java.lang.Object
java.util.concurrent.ForkJoinTask<V>
java.util.concurrent.RecursiveTask<V>
- All Implemented Interfaces:
Serializable,Future<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:
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionprotected abstract Vcompute()The main computation performed by this task.protected final booleanexec()Implements execution conventions for RecursiveTask.final VReturns the result that would be returned byForkJoinTask.join(), even if this task completed abnormally, ornullif this task is not known to have been completed.protected final voidsetRawResult(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
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Constructor Details
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RecursiveTask
public RecursiveTask()Constructor for subclasses to call.
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Method Details
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compute
The main computation performed by this task.- Returns:
- the result of the computation
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getRawResult
Description copied from class:ForkJoinTaskReturns the result that would be returned byForkJoinTask.join(), even if this task completed abnormally, ornullif 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:
getRawResultin classForkJoinTask<V>- Returns:
- the result, or
nullif not completed
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setRawResult
Description copied from class:ForkJoinTaskForces 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:
setRawResultin classForkJoinTask<V>- Parameters:
value- the value
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exec
protected final boolean exec()Implements execution conventions for RecursiveTask.- Specified by:
execin classForkJoinTask<V>- Returns:
trueif this task is known to have completed normally
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