single.py: A wrapper command to provide an advisory lock, without leaving stale lock files.
Usage: single.py [options] -c command args..
Options:
-h, --help show this help message and exit
-f LOCK_FILE, --lock-file=LOCK_FILE
Path to the lock file. Default is provided based on the command path if omitted.
-s, --status Check to see if the file is locked, and if so, by which process. Exit status is 0
if unlocked, 1 if locked.
flock(2)'ed file is used to provide locking. This will not leave stale lock files around.
Note that the existance of lock file does not mean that there is an outstanding lock;
exclusive flock must be held by a process.
So use 'single.py --status -f /tmp/foo.lock' to see if the lock is held.
The OS releases the lock upon process termination, so the lock file is released
regardless of how the job terminated.
Invocations:
* single.py -c long-running-scrit arg1 arg2
will ensure only one long-running-scrit will run at a time.
Default lock file, specific to the command, is used in the absence of -f option.
* Lockfile can be explicitely specified as:
single.py -f /tmp/lrs-foo.lock -c long-running-scrit foo
Two jobs using the same command could be run concurrently by using different lock files, like:
single.py -f /tmp/lrs-bar.lock -c long-running-scrit bar
* Use --status (-s) option to check if a command or a file is locked:
single.py -s -f /tmp/foo.lock
single.py -s -c long-running-scrit
Example: $ single.py -c sleep 3 & for x in {0..6}; do single.py -s -c sleep; sleep 1; done
[1] 32567
locked by 32567: /tmp/single.py_bin_sleep.flock
locked by 32567: /tmp/single.py_bin_sleep.flock
locked by 32567: /tmp/single.py_bin_sleep.flock
[1]+ Done single.py sleep 5
not locked: /tmp/single.py_bin_sleep.flock
not locked: /tmp/single.py_bin_sleep.flock