all Python 3multiprocessingterm

multiprocessing.BoundedSemaphore

synchronization

A semaphore shared between processes that will not let its counter rise above the initial value: an extra release() raises ValueError.

Syntax

sem = ctx.BoundedSemaphore(value=1)

An extra release() is caught at once instead of an hour later, when a "pool of three connections" limit has quietly become four. The exception is ValueError "released too many times"; threading.BoundedSemaphore also raises ValueError, with a different message. As with Semaphore, the acquire() argument is named block. Pass the primitive to the child as a Process argument at creation; it cannot go through a Queue or Pool arguments — RuntimeError "should only be shared between processes through inheritance".

Examples

import multiprocessing as mp
if __name__ == '__main__':
    sem = mp.get_context('spawn').BoundedSemaphore(2)
    sem.acquire()
    sem.release()
    try:
        sem.release()
    except ValueError as e:
        print(e)  # → semaphore or lock released too many times

See also

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