CPython Signal Handler Check for SIGKILL

[Scott McCarty]

Yes, yes, thank you both. That is exactly what I didn't understand, I knew
it was some how linked to the C library and wasn't exactly being handled or
decided at the Python layer, I just didn't understand the C part good
enough. I have found the CPython source code that checks. I see what you are
saying, it is basically checking for SIG_ERR like the C code and just
setting the RuntimeError which forces an exit, thereby making the python
module respond in a way very similar to the C library.

Here is the CPython code in Modules/signalmodule.c

        if (PyOS_setsig(sig_num, func) == SIG_ERR) {
                PyErr_SetFromErrno(PyExc_RuntimeError);
                return NULL;
        }

Second, I would like to apologize, this list is amazing, and I made a stupid
comment on the core developers mailing list this morning because I didn't
understand that this was the right place to post this question.

Thank You
Scott M

On Mon, Jul 19, 2010 at 2:06 PM, Antoine Pitrou <solipsis at pitrou.net> wrote:

>
> Hello,
>
> > I am not asking about the signals, I understand them,
> > I am asking about the registration of the SIGNAL handler and how it knows
> > that you are trying to register SIGKILL, you get an error like this.
> >
> >  ./signal-catcher.py
> > Traceback (most recent call last):
> >   File "./signal-catcher.py", line 22, in <module>
> >     signal.signal(signal.SIGKILL, signal_handler_kill)
> > RuntimeError: (22, 'Invalid argument')
>
> >>> import errno
> >>> errno.errorcode[22]
> 'EINVAL'
>
> EINVAL is the error returned by the standard POSIX signal() function
> when trying to register a handler for SIGKILL. As the signal() man page
> says:
>
> [...]
>       The signals SIGKILL and SIGSTOP cannot be caught or ignored.
> [...]
> ERRORS
>       EINVAL signum is invalid.
>
>
> So, in short, Python doesn't check SIGKILL by itself. It's just
> forbidden by the underlying C standard library, and Python propagates
> the error as a RuntimeError.
>
> Regards
>
> Antoine.
>
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>
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