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#!/bin/bash
# SPDX-FileCopyrightText: 2023 Brian Woods
# SPDX-License-Identifier: GPL-2.0-or-later
# settings
CMD=""
TIME_BASE=10 # always wait this time
TIME_RND=0 # above plus 0-120
# pathes
LOCK="queue.lock"
QUEUE="queue.file"
WORKER_PID="queue_worker.pid"
# references for why I went with sed, that and ease use
# https://www.baeldung.com/linux/remove-first-line-text-file
queue_shift ()
{
queue_item=""
local lock_fd="3"
# aquire lock
if ! exec {lock_fd}>"$LOCK" ; then
echo "Can't get lockfile fd"
return
fi
if ! flock -w 10 "$lock_fd" ; then
echo "couldn't get lock"
return
fi
if [ -f "$QUEUE" ] ; then
local line="$(head -n 1 $QUEUE)"
sed -i '1d' "$QUEUE"
#delete if empty
if [ ! -s "$QUEUE" ] ; then
rm "$QUEUE"
fi
fi
# release lock
flock -u "$lock_fd"
exec {lock_fd}>&-
queue_item="$line"
}
queue_work ()
{
local rv=1
local lock_fd="3"
# aquire lock
if ! exec {lock_fd}>"$LOCK" ; then
echo "Can't get lockfile fd"
return
fi
if ! flock -w 10 "$lock_fd" ; then
echo "couldn't get lock"
return
fi
# we have work
if [ -f "$QUEUE" ] ; then
rv=0
fi
# release lock
flock -u "$lock_fd"
exec {lock_fd}>&-
return $rv
}
sleep_pause ()
{
if [ "$TIME_RND" = "0" ] ; then
local sleep_period="$TIME_BASE"
else
local sleep_period=$(( RANDOM % TIME_RND + TIME_BASE ))
fi
sleep "$sleep_period"
}
# FIRST thing is to create PID file
if [ ! -f "$WORKER_PID" ] ; then
echo "$$" > "$WORKER_PID"
else
echo "worker already running, exiting"
exit 1
fi
# XXX
# add checks for PID file every .1 seconds so sleep for x2 that just to
# make sure
sleep .2
while queue_work ; do
queue_shift
if [ ! -z "$queue_item" ] ; then
if [ ! -z "$CMD" ] ; then
$CMD $queue_item
else
eval "$queue_item"
fi
fi
sleep_pause
done
# remove PID file right before exiting
rm -f "$WORKER_PID"
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