At a given time, a virtual processor can run only one thread. A virtual processor services multiple threads concurrently by switching between them. A virtual processor runs a thread until it yields. When a thread yields, the virtual processor switches to the next thread that is ready to run. The virtual processor continues this process, eventually returning to the original thread when that thread is ready to continue. Some threads complete their work, and the virtual processor starts new threads to process new work. Because a virtual processor continually switches between threads, it can keep the CPU processing continually. The speed at which processing occurs produces the appearance that the virtual processor processes multiple tasks simultaneously and, in effect, it does.
Running multiple concurrent threads requires scheduling and synchronization to prevent one thread from interfering with the work of another. Virtual processors use the following structures and methods to coordinate concurrent processing by multiple threads:
This section describes how virtual processors use these structures and methods.
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