java.lang.Objectjava.util.concurrent.Exchanger<V>
public class Exchanger<V>
A synchronization point at which
two
threads can
pair and swap elements within pairs.
exchange objects.
Each thread presents some object on entry to the
exchange
method, matches with a partner thread, and receives its partner's object on return.
method, and receives the object presented by the other thread on return.
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 = newExchanger<DataBuffer>();
Exchanger();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.full()) 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.empty()) 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 thread
happen-before
those subsequent to a return from the corresponding exchange() in the other thread.
Constructor Summary | |
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Exchanger
() ![]() ![]() |
Method Summary | |
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V |
exchange
(
V
x) Waits for another thread to arrive at this exchange point (unless it is interrupted ), and then transfers the given object to it, receiving its object in return. |
V |
exchange
(
V
x, long timeout,
TimeUnit
unit) Waits for another thread to arrive at this exchange point (unless it is interrupted , or the specified waiting time elapses), and then transfers the given object to it, receiving its object in return. |
Methods inherited from class java.lang. Object |
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clone , equals , finalize , getClass , hashCode , notify , notifyAll , toString , wait , wait , wait |
Constructor Detail |
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public Exchanger()
Method Detail |
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public V exchange(V x) throws InterruptedException
If another thread is already waiting at the exchange point then it is resumed for thread scheduling purposes and receives the object passed in by the current thread. The current thread returns immediately, receiving the object passed to the exchange by that other thread.
If no other thread is already waiting at the exchange then the current thread is disabled for thread scheduling purposes and lies dormant until one of two things happens:
If the current thread:
public V exchange(V x, long timeout, TimeUnit unit) throws InterruptedException, TimeoutException
If another thread is already waiting at the exchange point then it is resumed for thread scheduling purposes and receives the object passed in by the current thread. The current thread returns immediately, receiving the object passed to the exchange by that other thread.
If no other thread is already waiting at the exchange then the current thread is disabled for thread scheduling purposes and lies dormant until one of three things happens:
If the current thread:
If the specified waiting time elapses then TimeoutException is thrown. If the time is less than or equal to zero, the method will not wait at all.