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_add.sh | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100755 queue/queue_add.sh

(limited to 'queue/queue_add.sh')

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
-- 
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