在异步方法开始之前获取锁

Question

Let's say I have a multiprocessing.Lock instance ( lock below) that I want to acquire just before a coroutine foo actually begins to run (say it is triggered by some future I/O or signal and so I don't want to hold the lock for the entire period that it is blocked, but rather just while it runs.) Is there any way to do this without modifying the body of foo itself? To illustrate:

Without lock:

await foo()

With lock:

lock.acquire()
await foo()
lock.release()

As far as I can tell it doesn't help to wrap foo inside another async function because it still needs to be await ed in the same manner. It also doesn't help to deal with the asyncio.Future directly, because all I can do is add_done_callback . Or any other concept of "chaining" callbacks is the same as wrapping it in an async function-- if I put the lock acquisition future before the foo future, it will just run right away effectively, and the lock will be held for the whole duration until foo actually begins.

Is changing the body of foo the only way or is there a workaround I'm not seeing?

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To be a little more specific in case it sheds light, my situation is actually that foo is the get method of an asyncio.Queue instance. Therefore it may be enough to subclass and override this one-line method with a two-line one that does my desired lock acquisition first. Or monkeypatch the method on the instance. But this seems to be getting into ugly territory.

https://github.com/python/cpython/blob/1e1dbdf23f7a18f53a3257badc3541973831f2c4/Lib/asyncio/queues.py#L57-L58

Answer 1

Updated after comment.

In general, when using locks you should hold them for the shortest duration possible .

Writing a subclass is probably the way to go if you need to use locks.

Your question doesn't contain enough detail to give other sensible recommendations.