- Enclosing class:
- ForkJoinPool
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(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 SummaryModifier and TypeMethodDescriptionbooleanblock()Possibly blocks the current thread, for example waiting for a lock or condition.booleanReturnstrueif blocking is unnecessary.
- 
Method Details- 
blockPossibly 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)
 
- 
isReleasableboolean isReleasable()Returnstrueif blocking is unnecessary.- Returns:
- trueif blocking is unnecessary
 
 
-