Unstable unit test AsyncTasksTest.AsyncTasksNormal

[Lloyd-Pottiger]

Bug Report

https://ci.pingcap.net/blue/organizations/jenkins/tiflash-ghpr-unit-tests/detail/tiflash-ghpr-unit-tests/12996/pipeline

[JaySon-Huang]

The test AsyncTasksTest.AsyncTasksNormal can not finished within 45 minutes, seems it hangs. @CalvinNeo

[Lloyd-Pottiger]

https://ci.pingcap.net/blue/organizations/jenkins/tiflash-ghpr-unit-tests/detail/tiflash-ghpr-unit-tests/13003/pipeline

[CalvinNeo]

Can't repeat by while ./dbms/gtests_dbms --gtest_filter="AsyncTasksTest.AsyncTasksNormal"; do :; done.
Maybe this is due to blocking between tests.

[CalvinNeo]

3 -> 4 -> 1 -> block
3 -> 1 -> 4 -> 2 OK

    {
        auto async_tasks = std::make_unique<TestAsyncTasks>(1, 1, 2);
        auto m = std::make_shared<std::mutex>();
        auto m2 = std::make_shared<std::mutex>();
        int flag = 0;
        std::unique_lock cl(*m);
        async_tasks->addTask(1, [m, &flag, &async_tasks, m2, &log]() {
            auto cancel_handle = async_tasks->getCancelHandleFromExecutor(1);
            std::scoped_lock rl2(*m2); // 1
            std::scoped_lock rl(*m); // 2
            // Run after `cl` is released.
            if (cancel_handle->isCanceled())
            {
                return;
            }
            flag = 1;
        });
        async_tasks->asyncCancelTask(1);
        ASSERT_FALSE(async_tasks->isScheduled(1));
        async_tasks->addTask(1, [&flag]() { flag = 2; });
        cl.unlock(); // 3: Now can task 1 run.
        std::scoped_lock rl2(*m2); // 4: Wait until task1 finishes.
        ASSERT_NO_THROW(async_tasks->fetchResult(1));
        ASSERT_EQ(flag, 2);
    }