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- Enclosing class:
- ForkJoinPool
public static interface ForkJoinPool.ManagedBlocker
Interface for extending managed parallelism for tasks running inForkJoinPool
s.A
ManagedBlocker
provides two methods. MethodisReleasable
must returntrue
if blocking is not necessary. Methodblock
blocks the current thread if necessary (perhaps internally invokingisReleasable
before actually blocking). These actions are performed by any thread invokingForkJoinPool.managedBlock(java.util.concurrent.ForkJoinPool.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 methodisReleasable
must 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
Methods Modifier and Type Method and Description boolean
block()
Possibly blocks the current thread, for example waiting for a lock or condition.boolean
isReleasable()
Returnstrue
if blocking is unnecessary.
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Method Detail
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block
boolean block() throws InterruptedException
Possibly blocks the current thread, for example waiting for a lock or condition.- Returns:
true
if 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()
Returnstrue
if blocking is unnecessary.
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Steph