Metadata-Version: 1.1
Name: pqueue
Version: 0.1.4
Summary: A single process, persistent multi-producer, multi-consumer queue.
Home-page: http://github.com/balena/python-pqueue
Author: G. B. Versiani
Author-email: guibv@yahoo.com
License: BSD
Description: ======
        pqueue
        ======
        
        **pqueue** is a simple persistent (disk-based) FIFO queue for Python.
        
        **pqueue** goals are speed and simplicity. The development was initially based
        on the `Queuelib`_ code.
        
        Requirements
        ============
        
        * Python 2.7 or Python 3.3
        * no external libraries requirements
        
        Installation
        ============
        
        You can install **pqueue** either via Python Package Index (PyPI) or from
        source.
        
        To install using pip:
        
            $ pip install pqueue
        
        To install using easy_install:
        
            $ easy_install pqueue
        
        If you have downloaded a source tarball you can install it by running the
        following (as root):
        
            # python setup.py install
        
        How to use
        ==========
        
        **pqueue** provides a single FIFO queue implementation.
        
        Here is an example usage of the FIFO queue:
        
            >>> from pqueue import Queue
            >>> q = Queue("tmpqueue")
            >>> q.put(b'a')
            >>> q.put(b'b')
            >>> q.put(b'c')
            >>> q.pop()
            b'a'
            >>> del q
            >>> q = Queue("tmpqueue")
            >>> q.get()
            b'b'
            >>> q.get()
            b'c'
            >>> q.get_nowait()
            Traceback (most recent call last):
              File "<stdin>", line 1, in <module>
              File "/usr/lib/python2.7/Queue.py", line 190, in get_nowait
                return self.get(False)
              File "/usr/lib/python2.7/Queue.py", line 165, in get
                raise Empty
            Queue.Empty
            
        The Queue object is identical to Python's 'Queue' module (or 'queue' in Python
        3.x), with the difference that it requires a parameter 'path' indicating where
        to persist the queue data and 'chunksize' indicating how many enqueued items
        should be stored per file. The same 'maxsize' parameter available on the
        system wise 'Queue' has been maintained.
        
        In other words, it works exactly as Python's Queue, with the difference any
        abrupt interruption is `ACID-guaranteed`_:
        
            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
        
        Note that pqueue *is not intended to used by multiple processes*.
        
        How it works?
        =============
        
        Pushed data is serialized using pickle in sequence, on chunked files named as
        qNNNNN, with a maximum of 'chunksize' elements, all stored on the given 'path'.
        
        The queue is formed by a 'head' and a 'tail'. Pushed data goes on 'head',
        pulled data goes on 'tail'.
        
        An 'info' file is pickled in the 'path', having the following 'dict':
        
        * 'head': a list of three integers, an index of the 'head' file, the number of
          elements written, and the file position of the last write.
        * 'tail': a list of three integers, an index of the 'tail' file, the number of
          elements read, and the file position of the last read.
        * 'size': number of elements in the queue.
        * 'chunksize': number of elements that should be stored in each disk queue
          file.
        
        Both read and write operations depend on sequential transactions on disk. In
        order to accomplish ACID requirements, these modifications are protected by the
        Queue locks.
        
        If, for any reason, the application stops working in the middle of a head
        write, a second execution will remove any inconsistency by truncating the
        partial head write.
        
        On 'get', the 'info' file is not updated, only when you first call 'task_done',
        and only on the first time case you have to call it sequentially.
        
        The 'info' file is updated in the following way: a temporary file (using
        'mkstemp') is created with the new data and then moved over the previous 'info'
        file. This was designed this way as POSIX 'rename' is guaranteed to be atomic.
        
        In case of abrupt interruptions, one of the following conditions may happen:
        
        * A partial write of the last pushed element may occur and in this case only
          this last element pushed will be discarded.
        * An element pulled from the queue may be processing, and in this case a second
          run will consume same element again.
        
        Tests
        =====
        
        Tests are located in **pqueue/tests** directory. They can be run using
        Python's default **unittest** module with the following command:
        
            ./runtests.py
        
        The output should be something like the following::
        
            ./runtests.py
            test_MultiThreaded (pqueue.tests.test_queue.TestSuite_PersistenceTest)
            Create consumer and producer threads, check parallelism ... ok
            test_OpenCloseOneHundred (pqueue.tests.test_queue.TestSuite_PersistenceTest)
            Write 1000 items, close, reopen checking if all items are there ... ok
            test_OpenCloseSingle (pqueue.tests.test_queue.TestSuite_PersistenceTest)
            Write 1 item, close, reopen checking if same item is there ... ok
            test_PartialWrite (pqueue.tests.test_queue.TestSuite_PersistenceTest)
            Test recovery from previous crash w/ partial write ... ok
            test_RandomReadWrite (pqueue.tests.test_queue.TestSuite_PersistenceTest)
            Test random read/write ... ok
            
            ----------------------------------------------------------------------
            Ran 5 tests in 4.615s
            
            OK
        
        License
        =======
        
        This software is licensed under the BSD License. See the LICENSE file in the
        top distribution directory for the full license text.
        
        Versioning
        ==========
        
        This software follows `Semantic Versioning`_
        
        .. _Queuelib: http://github.com/scrapy/queuelib
        .. _ACID-guaranteed: http://en.wikipedia.org/wiki/ACID
        .. _Semantic Versioning: http://semver.org/
        
Platform: all
Classifier: Development Status :: 4 - Beta
Classifier: Operating System :: OS Independent
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: BSD License
Classifier: Programming Language :: Python :: 2
Classifier: Programming Language :: Python :: 2.7
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.3
Classifier: Programming Language :: Python :: 3.4
Classifier: Programming Language :: Python :: 3.5
Classifier: Topic :: Software Development :: Libraries
