disttask: refine dispatcher

[ywqzzy]

What problem does this PR solve?

Issue Number: ref #41495

Problem Summary:

Currently, the dispatcher use 2 for loop to dispatch and monitor tasks.

There is no abstraction for dispatcher and dispatcherManager.

1. dispatcher only handles one task.
2. dispatcherManager manages a bunch of dispatchers and transfer submitted tasks to different dispatchers.

What is changed and how it works?

1. remove DetectTaskLoop.
2. Don't call processFlow in DispatchTaskLoop, make it as light weight as possible.
3. add monitorTask which monitor the task status.
4. add scheduleTask which will call schedule one task with a for loop.
5. add executeTask interface which will trigger one goroutine to call scheduleTask.

Abstract dispatcher struct which only schedule and execute one task.

dispatcher will provide interface like:

1. scheduleTask: schedules the execution of subtasks.
2. monitorTask: check if the step is finished.
3. GenerateDistPlan: generate the task plan.

The dispatcher do the following job step by step:

1. Generate distributed plan which have multiple steps.
2. dispatch first step's subtasks.
3. monitor first step's subtasks status and decide if going to next step. If next step, go to 2. If all steps subtasks finished, mark task finished.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[tiprow]

Hi @ywqzzy. Thanks for your PR.

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[hawkingrei]

/ok-to-test

[codecov]

Codecov Report

Merging #45460 (61a4fe6) into master (a53fd2d) will increase coverage by 0.0190%.
Report is 7 commits behind head on master.
The diff coverage is 87.3303%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #45460        +/-   ##
================================================
+ Coverage   73.1995%   73.2185%   +0.0190%     
================================================
  Files          1265       1270         +5     
  Lines        390142     391401      +1259     
================================================
+ Hits         285582     286578       +996     
- Misses        86243      86434       +191     
- Partials      18317      18389        +72     

Flag	Coverage Δ
integration	78.1388% <ø> (?)
unit	73.2099% <87.3303%> (+0.0104%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	54.0444% <ø> (ø)
parser	85.0467% <ø> (+0.0108%)	⬆️
br	51.9865% <ø> (-0.0042%)	⬇️

[ywqzzy]

/retest

[zimulala]

We don't use this function. Could we remove it?

[ywqzzy]

I think Inited is better for checking of the dispatcher is started.

[GMHDBJD]

What does gpool do now?

[ywqzzy]

What does gpool do now?

Fixed

[GMHDBJD]

LGTM

[GMHDBJD]

how about move to dispatcher manager?

func (dm *DispatcherManager) StartDispathcer(){
      dm.gPool.Run(func() {
             d := newDispatcher()
             d.ExecuteTask()
             d.delRunningTask()
      })
} 

Then we no need finished channel.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Benjamin2037, GMHDBJD

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-07-20 01:57:47.182885524 +0000 UTC m=+1161158.953224223: ☑️ agreed by Benjamin2037.
• 2023-08-01 08:07:05.464021032 +0000 UTC m=+172709.406369562: ☑️ agreed by GMHDBJD.