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Trail: Essential Java Classes
Lesson: Threads: Doing Two or More Tasks At Once

Synchronizing Threads

So far the examples in this chapter have contained independent, asynchronous threads. Each thread contained all the data and methods required for its execution and didnít require any outside resources or methods. Also, the threads in those examples ran at their own pace without concern for the state or activities of any other concurrently running threads.

However, in many interesting situations, separate, concurrently running threads do share data and must consider the state and activities of other threads. In one such set of programming situations, called producer-consumer scenarios, the producer generates a stream of data that a consumer uses.

For example, imagine an application in which one thread (the producer) writes data to a file while a second thread (the consumer) reads data from the same file. Or, as you type characters on the keyboard, the producer thread places mouse events in an event queue and the consumer thread reads the events from the same queue. Both of these examples use concurrent threads that share a common resource: The first shares a file, and the second shares an event queue. Because the threads share a common resource, they must be synchronized.

The next section teaches you about thread synchronization through a simple producer-consumer example.


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