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1530 lines
59 KiB
1530 lines
59 KiB
/*
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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*/
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/*
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*
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*
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*
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*
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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.util.Collection;
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import java.util.List;
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import java.util.RandomAccess;
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import java.lang.ref.WeakReference;
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import java.lang.ref.ReferenceQueue;
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import java.util.concurrent.Callable;
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import java.util.concurrent.CancellationException;
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import java.util.concurrent.ExecutionException;
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import java.util.concurrent.Future;
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import java.util.concurrent.RejectedExecutionException;
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import java.util.concurrent.RunnableFuture;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.TimeoutException;
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import java.util.concurrent.locks.ReentrantLock;
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import java.lang.reflect.Constructor;
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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 do 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 java.util.concurrent.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 java.util.concurrent.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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* @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.
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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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* 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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* The status field holds run control status bits packed into a
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* single int to minimize footprint and to ensure atomicity (via
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* CAS). Status is initially zero, and takes on nonnegative
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* values until completed, upon which status (anded with
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* DONE_MASK) holds value NORMAL, CANCELLED, or EXCEPTIONAL. Tasks
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* undergoing blocking waits by other threads have the SIGNAL bit
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* set. Completion of a stolen task with SIGNAL set awakens any
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* waiters via notifyAll. Even though suboptimal for some
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* purposes, we use basic builtin wait/notify to take advantage of
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* "monitor inflation" in JVMs that we would otherwise need to
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* emulate to avoid adding further per-task bookkeeping overhead.
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* We want these monitors to be "fat", i.e., not use biasing or
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* thin-lock techniques, so use some odd coding idioms that tend
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* to avoid them, mainly by arranging that every synchronized
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* block performs a wait, notifyAll or both.
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*
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* These control bits occupy only (some of) the upper half (16
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* bits) of status field. The lower bits are used for user-defined
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* tags.
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*/
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/** The run status of this task */
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volatile int status; // accessed directly by pool and workers
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static final int DONE_MASK = 0xf0000000; // mask out non-completion bits
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static final int NORMAL = 0xf0000000; // must be negative
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static final int CANCELLED = 0xc0000000; // must be < NORMAL
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static final int EXCEPTIONAL = 0x80000000; // must be < CANCELLED
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static final int SIGNAL = 0x00010000; // must be >= 1 << 16
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static final int SMASK = 0x0000ffff; // short bits for tags
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/**
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* Marks completion and wakes up threads waiting to join this
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* task.
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*
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* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
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* @return completion status on exit
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*/
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private int setCompletion(int completion) {
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for (int s;;) {
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if ((s = status) < 0)
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return s;
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if (U.compareAndSwapInt(this, STATUS, s, s | completion)) {
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if ((s >>> 16) != 0)
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synchronized (this) { notifyAll(); }
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return completion;
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}
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}
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}
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/**
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* Primary execution method for stolen tasks. Unless done, calls
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* exec and records status if completed, but doesn't wait for
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* completion otherwise.
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*
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* @return status on exit from this method
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*/
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final int doExec() {
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int s; boolean completed;
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if ((s = status) >= 0) {
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try {
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completed = exec();
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} catch (Throwable rex) {
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return setExceptionalCompletion(rex);
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}
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if (completed)
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s = setCompletion(NORMAL);
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}
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return s;
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}
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/**
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* If not done, sets SIGNAL status and performs Object.wait(timeout).
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* This task may or may not be done on exit. Ignores interrupts.
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*
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* @param timeout using Object.wait conventions.
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*/
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final void internalWait(long timeout) {
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int s;
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if ((s = status) >= 0 && // force completer to issue notify
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U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
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synchronized (this) {
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if (status >= 0)
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try { wait(timeout); } catch (InterruptedException ie) { }
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else
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notifyAll();
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}
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}
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}
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/**
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* Blocks a non-worker-thread until completion.
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* @return status upon completion
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*/
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private int externalAwaitDone() {
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int s = ((this instanceof CountedCompleter) ? // try helping
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ForkJoinPool.common.externalHelpComplete(
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(CountedCompleter<?>)this, 0) :
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ForkJoinPool.common.tryExternalUnpush(this) ? doExec() : 0);
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if (s >= 0 && (s = status) >= 0) {
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boolean interrupted = false;
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do {
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if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
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synchronized (this) {
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if (status >= 0) {
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try {
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wait(0L);
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} catch (InterruptedException ie) {
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interrupted = true;
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}
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}
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else
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notifyAll();
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}
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}
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} while ((s = status) >= 0);
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if (interrupted)
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Thread.currentThread().interrupt();
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}
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return s;
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}
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/**
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* Blocks a non-worker-thread until completion or interruption.
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*/
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private int externalInterruptibleAwaitDone() throws InterruptedException {
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int s;
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if (Thread.interrupted())
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throw new InterruptedException();
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if ((s = status) >= 0 &&
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(s = ((this instanceof CountedCompleter) ?
