RecursiveTask (Java Platform SE 8 ) (original) (raw)

• java.lang.Object

• • java.util.concurrent.ForkJoinTask
  • • java.util.concurrent.RecursiveTask

• All Implemented Interfaces:
  Serializable, Future

public abstract class RecursiveTask
extends ForkJoinTask
A recursive result-bearing ForkJoinTask.
For a classic example, here is a task computing Fibonacci numbers:
class Fibonacci extends RecursiveTask<Integer> { final int n; Fibonacci(int n) { this.n = n; } Integer compute() { if (n <= 1) return n; Fibonacci f1 = new Fibonacci(n - 1); f1.fork(); Fibonacci f2 = new Fibonacci(n - 2); return f2.compute() + f1.join(); } }
However, besides being a dumb way to compute Fibonacci functions (there is a simple fast linear algorithm that you'd use in practice), this is likely to perform poorly because the smallest subtasks are too small to be worthwhile splitting up. Instead, as is the case for nearly all fork/join applications, you'd pick some minimum granularity size (for example 10 here) for which you always sequentially solve rather than subdividing.
Since:
1.7
See Also:
Serialized Form

• • Constructor Summary

  Constructors

  Constructor	Description
  RecursiveTask()

  • Method Summary

  All Methods Instance Methods Abstract Methods Concrete Methods

  Modifier and Type	Method	Description
  protected abstract V	compute()	The main computation performed by this task.
  protected boolean	exec()	Implements execution conventions for RecursiveTask.
  V	getRawResult()	Returns the result that would be returned by ForkJoinTask.join(), even if this task completed abnormally, or null if this task is not known to have been completed.
  protected void	setRawResult(V value)	Forces the given value to be returned as a result.

     * ### Methods inherited from class java.util.concurrent.[ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")  
     `[adapt](../../../java/util/concurrent/ForkJoinTask.html#adapt-java.util.concurrent.Callable-), [adapt](../../../java/util/concurrent/ForkJoinTask.html#adapt-java.lang.Runnable-), [adapt](../../../java/util/concurrent/ForkJoinTask.html#adapt-java.lang.Runnable-T-), [cancel](../../../java/util/concurrent/ForkJoinTask.html#cancel-boolean-), [compareAndSetForkJoinTaskTag](../../../java/util/concurrent/ForkJoinTask.html#compareAndSetForkJoinTaskTag-short-short-), [complete](../../../java/util/concurrent/ForkJoinTask.html#complete-V-), [completeExceptionally](../../../java/util/concurrent/ForkJoinTask.html#completeExceptionally-java.lang.Throwable-), [fork](../../../java/util/concurrent/ForkJoinTask.html#fork--), [get](../../../java/util/concurrent/ForkJoinTask.html#get--), [get](../../../java/util/concurrent/ForkJoinTask.html#get-long-java.util.concurrent.TimeUnit-), [getException](../../../java/util/concurrent/ForkJoinTask.html#getException--), [getForkJoinTaskTag](../../../java/util/concurrent/ForkJoinTask.html#getForkJoinTaskTag--), [getPool](../../../java/util/concurrent/ForkJoinTask.html#getPool--), [getQueuedTaskCount](../../../java/util/concurrent/ForkJoinTask.html#getQueuedTaskCount--), [getSurplusQueuedTaskCount](../../../java/util/concurrent/ForkJoinTask.html#getSurplusQueuedTaskCount--), [helpQuiesce](../../../java/util/concurrent/ForkJoinTask.html#helpQuiesce--), [inForkJoinPool](../../../java/util/concurrent/ForkJoinTask.html#inForkJoinPool--), [invoke](../../../java/util/concurrent/ForkJoinTask.html#invoke--), [invokeAll](../../../java/util/concurrent/ForkJoinTask.html#invokeAll-java.util.Collection-), [invokeAll](../../../java/util/concurrent/ForkJoinTask.html#invokeAll-java.util.concurrent.ForkJoinTask...-), [invokeAll](../../../java/util/concurrent/ForkJoinTask.html#invokeAll-java.util.concurrent.ForkJoinTask-java.util.concurrent.ForkJoinTask-), [isCancelled](../../../java/util/concurrent/ForkJoinTask.html#isCancelled--), [isCompletedAbnormally](../../../java/util/concurrent/ForkJoinTask.html#isCompletedAbnormally--), [isCompletedNormally](../../../java/util/concurrent/ForkJoinTask.html#isCompletedNormally--), [isDone](../../../java/util/concurrent/ForkJoinTask.html#isDone--), [join](../../../java/util/concurrent/ForkJoinTask.html#join--), [peekNextLocalTask](../../../java/util/concurrent/ForkJoinTask.html#peekNextLocalTask--), [pollNextLocalTask](../../../java/util/concurrent/ForkJoinTask.html#pollNextLocalTask--), [pollTask](../../../java/util/concurrent/ForkJoinTask.html#pollTask--), [quietlyComplete](../../../java/util/concurrent/ForkJoinTask.html#quietlyComplete--), [quietlyInvoke](../../../java/util/concurrent/ForkJoinTask.html#quietlyInvoke--), [quietlyJoin](../../../java/util/concurrent/ForkJoinTask.html#quietlyJoin--), [reinitialize](../../../java/util/concurrent/ForkJoinTask.html#reinitialize--), [setForkJoinTaskTag](../../../java/util/concurrent/ForkJoinTask.html#setForkJoinTaskTag-short-), [tryUnfork](../../../java/util/concurrent/ForkJoinTask.html#tryUnfork--)`  
     * ### Methods inherited from class java.lang.[Object](../../../java/lang/Object.html "class in java.lang")  
     `[clone](../../../java/lang/Object.html#clone--), [equals](../../../java/lang/Object.html#equals-java.lang.Object-), [finalize](../../../java/lang/Object.html#finalize--), [getClass](../../../java/lang/Object.html#getClass--), [hashCode](../../../java/lang/Object.html#hashCode--), [notify](../../../java/lang/Object.html#notify--), [notifyAll](../../../java/lang/Object.html#notifyAll--), [toString](../../../java/lang/Object.html#toString--), [wait](../../../java/lang/Object.html#wait--), [wait](../../../java/lang/Object.html#wait-long-), [wait](../../../java/lang/Object.html#wait-long-int-)`

