fbsd 5.4 python sigprocmask() issue

[Ewan Todd]

----- Forwarded message from Suleiman Souhlal <ssouhlal at freebsd.org> -----

Hello,

On May 9, 2005, at 3:54 PM, Daniel Eischen wrote:

>On Tue, 10 May 2005, Peter Jeremy wrote:
>
>
>>On Mon, 2005-May-09 11:00:18 -0400, Ewan Todd wrote:
>>
>>>I have what I think is a serious performance issue with fbsd 5.3
>>>release.  I've read about threading issues, and it seems to me that
>>>that is what I'm looking at, but I'm not confident enough to rule  
>>>out
>>>that it might be a hardware issue, a kernel configuration issue, or
>>>something to do with the python port.
>>>
>>
>>There does appear to be a problem in FreeBSD.  Python is built with
>>threading enabled by default, the threading libraries play with the
>>signal mask and there have been extensive changes there.  My
>>
>
>The threading libraries don't play with the signal mask.  In fact,
>libpthread has userland versions of sigprocmask() et. al. and won't
>even make the syscall() unless the threads are system scope.  There
>is a special thread in libpthread that handles signals which does
>use the system sigprocmask(), but unless the application is
>making heavy use of signals in general, it shouldn't matter.

I think I've found the problem: Python uses setjmp/longjmp to protect
against SIGFPU every time it does floating point operations. The
python script does not actually use threads, and libpthread assumes
non-threaded processes are system scope. So, it would end up using
the sigprocmask syscall, even though it doesn't really need to.  The
diff at
http://people.freebsd.org/~ssouhlal/testing/thr_sigmask-20050509.diff
fixes this, by making sure the process is  threaded, before using the
syscall.

--
Suleiman Souhlal     | ssouhlal at vt.edu
The FreeBSD Project  | ssouhlal at FreeBSD.org

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