[python-win32] python-win32 Digest, Vol 81, Issue 13

[Preston Landers]

On Sun, Dec 13, 2009 at 5:00 AM,  <python-win32-request at python.org> wrote:
> Do you have evidence that your Python code is running in multiple
> threads?  I.e. are you sure this isn't just ISAPI running some cleanup
> work in another thread?

Oh yes.  There was no doubt.  I used a debugger (pydevd) to put a
breakpoint at the start of each request.  And then ran a section of my
app which uses a frameset after limiting the app pool to 1 process.
This caused several more or less simultaneous requests.  The debugger
showed the separate threads with the Dummy-# name label assigned by
the Python threading module (plus MainThread) and I could switch back
and forth between them in the debugger.  I was also seeing other
behavior consistent with threaded execution; there are some singleton
guards in my app that were getting triggered.   I also verified w/o
the debugger by having each request log the thread ID via
threading.currentThread() as well as the process ID.

Everything I've read on ISAPI recently says it's always potentially
multithreaded and that extensions must be prepared to run threaded
e.g. by locking sensitive objects.  At least in my case this wouldn't
have been a problem if each thread ran in a separate interpreter (i.e,
with separate copies of all modules.)  Well, except for any
un-thread-safe C extensions and GIL performance issues. For now I am
using a thread lock to force sequential behavior within a process and
using a multi-process application pool to achieve concurrency.

thanks,
-Preston