operating system - Why semaphore? -

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why use binary semaphores when same functionality can achieved simple variable ?

because semaphore isn't simple variable, it's larger construct that.

specifically, counting semaphore (which binary semaphore is, effectively, count of 1), there's added capability of blocking process/thread tries increment semaphore above maximum value.

semaphores have additional facility state changed "atomically", means underlying memory surrounded logic ensure cpu caches , such flushed, , when value changed, it's changed "everyone". particularly important on modern multi-core processors.

the semaphore appropriate use when trying guard shared resource on use. binary semaphore perfect resources can used 1 process/thread @ time.


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