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[FlexCounter] Fix shutdown syncd hanging problem #1006

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[FlexCounter] Fix shutdown syncd hanging problem #1006

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9 changes: 6 additions & 3 deletions syncd/FlexCounter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2380,10 +2380,13 @@ void FlexCounter::flexCounterThreadRunFunction()

SWSS_LOG_DEBUG("End of flex counter thread FC %s, took %d ms", m_instanceId.c_str(), delay);

std::unique_lock<std::mutex> lk(m_mtxSleep);

m_cvSleep.wait_for(lk, std::chrono::milliseconds(correction));
// If m_runFlexCounterThread is already disabled, do not wait for signal
if (m_runFlexCounterThread)
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how this was hanging ? if m_runFlexCounterThread is already false, then wait_for will wait for correction time and in next loop iteration it will break since m_runFlexCounterThread is false on line 2360
so where was hanging problem? was that deadlock? is m_mtxSleep used somewhere else?

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also this does not solve problem completely, since ther can be race condition, and m_runFlexCounters can be TRUE on line 2384 but it can be set to FALSE at line 2386 by other thread, so swill wait_for will be executed

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It won't hang forever but about 10 seconds for some kinds of counter thread. And the 10 seconds is also a threshold of the test. The root cause just like your second comment. The m_runFlexCounterThread turns from TRUE to FALSE before the thread run to line 2385.

This is not a solution to solve the race condition but just a simple trick to solve 99% hanging 10 seconds situation.

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i would prefer to solve this completely to not get back to this

{
std::unique_lock<std::mutex> lk(m_mtxSleep);

m_cvSleep.wait_for(lk, std::chrono::milliseconds(correction));
}
continue;
}

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