On 16 May 2017 at 12:56, <[email protected]> wrote:
>
> [... kill does not kill all the processes ...] Is this normal behavior? It
> seems strange.
>
One moment of enlightenment for me was to discover why CTRL-C at the
terminal kills all of the processes, while kill(pid, SIG{whatever}) to the
parent process does not.
It's that CTRL-C doesn't just signal the parent process! It signals all
processes in the process group of the session leader process whose
controlling terminal is the current terminal. Phew, what a mouthful - I'm
not even sure I stated that correctly. But anyway, CTRL-C doesn't do kill.
It does kill_pgrp.
Anyway, here's where it happens in linux:
https://github.com/torvalds/linux/blob/a95cfad947d5f40cfbf9a
d3019575aac1d8ac7a6/drivers/tty/n_tty.c#L1258
and ultimately... https://github.com/torvalds/linux/blob/a95cfad
947d5f40cfbf9ad3019575aac1d8ac7a6/drivers/tty/n_tty.c#L1085
Some more docs:
http://www.informit.com/articles/article.aspx?p=397655&seqNum=6
I think this can be surprising, and it's not so obvious at first glance.
Anyway, one implication of this is that if your process escapes the process
group, then CTRL-C won't kill it. Also, Unix processes may quit for other
reasons than receiving a signal, for example if a file descriptor they're
reading from is closed (which might also happen when another process dies).
Food for thought.
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