[Python-Dev] No longer enable Py_TRACE_REFS by default in debug build (original) (raw)

Brett Cannon brett at python.org
Wed Apr 10 15:44:54 EDT 2019

On Wed, Apr 10, 2019 at 12:30 PM Nathaniel Smith <njs at pobox.com> wrote:

On Wed, Apr 10, 2019, 04:04 Victor Stinner <vstinner at redhat.com> wrote:

Le mar. 9 avr. 2019 à 22:16, Steve Dower <steve.dower at python.org> a écrit : > What are the other changes that would be required?

I don't know. > And is there another > way to get the same functionality without ABI modifications? PyTRACEREFS is a double linked list of all Python objects. To get this functionality, you need to store the list somewhere. I don't know how to maintain such list outside the PyObject structure. I assume these pointers get updated from some generic allocation/free code. Could that code instead overallocate by 16 bytes, use the first 16 bytes to hold the pointers, and then return the PyObject* as (actual allocated pointer + 16)? Basically the "containerof" trick. I don't think that I ever used sys.getobjects(), whereas many projects use gc.getobjects() which is also available in release builds (not only in debug builds). Can anyone explain what pydebug builds are... for? Confession: I've never used them myself, and don't know why I would want to.

There is a bunch of extra things done in a debug build, e.g. all freed memory is blanked out with a known pattern so it's easy to tell when you're reading from freed memory (and thus probably messed up your refcounts). And then various extras are tossed on to the sys module to help with things. Basically anything people have found useful and require being compiled in typically get clumped in under the debug build.

-Brett

(I have to assume that most of Steve's Windows downloads are from folks who thought they were downloading a python debugger.) -n

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