This interface is pretty simple. The initial count is specified in the constructor. A couple of overloaded methods are provided for threads to wait for the count to reach zero. And a couple of methods are provided to control the count--one to decrement and one to retrieve the count. The boolean return value for the timeout variant of the await() method indicates whether the latch was triggered--it returns true if it is returning because the latch was released.
Exchanger
The exchanger implements a synchronization tool that does not really have equivalents in any other threading system. The easiest description of this tool is that it is a combination of a barrier with data passing. It is a barrier in that it allows pairs of threads to rendezvous with each other; upon meeting in pairs, it then allow the pairs to exchange one set of data with each other before separating.
This class is closer to a collection class than a synchronization tool--it is mainly used to pass data between threads. It is also very specific in that threads have to be paired up, and a specific data type must be exchanged. But this class does have its advantages. Here is its interface:
public class Exchanger<V> { public Exchanger( ); public V exchange(V x) throws InterruptedException; public V exchange(V x, long timeout, TimeUnit unit) throws InterruptedException, TimeoutException;}
