Re: [PATCH] manual: don't ignore SIGCHLD when calling waitpid

[Paul Eggert <eggert@cs.ucla.edu>]

On 4/17/19 12:05 PM, Adhemerval Zanella wrote:
> My understanding of the example is for interactive shells (shell_is_interactive),
> the idea is only to get child information to the explicit launched processes done
> by launch_process, so ignoring and reseting SIGCHLD seems ok.

Sure, but the problem is that launch_process is used only in the child,
which means the parent shell always ignores SIGCHLD, so if the parent
calls do_job_notification it won't get any info about children. Perhaps
this could be fixed by documenting do_job_notification as requiring that
SIGCHLD be reenabled before calling it, but that's pretty confusing.

Also the proposed change to the manual is not enough, as there's other
text saying that the sample shell program ignores SIGCHLD. Presumably
this is to avoid races in the parent shell. But if SIGCHLD causes races
in the parent, then the parent typically should block SIGCHLD instead of
ignoring it and similarly for the other signals - otherwise the fact
that the signals arrived will be lost. So the whole example needs to be
rethought.