On 01/19/2016 10:42 AM, Victor Stinner wrote:
Hi,
While working on my FAT Python optimizer project, I found an annoying bug in my code. When at least one guard is created with a reference to the global namespace (globals(), the module dictionary), objects of the module are no more removed at exit.
Example: --- import sys
class MessageAtExit: def __del__(self): print('__del__ called')
# display a message at exit, when message_at_exit is removed message_at_exit = MessageAtExit()
# create a reference cycle: # module -> module dict -> Guard -> module dict guard = sys.Guard(globals()) --- (the code is adapted from a test of test_gc)
Apply attached patch to Python 3.6 to get the sys.Guard object. It's a minimalist object to keep a strong reference to an object.
I expected the garbage collector to break such (simple?) reference cycle.
The Guard object implements a traverse module, but it is never called.
Did I miss something obvious, or is it a known issue of the garbage collector on modules?
The default type flags are for objects that don't store references. Since you're creating a mutable container, you need to set Py_TPFLAGS_HAVE_GC. See https://docs.python.org/3/c-api/gcsupport.html for all the details.