ForkJoinPool.ManagedBlocker (Java SE 10 & JDK 10 ) (original) (raw)

• Enclosing class:
  ForkJoinPool

public static interface ForkJoinPool.ManagedBlocker
Interface for extending managed parallelism for tasks running in ForkJoinPools.
A ManagedBlocker provides two methods. MethodisReleasable() 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

  All Methods Instance Methods Abstract Methods

  Modifier and Type	Method	Description
  boolean	block()	Possibly blocks the current thread, for example waiting for a lock or condition.
  boolean	isReleasable()	Returns true if blocking is unnecessary.

• • Method Detail

     * #### block  
     boolean block()  
            throws [InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang")  
     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](../../../java/lang/InterruptedException.html "class in java.lang")` \- 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

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