[Pyrex] GIL question

[Lenard Lindstrom]

On Wed, 06 Oct 2004 17:28:37 -0400 "Phillip J. Eby" <pje at telecommunity.com> wrote:

> At 03:00 PM 10/6/04 -0400, Bob Ippolito wrote:
> 
> >On Oct 6, 2004, at 2:51 PM, Phillip J. Eby wrote:
> >
> >>At 11:36 AM 10/6/04 -0700, Cory Dodt wrote:
> >>
> >>>Does Pyrex provide any way to release the GIL?
> >
> ><PyEval_SaveThread() / PyEval_RestoreThread() example>
> >
> >>I pretty much translated the above straight from "8.1 Thread State and 
> >>the Global Interpreter Lock" in the Python/C API manual.  Note, however, 
> >>that you should only invoke the functions if thread support is 
> >>present.  (#ifdef WITH_THREAD), so you may need to actually use a 
> >>different header file, with something like this in it:
> >
> >Thread support is always present in this case so that is not an issue.
> >However, the problem is the opposite of what was previously described.
> >cfreactor has its callbacks called without the GIL so they need to acquire 
> >the GIL, run Python code, and release the GIL... without generating any 
> >exception blocks, reference counting, etc. after the PyGILState_Release().
> 
> Ah.  For that, you need a 'cdef' function without any 'object' parameters 
> or variables.  e.g.:
> 
> cdef void this_is_a_callback():
>      PyGILState_Ensure()
>      # do stuff w/Python...
>      PyGILState_Release()
> 
> Avoid using any "object" or non-cdef variables anywhere in the body of your 
> routine, in order to avoid any refcount cleanup code being 
> generated.  Temporary casts to <object> are probably okay.
> 
> If that still doesn't work, you'll have to write your callback as a C 
> routine with the Ensure/Release wrapping a call to the cdef function.
> 
> (It's relatively easy to mix C with Pyrex; just add the needed '.c' file's 
> name to the list of source files in the Extension sources of your setup.py.)
> 
Place the python stuff in a separate cdef function called by the callback:

cdef void this_is_a_callback():
     PyGILState_Ensure()
     do_python_stuff()
     PyGILState_Release()

cdef void do_python_stuff():
     # callback code here.

This will contain the python api accesses within the ..._Ensure() and
..._Release() calls.

Lenard Lindstrom
<len-l at telus.net>