Interface ForkJoinPool.ManagedBlocker
- Enclosing class:
ForkJoinPool
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. Neither method is invoked after a prior invocation
of isReleasable
or block
returns true
.
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 TypeMethodDescriptionboolean
block()
Possibly blocks the current thread, for example waiting for a lock or condition.boolean
Returnstrue
if blocking is unnecessary.
-
Method Details
-
block
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()Returnstrue
if blocking is unnecessary.- Returns:
true
if blocking is unnecessary
-