Queue shutdown

Add a shutdown method to queue class (threading queue, multiprocessing, asyncio) which causes all future puts to raise (a queue.QueueShutdown) and all future gets once the queue is empty to also raise, unblocking all waiters. An optional argument immediate=True will skip the requirement for the queue to be empty.

This will enable producers and consumers to use the queue to know when to stop. This is important because both producers and consumers can be blocked waiting on the queue.

Previous discussion:

• queue termination on Discourse
• #81515

Linked PRs

• gh-96474
• gh-102499
• gh-104225
• gh-104228
• gh-104230
• gh-104750
• gh-115265
• gh-115838
• gh-116699
• gh-117621
• gh-138828

開始之前，請先查看連結的 pull requests 以及先前關於 Queue 終止的討論，因為這項工作已經在多個地方進行過探索。所要求的行為涵蓋 threading queue、multiprocessing queue 和 asyncio：關閉應拒絕後續的 put、解除等待者的阻塞，並在排空後讓 get 擲出例外，而 immediate=True 則跳過排空。