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Context added TSA #55278

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merged 3 commits into from Oct 25, 2023
Merged

Context added TSA #55278

merged 3 commits into from Oct 25, 2023

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kitaisreal
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@kitaisreal kitaisreal commented Oct 6, 2023

Follow-up to #55121

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  • Not for changelog (changelog entry is not required)

@robot-ch-test-poll4 robot-ch-test-poll4 added the pr-not-for-changelog This PR should not be mentioned in the changelog label Oct 6, 2023
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robot-ch-test-poll4 commented Oct 6, 2023

This is an automated comment for commit 0e176fa with description of existing statuses. It's updated for the latest CI running

✅ Click here to open a full report in a separate page

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@kitaisreal kitaisreal added the can be tested Allows running workflows for external contributors label Oct 7, 2023
@rschu1ze rschu1ze self-assigned this Oct 9, 2023
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The direction is good but TBH the SharedMutexHelper / ContextSharedMutex / SharedLockGuard machine seem overengineered. As far as I see, it addresses two problems:

  1. Only the non-relockable locker classes in libcxx (std::lock_guard and std::scoped_lock) have TSA annotations, the relockable ones (std::unique_lock, std::shared_lock) lack them.
  2. Additional code (update profile events) should run when the lock is aquired/released. As none of the locker classes in libcxx allows that, a custom implementation is needed.

I believe that 2. is quite a special case throughout the codebase, and that a non-generic (= Context-specific) class would do the job. I also think that the problem can be solved with small wrappers around std::unique_lock and std::shared_lock which behave like non-relockable locker classes and run some code in their ctors/dtors. Let me try to implement this (in a separate PR).

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The direction is good but TBH the SharedMutexHelper / ContextSharedMutex / SharedLockGuard machine seem overengineered. As far as I see, it addresses two problems:

  1. Only the non-relockable locker classes in libcxx (std::lock_guard and std::scoped_lock) have TSA annotations, the relockable ones (std::unique_lock, std::shared_lock) lack them.
  2. Additional code (update profile events) should run when the lock is aquired/released. As none of the locker classes in libcxx allows that, a custom implementation is needed.

I believe that 2. is quite a special case throughout the codebase, and that a non-generic (= Context-specific) class would do the job. I also think that the problem can be solved with small wrappers around std::unique_lock and std::shared_lock which behave like non-relockable locker classes and run some code in their ctors/dtors. Let me try to implement this (in a separate PR).

  1. It does not do the same logic at all https://github.com/ClickHouse/ClickHouse/pull/55573/files#diff-c7c4cea868f661341c1e9866836dc34c1c88723f9f33b4e09db530c2ea074036R214. If we take mutex in LockGuard constructor and start to record time, and in destructor try to add elapsed time to ProfileEvents. It is not the same as implemented in my pull request, we need to record time that we actually waited for mutex to be acquired.
  2. std::unique_lock, std::shared_lock provide additional overhead that is not needed at all, because your class now is movable and for TSA it is harder to analyze such classes.
  3. SharedMutexHelper is needed in a lot of other places in codebase when we want to add custom logic for lock and unlock methods.

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Additionally:
4. We should add custom logic to mutex not to LockGuards because we actually can lock mutex without this special guard and that way we does not get custom logic to run.
5. SharedLockGuard is also needed in a lot of places in codebase where we use shared_mutex and want to add TSA.

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After checking your PR in more detail, I think it is okay to merge (after incorporating the feedback).

1. It does not do the same logic at all https://github.com/ClickHouse/ClickHouse/pull/55573/files#diff-c7c4cea868f661341c1e9866836dc34c1c88723f9f33b4e09db530c2ea074036R214. If we take mutex in `LockGuard` constructor and start to record time, and in destructor try to add elapsed time to `ProfileEvents`. It is not the same as implemented in my pull request, we need to record time that we actually waited for mutex to be acquired.

True, that was a glitch on my end.

2. std::unique_lock, std::shared_lock provide additional overhead that is not needed at all, because your class now is movable and for TSA it is harder to analyze such classes.

In my PR, TSA doesn't care what is inside both new lock classes. It only looks at the interface of the lock class (which is the same as in your PR - the constructor and destructor with annotation). There was a little bit of extra overhead but I don't think it would be significant.

3. SharedMutexHelper is needed in a lot of other places in codebase when we want to add custom logic for `lock` and `unlock` methods.

Not sure if there are "a lot" of other places but it is a good to make custom logic around lock/unlock possible.

  1. We should add custom logic to mutex not to LockGuards because we actually can lock mutex without this special guard and that way we does not get custom logic to run.

That was where my PR took a different approach (to reduce complexity) but you are right that it also allowed to evade the custom logic.

  1. SharedLockGuard is also needed in a lot of places in codebase where we use shared_mutex and want to add TSA.

I added a comment about SharedLockGuard into the PR.

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src/Common/MutexUtils.h Outdated Show resolved Hide resolved
src/Common/MutexUtils.h Outdated Show resolved Hide resolved
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@rschu1ze can you please check this pull request ? I want to continue with adding TSA coverage for non shared Context, on top of this pull request.

@rschu1ze rschu1ze merged commit 665dfe6 into ClickHouse:master Oct 25, 2023
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yokofly added a commit to timeplus-io/proton that referenced this pull request Nov 21, 2023
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