Redo timeout handling in get()

[jobh]

What is the new behavior?

Suggested fix for #53.

This is a request for comments, not tested yet. The reason is that I don't understand the previous implementation, especially why last_timeout was saved between calls. So, possibly, the new implementation might be misguided.

The new implementation only uses self.timeout as default value for timeout if not specified, never writes to it. last_timeout is removed completely. The timeout (cur_timeout) is recalculated every loop iteration to match the initial deadline.

The following are the intended timeout semantics:

• If block=False, the call returns immediately. Otherwise,
• If timeout=None, self.timeout is used (1s by default).
• If timeout=0, the call blocks indefinitely (until an item is ready)
• If timeout>0, the call blocks never returns early (unless an item is ready).

Checklist

Please make sure the following requirements are complete:

• [x] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been reviewed and added / updated if needed (for bug fixes / features)
• [x] All automated checks pass (CI/CD)

[jobh]

Reorder commits: Add (failing) test as first commit, then fix the test failure in second commit.

The state of the PR is now "tested" and merge ready, but still a bit unclear whether there are missed edge cases (regarding the removal of last_timeout).

[malthe]

The reason last_time exists is to reduce latency in the case where we're blocked waiting for an item and there's an item scheduled for processing some time in the future which lies before the timeout.

That is, if we know that in 5 seconds, an item will be ready for processing and the timeout is 10 seconds, then last_time serves to lower the effective timeout to 5 seconds.

That's my interpretation of the semantics around this value. There should be a test case in there which demonstrates this behavior.

[stas]

I second @malthe and find it hard to understand why last_timeout is the issue here. Let's discuss the issue #53 first and jump to the coding once we're all on the same page please.