(Fixes #358.)
Subprocesses created for custom module scripts were previously left
running when the parent Waybar process exited. This patch sets the
parent-death signal of child processes (PR_SET_PDEATHSIG on Linux,
PROC_PDEATHSIG_CTL on FreeBSD) to SIGTERM.
Caveats:
* This uses Linux-specific or FreeBSD-specific calls. I don’t know if
this project targets other systems?
* There is a possibility that Waybar exits after calling `fork()`, but
before calling `prctl` to set the parent-death signal. In this case,
the child will not receive the SIGTERM signal and will continue to
run. I did not handle this case as I consider it quite unlikely, since
module scripts are usually launched only when Waybar starts. Please
let me know if you think it needs to be handled.
Testing:
* With `htop` open, run Waybar v0.9.5 with a custom module that has an
`exec` script. Terminate the Waybar process and notice that the
script’s subprocess stays alive and is now a child of the init
process.
* Run Waybar with this patch and follow the same steps as above. Notice
that this time the script’s subprocess terminates when the parent
exits.
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