Interface ForkJoinPool.ManagedBlocker
- Enclosing class:
- ForkJoinPool
public static interface ForkJoinPool.ManagedBlocker
Interface for extending managed parallelism for tasks running in ForkJoinPool
s.
A ManagedBlocker
provides two methods. Method isReleasable()
must return true
if blocking is not necessary. Method block()
blocks the current thread if necessary (perhaps internally invoking isReleasable
before actually blocking). These actions are performed by any thread invoking ForkJoinPool.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 method isReleasable
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; } }
Method Summary
Modifier and Type | Method | Description |
---|---|---|
boolean | block() | Possibly blocks the current thread, for example waiting for a lock or condition. |
boolean | isReleasable() | Returns |
Method Detail
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)
isReleasable
boolean isReleasable()
Returns true
if blocking is unnecessary.
- Returns:
-
true
if blocking is unnecessary