avoid deadlock when calling s3async callback, issue #1854

[h0hmj]

Signed-off-by: h0hmj [email protected]

What problem does this PR solve?

Issue Number: #1854

Problem Summary:

What is changed and how it works?

What's Changed:

add a work queue and a thread to handle async s3 request

How it Works:

move throttle check outside main loop, async s3 request will not block main loop

Side effects(Breaking backward compatibility? Performance regression?):

Check List

• Relevant documentation/comments is changed or added
• I acknowledge that all my contributions will be made under the project's license

[h0hmj]

recheck

[h0hmj]

let callbacks run in a separate thread rather than the event main loop to avoid deadlock.
num of callback ~= num of request (limited by inflight bytes)