See Also: Exchanger Members
A synchronization point at which threads can pair and swap elements within pairs. Each thread presents some object on entry to the Exchanger.exchange(V) 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 Java.Util.Concurrent.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.
java Example
class FillAndEmpty {
Exchanger exchanger = 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 Exchanger, actions prior to the exchange() in each thread those subsequent to a return from the corresponding exchange() in the other thread.