Sending -ABRT signal to multi-threaded process

I'm having trouble sending signals to a multi-threaded process on FreeBSD
5-current (cvsup'ed today Feb 18 2004) using -pthread (libpthread.so.1).
The process seems to lock up, possibly due to a mutex problem (the lockup
also occurs when built with LinuxThreads), but when I try to "kill -ABRT"
the process to kill it and obtain a core dump, nothing happens.  Then I try
to "kill -9" the process: under SCHED_4BSD, none of the threads were
terminated; under SCHED_ULE, three of the five threads seemed to have
terminated.  I have to shutdown the machine to get rid of the process.

Any hints on debugging threaded processes on FreeBSD 5?

Guy Helmer, Ph.D., Principal System Architect, Palisade Systems, Inc.
http://www.palisadesys.com/~ghelmer/