Module java.base

Package java.util.concurrent

Class RecursiveTask<V>

java.lang.Object

java.util.concurrent.ForkJoinTask<V>

java.util.concurrent.RecursiveTask<V>

All Implemented Interfaces:

Serializable, Future<V>

public abstract class RecursiveTask<V>
extends ForkJoinTask<V>

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; }
   protected 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()	Constructor for subclasses to call.

Method Summary

Modifier and Type	Method	Description
protected abstract V	compute()	The main computation performed by this task.
protected final boolean	exec()	Implements execution conventions for RecursiveTask.
final 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 final void	setRawResult(V value)	Forces the given value to be returned as a result.

Methods declared in class java.util.concurrent.ForkJoinTask

adapt, adapt, adapt, cancel, compareAndSetForkJoinTaskTag, complete, completeExceptionally, fork, get, get, getException, getForkJoinTaskTag, getPool, getQueuedTaskCount, getSurplusQueuedTaskCount, helpQuiesce, inForkJoinPool, invoke, invokeAll, invokeAll, invokeAll, isCancelled, isCompletedAbnormally, isCompletedNormally, isDone, join, peekNextLocalTask, pollNextLocalTask, pollSubmission, pollTask, quietlyComplete, quietlyInvoke, quietlyJoin, reinitialize, setForkJoinTaskTag, tryUnfork

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

RecursiveTask

public RecursiveTask()

Constructor for subclasses to call.

Method Details

compute

protected abstract V compute()

The main computation performed by this task.

Returns:

the result of the computation

getRawResult

public final V getRawResult()

Description copied from class: ForkJoinTask

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. This method is designed to aid debugging, as well as to support extensions. Its use in any other context is discouraged.

Specified by:

getRawResult in class ForkJoinTask<V>

Returns:

the result, or null if not completed

setRawResult

protected final void setRawResult(V value)

Description copied from class: ForkJoinTask

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 in class ForkJoinTask<V>

Parameters:

value - the value

exec

protected final boolean exec()

Implements execution conventions for RecursiveTask.

Specified by:

exec in class ForkJoinTask<V>

Returns:

true if this task is known to have completed normally