On Jun 30, 1:55 pm, Tom Davis <[EMAIL PROTECTED]> wrote: > On Jun 26, 5:38 am, Carl Banks <[EMAIL PROTECTED]> wrote: > > > > > On Jun 26, 5:19 am, Tom Davis <[EMAIL PROTECTED]> wrote: > > > > I am having a problem where a long-running function will cause a > > > memory leak / balloon for reasons I cannot figure out. Essentially, I > > > loop through a directory of pickled files, load them, and run some > > > other functions on them. In every case, each function uses only local > > > variables and I even made sure to use `del` on each variable at the > > > end of the loop. However, as the loop progresses the amount of memory > > > used steadily increases. > > > Do you happen to be using a single Unpickler instance? If so, change > > it to use a different instance each time. (If you just use the module- > > level load function you are already using a different instance each > > time.) > > > Unpicklers hold a reference to everything they've seen, which prevents > > objects it unpickles from being garbage collected until it is > > collected itself. > > > Carl Banks > > Carl, > > Yes, I was using the module-level unpickler. I changed it with little > effect. I guess perhaps this is my misunderstanding of how GC works. > For instance, if I have `a = Obj()` and run `a.some_method()` which > generates a highly-nested local variable that cannot be easily garbage > collected, it was my assumption that either (1) completing the method > call or (2) deleting the object instance itself would automatically > destroy any variables used by said method. This does not appear to be > the case, however. Even when a variable/object's scope is destroyed, > it would seem t hat variables/objects created within that scope cannot > always be reclaimed, depending on their complexity. > > To me, this seems illogical. I can understand that the GC is > reluctant to reclaim objects that have many connections to other > objects and so forth, but once those objects' scopes are gone, why > doesn't it force a reclaim?
Are your objects involved in circular references, and do you have any objects with a __del__ method? Normally objects are reclaimed when the reference count goes to zero, but if there are cycles then the reference count never reaches zero, and they remain alive until the generational garbage collector makes a pass to break the cycle. However, the generational collector doesn't break cycles that involve objects with a __del__method. Are you calling any C extensions that might be failing to decref an object? There could be a memory leak. Are you keeping a reference around somewhere. For example, appending results to a list, and the result keeps a reference to all of your unpickled data for some reason. You know, we can throw out all these scenarios, but these suggestions are just common pitfalls. If it doesn't look like one of these things, you're going to have to do your own legwork to help isolate what's causing the behavior. Then if needed you can come back to us with more detailed information. Start with your original function, and slowly remove functionality from it until the bad behavior goes away. That will give you a clue what's causing it. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
