[Toybox] [PATCH] pidof.test: block on sleep rather than read.

[enh]

Can we use /dev/ptmx to get a pty and use that? I'll try that in the PST
morning if you haven't done it yourself or explained why it doesn't work by
then 😀

On Thu, Jan 23, 2020, 20:43 Rob Landley <rob at landley.net> wrote:

> On 1/22/20 11:02 PM, enh via Toybox wrote:
> > The commit that added the read mentioned the killall tests, but they use
> > sleep. Blocking on a read of stdout is failing in some of the Android
> > test infrastructure where it seems to end up connected to a socket.
> >
> >   ./pidof-12488.test[2]: can't open /proc/self/fd/1: No such device or
> address
>
> Sleep was spawning a child process, which meant it would fork() another
> instance
> of the same process before calling exec(), and thus kill and such were
> reporting
> multiple processes matched if they happened at exactly the wrong time,
> which was
> intermittently breaking your testing.
>
> That's why I changed it. You're reintroducing the old problem. I don't see
> how
> we can fork() without that window. (Now maybe we can have a LONG pause to
> let
> the fork flush through, but that's a question of the system you're running
> it on?)
>
> And we can't do the "ln -s $(which sleep) spleep" trick because we're
> specifically checking the "/bin/bash script.sh matches script.sh" part of
> the
> plumbing here, so it has to have an interpreter...
>
> Oh: Maybe we could #!/bin/sleep and then call the script "10". :)
>
> $ echo -e '#!'"$(which sleep)\nblah\n" > 10; chmod +x 10; ./10
> /bin/sleep: invalid time interval ‘./10’
> Try '/bin/sleep --help' for more information.
>
> Hmmm...
>
> $ echo -e '#!'"$(which sleep)\nblah\n" > 10; chmod +x 10; PATH=":$PATH" 10
> /bin/sleep: invalid time interval ‘./10’
> Try '/bin/sleep --help' for more information.
>
> Seriously? That's really how you're gonna play this bash?
>
> Sigh, skip all the previous ratholes I've been down ("wait" can't take an
> arbitrary PID only an existing child process, and wait -n with no children
> returns immediately...)
>
> Sadly, when debian's "flock" says it can take a filename in its man page:
>
>   $ cat blah
>   #!/usr/bin/flock
>   true
>   $ flock blah -c ./blah
>   flock: bad file descriptor: './blah'
>
>
> it lies. (And toybox never implemented the non-fd stuff anyway; no idea
> why it
> implemented the _fd_ stuff but clearly somebody wanted this...)
>
> Sigh, I can "yes > /dev/null" but that's a CPU eating loop if it doesn't
> work
> and I hate leaving those around as debris.)
>
> How about:
>
>   tty -s && skip_test
>   blah < /dev/tty
>
> Which is a sad aribtrary limitation I don't like but would at least
> probably
> skip the test entirely on your irreproducible test environment?
>
> I can create a dedicated C program to act as the test?
>
> (Sigh, why couldn't we trust a read from stdin to block again? Just running
> "cat" would give us something to kill that doesn't eat CPU if we don't. I
> think
> one of your test containers was broken with that, but I forget?)
>
> Rob
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