From fd95baa09a45fa657cd83144d63e0110f8d75a59 Mon Sep 17 00:00:00 2001
From: Brian Woods
Date: Sun, 19 Mar 2023 15:34:13 -0400
Subject: queue: add base files for queuing system

Add a simple command queuing system.  Simple but useful for adding
multiple commands to a queue to run sequentially.
---
 queue/queue_worker.sh | 113 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100755 queue/queue_worker.sh

(limited to 'queue/queue_worker.sh')

diff --git a/queue/queue_worker.sh b/queue/queue_worker.sh
new file mode 100755
index 0000000..8b2b0b2
--- /dev/null
+++ b/queue/queue_worker.sh
@@ -0,0 +1,113 @@
+#!/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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