Queues

Source code: Lib/asyncio/queues.py

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asyncio queues are designed to be similar to classes of the queue module. Although asyncio queues are not thread-safe, they are designed to be used specifically in async/await code.

Note that methods of asyncio queues don’t have a timeout parameter; use asyncio.wait_for() function to do queue operations with a timeout.

See also the Examples section below.

Queue

class asyncio.Queue(maxsize=0)

A first in, first out (FIFO) queue.

If maxsize is less than or equal to zero, the queue size is infinite. If it is an integer greater than 0, then await put() blocks when the queue reaches maxsize until an item is removed by get().

Unlike the standard library threading queue, the size of the queue is always known and can be returned by calling the qsize() method.

Changed in version 3.10: Removed the loop parameter.

This class is not thread safe.

maxsize

Number of items allowed in the queue.

empty()

Return True if the queue is empty, False otherwise.

full()

Return True if there are maxsize items in the queue.

If the queue was initialized with maxsize=0 (the default), then full() never returns True.

async get()

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

Raises QueueShutDown if the queue has been shut down and is empty, or if the queue has been shut down immediately.

get_nowait()

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

async join()

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

The count of unfinished tasks goes up whenever an item is added to the queue. The count goes down whenever a consumer coroutine 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.

async put(item)

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

Raises QueueShutDown if the queue has been shut down.

put_nowait(item)

Put an item into the queue without blocking.

If no free slot is immediately available, raise QueueFull.

qsize()

Return the number of items in the queue.

shutdown(immediate=False)

Put a Queue instance into a shutdown mode.

The queue can no longer grow. Future calls to put() raise QueueShutDown. Currently blocked callers of put() will be unblocked and will raise QueueShutDown in the formerly blocked thread.

If immediate is false (the default), the queue can be wound down normally with get() calls to extract tasks that have already been loaded.

And if task_done() is called for each remaining task, a pending join() will be unblocked normally.

Once the queue is empty, future calls to get() will raise QueueShutDown.

If immediate is true, the queue is terminated immediately. The queue is drained to be completely empty and the count of unfinished tasks is reduced by the number of tasks drained. If unfinished tasks is zero, callers of join() are unblocked. Also, blocked callers of get() are unblocked and will raise QueueShutDown because the queue is empty.

Use caution when using join() with immediate set to true. This unblocks the join even when no work has been done on the tasks, violating the usual invariant for joining a queue.

Added in version 3.13.

task_done()

Indicate that a formerly enqueued work item is complete.

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

If a