18.5.8. Queues
**************

**Source code:** Lib/asyncio/queues.py

Queues:

* "Queue"

* "PriorityQueue"

* "LifoQueue"

asyncio queue API was designed to be close to classes of the "queue"
module ("Queue", "PriorityQueue", "LifoQueue"), but it has no
*timeout* parameter. The "asyncio.wait_for()" function can be used to
cancel a task after a timeout.


18.5.8.1. Queue
===============

class asyncio.Queue(maxsize=0, *, loop=None)

   A queue, useful for coordinating producer and consumer coroutines.

   If *maxsize* is less than or equal to zero, the queue size is
   infinite. If it is an integer greater than "0", then "yield from
   put()" will block when the queue reaches *maxsize*, until an item
   is removed by "get()".

   Unlike the standard library "queue", you can reliably know this
   Queue's size with "qsize()", since your single-threaded asyncio
   application won't be interrupted between calling "qsize()" and
   doing an operation on the Queue.

   This class is not thread safe.

   Modifié dans la version 3.4.4: Les nouvelles méthodes "join()" et
   "task_done()".

   empty()

      Renvoie "True" si la queue est vide, "False" sinon.

   full()

      Return "True" if there are "maxsize" items in the queue.

      Note:

        If the Queue was initialized with "maxsize=0" (the default),
        then "full()" is never "True".

   coroutine get()

      Remove and return an item from the queue. If queue is empty,
      wait until an item is available.

      Cette méthode est une coroutine.

      Voir aussi: La méthode "empty()".

   get_nowait()

      Supprime et donne un élément de la queue.

      Return an item if one is immediately available, else raise
      "QueueEmpty".

   coroutine join()

      Bloque jusqu'à ce que tous les éléments de la queue aient été
      récupérés et traités.

      The count of unfinished tasks goes up whenever an item is added
      to the queue. The count goes down whenever a consumer thread
      calls "task_done()" to indicate that the item was retrieved and
      all work on it is complete.  When the count of unfinished tasks
      drops to zero, "join()" unblocks.

      Cette méthode est une coroutine.

      Nouveau dans la version 3.4.4.

   coroutine put(item)

      Put an item into the queue. If the queue is full, wait until a
      free slot is available before adding item.

      Cette méthode est une coroutine.

      Voir aussi: La méthode "full()".

   put_nowait(item)

      Ajoute un élément dans la queue sans bloquer.

      If no free slot is immediately available, raise "QueueFull".

   qsize()

      Nombre d'éléments dans la queue.

   task_done()

      Indicate that a formerly enqueued task is complete.

      Used by queue consumers. For each "get()" used to fetch a task,
      a subsequent call to "task_done()" tells the queue that the
      processing on the task is complete.

      If a "join()" is currently blocking, it will resume when all
      items have been processed (meaning that a "task_done()" call was
      received for every item that had been "put()" into the queue).

      Raises "ValueError" if called more times than there were items
      placed in the queue.

      Nouveau dans la version 3.4.4.

   maxsize

      Nombre d'éléments autorisés dans la queue.


18.5.8.2. PriorityQueue
=======================

class asyncio.PriorityQueue

   A subclass of "Queue"; retrieves entries in priority order (lowest
   first).

   Entries are typically tuples of the form: (priority number, data).


18.5.8.3. LifoQueue
===================

class asyncio.LifoQueue

   A subclass of "Queue" that retrieves most recently added entries
   first.


18.5.8.3.1. Exceptions
----------------------

exception asyncio.QueueEmpty

   Exception raised when the "get_nowait()" method is called on a
   "Queue" object which is empty.

exception asyncio.QueueFull

   Exception raised when the "put_nowait()" method is called on a
   "Queue" object which is full.
