Re: waiting for process substitutions

[Zachary Santer]

On Mon, Aug 5, 2024 at 9:54 AM Chet Ramey <chet.ramey@case.edu> wrote:
>
> On 7/31/24 11:48 AM, Zachary Santer wrote:
> >
> > $ wait -n > >( cat )
> > would hang, in the event that there are no other un-waited-for child
> > processes, right?
>
> Yes, it will wait for the next job or procsub to terminate.

Basically the same situation as Oğuz's bug here:

On Fri, Jul 5, 2024 at 2:38 PM Chet Ramey <chet.ramey@case.edu> wrote:
>
> On 6/29/24 10:51 PM, Zachary Santer wrote:
> >
> > 1) When all child processes are process substitutions:
> > a. wait without arguments actually appears to wait for all of them,
> > not just the last-executed one, contradicting the man page.
>
> This is how it is in bash-5.2. It does contradict the man page, and I
> reverted it to match the man page in October, 2022, after
>
> https://lists.gnu.org/archive/html/bug-bash/2022-10/msg00107.html
>
> The whole business is kind of a mess. Let's see if we can figure out the
> best behavior.

So $! is only set to the pid for a procsub that's being redirected
to/from after the command (or compound command) whose output/input is
being redirected to/from it has completed? If that's the case, maybe
the ideal solution for both 'wait' and 'wait -n' would be to wait for
all background jobs and all procsubs that have ever been assigned to
$! at that point.

Bash already knows the pids for the procsubs before they are assigned
to $!, right? During that time, those pids can be kept in a separate
list, and then the list of all procsub pids that have ever been
assigned to $! can be waited for.

This still removes the potential for hanging, I think, while being more useful.