persist-queue 0.2.0

A thread-safe disk based persistent queue in Python.

This project is based on the achievements of python-pqueue and queuelib

The goals is to achieve following requirements:

• Disk-based: each queued item should be stored in disk in case of any crash.

• Thread-safe: can be used by multi-threaded producers and multi-threaded consumers.

• Recoverable: Items can be read after process restart.

• Green-compatible: can be used in greenlet or eventlet environment.

While queuelib and python-pqueue cannot fulfil all of above. After some try, I found it’s hard to achieve based on their current implementation without huge code change. this is the motivation to start this project.

persist-queue use pickle object serialization module to support object instances. To support customized objects, please refer to Pickling and unpickling extension types(Python2) and Pickling Class Instances(Python3)

Requirements

• Python 2.7 or Python 3.x.

• Full support for Linux.

• Windows support (with Caution if persistqueue.Queue is used).

Installation

from pypi

pip install persist-queue

from source code

git clone https://github.com/peter-wangxu/persist-queue
cd persist-queue
python setup.py install

Examples

>>> from persistqueue import Queue
>>> q = Queue("mypath")
>>> q.put('a')
>>> q.put('b')
>>> q.put('c')
>>> q.get()
'a'
>>> q.task_done()

Close the python console, and then we restart the queue from the same path,

>>> from persistqueue import Queue
>>> q = Queue('mypath')
>>> q.get()
'b'
>>> q.task_done()

example usage with multi-thread(referred from github project python-pqueue):

from persistqueue import Queue

q = Queue()

def worker():
    while True:
        item = q.get()
        do_work(item)
        q.task_done()

for i in range(num_worker_threads):
     t = Thread(target=worker)
     t.daemon = True
     t.start()

for item in source():
    q.put(item)

q.join()       # block until all tasks are done

example usage for SQLite3 based queue.

from persistqueue import FIFOSQLiteQueue

q = FIFOSQLiteQueue(path="./test", multithreading=True)

def worker():
    while True:
        item = q.get()
        do_work(item)

for i in range(num_worker_threads):
     t = Thread(target=worker)
     t.daemon = True
     t.start()

for item in source():
    q.put(item)

Tests

persist-queue use tox to trigger tests.

to trigger tests based on python2.7/python3.x, use:

tox -e py27

tox -e py34

tox -e py35

tox -e py36

to trigger pep8 check, use:

tox -e pep8

pyenv is usually a helpful tool to manage multiple versions of Python.

Caution

Currently, the atomic operation is not supported on Windows due to the limitation of Python’s os.rename, That’s saying, the data in persistqueue.Queue could be in unreadable state when an incidential failure occurs during Queue.task_done.

DO NOT PUT ANY CRITICAL DATA ON persistqueue.QUEUE WHEN RUNNING ON WINDOWS.

Contribution

Simply fork this repo and send PR for your code change(also tests to cover your change), remember to give a title and description of your PR. I am willing to enhance this project with you :).

License

BSD

FAQ

• sqlite3.OperationalError: database is locked is raised.

persistquest open 2 connections for the db if multithreading=True, the SQLite database is locked until that transaction is committed. The timeout parameter specifies how long the connection should wait for the lock to go away until raising an exception. Default time is 10, increase timeout when creating the queue if above error occurs.