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ForkJoinPool.common.externalHelpComplete(
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(CountedCompleter<?>)this, 0) :
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ForkJoinPool.common.tryExternalUnpush(this) ? doExec() :
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0)) >= 0) {
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while ((s = status) >= 0) {
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if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
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synchronized (this) {
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if (status >= 0)
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wait(0L);
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else
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notifyAll();
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}
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}
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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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* Implementation for join, get, quietlyJoin. Directly handles
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* only cases of already-completed, external wait, and
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* unfork+exec. Others are relayed to ForkJoinPool.awaitJoin.
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*
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* @return status upon completion
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*/
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private int doJoin() {
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int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
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return (s = status) < 0 ? s :
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((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
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(w = (wt = (ForkJoinWorkerThread)t).workQueue).
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tryUnpush(this) && (s = doExec()) < 0 ? s :
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wt.pool.awaitJoin(w, this, 0L) :
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externalAwaitDone();
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}
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/**
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* Implementation for invoke, quietlyInvoke.
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*
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* @return status upon completion
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*/
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private int doInvoke() {
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int s; Thread t; ForkJoinWorkerThread wt;
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return (s = doExec()) < 0 ? s :
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((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
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(wt = (ForkJoinWorkerThread)t).pool.
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awaitJoin(wt.workQueue, this, 0L) :
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externalAwaitDone();
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}
|
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// Exception table support
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/**
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* Table of exceptions thrown by tasks, to enable reporting by
|
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* callers. Because exceptions are rare, we don't directly keep
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* them with task objects, but instead use a weak ref table. Note
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* that cancellation exceptions don't appear in the table, but are
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* instead recorded as status values.
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*
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* Note: These statics are initialized below in static block.
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*/
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private static final ExceptionNode[] exceptionTable;
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private static final ReentrantLock exceptionTableLock;
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private static final ReferenceQueue<Object> exceptionTableRefQueue;
|
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|
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/**
|
|
* Fixed capacity for exceptionTable.
|
|
*/
|
|
private static final int EXCEPTION_MAP_CAPACITY = 32;
|
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|
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/**
|
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* 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
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* maintains task exceptions long enough for joiners to access
|
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* them, so should never become very large for sustained
|
|
* periods. However, since we do not know when the last joiner
|
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* 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
|
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* pool becomes isQuiescent.
|
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*/
|
|
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) {
|
|
super(task, exceptionTableRefQueue);
|
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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]);
|
|
break;
|
|
}
|
|
if (e.get() == this) // already present
|
|
break;
|
|
}
|
|
} finally {
|
|
lock.unlock();
|
|
}
|
|
s = setCompletion(EXCEPTIONAL);
|
|
}
|
|
return s;
|
|
}
|
|
|
|
/**
|
|
* Records exception and possibly propagates.
|
|
*
|
|
* @return status on exit
|
|
*/
|
|
private int setExceptionalCompletion(Throwable ex) {
|
|
int s = recordExceptionalCompletion(ex);
|
|
if ((s & DONE_MASK) == EXCEPTIONAL)
|
|
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 the given 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() {
|
|
if ((status & DONE_MASK) != EXCEPTIONAL)
|
|
return null;
|
|
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()) {
|
|
Class<? extends Throwable> ec = ex.getClass();
|
|
try {
|
|
Constructor<?> noArgCtor = null;
|
|
Constructor<?>[] cs = ec.getConstructors();// public ctors only
|
|
for (int i = 0; i < cs.length; ++i) {
|
|
Constructor<?> c = cs[i];
|
|
Class<?>[] ps = c.getParameterTypes();
|
|
if (ps.length == 0)
|
|
noArgCtor = c;
|
|
else if (ps.length == 1 && ps[0] == Throwable.class) {
|
|
Throwable wx = (Throwable)c.newInstance(ex);
|
|
return (wx == null) ? ex : wx;
|
|
}
|
|
}
|
|
if (noArgCtor != null) {
|
|
Throwable wx = (Throwable)(noArgCtor.newInstance());
|
|
if (wx != null) {
|
|
wx.initCause(ex);
|
|
return wx;
|
|
}
|
|
}
|
|
} catch (Exception ignore) {
|
|
}
|
|
}
|
|
return ex;
|
|
}
|
|
|
|
/**
|
|
* Poll stale refs and remove them. Call only while holding lock.
|
|
*/
|
|
private static void expungeStaleExceptions() {
|
|
for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
|
|
if (x instanceof ExceptionNode) {
|
|
int hashCode = ((ExceptionNode)x).hashCode;
|
|
ExceptionNode[] t = exceptionTable;
|
|
int i = 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, poll stale refs and remove 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) {
|
|
if (ex != null)
|
|
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 {
|
|
throw (T)t; // rely on vacuous cast
|
|
}
|
|
|
|
/**
|
|
* Throws exception, if any, associated with the given status.
