Davin Potts added the comment:
In the docs for 2.7, multiprocessing.Lock refers to threading.Lock in which the
signature for acquire looks like:
threading.Lock.acquire([blocking])
However, in the current code in 2.7, Modules/_multiprocessing/semaphore.c
implements multiprocessing.Lock.acquire to support two arguments: 'block' and
'timeout'.
In the docs for 3.4, threading.Lock.acquire now has both 'blocking' and
'timeout' arguments. Notably, it specifies: "It is forbidden to specify a
timeout when blocking is false." This is indeed enforced by threading.Lock but
not at all by multiprocessing.Lock. In a 3.4.3 shell:
>>> import multiprocessing
>>> import threading
>>> ml = multiprocessing.Lock()
>>> ml.acquire(False, 20.0)
True
>>> ml.release()
>>> tl = threading.Lock()
>>> tl.acquire(False, 20.0)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: can't specify a timeout for a non-blocking call
In 2.7, acquire similarly permits a supplied value for timeout even when set to
be non-blocking.
A further difference: the code in Modules/_multiprocessing/semaphore.c appears
to translate a timeout=None into an infinite wait whereas the threading
implementation rejects any attempt to supply a None for timeout, demanding a
float instead. (In 3.4, threading uses timeout=-1 to request an infinite wait.)
Given these discrepancies between threading's and multiprocessing's
implementations for Lock and given the difficulties in renaming an argument
that can be supplied as a non-keyword parameter, the right thing to do at this
point is to properly document multiprocessing.Lock's acquire as using 'block'
and 'timeout'.
----------
assignee: -> docs@python
components: +Documentation -Extension Modules
nosy: +docs@python
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue23484>
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