Exchanger (Java Platform SE 8 ) (original) (raw)


public class Exchanger
extends Object
A synchronization point at which threads can pair and swap elements within pairs. Each thread presents some object on entry to theexchange method, matches with a partner thread, and receives its partner's object on return. An Exchanger may be viewed as a bidirectional form of a SynchronousQueue. Exchangers may be useful in applications such as genetic algorithms and pipeline designs.
Sample Usage: Here are the highlights of a class that uses an Exchanger to swap buffers between threads so that the thread filling the buffer gets a freshly emptied one when it needs it, handing off the filled one to the thread emptying the buffer.
class FillAndEmpty { Exchanger<DataBuffer> exchanger = new Exchanger<DataBuffer>(); DataBuffer initialEmptyBuffer = ... a made-up type DataBuffer initialFullBuffer = ... class FillingLoop implements Runnable { public void run() { DataBuffer currentBuffer = initialEmptyBuffer; try { while (currentBuffer != null) { addToBuffer(currentBuffer); if (currentBuffer.isFull()) currentBuffer = exchanger.exchange(currentBuffer); } } catch (InterruptedException ex) { ... handle ... } } } class EmptyingLoop implements Runnable { public void run() { DataBuffer currentBuffer = initialFullBuffer; try { while (currentBuffer != null) { takeFromBuffer(currentBuffer); if (currentBuffer.isEmpty()) currentBuffer = exchanger.exchange(currentBuffer); } } catch (InterruptedException ex) { ... handle ...} } } void start() { new Thread(new FillingLoop()).start(); new Thread(new EmptyingLoop()).start(); } }
Memory consistency effects: For each pair of threads that successfully exchange objects via an Exchanger, actions prior to the exchange() in each threadhappen-before those subsequent to a return from the corresponding exchange() in the other thread.
Since:
1.5

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