gestion des locks

Scripts/transmission-script.sh

@@ -1,5 +1,60 @@
 #!/bin/bash
 # script to check for completed torrents and stop and move them
+
+# lock dirs/files
+LOCKDIR="/tmp/statsgen-lock"
+PIDFILE="${LOCKDIR}/PID"
+
+# exit codes and text for them - additional features nobody needs :-)
+ENO_SUCCESS=0; ETXT[0]="ENO_SUCCESS"
+ENO_GENERAL=1; ETXT[1]="ENO_GENERAL"
+ENO_LOCKFAIL=2; ETXT[2]="ENO_LOCKFAIL"
+ENO_RECVSIG=3; ETXT[3]="ENO_RECVSIG"
+
+###
+### start locking attempt
+###
+
+trap 'ECODE=$?; echo "[statsgen] Exit: ${ETXT[ECODE]}($ECODE)" >&2' 0
+echo -n "[statsgen] Locking: " >&2
+
+if mkdir "${LOCKDIR}" &>/dev/null; then
+        # lock succeeded, install signal handlers before storing the PID just in case
+        # storing the PID fails
+        trap 'ECODE=$?;
+                echo "[statsgen] Removing lock. Exit: ${ETXT[ECODE]}($ECODE)" >&2
+                rm -rf "${LOCKDIR}"' 0
+        echo "$$" >"${PIDFILE}"
+        # the following handler will exit the script on receiving these signals
+        # the trap on "0" (EXIT) from above will be triggered by this trap's "exit" command!
+        trap 'echo "[statsgen] Killed by a signal." >&2
+                exit ${ENO_RECVSIG}' 1 2 3 15
+        echo "success, installed signal handlers"
+else
+        # lock failed, now check if the other PID is alive
+        OTHERPID="$(cat "${PIDFILE}")"
+
+        # if cat wasn't able to read the file anymore, another instance probably is
+        # about to remove the lock -- exit, we're *still* locked
+        #  Thanks to Grzegorz Wierzowiecki for pointing this race condition out on
+        #  http://wiki.grzegorz.wierzowiecki.pl/code:mutex-in-bash
+        if [ $? != 0 ]; then
+                echo "lock failed, PID ${OTHERPID} is active" >&2
+                exit ${ENO_LOCKFAIL}
+        fi
+
+        if ! kill -0 $OTHERPID &>/dev/null; then
+                # lock is stale, remove it and restart
+                echo "removing stale lock of nonexistant PID ${OTHERPID}" >&2
+                rm -rf "${LOCKDIR}"
+                echo "[statsgen] restarting myself" >&2
+                exec "$0" "$@"
+        else
+                # lock is valid and OTHERPID is active - exit, we're locked!
+                echo "lock failed, PID ${OTHERPID} is active" >&2
+                exit ${ENO_LOCKFAIL}
+        fi
+fi
  
 BLOCKLIST="/var/lib/transmission/.config/transmission-daemon/blocklists/blocklist.bin"
 # Update blocklist if older than 1 day