[Python-Dev] Re: tp_clear return value (original) (raw)

Tim Peters tim.one@comcast.net
Thu, 10 Apr 2003 14:09:57 -0400

[Tim]

Still, I expect both could be handled by setjmp in the gc module getref* driver functions and longjmp (as needed) in the gc module visitor functions. IOW, the tptraverse slot functions don't really need to cooperate, or even know anything about "early returns".

[martin@v.loewis.de]

That would require that tptraverse does not modify any refcount while iterating, right?

Or do anything else that relies on calls to visit() returning. I've looked at every traverse slot in the core, and there's no problem with those. I don't think that's an accident -- the only purpose of an object's tp_traverse is to invoke the visit callback on the non-NULL PyObject* pointers the object has. So, e.g., there isn't an incref or decref in any of 'em now; at worst there's an int loop counter.

It seems unpythonish to use setjmp/longjmp for exceptions.

I'm not suggesting adding setjmp/longjmp to the Python language <0.9 wink>. I'm suggesting using them for two specific and obscure gc module callbacks that aren't normally used (most of the gc module callbacks wouldn't use setjmp/longjmp); in return, mounds of frequently executed code like

static int func_traverse(PyFunctionObject *f, visitproc visit, void *arg) { int err; if (f->func_code) { err = visit(f->func_code, arg); if (err) return err; } if (f->func_globals) { err = visit(f->func_globals, arg); if (err) return err; } if (f->func_module) { err = visit(f->func_module, arg); if (err) return err; } if (f->func_defaults) { err = visit(f->func_defaults, arg); if (err) return err; } if (f->func_doc) { err = visit(f->func_doc, arg); if (err) return err; } ... return 0; }

could become the simpler and faster

static int func_traverse(PyFunctionObject *f, visitproc visit, void *arg) { int err; if (f->func_code) visit(f->func_code, arg); if (f->func_globals) visit(f->func_globals, arg); if (f->func_module) visit(f->func_module, arg); if (f->func_defaults) visit(f->func_defaults, arg); if (f->func_doc) visit(f->func_doc, arg); ... return 0; }

(I kept the final return 0 so that the signature wouldn't change.)