[Toybox] [PATCH] killall.test, pidof.test: deflake.

[Rob Landley]

On 9/19/19 9:45 AM, enh wrote:
> On Thu, Sep 19, 2019 at 7:37 AM Rob Landley <rob at landley.net> wrote:
>>
>> On 9/16/19 3:17 PM, enh via Toybox wrote:
>>> Rarely (but these tests now get run often), it seems like we catch the
>>> shell between its fork and exec of sleep, which counts as false
>>> positives for killall/pidof. Since we don't actually need to sleep, just
>>> have the shell script spin instead.
>>
>> What's the failure here? The fork but not yet exec means we think the shell has
>> done a (subshell) or backgrounded& something, so we killed two instances of the
>> test. Ok. This is bad how? Isn't killall supposed to kill all? (What test
>> actually fails?)
> 
> the test is checking the list of pids (so we can tell it's actually
> doing anything), so there's an unexpected extra entry.

Ok, let's see...

wait and wait -n both exit immediately if it knows you have no child processes,
wait 1 says pid 1 is not a child of this shell....

"suspend" requires SIGCONT to continue and other signals are blocked, plus the
Defective Annoying SHell in debian hasn't got it and you're doing $(which
randomshell).

Hmmm, can't symlink it straight to sleep because it's testing -x to see through
script, so I have to have a test _script_.

I don't want a failed test to leave a cpu-eating loop running because I didn't
notice and it drained my battery a couple times...

Hmmm... maybe a max count in the loop? Except how big the count should be varies
WILDLY over various hardware and it could theoretically get fast enough to cause
failures. It's a pity there isn't a $UNIXTIME builtin...

Aha!

echo -e "#!$(which sh)\nread i < /proc/self/fd/1" > pidof.test

That hangs. And now I want the "process killed" lines to go away, but I need the
PID... Ugh, seriously? This is hanging?

  pid=$(./pidof.test & echo $!)

That is an ampersand. It is BACKGROUNDING pidof.test. It works as (thingy&) and
then thingy doesn't show up in job control because the subshell exited (the
classic double fork and exec) except I need the PID of the child process, and
that syntax should do it! Ugh, let's see, redirecting the $! to >&2 does give me
output so it's RUNNING, it's just $() is refusing to exit until background jobs
exit (WHO ASKED YOU, is this a bash behavior I need to match in toysh?
Probably.) and adding ; disown $! wasn't enough (although $! probably blanks
after reading once) so how about...

Ok, I've made it as far as:

  pid="$( (./pidof.test & echo $!)& disown $! )"

And it's still hanging, I'm breaking for lunch.

Rob