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https://issues.apache.org/jira/browse/HBASE-20939?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16559200#comment-16559200
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Duo Zhang commented on HBASE-20939:
-----------------------------------
To speak clearer, the procedure lock is to prevent other procedures run at the
same time, but it can not prevent the same procedure to be executed parallel
with multiple workers...
> There will be race when we call suspendIfNotReady and then throw
> ProcedureSuspendedException
> --------------------------------------------------------------------------------------------
>
> Key: HBASE-20939
> URL: https://issues.apache.org/jira/browse/HBASE-20939
> Project: HBase
> Issue Type: Sub-task
> Components: amv2
> Reporter: Duo Zhang
> Assignee: Duo Zhang
> Priority: Critical
> Fix For: 3.0.0, 2.0.1, 2.2.0, 2.1.1
>
> Attachments: HBASE-20939.patch
>
>
> This is very typical usage in our procedure implementation, for example, in
> AssignProcedure, we will call AM.queueAssign and then suspend ourselves to
> wait until the AM finish processing our assign request.
> But there could be races. Think of this:
> 1. We call suspendIfNotReady on a event, and it returns true so we need to
> wait.
> 2. The event has been waked up, and the procedure will be added back to the
> scheduler.
> 3. A worker picks up the procedure and finishes it.
> 4. We finally throw ProcedureSuspendException and the ProcedureExecutor
> suspend us and store the state in procedure store.
> So we have a half done procedure in the procedure store for ever... This may
> cause assertion when loading procedures. And maybe the worker can not finish
> the procedure as when suspending we need to restore some state, for example,
> add something to RootProcedureState. But anyway, it will still lead to
> assertion or other unexpected errors.
> And this can not be done by simply adding a lock in the procedure, as most
> works are done in the ProcedureExecutor after we throw
> ProcedureSuspendException.
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