Summary:
Sometimes the hg process gets stuck, and we want to get the stack traces to
learn what it's doing. It's not a big issue if gdb can be used with python
debugging support [1]. However, that feature could not be easily set up on
OS X. This extension will make debugging on OS X easier by providing the
Python stack traces on SIGUSR1.
It's similar to OpenStack's "GuruMeditationReport" feature [2].
Unlike `contrib/showsstack.py`, this extension uses SIGUSR1 instead of SIGQUIT,
and writes to a file, instead of stderr, and prints all threads, instead of
just the current one. So it's more practically useful. We may want to
replace `showstack.py` eventually.
[1]: https://wiki.python.org/moin/DebuggingWithGdb
[2]: https://wiki.openstack.org/wiki/GuruMeditationReport
Test Plan: Added a new test
Reviewers: #sourcecontrol, rmcelroy
Reviewed By: rmcelroy
Subscribers: rmcelroy, mjpieters
Differential Revision: https://phabricator.intern.facebook.com/D4660938
Signature: t1:4660938:1488927878:c751856681816a739160c361ed5cc10bab325000
