Bug 21366: Add koha-plack --reload to gracefully restart Plack/Starman

This patch adds a "--reload" option to koha-plack, which allows
a sysadmin to gracefully restart Koha.

This is very useful when installing Koha plugins or deploying a hot fix
where you need to change code but don't want to interrupt anyone's
usage of Koha.

0. Apply patch
1. cp /usr/sbin/koha-plack /usr/sbin/koha-plack.bak
2. cp debian/scripts/koha-plack /usr/sbin/koha-plack
3. ps -efww | grep "starman"
4. Now at roughly the same time do the following two actions:
    4a. Go to http://localhost:8081/cgi-bin/koha/about.pl
    4b. koha-plack --reload kohadev
5. Note that the web request completes successfully
6. ps -efww | grep "starman"
7. Note that the "starman master" process stays alive, but the "starman worker" processes have been restarted

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>

debian/scripts/koha-plack

@@ -169,6 +169,26 @@ restart_plack()
     fi
 }
 
+reload_plack()
+{
+    local instancename=$1
+
+    local PIDFILE="/var/run/koha/${instancename}/plack.pid"
+
+    if is_plack_running ${instancename}; then
+        log_daemon_msg "Reloading Plack daemon for ${instancename}"
+
+        if start-stop-daemon --pidfile ${PIDFILE} --user="${instancename}-koha" --stop --signal HUP; then
+            log_end_msg 0
+        else
+            log_end_msg 1
+        fi
+    else
+        log_daemon_msg "Error: Plack not running for ${instancename}"
+        log_end_msg 1
+    fi
+}
+
 enable_plack()
 {
     local instancename=$1
@@ -360,6 +380,9 @@ _do_instance() {
         "restart")
             restart_plack $name
             ;;
+        "reload")
+            reload_plack $name
+            ;;
         "enable")
             enable_plack $name
             ;;
@@ -398,6 +421,9 @@ while [ $# -gt 0 ]; do
         --restart)
             set_action "restart"
             shift ;;
+        --reload)
+            set_action "reload"
+            shift ;;
         --enable)
             set_action "enable"
             shift ;;