[Python-Dev] Re: C new-style classes and GC (original) (raw)

Jim Fulton jim@zope.com
Fri, 16 May 2003 17:08:27 -0400

Jim Fulton wrote:

Lately I've been re-learning how to write new types in C. Things changed drastically (for the better) in 2.2. I've been updating the documentation on writing new types as I go:

http://www.python.org/dev/doc/devel/ext/defining-new-types.html (I'm also updating modulator.) I'm starting to try to figure out how to integrate support for GC. The current documentation in the section "Supporting the Cycle Collector" doesn't reflect new-style types and is, thus, out of date. Frankly, I'm taking the approach that there is only One Way to create types in C, the new way, based on new-style types as now documented in the manual. I'll also note that most new-style types don't need and thus don't implement custom allocators. They leave the tpalloc and tpfree slots empty. So given that we have a new style type, to add support for GC, we need to: - Set the PyTPFLAGSHAVEGC type flag, - Provide implementations of tptraverse and tpclear, as described in the section "Supporting the Cycle Collector" section of the docs. - Call PyObjectGCUnTrack at the beginning of the deallocator, before decrefing any members. I think that that is all we have to do.

It looks like the answer is "no". :)

I tried to write a type using this formula and segfaulted. Looking at other types, I found that if I want to support GC and am using the default allocator, which I get for free, I have to fill the tp_free slot with PyObject_GC_Del (_PyObject_GC_Del if I want to support Python 2.2 and 2.3).

I think this is all I have to do.

Jim

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