public static interface ForkJoinPool.ManagedBlocker
ForkJoinPools.
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(jsr166y.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 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;
}
}| Modifier and Type | Method and Description |
|---|---|
boolean |
block()
Possibly blocks the current thread, for example waiting for
a lock or condition.
|
boolean |
isReleasable()
Returns
true if blocking is unnecessary. |
boolean block()
throws java.lang.InterruptedException
true if no additional blocking is necessary
(i.e., if isReleasable would return true)java.lang.InterruptedException - if interrupted while waiting
(the method is not required to do so, but is allowed to)boolean isReleasable()
true if blocking is unnecessary.