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https://issues.apache.org/jira/browse/HBASE-28792?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Charles Connell updated HBASE-28792:
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Status: Patch Available (was: Open)
> AsyncTableImpl calls coprocessor callbacks in undefined order
> -------------------------------------------------------------
>
> Key: HBASE-28792
> URL: https://issues.apache.org/jira/browse/HBASE-28792
> Project: HBase
> Issue Type: Bug
> Components: Client
> Reporter: Charles Connell
> Assignee: Charles Connell
> Priority: Major
> Labels: pull-request-available
>
> To call a coprocessor endpoint asynchronously, you start by calling
> {{AsyncTable#coprocessorService()}}, which gives you a
> {{CoprocessorServiceBuilder}}, and a few steps later you can talk to your
> coprocessor over the network. One argument to
> {{AsyncTable#coprocessorService()}} is a {{CoprocessorCallback}} object,
> which contains several methods that will be called during the lifecycle of a
> coprocessor endpoint call. {{AsyncTableImpl}}'s implementation of
> {{AsyncTable#coprocessorService()}} wraps your {{CoprocessorCallback}} with
> its own that delegates the work to a thread pool. A snippet of this:
> {code}
> @Override
> public void onRegionComplete(RegionInfo region, R resp) {
> pool.execute(context.wrap(() -> callback.onRegionComplete(region,
> resp)));
> }
> ...
> @Override
> public void onComplete() {
> pool.execute(context.wrap(callback::onComplete));
> }
> {code}
> The trouble with this is that your implementations of {{onRegionComplete()}}
> and {{onComplete()}} will end up getting called in a random order, and/or at
> the same time. The tasks of calling them are delegated to a thread pool, and
> the completion of those tasks is not waited on, so the thread pool can choose
> any ordering it wants to. Troublingly, {{onComplete()}} can be called before
> the final {{onRegionComplete()}}, which is an violation of [the contract
> specified in the {{CoprocessorCallback#onComplete()}}
> javadoc|https://github.com/apache/hbase/blob/41dd87cd908d4d089d0b8cff6c88c01ed60622c5/hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncTable.java#L671].
> I discovered this while working on HBASE-28770. I found that
> {{AsyncAggregationClient#rowCount()}} returns incorrect results 5-10% of the
> time, and this bug is the reason. Other {{AsyncAggregationClient}} methods I
> presume are similarly affected.
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