On Fri, Jul 06, 2007 at 02:46:38PM +0200, [EMAIL PROTECTED] wrote:
> I think I found the cause of my deadlock, which is (if I'm right that is),
> located in main.py:912:
>
> val = cache.get(id, cls)
> if val is None:
> try:
> val = cls(_SO_fetch_no_create=1)
>
> We reach this place e.g. by resolving a foreign key through
> _SO_foreignKey() and get().
>
> If I read the code correctly, the cache's lock is acquired in cache.get()
> (but not released, which would be done in cache.finishPut(cls)), if the
> object doesn't already exist. cls(_SO_fetch_no_create=1) then acquires the
> class' lock through the threadSafeMethod() wrapper in declarative.py.
>
> On the other hand, if I'm creating an object of the same type, at exactly
> the time between the cache.get() and cls() calls, I'll be able to acquire
> the class' lock and then pend on the cache's lock, through threadSafe
> __init__(), then _create(), then _SO_finishCreate(), cacheSet.created(),
> CacheFactory.created() and finally CashFactory.cull().
>
> This leaves us with the first thread having acquired the cache's lock while
> pending for the class' lock, and the second thread having acquired the
> class' lock and pending for the cache's lock -> deadlock. The situation can
> only occur, if the creation of the object triggers a cache.cull(). In any
> other case, the cache isn't locked and thus there are no problems.
>
> Does this all make sense?
Absolutely. Thank you for the excellent analysis! But could the cache
release the lock before the new row (SQLObject) is put to the cache? I
doubt it.
Oleg.
--
Oleg Broytmann http://phd.pp.ru/ [EMAIL PROTECTED]
Programmers don't die, they just GOSUB without RETURN.
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