fix thread status synchronization in thread_list_test #7825
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The test was flaky because the BG threads could increase `running_count_` up to `job_count_` before applying their thread status updates. Then the test thread would see non-deterministic results when counting threads with each status. The fix is to acquire mutex in test thread so it sees `running_count_` and thread status updated atomically. I think simply reordering the two updates would have been insufficient since the thread status update uses `memory_order_relaxed`. This change happens to also eliminate an undesirable sleep loop. Test Plan: injected sleeps to verify the failure repros before this PR and does not repro after.
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The test failure is unrelated: |
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Thanks for the review! |
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Summary: The test was flaky because the BG threads could increase `running_count_` up to `job_count_` before applying their thread status updates. Then the test thread would see non-deterministic results when counting threads with each status. The fix is to acquire mutex in test thread so it sees `running_count_` and thread status updated atomically. I think simply reordering the two updates would have been insufficient since the thread status update uses `memory_order_relaxed`. This change happens to also eliminate an undesirable sleep loop. Pull Request resolved: facebook#7825 Test Plan: injected sleeps to verify the failure repros before this PR and does not repro after. Reviewed By: jay-zhuang Differential Revision: D25742409 Pulled By: ajkr fbshipit-source-id: 926a2223fe856e20bc4c0c27df6736ee5cb02c97
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The test was flaky because the BG threads could increase
running_count_up tojob_count_before applying their thread statusupdates. Then the test thread would see non-deterministic results when
counting threads with each status. The fix is to acquire mutex in test
thread so it sees
running_count_and thread status updated atomically.I think simply reordering the two updates would have been insufficient
since the thread status update uses
memory_order_relaxed. This changehappens to also eliminate an undesirable sleep loop.
Test Plan: injected sleeps to verify the failure repros before this PR and does not
repro after.