
|
|
}
|
|
}
|
|
private static final long serialVersionUID = 5232453952276885070L;
|
|
}
|
|
|
|
/**
|
|
* Task (that is never forked) to hold results for
|
|
* ForkJoinPool.invokeAny, or to report exception if all subtasks
|
|
* fail or are cancelled or the pool is terminating. Both
|
|
* InvokeAnyRoot and InvokeAnyTask objects exist only transiently
|
|
* during invokeAny invocations, so serialization support would be
|
|
* nonsensical and is omitted.
|
|
*/
|
|
@SuppressWarnings("serial")
|
|
static final class InvokeAnyRoot<T> extends InterruptibleTask<T> {
|
|
volatile T result;
|
|
volatile int count; // number of tasks; decremented in case all tasks fail
|
|
InvokeAnyRoot() { }
|
|
final void tryComplete(InvokeAnyTask<T> f, T v, Throwable ex,
|
|
boolean completed) {
|
|
if (f != null && !isDone()) {
|
|
if (ForkJoinPool.poolIsStopping(getPool()))
|
|
trySetCancelled();
|
|
else if (f.setForkJoinTaskStatusMarkerBit() == 0) {
|
|
if (completed) {
|
|
result = v;
|
|
quietlyComplete();
|
|
}
|
|
else if (U.getAndAddInt(this, COUNT, -1) <= 1) {
|
|
if (ex == null)
|
|
trySetCancelled();
|
|
else
|
|
trySetException(ex);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
public final T compute() { return null; } // never forked
|
|
public final T getRawResult() { return result; }
|
|
public final void setRawResult(T v) { }
|
|
|
|
// Common support for timed and untimed versions of invokeAny
|
|
final T invokeAny(Collection<? extends Callable<T>> tasks,
|
|
ForkJoinPool pool, boolean timed, long nanos)
|
|
throws InterruptedException, ExecutionException, TimeoutException {
|
|
if ((count = tasks.size()) <= 0)
|
|
throw new IllegalArgumentException();
|
|
if (pool == null)
|
|
throw new NullPointerException();
|
|
InvokeAnyTask<T> t = null; // list of submitted tasks
|
|
try {
|
|
for (Callable<T> c : tasks)
|
|
pool.execute((ForkJoinTask<?>)
|
|
(t = new InvokeAnyTask<T>(c, this, t)));
|
|
return timed ? get(nanos, TimeUnit.NANOSECONDS) : get();
|
|
} finally {
|
|
for (; t != null; t = t.pred)
|
|
t.onRootCompletion();
|
|
}
|
|
}
|
|
|
|
private static final Unsafe U;
|
|
private static final long COUNT;
|
|
static {
|
|
U = Unsafe.getUnsafe();
|
|
COUNT = U.objectFieldOffset(InvokeAnyRoot.class, "count");
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Task with results in InvokeAnyRoot (and never independently
|
|
* joined).
|
|
*/
|
|
@SuppressWarnings("serial")
|
|
static final class InvokeAnyTask<T> extends InterruptibleTask<Void> {
|
|
final Callable<? extends T> callable;
|
|
final InvokeAnyRoot<T> root;
|
|
final InvokeAnyTask<T> pred; // to traverse on cancellation
|
|
InvokeAnyTask(Callable<T> callable, InvokeAnyRoot<T> root,
|
|
InvokeAnyTask<T> pred) {
|
|
Objects.requireNonNull(callable);
|
|
this.callable = callable;
|
|
this.root = root;
|
|
this.pred = pred;
|
|
}
|
|
final Void compute() throws Exception {
|
|
InvokeAnyRoot<T> r = root;
|
|
T v = null; Throwable ex = null; boolean completed = false;
|
|
if (r != null && !r.isDone()) {
|
|
try {
|
|
v = callable.call();
|
|
completed = true;
|
|
} catch (Exception rex) {
|
|
ex = rex;
|
|
} finally {
|
|
r.tryComplete(this, v, ex, completed);
|
|
}
|
|
}
|
|
return null;
|
|
}
|
|
public final boolean cancel(boolean mayInterruptIfRunning) {
|
|
InvokeAnyRoot<T> r;
|
|
boolean stat = super.cancel(mayInterruptIfRunning);
|
|
if ((r = root) != null)
|
|
r.tryComplete(this, null, null, false);
|
|
return stat;
|
|
}
|
|
final void onRootCompletion() {
|
|
if (!isDone())
|
|
super.cancel(true); // no need for tryComplete
|
|
}
|
|
public final Void getRawResult() { return null; }
|
|
public final void setRawResult(Void v) { }
|
|
final Object adaptee() { return callable; }
|
|
}
|
|
}
|