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https://issues.apache.org/jira/browse/HDFS-9108?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14903536#comment-14903536
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James Clampffer commented on HDFS-9108:
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Thanks for the patch! Looks like everything works; I'm going to write a test
that uses more threads and check it out just to be safe.
Re: I'm surprised that running the inputstream_test under valgrind fails to
uncover the problem.
>From my understanding of how inputstream_test works (correct me if I'm wrong)
>it looks like everything is running in a single thread. So the MockConnection
>emulates the the various asio calls on the same stack and they'll look more
>like blocking calls at runtime. If that's the case the referenced object will
>still be living on the stack so the reference will point to valid memory and
>valgrind won't complain.
> InputStreamImpl::ReadBlockContinuation stores wrong pointers of buffers
> -----------------------------------------------------------------------
>
> Key: HDFS-9108
> URL: https://issues.apache.org/jira/browse/HDFS-9108
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: hdfs-client
> Environment: Ubuntu x86_64, gcc 4.8.2
> Reporter: James Clampffer
> Assignee: Haohui Mai
> Priority: Blocker
> Attachments: 9108-async-repro.patch, 9108-async-repro.patch1,
> HDFS-9108.000.patch
>
>
> Somewhere between InputStream->PositionRead and the asio code the pointer to
> the destination buffer gets lost. PositionRead will correctly return the
> number of bytes read but the buffer won't be filled.
> This only seems to effect the remote_block_reader, RPC calls are working.
> Valgrind error:
> Syscall param recvmsg(msg.msg_iov) points to uninitialised byte(s)
> msg.msg_iov[0] should equal the buffer pointer passed to PositionRead
> Hit when using a promise to make the async call block until completion.
> auto stat = std::make_shared<std::promise<Status>>();
> std::future<Status> future(stat->get_future());
> size_t readCount = 0;
> auto h = [stat, &readCount,buf](const Status &s, size_t bytes) {
> stat->set_value(s);
> readCount = bytes;
> };
> char buf[50];
> inputStream->PositionRead(buf, 50, 0, h);
>
> //wait for async to finish
> future.get();
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