Fix background_pool_size not take effect and BackgroundProcessingPool::getThreadIds may misses some thread_ids. (#4686)

[ti-chi-bot]

This is an automated cherry-pick of #4686

What problem does this PR solve?

Issue Number: close #4684 #4685

Problem Summary:

1. Context::setDefaultProfiles should be called before Context::initializeRateLimiter. Because Context::initializeRateLimiter calls Context::getBackgroundPool and Context::getBlockableBackgroundPool inside to get background thread ids.
2. BackgroundProcessingPool::getThreadIds and BackgroundProcessingPool::addThreadId are executing concurrently. BackgroundProcessingPool::getThreadIds may be called before all background threads executing ``BackgroundProcessingPool::addThreadId` completely.

What is changed and how it works?

1. Adjust the initialization sequence of Context.
2. Add absl::BlockingCounter to count all background threads executing BackgroundProcessingPool::addThreadId completely.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

1. Set configuration profiles.default.background_pool_size: 8.
2. The expected log is found:

[2022/04/16 11:22:31.740 +08:00] [INFO] [BackgroundProcessingPool.cpp:90] ["BackgroundProcessingPool:Create BackgroundProcessingPool with 8 threads"] [thread_id=1]
[2022/04/16 11:22:31.763 +08:00] [INFO] [BackgroundProcessingPool.cpp:90] ["BackgroundProcessingPool:Create BackgroundProcessingPool with 8 threads"] [thread_id=1]
[2022/04/16 11:22:31.775 +08:00] [INFO] [RateLimiter.cpp:526] ["IORateLimiter:bg_thread_ids 16 => [9489, 9491, 9492, 9493, 9494, 9495, 9496, 9490, 9504, 9505, 9506, 9507, 9508, 9509, 9510, 9511]"] [thread_id=1]

• 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

None

[ti-chi-bot]

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This pull request has been approved by:

• JaySon-Huang

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[Lloyd-Pottiger]

changes needed according to #4704

[JaySon-Huang]

close as no further patch version for the 6.0 branch