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#!/bin/sh
# nq CMD... - run CMD... in background and in order, saving output to ,* files
#
# - needs POSIX sh + util-linux flock(1) (see nq.c for portable version)
# - when run from tmux, display output in a new window (needs
# GNU tail, C-c to abort the job.)
# - we try hard to make the currently running ,* file have +x bit
# - enforcing order works like this:
# - every job has a flock(2)ed file
# - every job starts only after all earlier flock(2)ed files finished
# - the lock is released when job terminates
#
# To the extent possible under law, Christian Neukirchen <chneukirchen@gmail.com>
# has waived all copyright and related or neighboring rights to this work.
# http://creativecommons.org/publicdomain/zero/1.0/
if [ -z "$NQ" ]; then
export NQ=$(date +%s)
"$0" "$@" & c=$!
(
# wait for job to finish
flock -x .,$NQ.$c -c true
flock -x ,$NQ.$c -c true
chmod -x ,$NQ.$c
) &
exit
fi
us=",$NQ.$$"
exec 9>>.$us
# first flock(2) the file, then make it known under the real name
flock -x 9
mv .$us $us
printf "## nq $*" 1>&9
if [ -n "$TMUX" ]; then
tmux new-window -a -d -n '<' -c '#{pane_current_path}' \
"trap true INT QUIT TERM EXIT;
tail -F --pid=$$ $us || kill $$;
printf '\n[%d exited, ^D to exit.]\n' $$;
cat >/dev/null"
fi
waiting=true
while $waiting; do
waiting=false
# this must traverse in lexical (= numerical) order:
# check all older locks are released
for f in ,*; do
# reached the current lock, good to go
[ $f = $us ] && break
if ! flock -x -n $f -c "chmod -x $f"; then
# force retrying all locks again;
# an earlier lock could just now have really appeared
waiting=true
flock -x $f -c true
fi
done
done
printf '\n' 1>&9
chmod +x $us
exec "$@" 2>&1 1>&9
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