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Re: how avoid delay while returning from C-python api?

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  Re: how avoid delay while returning from C-python api? Stefan Behnel <stefan_ml@behnel.de> - 2014-05-28 21:00 +0200

#72177 — Re: how avoid delay while returning from C-python api?

Lakshmipathi.G, 28.05.2014 12:22:
> I have C-Python api like below.  It works fine, but the problem is
> while invoking this method
> from python script say
> 
> #cat script.py
> <snip>
> offset=0
> size=4
> write_object(offset,size)
> </snip>
> 
> 
> This calls write_this_c() C api and returns quickly to next printf statement.
> But the return call (Py_RETURN_NONE) takes something like 4-6 seconds.
> 
> -----
> static
> PyMethodDef xyz_methods[] = {
> {"write_object", write_object, METH_VARARGS,"write some stuff "},
> {NULL, NULL, 0, NULL}
> };
> 
> 
> ----
> static PyObject *
> write_object(PyObject *self, PyObject *args)
> {
>         int offset, size;
>         if (!PyArg_ParseTuple(args,"ii", &offset, &size))
>                 Py_RETURN_NONE;
> 
>         printf("before call");
>         write_this_c(offset, size);
>         printf("after call");
>         Py_RETURN_NONE;          ##delay happens here
> }
> 
> How to avoid this delay time? Thanks for any help/pointers!

You already found the problem yourself, so let me just give you a general
advice that you can avoid a lot of the hassle of writing code like the
above and struggling to get it right by writing it in Cython instead of
plain C. Here's a complete example of the above code in Cython, including
the module setup code etc., but without the bugs:

    # external declarations:

    cdef extern from "someheader.h":
         void write_this_c(int offset, int size)

    # your module function:

    def write_object(int offset, int size):
        """write some stuff"""
        print("before call")
        write_this_c(offset, size)
        print("after call")

That's it.

Stefan

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