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- Enclosing class:
- ForkJoinPool
public static interface ForkJoinPool.ManagedBlockerInterface for extending managed parallelism for tasks running inForkJoinPools.A
ManagedBlockerprovides two methods. MethodisReleasable()must returntrueif blocking is not necessary. Methodblock()blocks the current thread if necessary (perhaps internally invokingisReleasablebefore actually blocking). These actions are performed by any thread invokingForkJoinPool.managedBlock(ManagedBlocker). The unusual methods in this API accommodate synchronizers that may, but don't usually, block for long periods. Similarly, they allow more efficient internal handling of cases in which additional workers may be, but usually are not, needed to ensure sufficient parallelism. Toward this end, implementations of methodisReleasablemust be amenable to repeated invocation.For example, here is a ManagedBlocker based on a ReentrantLock:
class ManagedLocker implements ManagedBlocker { final ReentrantLock lock; boolean hasLock = false; ManagedLocker(ReentrantLock lock) { this.lock = lock; } public boolean block() { if (!hasLock) lock.lock(); return true; } public boolean isReleasable() { return hasLock || (hasLock = lock.tryLock()); } }Here is a class that possibly blocks waiting for an item on a given queue:
class QueueTaker<E> implements ManagedBlocker { final BlockingQueue<E> queue; volatile E item = null; QueueTaker(BlockingQueue<E> q) { this.queue = q; } public boolean block() throws InterruptedException { if (item == null) item = queue.take(); return true; } public boolean isReleasable() { return item != null || (item = queue.poll()) != null; } public E getItem() { // call after pool.managedBlock completes return item; } }
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description booleanblock()Possibly blocks the current thread, for example waiting for a lock or condition.booleanisReleasable()Returnstrueif blocking is unnecessary.
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Method Detail
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block
boolean block() throws InterruptedExceptionPossibly blocks the current thread, for example waiting for a lock or condition.- Returns:
trueif no additional blocking is necessary (i.e., if isReleasable would return true)- Throws:
InterruptedException- if interrupted while waiting (the method is not required to do so, but is allowed to)
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isReleasable
boolean isReleasable()
Returnstrueif blocking is unnecessary.- Returns:
trueif blocking is unnecessary
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