On Sat, 27 Aug 2011 15:08:36 +0200
Armin Rigo <[email protected]> wrote:
> Hi Nick,
>
> On Sat, Aug 27, 2011 at 2:40 PM, Nick Coghlan <[email protected]> wrote:
> > 1. How does the patch interact with C code that explicitly releases
> > the GIL? (e.g. IO commands inside a "with atomic:" block)
>
> As implemented, any code in a "with atomic" is prevented from
> explicitly releasing and reacquiring the GIL: the GIL remain acquired
> until the end of the "with" block. In other words
> Py_BEGIN_ALLOW_THREADS has no effect in a "with" block.
You then risk deadlocks. Say:
- thread A is inside a "with atomic" and calls a library function which
tries to take lock L
- thread B has already taken lock L and is currently executing an I/O
function with GIL released
- thread B then waits for the GIL (and hence depends on thread A going
forward), while thread A waits for lock L (and hence depends on
thread B going forward)
Lock L could simply be the lock used by the file object (a
Buffered{Reader,Writer,Random}) which thread B is reading or writing
from.
Regards
Antoine.
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