[Python-Dev] Re: Extension modules, Threading, and the GIL

[David Abrahams]

"Mark Hammond" <mhammond@skippinet.com.au> writes:

> [Martin]
>> David Abrahams <dave@boost-consulting.com> writes:
>>
>> > We also have a TSS implementation in the Boost.Threads library.  I
>> > haven't looked at the ACE code myself, but I've heard that every
>> > component depends on many others, so it might be easier to extract
>> > useful information from the Boost implementation.
>>
>> Without looking at either Boost or ACE, I would guess that neither
>> will help much: We would be looking for TLS support for AtheOS, BeOS,
>> cthreads, lwp, OS/2, GNU pth, Solaris threads, SGI threads, and Win
>> CE.  I somewhat doubt that either Boost or ACE aim for such a wide
>> coverage.
>
> We could simply have a "pluggable TLS" design.
>
> It seems that everyone who has this requirement is interfacing to a
> complex library (com, xpcom, Boost, ACE), and in general, these
> libraries also require TLS.

Boost isn't in that category.  Boost provides a threading library to
establish a platform-independent C++ interface for threading, but to
date none of the other Boost libraries depend on the use of
Boost.Threads.  In other words, Boost doesn't require TLS, but it can
provide TLS ;-)

> So consider an API such as:
>
> PyTSM_HANDLE Py_InitThreadStateManager(
> 			void (*funcTLSAlloc)(...),
> 			...
> 			PyInterpreterState = NULL);
>
> void Py_EnsureReadyToRock(PyTSM_HANDLE);
> void Py_DoneRocking(PyTSM_HANDLE);
> ...
>
> Obviously the spelling is drastically different, but the point is
> that we can lean on the extension module itself, rather than the
> platform, to provide the TLS.  In the case of Windows and a number
> of other OS's, you could fallback to a platform implementation if
> necessary, but in the case of xpcom, for example, you know that
> xpcom also defines its own TLS API, so anywhere we need the
> extension module, TLS comes for "free", even if no one has ported
> the platform TLS API to the Python TLS API.  Our TLS requirements
> are very simple, and could be "spelt" in a small number of function
> pointers.

I take it you are planning to provide a way to get the neccessary TLS
from Python's API (in case it isn't lying about elsewhere), but not
neccessarily port it to every platform?

If so, that sounds like a fine approach.

-- 
                       David Abrahams
   dave@boost-consulting.com * http://www.boost-consulting.com
Boost support, enhancements, training, and commercial distribution