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From: sturlamolden on 28 Jun 2010 23:32
On 29 Jun, 05:11, Ryan Kelly <r...(a)rfk.id.au> wrote:

> Very interesting idea.  Will it work if accessed through ctypes?
>
>    ticker = ctypes.c_int.in_dll(ctypes.pythonapi,"_Py_Ticker")
>    ticker.value = 0x7fffffff
>
> Or does ctypes muck with the GIL in a way that would break this idea?
>

>>> ctypes.pythonapi
<PyDLL 'python dll', handle 1e000000 at 1ffead0>

It's a PyDLL, so it should not mock with the GIL.


from contextlib import contextmanager
import ctypes
_Py_Ticker = ctypes.c_int.in_dll(ctypes.pythonapi,"_Py_Ticker")

@contextmanager
def atomic():
tmp = _Py_Ticker.value
_Py_Ticker.value = 0x7fffffff
yield
_Py_Ticker.value = tmp - 1


Now we can do

with atomic():
# whatever
pass

Just make sure we don't call extension code that releases the GIL :)





From: Antoine Pitrou on 2 Jul 2010 16:26
On Mon, 28 Jun 2010 16:46:41 -0700
Zac Burns <zac256(a)gmail.com> wrote:
> In my experience it is far more expensive to allocate a lock in python then
> it is the types that use them. Here are some examples:
>
> >>> timeit.timeit('Lock()', 'from threading import Lock')
> 1.4449114807669048
>
> >>> timeit.timeit('dict()')
> 0.2821554294221187
>
> >>> timeit.timeit('list()')
> 0.17358153222312467

I'm not sure what Python version on what machine you are using, but
here (Python 2.7):

>>> timeit.timeit('Lock()', 'from threading import Lock')
0.09944796562194824
>>> timeit.timeit('dict()')
0.17817902565002441
>>> timeit.timeit('list()')
0.19633007049560547
>>> timeit.timeit('{}')
0.03823709487915039
>>> timeit.timeit('[]')
0.05156302452087402



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