[Octave-bug-tracker] [bug #49532] parallel package: segmentation fault on matrix multiplication on macOS

[Olaf Till]

Follow-up Comment #10, bug #49532 (project octave):

It should be added that, since the segfault is in one of the two child
processes, you should attach to a child process with gdb -p PID. For this, you
can insert a 'pause (long_time)' as the first command into your function
'par_test'. Or better, as the second command, and the first command should
print out the pid of the process (getpid, as mentioned in the last post), but
set page_screen_output to false before doing this.

For clarity: run pararrayfun with your changed par_test, and from another
terminal, attach with gdb to the printed out pid, before par_test finishes its
'pause()'. Then give the command 'run' from gdb and hope to see the caught
segfault. Then 'bt'.

But in debugging parallel processes it can happen that the segfault doesn't
occur under debugging conditions. I'd believe you have good chances if the
segfault occurs even if you set nproc to 1 in pararrayfun. Then you should try
the debugging with nproc==1.

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