queue: add base files for queuing systemHEADmaster

Add a simple command queuing system.  Simple but useful for adding
multiple commands to a queue to run sequentially.

3 files changed, 197 insertions, 0 deletions

diff --git a/queue/README.md b/queue/README.md
new file mode 100644
index 0000000..be3fbdd
--- /dev/null
+++ b/queue/README.md
@@ -0,0 +1,24 @@
+# Queue scripts
+
+Basically these scripts are used for throwing commands in a queue and
+then running them sequentially with a configurable about of time between
+them.
+This allows for just throwing things in the queue and forgetting about
+them without having to manually run commands one after the other.
+
+## Usage
+Configuring the paths is highly suggested.  You can have everything
+other than the queue\_add.sh script in a queue directory.
+There's also the `CMD` variable useful if you're just running one
+command with differing or even the same options.
+The `TIME_BASE` and `TIME_RND` are useful to spacing the queue tasks
+out if need be.
+
+## Example
+	./queue_add.sh 'echo 1 >> log.txt'
+	./queue_add.sh 'echo 2 >> log.txt'
+	./queue_add.sh 'echo 3 >> log.txt'
+	./queue_add.sh 'echo 4 >> log.txt'
+	./queue_add.sh 'echo 5 >> log.txt'
+	sleep 1         # give it enough time to run the first job
+	tail -f log.txt # see the output
diff --git a/queue/queue_add.sh b/queue/queue_add.sh
new file mode 100755
index 0000000..74fb2df
--- /dev/null
+++ b/queue/queue_add.sh
@@ -0,0 +1,60 @@
+#!/bin/bash
+# SPDX-FileCopyrightText: 2023 Brian Woods
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+# paths
+LOCK="queue.lock"
+QUEUE="queue.file"
+WORKER="./queue_worker.sh"
+WORKER_PID="queue_worker.pid"
+WORKER_LOG="queue_worker.log"
+
+queue_push ()
+{
+	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
+
+	# actually write it out
+	echo "$@" >> "$QUEUE"
+
+	# release lock
+	flock -u "$lock_fd"
+	exec {lock_fd}>&-
+}
+
+spawn_worker ()
+{
+	nohup "$WORKER" >> "$WORKER_LOG" &
+
+	# 5 seconds of waiting
+	local max=50
+	local tries=0
+	while [ "$tries" -lt "$max" ]  ; do
+		sleep .1
+		tries=$(( tries + 1 ))
+
+		if [ -f "$WORKER_PID" ] ; then
+			break
+		fi
+	done
+	if [ "$tries" = "$max" ] ; then
+		echo "warning waiting period without worker PID created"
+	fi
+}
+
+queue_push $@
+
+# need to do some locking if we want this to be actually safe
+# 1. get lock, 2. spin off worker, 3. wait until pid, 4. release lock
+if [ ! -f "$WORKER_PID" ] ; then
+	spawn_worker
+fi
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"