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Python Library Reference

Previous: 7.5.4 Semaphore Objects Up: 7.5.4 Semaphore Objects Next: 7.5.5 Event Objects

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7.5.4.1 Semaphore Example

Semaphores are often used to guard resources with limited capacity, for example, a database server. In any situation where the size of the resource size is fixed, you should use a bounded semaphore. Before spawning any worker threads, your main thread would initialize the semaphore:

maxconnections = 5
...
pool_sema = BoundedSemaphore(value=maxconnections)

Once spawned, worker threads call the semaphore's acquire and release methods when they need to connect to the server:

pool_sema.acquire()
conn = connectdb()
... use connection ...
conn.close()
pool_sema.release()

The use of a bounded semaphore reduces the chance that a programming error which causes the semaphore to be released more than it's acquired will go undetected.

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Python Library Reference

Previous: 7.5.4 Semaphore Objects Up: 7.5.4 Semaphore Objects Next: 7.5.5 Event Objects

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Release 2.2.3, documentation updated on 30 May 2003.