# 18.5.8. 队列集

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. 队列

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.

  这个类不是线程安全的（not thread safe）。

  3.4.4 版更變: New `join()` and `task_done()` methods.

  `empty`()

    如果队列为空返回 `True` ，否则返回 `False` 。

  `full`()

    如果有 `maxsize` 个条目在队列中，则返回 `True` 。

    備註

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

  coroutine `get`()

    从队列中删除并返回一个元素。如果队列为空，则等待，直到队列中有元素。

    This method is a coroutine.

    也參考

    The `empty()` method.

  `get_nowait`()

    Remove and return an item from the queue.

    立即返回一个队列中的元素，如果队列内有值，否则引发异常 `QueueEmpty` 。

  coroutine `join`()

    Block until all items in the queue have been gotten and processed.

    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.

    This method is a coroutine.

    3.4.4 版新加入.

  coroutine `put`(item)

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

    This method is a coroutine.

    也參考

    The `full()` method.

  `put_nowait`(item)

    不阻塞的放一个元素入队列。

    如果没有立即可用的空闲槽，引发 `QueueFull` 异常。

  `qsize`()

    Number of items in the queue.

  `task_done`()

    表明前面排队的任务已经完成，即get出来的元素相关操作已经完成。

    由队列使用者控制。每个 `get()` 用于获取一个任务，任务最后调用 `task_done()` 告诉队列，这个任务已经完成。

    如果 `join()` 当前正在阻塞，在所有条目都被处理后，将解除阻塞(意味着每个 `put()` 进队列的条目的 `task_done()` 都被收到)。

    如果被调用的次数多于放入队列中的项目数量，将引发 `ValueError` 。

    3.4.4 版新加入.

  `maxsize`

    队列中可存放的元素数量。

## 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. 异常

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.