[Python-Dev] cycle-GC question

[Guido van Rossum]

> The following program:
> 
> import rexec
> while 1:
>       x = rexec.RExec()
>       del x
> 
> leaks memory at a fantastic rate.
> 
> It seems clear (?) that this is due to the call to "set_rexec" at
> rexec.py:140, which creates a circular reference between the `rexec'
> and `hooks' objects.  (There's even a nice comment to that effect).
> 
> I'm curious however as to why the spiffy new cyclic-garbage collector
> doesn't pick this up?

Me too.  I turned on gc debugging (gc.set_debug(077) :-) and got
messages suggesting that it is not collecting everything.  The
output looks like this:

   .
   .
   .
gc: collecting generation 0...
gc: objects in each generation: 764 6726 89174
gc: done.
gc: collecting generation 1...
gc: objects in each generation: 0 8179 89174
gc: done.
gc: collecting generation 0...
gc: objects in each generation: 764 0 97235
gc: done.
gc: collecting generation 0...
gc: objects in each generation: 757 747 97184
gc: done.
gc: collecting generation 0...
gc: objects in each generation: 764 1386 97184
gc: done.
gc: collecting generation 0...
gc: objects in each generation: 757 2082 97184
gc: done.
gc: collecting generation 0...
gc: objects in each generation: 764 2721 97184
gc: done.
gc: collecting generation 0...
gc: objects in each generation: 757 3417 97184
gc: done.
gc: collecting generation 0...
gc: objects in each generation: 764 4056 97184
gc: done.
   .
   .
   .

With the third number growing each time a "generation 1" collection is
done.

Maybe Neil can shed some light?  The gc.garbage list is empty.

This is about as much as I know about the GC stuff...

--Guido van Rossum (home page: http://www.python.org/~guido/)