[Python-Dev] Vestigial code in threadmodule?

[Neal Norwitz]

On 6/2/05, A.M. Kuchling <amk at amk.ca> wrote:
> Looking at bug #1209880, the following function from threadmodule.c is
> referenced.  I think the args==NULL case, which can return None
> instead of a Boolean value, can never be reached because
> PyArg_ParseTuple() will fail if args==NULL.
> 
> Before ripping the args==NULL code out, I wanted to be sure my
> analysis is correct; is there some subtlety here I'm missing that
> makes args==NULL possible?

I think the args == NULL code should be ripped out, but there seems to
be a different problem.

If args is NULL to PyArg_ParseTuple() an assertion will be triggered
(or it'll just crash).  See vgetargs1() in Python/getargs.c::138.

args can be NULL if load_args() in Python/ceval.c fails (line 3724). 
The trace starts at line 3551, PyCFunction_Call() will be called with
the NULL args on line 3553.  PyCFunction_Call() will call a PyMethod
that will likely call PyArg_ParseTuple() or something like it.

I think the following patch should fix this (it just adds an if condition).

Does this make sense or am I missing something?

n
--
Index: Python/ceval.c
===================================================================
RCS file: /cvsroot/python/python/dist/src/Python/ceval.c,v
retrieving revision 2.422
diff -u -r2.422 ceval.c
--- Python/ceval.c      4 Apr 2005 15:49:02 -0000       2.422
+++ Python/ceval.c      2 Jun 2005 13:16:14 -0000
@@ -3549,9 +3549,13 @@
                else {
                        PyObject *callargs;
                        callargs = load_args(pp_stack, na);
-                       READ_TIMESTAMP(*pintr0);
-                       C_TRACE(x=PyCFunction_Call(func,callargs,NULL));
-                       READ_TIMESTAMP(*pintr1);
+                       if (callargs) {
+                               READ_TIMESTAMP(*pintr0);
+                              
C_TRACE(x=PyCFunction_Call(func,callargs,NULL));+                     
         READ_TIMESTAMP(*pintr1);
+                       }
+                       else
+                               x = NULL;
                        Py_XDECREF(callargs);
                }
        } else {