[Python-Dev] Fault handler updated, now disabled by default

[Victor Stinner]

Hi,

Thanks to all your useful remarks, I improved my patch twice (version 10
and 11). I think that the last version (11) addresses all reported
issues. The most notable change is that the fault handler is now
disabled by default. It fixes also the function getting the thread
state, it now works in all cases (especially if the thread causing the
fault doesn't hold the GIL).

Summary of the patch (#8863):

 - Add an optional fault handler for SIGSEGV, SIGFPE, SIGILL and SIGBUS
signals displaying the Python backtrace
 - Setting PYTHONFAULTHANDLER environment variable, or using
   "-X faulthandler" command line option, enables it
 - If it's enabled, display also the Python backtrace on a fatal error

Use case: when a program crashs, the user reruns its application with
the fault handler enabled and tries to reproduce the crash. He/She can
send the Python backtrace to the developer, or use it directly (if
he/she understands it).

I think that this patch helps to isolate crashs in Python or libraries,
especially if the user doesn't have all tools needed to get a Python
backtrace (on a crash) and the developer is unable to reproduce the bug
(because it doesn't have the same OS or libraries). For example, gdb 7
and python-gdb.py are rare on Windows :-) (even on Linux!)

So, do you agree with the fault handler? Does someone want to give a
last review because I commit it?

http://bugs.python.org/issue8863

Victor