qwurx [shmem] ~ > gdb perl
... (legal mumbo) ...
(gdb) run pari-threaded.pl 
Starting program: /usr/bin/perl pari-threaded.pl
(no debugging symbols found)
...

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -1209108800 (LWP 31332)]
0x007046cc in moveoffstack_newer_than () from /usr/lib/perl5/site_perl
+/5.8.8/i386-linux-thread-multi/auto/Math/Pari/Pari.so
(gdb)
[download]

Conclusion: Math::Pari is not thread-safe.

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}