wait for timeout before cancelling scheduled tasks

[n8sty]

Resolves #72

What do these changes do?

Resolves issue raised by @Dock1100 in #72. Brief description of the issue is that handlers were not being gracefully shutdown.

Are there changes in behavior for the user?

This should make aiojobs operate in a manner that I believe is consistent with what is promised by its documentation.

Related issue number

#72

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> (e.g. 588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the PR
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: Fix issue with non-ascii contents in doctest text files.

[Dreamsorcerer]

I don't think this change is correct. A task should be cancelled immediately, as the code currently does. After cancellation, a task must then be awaited to give it a chance to handle the cancellation. The timeout is there in case the task is misbehaving and not cancelling quickly.

Your change results in cancelling without awaiting afterwards, which means the task may not get to handle any cleanup from the cancellation. You'll likely also end up with unawaited warnings.

I think to fix the original bug, would either need some explicit logic for @atomic, or maybe a new Scheduler.wait_and_close() method or similar, which actually waits on the existing jobs with a timeout before initiating a close.

Personally, I'd be more interested in fixing this from the aiohttp side and having aiohttp give handlers a moment to finish processing before shutting everything down.