Access violation when no memory

[Pat Szuta]

I think that this might be a problem with the python GC.  Basically you
create circular lists,  and because their reference count never goes down
to zero, the GC never frees them.  For example:
ython 1.5.2 (#1, Feb  1 2000, 16:32:16)  [GCC egcs-2.91.66 19990314/Linux
(egcs- on linux-i386
Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
>>> while 1 == 1:
...     x = [1]
...     y = [2]
...     x[0] = y
...     y[0] = x
... 

This will eat up your memory like there is no tomorrow.  I think that the
problem that you're describing my be similar.

On Mon, 19 Jun 2000 22:20:46 -0700, Phil Mayes <nospam at bitbucket.com> wrote:
>The following program progressively allocates all memory:
>    size = 1 << 20
>    list = [None,]
>    while size:
>        try:
>            mem = [None] * size
>            mem[0] = list
>            list = mem
>        except:
>            size = size / 2
>
>It fails with an access violation.  (Turn off virtual memory
>to provoke it.)  This is not a theoretical situation for me:
>I have a beta release in the field that is crashing like this.
>The immediate cause is this:
>
>1. we are handling a MemoryError
>2. the following call cannot allocate a traceback object
>     ceval.c line 1800:    PyErr_Fetch(&exc, &val, &tb);
>3. the NULL pointer at tb is pushed here:
>     ceval.c line 1816:    PUSH(tb);
>     ceval.c line 1817:    PUSH(val);
>     ceval.c line 1818:    PUSH(exc);
>4. later it is popped here and its ref count is decremented:
>     ceval.c line 682:    case POP_TOP:
>     ceval.c line 683:        v = POP();
>     ceval.c line 684:        Py_DECREF(v);
>     ceval.c line 685:        continue;
>
>This is with 1.5.2 but the crash still happens with 1.6a2.
>At this stage I am way out of my depth, and  the only way I
>see to fix this is to change Py_DECREF to Py_XDECREF, which
>is a (minor?) inefficiency. Can anyone recommend a better way?
>
>And should I report this at http://www.python.org/python-bugs?
>I do not have access to the current CVS tree.
>
>TIA, Phil Mayes
>--
>pmayes AT olivebr DOT com
>
>
>


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Pat Szuta						www.sourcelight.com
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