[charlie strauss] > Steve, digging into the gc docs a bit more, I think the behaviour I am seeing > is still > not expected. Namely, the program I offered has no obvious place where > objects > are deallocated. The way GC is supposed to work is thate there are three > levels of > objects > > level0: newly created objects > level1: objects that survived 1 round of garbage collection > level2: objects that survivied 2+ rounds of gargbage collection
Yes. > Since all of my numerous objects are level2 objects, No. All newly created objects start in level0. Over time, most (but never all) of your objects end up in level 2. > and none of them are every deallocated, then I should never trip the GC for > these. Cyclic gc scans /all/ container objects at or under level N, whenever cyclic gc runs. N varies from run to run of cyclic gc, according to the scheme described in the docs for the gc.set_threshold() function. N=2 is certainly a possible value. There is never a time when a live container object becomes exempt from all future runs of cyclic gc. If a live container object survives two rounds of cyclic gc, it ends up lin level2. That doesn't mean it's never looked at again, it just means it's not looked at during level0 or level1 (N=0 or N=1) runs of cyclic gc. It will still be looked at during all level2 (N=2) runs of cyclic gc. > Your explanation would require this to be tripped so I can't explain it. For > your > explanation to be correct then there as to be some non-obvious step in the > program > that is deallocating level2 items in sufficient numbers to trip the GC. Deallocations never trigger cyclic gc. As the docs say, cyclic gc is triggered by an /excess/ of allocations /over/ deallocations. So, e.g., if you delete container objects just as fast as you create them, cyclic gc will never run. But that's not what you're doing. Instead you're allocating new objects but never deallocating them. That makes cyclic gc run as frequently as it's possible for it to run. -- http://mail.python.org/mailman/listinfo/python-list
