Hello Jim, On Sun, Sep 21, 2003 at 06:06:45AM -0400, Jim Fulton wrote:
Or, given cyclic GC, why isn't it enough to clear sys.modules?
Because the modules dictionary is stored in PyThreadState_Get()->interp->modules, where the GC cannot see it, which prevent the dictionary from being freed; in turn, it prevents any module from being freed. Still, it means (at a first sight) that there is actually no need to clear each module's globals at all. Just removing them all from interp->modules is fine. In practice there are probably a few issues that I'm not fully aware of, like what occurs if we change module_dealloc() so that it no longer clears the module's global dictionary -- a tweak that seems to come from a pre-GC history. Not speaking about threads in particular, and compatibility problems apart, wouldn't it make sense to change sys.modules and interp->modules into a WeakValueDictionary (or some equivalent refcount-based hack like the one for interned strings)? This would give memory management at the module level, and would allow a cleaner shutdown procedure as well. It would however change Python's semantics of "a module is only loaded once unless you ask or you mess with sys.modules explicitely". A bientot, Armin.