These small utilities allow creating very lightweight job queue systems which require no setup, maintenance, supervision, or any long-running processes.
nq should run on any POSIX.1-2008 compliant system which also
provides a working flock(2). Tested on Linux 2.6.37, Linux 4.1,
OpenBSD 5.7, FreeBSD 10.1, and Mac OS X 10.3.
The intended purpose is ad-hoc queuing of command lines (e.g. for
building several targets of a Makefile, downloading multiple files one
at a time, running benchmarks in several configurations, or simply as
a glorified nohup), but as any good Unix tool, it can be abused for
whatever you like.
Job order is enforced by a timestamp nq gets immediately when
started. Synchronization happens on file-system level. Timer
resolution is milliseconds. No sub-second file system time stamps are
required. Polling is not used. Exclusive execution is maintained
strictly.
Enforcing job order works like this:
- every job has a flock(2)ed output file ala
,TIMESTAMP.PID - every job starts only after all earlier flock(2)ed files are unlocked
- the lock is released by the kernel after the job terminates
You enqueue (get it?) new jobs using nq CMDLINE.... The job id is
output and nq detaches immediately, running the job in the background.
STDOUT and STDERR are redirected into the log file.
nq tries hard (but does not guarantee) to ensure the log file of the
currently running job has +x bit set. Thus you can use ls -F to get
a quick overview of the state of your queue.
The "file extension" of the log file is the actually PID, so you can
kill jobs easily. Before the job is started, it is the PID of nq,
so you can cancel a queued job by killing it as well.
Due to the initial exec line in the log files, you can resubmit a
job by executing it as a shell command file, i.e. running sh $jobid.
You can wait for jobs to finish using nq -w, possibly listing job
ids you want to wait for; the default is all of them. Likewise, you
can test if there are jobs which need to be waited upon using -t.
By default, job ids are per-directory, but you can set $NQDIR to put
them elsewhere. Creating nq wrappers setting $NQDIR to provide
different queues for different purposes is encouraged.
All these operations take worst-case quadratic time in the amount of lock files produced, so you should clean them regularly.
Two helper scripts are provided:
tq wraps nq and displays the output in a new tmux window (it needs
tmux and GNU tail).
fq outputs the log of the currently running jobs, exiting when the
jobs are done. If no job is running, the output of the last job is
shown. fq uses inotify on Linux and falls back to polling for
size change else. fq.sh is a similar tool, not quite as robust,
implemented as shell-script calling tail.
(A pure shell implementation of nq is provided as nq.sh. It needs
flock from util-linux, and only has a timer resolution of 1s.
Lock files from nq and nq.sh should not be mixed.)
nq is in the public domain.
To the extent possible under law, Christian Neukirchen chneukirchen@gmail.com has waived all copyright and related or neighboring rights to this work.