fix lost prometheus metric in OrderedExecutor

[TakaHiR07]

Descriptions of the changes in this PR:

Fix #4373

Motivation

As shown in the issue.

This is the first pr to fix the lost metric problem. And the other pr improve the metric in SingleThreadExecutor.

Changes

If we only fix the problem but do not change the metric , the metric is as follow, the metric become visible, though the format is not same.

[TakaHiR07]

@merlimat Could you take a look of this problem?

[hezhangjian]

Nice catch.

I think we can change createSingleThreadExecutor return SingleThreadExecutor directly.
BTW, I prefer split this pr, one to fix problem, one to modify the metric name.

[StevenLuMT]

LGTM,
I think this kind of metric change require adding a testcase to cover it

[TakaHiR07]

Nice catch.

I think we can change createSingleThreadExecutor return SingleThreadExecutor directly. BTW, I prefer split this pr, one to fix problem, one to modify the metric name.

ok, I would split to 2 pr. But I guess we can't change createSingleThreadExecutor return SingleThreadExecutor directly, because OrderedScheduler#createSingleThreadExecutor do not return SingleThreadExecutor

[hezhangjian]

Would you mind update the description since we split the PR? I would be glad to proceed with the merge once the updates are made.

[hezhangjian]

Thanks for your contribution. :)

[hangc0276]

We can registerMetrics here instead of the instanceOf check

[TakaHiR07]

Do you mean that remove the check if (thread instanceof SingleThreadExecutor) directly ?
But createSingleThreadExecutor() is also triggered in OrderedScheduler. In OrderedScheduler, createSingleThreadExecutor() do not return SingleThreadExecutor, so I keep the check here.