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Date: Mon, 12 Mar 2018 14:23:59 +0100 (CET)
From: "Antoine C." <acalando@free.fr>
To: zsh-workers@zsh.org
Message-ID: <1328064061.551458859.1520861039419.JavaMail.root@zimbra62-e11.priv.proxad.net>
Subject: [BUG?] "wait <PID>" sometimes confused with multiple childs
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Hello,

I have a problem with a script starting several subshells in background then checking their return code. It looks like the "wait <PID>" builtin is sometimes returning the error code of another child.

Here is a script reproducing this behavior. Several childs are started in a first loop with predefined return code, their PID saved, then we wait for each of them in a second loop and check their RC:
------start-----
#!/bin/zsh

while true; do
	pids=()
	for task in {1..16} ; do
		( sleep .1 ; exit $task ) &
		pids+=($!)
		# uncomment to prevent bug
		#sleep .1
	done
	for task in {1..16} ; do
		wait $pids[task]
		rc=$?
		if (( rc != task )) ; then
			echo "  FAIL $pids[task]" $rc $task
		fi
	done
	echo "done $pids"
done
------end-----

On my machine, I have many "FAIL ..." printed, around 1 "FAIL" every 2 "done".
If we comment out the "sleep" above, no more fails are printed. I also tried with bash (with a few syntax changes), and it is always working as expected.

Is it a bug or am I missing something?

Antoine