fsq is a standard for implementing queueing structures in POSIX file-systems. fsq provides a standard for both directory layouts and work-item naming, which allow for idempotent work-item construction, atomic enqueueing, and atomic completion.
The fsq python library (import fsq) provides a programattic way to
enqueue, scan, introspect and manipulate queues from Python.
The fsq program provides mechanisms for enqueueing, scanning, introspecting, auditing and repairing queues from the command line.
For more on the fsq standard see man 7 fsq, for more on the fsq program
see man 1 fsq.
The fsq project lives on github, and is available via pip.
sudo pip install fsq==0.2.4
curl https://github.com/axialmarket/fsq/archive/version_0.2.4.tar.gz | tar vzxf - cd fsq sudo python setup.py install
To install a queue, simply run:
$ fsq install a_queue
Or via the Python API:
>>> import fsq
>>> fsq.install('a_queue')
Installing a queue will create a directory in FSQ_ROOT (/var/fsq/):
/var/fsq/a_queue ├── done ├── fail ├── queue └── tmp
To enqueue work to the a_queue queue, simply run:
$ echo "data" | fsq enqueue a_queue args to enqueue
Or from the Python API:
>>> import fsq
>>> # enqueue a string
>>> fsq.senqueue('a_queue', 'data', 'args', 'to', 'enqueue')
>>> # ... or a file
>>> fsq.senqueue('a_queue', '/path/to/data.file', 'args', 'to', 'enqueue')
Enqueueing adds a file to the queue directory of a_queue:
/var/fsq/a_queue ├── done ├── fail ├── queue | └── _20131005205643_0_25577_mss_0_args_to_enqueue └── tmp
To process jobs, use the fsq scan program:
$ # echo gets "args", "to", "enqueue" as $1..$3 and "data" on stdin $ fsq scan a_queue echo args to enqueue
Or from the Python API:
>>> import fsq
>>> for work in fsq.scan('a_queue'):
... print " ".join(work.arguments)
... fsq.done(work)
args to enqueue
Work that is successfully completed moves to the done directory:
/var/fsq/a_queue ├── done | └── _20131005205643_0_25577_mss_0_args_to_enqueue ├── fail ├── queue └── tmp
As fsq scans each work item, it obtains an exclusive lock on the work item file, so it is safe to run multiple scan processes (or threads) in parallel on the same queue with no fear of duplicating effort.
Should work fail during processing:
$ fsq scan a_queue sh -c 'exit 100'
Or from the Python API:
>>> import fsq
>>> for work in fsq.scan('a_queue'):
... fsq.fail(work)
The failed work will be moved to the fail directory:
/var/fsq/a_queue ├── done ├── fail | └── _20131005205643_0_25577_mss_0_args_to_enqueue ├── queue └── tmp
Work can also fail temporarily, which will cause the work to remain in the
queue directory until it is older than FSQ_TTL seconds old, or until
it has been tried more than FSQ_MAX_TRIES times unsuccessfully:
$ # exit code 111 indicates temporary failure $ FSQ_MAX_TRIES=2 fsq scan a_queue sh -c 'exit 100'
Or from the Python API:
>>> import fsq
>>> fsq.set_const('FSQ_MAX_TRIES', 2)
>>> for work in fsq.scan('a_queue'):
... fsq.fail_tmp(work)
The name of the work item will change to indicate that the item has failed once:
/var/fsq/a_queue ├── done ├── fail ├── queue | └── _20131005205643_0_25577_mss_1_args_to_enqueue └── tmp
To temporaily stop all scanning of any queue, you simply use the fsq down
program:
$ fsq down a_queue
Or from the Python API:
>>> import fsq
>>> fsq.down('a_queue')
Which creates a regular file named down in the a_queue directory
preventing scan from working on the queue:
/var/fsq/a_queue ├── done ├── down ├── fail ├── queue | └── _20131005205643_0_25577_mss_0_args_to_enqueue └── tmp
To bring a queue back up again, you simply use the fsq up program:
$ fsq up a_queue
Or from the Python API:
>>> import fsq
>>> fsq.up('a_queue')
Which removes the down file, and allows the queue to be scanned properly
again.
The tmp directory within a_queue is used by fsq under the hood to ensure that all items are enqueued atomically.
_20120710213904_0_13044_mss_0_args_to_enqueue _20120710213904_1_13044_mss_0_args_to_enqueue +|-----+------| + |-+-| |+| + |------+------| | | | | | | | | | | | | | +-> FSQ_DELIMITER seperated | | | | | | arguments | | | | | +-> tries: number of failed attempts | | | | | to process | | | | +-> hostname: the name of the host on | | | | which the work-item was enqueued. | | | +-> pid of the process which enqueued the | | | work-item | | +-> entropy: should a work-item be generated | | with the same arguments, pid, hostname | | and timestamp, entropy is incremented to | | generate uniqueness. | +-> timestamp in FSQ_TIMEFMT format +-> FSQ_DELIMITER used at enqueue time
The fsq suite and python library makes use of a number of environment
variables (each prefixed by FSQ_), which modify its behavior. Each
environment variable is also available as a package-level constant.
Please refer to man 7 fsq for a complete list.