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From "James Clampffer (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-9108) Pointer to read buffer isn't being passed to recvmsg syscall
Date Mon, 21 Sep 2015 15:59:04 GMT

     [ https://issues.apache.org/jira/browse/HDFS-9108?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

James Clampffer updated HDFS-9108:
----------------------------------
    Attachment: 9108-async-repro.patch1

Attached a reproducer with a temporary bandaid fix for the shared pointer issue.

Haohui, could you take a look please?  It looks like it's due capturing stack objects by ref
and then passing between threads in remote_block_reader.

> Pointer to read buffer isn't being passed to recvmsg syscall
> ------------------------------------------------------------
>
>                 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: James Clampffer
>         Attachments: 9108-async-repro.patch, 9108-async-repro.patch1
>
>
> 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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