mtest: limit "magic" CTRL+C behavior to process group leaders

[bonzini]

If meson is not a process group leader, a SIGINT will be delivered also to its parent process (and possibly other processes). The parent process then will probably exit and mtest will continue running in the background, without any way to interrupt the run completely.

To fix this, treat SIGINT and SIGTERM the same way unless mtest is a process group leader.

This can be reproduced when a parallel make invokes "meson test".

[codecov]

Codecov Report

Merging #9410 (03cb208) into master (6718556) will decrease coverage by 0.00%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #9410      +/-   ##
==========================================
- Coverage   67.26%   67.26%   -0.01%     
==========================================
  Files         396      396              
  Lines       85388    85392       +4     
  Branches    17477    17479       +2     
==========================================
- Hits        57440    57439       -1     
- Misses      23252    23255       +3     
- Partials     4696     4698       +2     

Impacted Files	Coverage Δ
mesonbuild/mtest.py	77.65% <33.33%> (-0.12%)	⬇️
mesonbuild/scripts/vcstagger.py	87.50% <0.00%> (-4.17%)	⬇️
mtest.py	76.14% <0.00%> (-0.11%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6718556...03cb208. Read the comment docs.

[xclaesse]

Seems to make sense. OOC, when is meson not the group leader? You wrote a scrip that does that specifically?

[bonzini]

when is meson not the group leader

The shell's job control functionality places each process started by the shell in a separate process group, but otherwise Meson is never the group leader. In particular, it is not a group leader if invoked by a program other than the shell, or if the shell does not perform job control (as is the case when running a shell script).

[bonzini]

(In fact you can see from the coverage report that Meson is never a group leader during a CI run).

[xclaesse]

Ok, LGTM.