[Pyrex] "Dynamic" callbacks?

[Greg Ewing]

Timothy Toroni wrote:
> 
> Hello all,
> 
> I've got a C library with timers which provide callbacks.  I can 
> successfully use the callback as per the demo find cheese example.  
> However it uses a cdef function as the actual callback, and suppose you 
> can't use a "userdata" data passback, is it possible to "CLASSify 
> this?"  For example,
> 
> cdef CLibFunctionRegisterCallback( void (*func)(void), timeout )
> 
> cdef class Timer:
>    def __init__(self, python_callback_function, timeout):
>        self.python_callback_function = python_callback_function
>        CLibFunctionRegisterCallback( <void *> self.c_callback, timeout)
>          cdef void c_callback(self):
>        self.python_callback_function()

No, that won't work, because a C method expects 'self' as the
first parameter. There's no way you can make it conform to the
signature expected by the library.

The best you can do in a portable way is have a global variable
somewhere that holds a Python function, and install a C callback
that calls that function. This means you can only have one Python
callback function installed at a time, but that's all the C library's
API provides anyway.

Someone mentioned earlier that ctypes provides some way of
creating the C equivalent of a bound method, but I don't
know any details.

-- 
Greg Ewing, Computer Science Dept, +--------------------------------------+
University of Canterbury,	   | A citizen of NewZealandCorp, a	  |
Christchurch, New Zealand	   | wholly-owned subsidiary of USA Inc.  |
greg.ewing at canterbury.ac.nz	   +--------------------------------------+