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https://issues.apache.org/jira/browse/DRILL-2509?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14372296#comment-14372296
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Parth Chandra commented on DRILL-2509:
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I think the way to address this is to protect m_pendingRequests with it's own
mutex. The real issue is that as part of handling a response, the read handler
sends back an ack _synchronously_. The locking is messed up because obtaining
the mutex so that m_pendingRequests is correctly protected causes a deadlock.
Longer term (post release 1.0) we can spend some time looking at how to clean
up the state management.
> Drill Client threading issue with m_pendingRequests
> ---------------------------------------------------
>
> Key: DRILL-2509
> URL: https://issues.apache.org/jira/browse/DRILL-2509
> Project: Apache Drill
> Issue Type: Bug
> Components: Client - C++
> Affects Versions: 0.7.0
> Reporter: Norris Lee
> Assignee: Norris Lee
> Fix For: 0.9.0
>
>
> 1. (Thread 1) 1st query receives the last record batch (no data, only
> contains the query state. Eg. QueryResult_QueryState_COMPLETED) and calls
> processQueryResult. At this moment, it grabs the lock. Assume
> m_pendingRequests = 1.
> 2. (Thread 1) processQueryStatusResult is called and drops
> m_pendingRequests to 0. The lock is still held at this point.
> 3. (Thread 1) It returns from processQueryStatusResult, immediately
> followed by returning from processQueryResult. At this point the lock is
> released.
> 4. (Thread 2) SubmitQuery for the next query sees the lock has been
> freed so it swoops in and grabs the lock. It bumps m_pendingRequests up to 1
> and sets sendResusts=true since it sees that m_pendingRequests was previously
> 0, causing it to call getNextResult
> 5. (Thread 1) After returning from processQueryResult, it sees that
> m_pendingRequests is now set to 1 so it calls getNextResult
> 6. So now 2 threads end up calling getNextResult. For whatever reason,
> the server then sends a record batch with no data, has_rpc_type = false, and
> rpc_type = 0, leading to throwing a ERR_QRY_INVRPCTYPE error.
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