V - The type of objects that may be exchangedpublic class Exchanger<V> extends Object
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 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 thread
happen-before
those subsequent to a return from the corresponding exchange()
in the other thread.
| Constructor and Description |
|---|
Exchanger()
Creates a new Exchanger.
|
| Modifier and Type | Method and Description |
|---|---|
V |
exchange(V x)
Waits for another thread to arrive at this exchange point (unless
the current thread 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
the current thread is interrupted or
the specified waiting time elapses), and then transfers the given
object to it, receiving its object in return.
|
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:
InterruptedException is thrown and the current thread's
interrupted status is cleared.x - the object to exchangeInterruptedException - if the current thread was
interrupted while waitingpublic 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:
InterruptedException is thrown and the current thread's
interrupted status is cleared.
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.
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 Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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