• • Constructor Detail

     * #### RecursiveTask  
     public RecursiveTask()  

  • Method Detail

    * #### compute  
    protected abstract [V](../../../java/util/concurrent/RecursiveTask.html "type parameter in RecursiveTask") compute()  
    The main computation performed by this task.  
    Returns:  
    the result of the computation  
    * #### getRawResult  
    public final [V](../../../java/util/concurrent/RecursiveTask.html "type parameter in RecursiveTask") getRawResult()  
    Returns the result that would be returned by [ForkJoinTask.join()](../../../java/util/concurrent/ForkJoinTask.html#join--), even if this task completed abnormally, or `null` if this task is not known to have been completed. This method is designed to aid debugging, as well as to support extensions. Its use in any other context is discouraged.  
    Specified by:  
    `[getRawResult](../../../java/util/concurrent/ForkJoinTask.html#getRawResult--)` in class `[ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")<[V](../../../java/util/concurrent/RecursiveTask.html "type parameter in RecursiveTask")>`  
    Returns:  
    the result, or `null` if not completed  
    * #### setRawResult  
    protected final void setRawResult([V](../../../java/util/concurrent/RecursiveTask.html "type parameter in RecursiveTask") value)  
    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.  
    Specified by:  
    `[setRawResult](../../../java/util/concurrent/ForkJoinTask.html#setRawResult-V-)` in class `[ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")<[V](../../../java/util/concurrent/RecursiveTask.html "type parameter in RecursiveTask")>`  
    Parameters:  
    `value` \- the value  
    * #### exec  
    protected final boolean exec()  
    Implements execution conventions for RecursiveTask.  
    Specified by:  
    `[exec](../../../java/util/concurrent/ForkJoinTask.html#exec--)` in class `[ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")<[V](../../../java/util/concurrent/RecursiveTask.html "type parameter in RecursiveTask")>`  
    Returns:  
    `true` if this task is known to have completed normally

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