|
|
*/
|
|
private void reportException(int s) {
|
|
if (s == CANCELLED)
|
|
throw new CancellationException();
|
|
if (s == EXCEPTIONAL)
|
|
rethrow(getThrowableException());
|
|
}
|
|
|
|
// 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 {@link #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() & DONE_MASK) != NORMAL)
|
|
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() & DONE_MASK) != NORMAL)
|
|
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() & DONE_MASK) != NORMAL)
|
|
t1.reportException(s1);
|
|
if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL)
|
|
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() < NORMAL && 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() < NORMAL)
|
|
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<?>[tasks.size()]));
|
|
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() < NORMAL && 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() < NORMAL)
|
|
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) {
|
|
return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
|
|
}
|
|
|
|
public final boolean isDone() {
|
|
return status < 0;
|
|
}
|
|
|
|
public final boolean isCancelled() {
|
|
return (status & DONE_MASK) == CANCELLED;
|
|
}
|
|
|
|
/**
|
|
* 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 < NORMAL;
|
|
}
|
|
|
|
/**
|
|
* 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_MASK) == NORMAL;
|
|
}
|
|
|
|
/**
|
|
* 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 & DONE_MASK;
|
|
return ((s >= NORMAL) ? null :
|
|
(s == CANCELLED) ? 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;
|
|
}
|
|
setCompletion(NORMAL);
|
|
}
|
|
|
|
/**
|
|
* 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() {
|
|
setCompletion(NORMAL);
|
|
}
|
|
|
|
/**
|
|
* 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();
|
|
Throwable ex;
|
|
if ((s &= DONE_MASK) == CANCELLED)
|
|
throw new CancellationException();
|
|
if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
|
|
throw new ExecutionException(ex);
|
|
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 &&
|
|
U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
|
|
synchronized (this) {
|
|
if (status >= 0)
|
|
wait(ms); // OK to throw InterruptedException
|
|
else
|
|
notifyAll();
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
if (s >= 0)
|
|
s = status;
|
|
if ((s &= DONE_MASK) != NORMAL) {
|
|
Throwable ex;
|
|
if (s == CANCELLED)
|
|
throw new CancellationException();
|
|
if (s != EXCEPTIONAL)
|
|
throw new TimeoutException();
|
|
if ((ex = getThrowableException()) != null)
|
|
throw new ExecutionException(ex);
|
|
}
|
|
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
|
|
* {@link 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 & DONE_MASK) == EXCEPTIONAL)
|
|
clearExceptionalCompletion();
|
|
else
|
|
status = 0;
|
|
}
|
|
|
|
/**
|
|
* Returns the pool hosting the current task execution, or null
|
|
* if this task is executing outside of any ForkJoinPool.
|
|
*
|
|
* @see #inForkJoinPool
|
|
* @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;
|
|
}
|
|
|
|
// 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.
|
|
*
|
|
* @param tag the tag value
|
|
* @return the previous value of the tag
|
|
* @since 1.8
|
|
*/
|
|
public final short setForkJoinTaskTag(short tag) {
|
|
for (int s;;) {
|
|
if (U.compareAndSwapInt(this, STATUS, s = status,
|
|
(s & ~SMASK) | (tag & 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 e the expected tag value
|
|
* @param tag the new tag value
|
|
* @return {@code true} if successful; i.e., the current value was
|
|
* equal to e and is now tag.
|
|
* @since 1.8
|
|
*/
|
|
public final boolean compareAndSetForkJoinTaskTag(short e, short tag) {
|
|
for (int s;;) {
|
|
if ((short)(s = status) != e)
|
|
return false;
|
|
if (U.compareAndSwapInt(this, STATUS, s,
|
|
(s & ~SMASK) | (tag & SMASK)))
|
|
return true;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Adaptor 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(); }
|
|
private static final long serialVersionUID = 5232453952276885070L;
|
|
}
|
|
|
|
/**
|
|
* Adaptor 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(); }
|
|
private static final long serialVersionUID = 5232453952276885070L;
|
|
}
|
|
|
|
/**
|
|
* Adaptor 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;
|
|
}
|
|
|
|
/**
|
|
* Adaptor 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 (Error err) {
|
|
throw err;
|
|
} catch (RuntimeException rex) {
|
|
throw rex;
|
|
} catch (Exception ex) {
|
|
throw new RuntimeException(ex);
|
|
}
|
|
}
|
|
public final void run() { invoke(); }
|
|
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);
|
|
}
|
|
|
|
// Unsafe mechanics
|
|
private static final sun.misc.Unsafe U;
|
|
private static final long STATUS;
|
|
|
|
static {
|
|
exceptionTableLock = new ReentrantLock();
|
|
exceptionTableRefQueue = new ReferenceQueue<Object>();
|
|
exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
|
|
try {
|
|
U = sun.misc.Unsafe.getUnsafe();
|
|
Class<?> k = ForkJoinTask.class;
|
|
STATUS = U.objectFieldOffset
|
|
(k.getDeclaredField("status"));
|
|
} catch (Exception e) {
|
|
throw new Error(e);
|
|
}
|
|
}
|
|
|
|
}
|