From: Matthias Kruk <matthias.kruk@miraclelinux.com>
Date: Sat, 29 May 2021 04:17:48 +0000 (+0900)
Subject: include/{mutex,wmutex,sem,queue}: Add timeout argument to blocking functions
X-Git-Url: https://git.corax.cc/?a=commitdiff_plain;h=df97069dce689b550183704d00cee8a9e51e4054;p=toolbox

include/{mutex,wmutex,sem,queue}: Add timeout argument to blocking functions

The following functions potentially block the executing script indefinitely,
without a way to recover from the situation.
 - queue_get()
 - queue_get_file()
 - sem_wait()
 - mutex_lock()
 - wmutex_lock()

It is a common pattern to implement deamons dispatching messages from a queue
in the following way using the "inst" module.

    while inst_running; do
        local msg

        if msg=$(queue_get "$queue"); then
            handle_message "$msg"
        fi
    done

The problem with this code is that queue_get() potentially waits indefinitely,
and the daemon won't terminate even if it was instructed to. To mitigate this
situation, this commit adds a timeout argument to all of the above functions,
allowing the caller to specify the number of seconds the functions should wait
at most. If the timeout parameter is 0 or omitted, the functions will wait
forever (as is the current behavior), so existing code that uses any of the
above functions and that wishes to retain the current behavior does not need to
be modified.
---

diff --git a/include/mutex.sh b/include/mutex.sh
index c05652f..4efd905 100644
--- a/include/mutex.sh
+++ b/include/mutex.sh
@@ -21,6 +21,7 @@ mutex_trylock() {
 
 mutex_lock() {
 	local lock="$1"
+	local -i timeout="$2"
 
 	while ! mutex_trylock "$lock"; do
 		# We can't inotifywait on symlinks. Which is
@@ -28,7 +29,7 @@ mutex_lock() {
 		# containing directory is changed. Hence, we can
 		# watch the containing directory instead.
 
-		if ! inotifywait -qq "${lock%/*}"; then
+		if ! inotifywait -qq "${lock%/*}" -t "$timeout"; then
 			return 1
 		fi
 	done
diff --git a/include/queue.sh b/include/queue.sh
index 868d61b..8308ab4 100644
--- a/include/queue.sh
+++ b/include/queue.sh
@@ -363,6 +363,7 @@ queue_put_file() {
 
 queue_get() {
 	local queue="$1"
+	local -i timeout="$2"
 
 	local sem
 	local mutex
@@ -376,7 +377,7 @@ queue_get() {
 
 	err=false
 
-	if ! sem_wait "$sem"; then
+	if ! sem_wait "$sem" "$timeout"; then
 		return 1
 	fi
 
@@ -403,6 +404,7 @@ queue_get() {
 queue_get_file() {
 	local queue="$1"
 	local destdir="$2"
+	local -i timeout="$3"
 
 	local sem
 	local mutex
@@ -424,7 +426,7 @@ queue_get_file() {
 
 	err=false
 
-	if ! sem_wait "$sem"; then
+	if ! sem_wait "$sem" "$timeout"; then
 		return 1
 	fi
 
diff --git a/include/sem.sh b/include/sem.sh
index 2a1e397..6c6ef6e 100644
--- a/include/sem.sh
+++ b/include/sem.sh
@@ -173,6 +173,7 @@ sem_destroy() {
 
 sem_wait() {
 	local name="$1"
+	local -i timeout="$2"
 
 	local waitlock
 	local countlock
@@ -184,7 +185,7 @@ sem_wait() {
 	counter=$(_sem_get_counter "$name")
 	err=1
 
-	if ! wmutex_lock "$waitlock"; then
+	if ! wmutex_lock "$waitlock" "$timeout"; then
 		return 1
 	fi
 
diff --git a/include/wmutex.sh b/include/wmutex.sh
index 3b78d61..ff732bd 100644
--- a/include/wmutex.sh
+++ b/include/wmutex.sh
@@ -21,9 +21,10 @@ wmutex_trylock() {
 
 wmutex_lock() {
 	local lock="$1"
+	local -i timeout="$2"
 
 	while ! wmutex_trylock "$lock"; do
-		if ! inotifywait -qq "${lock%/*}"; then
+		if ! inotifywait -qq "${lock%/*}" -t "$timeout"; then
 			return 1
 		fi
 	done