[Python-Dev] Thread locked sections

[M.-A. Lemburg]

Gordon McMillan wrote:
> 
> M.-A. Lemburg writes:
> 
> > True, sys.lock.acquire() would have to set a flag *not* to release
> > the lock until the next call to sys.lock.release(), which then
> > clears this flag again. Sort of a lock for the unlocking the lock
> > ;-)
> >
> > Could this work, or am I having a mind twister somewhere in
> > there again ?
> 
> Sounds like a critical section to me. On Windows, those are
> lightweight and very handy. You can build one with Python thread
> primitives, but unfortunately, they come out on the heavy side.
> 
> Locks come in 4 types, categorized by whether they can be released
> only by the owning thread, and whether they can be acquired
> recursively. The interpreter lock is in the opposite quadrant from a
> critical section, so "sys.lock.freeze()" and "sys.lock.thaw()" have
> little chance of having an efficient implementation on any platform.

Actually, I think all that's needed is another global like
the interpreter_lock in ceval.c. Since this lock is only
accessed via abstract functions, I presume the unlock flag could
easily be added.

The locking section would only focus on Python, though: other
threads could still be running provided they don't execute
Python code, e.g. write data to a spooler. So it's not really
the equivalent of a critical section as the one you can define in C.

PS: I changed the subject line... hope this doesn't kill the
thread ;)

-- 
Marc-Andre Lemburg
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