On 18 September 2017 at 09:31, Victor Stinner <victor.stin...@gmail.com> wrote: > Last years, I fixed many reference cycles in various parts of the > Python 3 standard library. Sometimes, it takes years to become aware > of the reference cycle and finally fix it. > > For example, recently, I worked on fixing all "dangling threads" > leaked by tests of the Python test suite, and I found and fixed many > reference cycles which probably existed since Python 3 was created > (forked from Python 2)
My instinct is to suggest to make the “dangling threads” test tolerate Thread objects that are no longer running. Last time I looked, it tests a list of weak references to Thread objects. But maybe it should check “Thread.is_alive” or use “threading.enumerate”. > . . . > > Ideally, CPython 3.x should never create reference cycles. Removing > Exception.__traceback__ is the obvious "fix" for the issue. But I > expect that slowly, a lot of code started to rely on the attribute, > maybe even for good reasons :-) > > A more practical solution would be to log a warning. Maybe the garbage > collector can emit a warning if it detects an exception part of a > reference cycle? Or maybe detect frames? The “gc” module can do some of this already. In the past (when __del__ used to prevent garbage collection) I used DEBUG_SAVEALL to and graphed the result to figure out where code was creating reference cycles. Or maybe if you turned on DEBUG_COLLECTABLE and filtered the objects printed out, or played with the new “gc.callbacks” API. > If the GC cannot do it, maybe we might use a debug thread (enabled > manually) which checks manually if an exception is part of a reference > cycle using gc.get_objects(): check if an exception remains alive > longer than X seconds? I had the same idea for asyncio, to detect > reference cycles or if a task is never "awaited", but I never > implemented the idea. _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
