[Python-Dev] Proposed addition to threading module (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Tue Apr 25 01:03:46 CEST 2006

Guido van Rossum wrote:

Actually, what Nick describes is exactly how one should write code using a condition variable:

LOCK while nothing to do: UNLOCK wait for the condition variable (or sleep, or whatever) LOCK # here we have something to do with the lock held remove the to-do item UNLOCK except that the outer LOCK/UNLOCK pair should be using a try/except and the inner UNLOCK/LOCK pair should too. I don't see how you can do this easily by rewriting the code; the rewrite would be considerably ugly (or requires a GOTO :-).

I thought the trick is that the condition variable atomically releases the lock, waits for the condition, and then reacquires the condition variable. I.e.

c = threading.Condition() c.lock() while nothing to do: c.wait() # here we have something to do with the lock held c.unlock()

So the refactoring is to move the unlock/wait/lock sequence into the condition object. Using with, you could write this as

with threading.Condition() as c: while nothing to do: c.wait() # do work

So no need for an additional context manager here.

Regards, Martin

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