java.lang.Object
java.util.concurrent.ForkJoinTask<V>
java.util.concurrent.RecursiveTask<V>
- Type Parameters:
V
- the type of the result of the task
- All Implemented Interfaces:
Serializable
,Future<V>
A recursive result-bearing
ForkJoinTask
.
For example, here is a task-based program for computing Factorials:
import java.util.concurrent.RecursiveTask;
import java.math.BigInteger;
public class Factorial {
static class FactorialTask extends RecursiveTask<BigInteger> {
private final int from, to;
FactorialTask(int from, int to) { this.from = from; this.to = to; }
protected BigInteger compute() {
int range = to - from;
if (range == 0) { // base case
return BigInteger.valueOf(from);
} else if (range == 1) { // too small to parallelize
return BigInteger.valueOf(from).multiply(BigInteger.valueOf(to));
} else { // split in half
int mid = from + range / 2;
FactorialTask leftTask = new FactorialTask(from, mid);
leftTask.fork(); // perform about half the work locally
return new FactorialTask(mid + 1, to).compute()
.multiply(leftTask.join());
}
}
}
static BigInteger factorial(int n) { // uses ForkJoinPool.commonPool()
return (n <= 1) ? BigInteger.ONE : new FactorialTask(1, n).invoke();
}
public static void main(String[] args) {
System.out.println(factorial(Integer.parseInt(args[0])));
}
}
- Since:
- 1.7
- See Also:
-
Nested Class Summary
Nested classes/interfaces declared in interface java.util.concurrent.Future
Future.State
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Constructor Summary
-
Method Summary
Modifier and TypeMethodDescriptionprotected abstract V
compute()
The main computation performed by this task.protected final boolean
exec()
Implements execution conventions for RecursiveTask.final V
Returns the result that would be returned byForkJoinTask.join()
, even if this task completed abnormally, ornull
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, adaptInterruptible, 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, quietlyJoin, quietlyJoinUninterruptibly, reinitialize, setForkJoinTaskTag, tryUnfork
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Methods declared in interface java.util.concurrent.Future
exceptionNow, resultNow, state
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Constructor Details
-
RecursiveTask
public RecursiveTask()Constructor for subclasses to call.
-
-
Method Details
-
compute
The main computation performed by this task.- Returns:
- the result of the computation
-
getRawResult
Description copied from class:ForkJoinTask
Returns the result that would be returned byForkJoinTask.join()
, even if this task completed abnormally, ornull
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 classForkJoinTask<V>
- Returns:
- the result, or
null
if not completed
-
setRawResult
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 classForkJoinTask<V>
- Parameters:
value
- the value
-
exec
protected final boolean exec()Implements execution conventions for RecursiveTask.- Specified by:
exec
in classForkJoinTask<V>
- Returns:
true
if this task is known to have completed normally
-