Streams causing heap crash using Python C-Extensions

[Raj Batra]

Hi,

I've created a dll that you can import into python. The function
calls an ostringstream class. Calling this function repeatedly in python
will cause a Microsoft Visual C++ Debug Library error:

Debug Assertion Failed!
Program: C:\Program Files\Python22\ python.exe
File: dbgheap.c
Line: 346

Expression: _CrtCheckMemory ()

Here are snippets of the code:

// Method called by python via a PySwitchObject
static PyObject * pyCircuit(PySwi tchObject * self, PyObject * args)
{
int circuit;

if (!PyArg_ParseTu ple(args, "i", &circuit))
{
// Error handling...
}

self->_switch->circuit((U8) circuit);
Py_INCREF(Py_No ne);
return(Py_None) ;
}

// Called by pyCircuit method above. Multiple calls to this method
// yield a heap assertion.
void Switch::circuit (U8 c)
{
std::ostringstr eam close;

close << "Some formating...";

// Use the close method - doesn't really matter.
}


The error is always within the constructor or destructor of ostringstream and
in the file called xmutex.cpp (implements mutex lock for iostreams) which
calls the malloc/dealloc functions.

I have tried other streams such as fstream, and get similar behavior.
Switching to a char buffer[] and sprintf is my current work around the
ostringstream issue.

Any thoughts about what is going on?

I'm using Python2.2.2, with Visual C++ 7 (.NET). The error occurs using
both pythonwin and the standard command line python.

Thanks,

Raj

[Raj Batra]

Re: Streams causing heap crash using Python C-Extensions

Just a follow up - It appears that the crash isn't related to
just C++ i/o streaming. I tried using the fopen/fclose (e.g for logging)
and again repeated calls from python to the code causes the same
_CrtCheckMemory () error.

E.g.

void void Switch::circuit (U8 c)
{
if (!_filename) return;

FILE *out = fopen(_filename , "a");

if (!out) return;

time_t t = time(0);
fprintf(out,"%s \n %s%s\n", asctime(localti me(&t)), "Header", "Log stuff");

fclose(out);

}

Another person solved the problem by using cout and then in python
redirected stdout to a file. Then all calls to the cextension
forced cout to write to a file. I prefer not to go down that road.

Any thoughts appreciated as to what may be going on.

Thanks,

Raj


batraraj@hotmai l.com (Raj Batra) wrote in message news:<ee04f1ee. 0309161604.2f13 c59b@posting.go ogle.com>...[color=blue]
> Hi,
>
> I've created a dll that you can import into python. The function
> calls an ostringstream class. Calling this function repeatedly in python
> will cause a Microsoft Visual C++ Debug Library error:
>
> Debug Assertion Failed!
> Program: C:\Program Files\Python22\ python.exe
> File: dbgheap.c
> Line: 346
>
> Expression: _CrtCheckMemory ()
>
> Here are snippets of the code:
>
> // Method called by python via a PySwitchObject
> static PyObject * pyCircuit(PySwi tchObject * self, PyObject * args)
> {
> int circuit;
>
> if (!PyArg_ParseTu ple(args, "i", &circuit))
> {
> // Error handling...
> }
>
> self->_switch->circuit((U8) circuit);
> Py_INCREF(Py_No ne);
> return(Py_None) ;
> }
>
> // Called by pyCircuit method above. Multiple calls to this method
> // yield a heap assertion.
> void Switch::circuit (U8 c)
> {
> std::ostringstr eam close;
>
> close << "Some formating...";
>
> // Use the close method - doesn't really matter.
> }
>
>
> The error is always within the constructor or destructor of ostringstream and
> in the file called xmutex.cpp (implements mutex lock for iostreams) which
> calls the malloc/dealloc functions.
>
> I have tried other streams such as fstream, and get similar behavior.
> Switching to a char buffer[] and sprintf is my current work around the
> ostringstream issue.
>
> Any thoughts about what is going on?
>
> I'm using Python2.2.2, with Visual C++ 7 (.NET). The error occurs using
> both pythonwin and the standard command line python.
>
> Thanks,
>
> Raj[/color]

[Thomas Heller]

Re: Streams causing heap crash using Python C-Extensions

batraraj@hotmai l.com (Raj Batra) writes:
[color=blue][color=green]
>> I'm using Python2.2.2, with Visual C++ 7 (.NET). The error occurs using
>> both pythonwin and the standard command line python.[/color][/color]

I don't know whether you can use C++ stream I/O in a Python extension or
not, but if you use MSVC7 to compile the extension, your Python must
also be compiled with this one (generally).

Thomas