Comment

Currently, when the queue is full, new items are added to the queue._putters deque via an attached future. As soon as an item is removed from this queue, one future of the deque is set to done, then removed. This future is in transit, not referenced anywhere.

First I suggest removing the future from queue._putters only after it had been woken up, not before. All pending or moving item/task will stay into queue._putters
Second when put() is called, if the queue is full or if queue._putters is not empty, this item/task will be added to queue._putters.
When put_nowait() is called, if the queue is not full and queue._putters is not empty, we raise a new QueueFullWithPendingPutTasks exception derived from QueueFull.

The behavior of the get part should be identical.

Modified methods of Queue class :

• put()
• put_nowait()
• get()
• get_nowait()
• _wakeup_next()

New private methods of Queue class:

• _put_and_wakeup_next() called from put() and put_nowait().
• _get_and_wakeup_next() called from get()and get_nowait().

New exceptions of queues.py:

• QueueFullWithPendingPutTasks raised from put_nowait()
• QueueEmptyWithPendingGetTasks raised from get_nowait()

Update:
These two exceptions are derived from QueueFull and QueueEmpy respectively. This is necessary to preserve the
backwards compatibility of put_nowait() and get_nowait() methods.
May be their names are too long or not explicit enough, so I am open to suggestions.

• Issue: asyncio.Queue: putting items out of order when it is full #83055