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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 the {@link #exchange exchange} 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 {@link 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 {@code 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.
{@code class FillAndEmpty { Exchangerexchanger = new 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.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 {@code Exchanger}, actions prior to the {@code exchange()} in each thread happen-before those subsequent to a return from the corresponding {@code exchange()} in the other thread.
Constructor Summary | |
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Creates a new Exchanger. |
Method Summary | |
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Object |
Waits for another thread to arrive at this exchange point (unless the current thread is java.lang.Thread.interrupt), and then transfers the given object to it, receiving its object in return. |
Object |
Waits for another thread to arrive at this exchange point (unless the current thread is java.lang.Thread.interrupt 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 Object exchange(Object 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:
x
- the object to exchangeInterruptedException
- if the current thread was
interrupted while waitingpublic Object exchange(Object 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 {@link TimeoutException} is thrown. If the time is less than or equal to zero, the method will not wait at all.
x
- the object to exchangetimeout
- the maximum time to waitunit
- the time unit of the timeout argumentInterruptedException
- if the current thread was
interrupted while waitingTimeoutException
- if the specified waiting time elapses
before another thread enters the exchange
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