18.5.8. 队列集

Queues:

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.