[jira] [Commented] (HADOOP-17462) Hadoop Client getRpcResponse May Return Wrong Result

["Íñigo Goiri (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-17462?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17261524#comment-17261524 ] 

Íñigo Goiri commented on HADOOP-17462:
--------------------------------------

Interesting finding.
Can you share in what scenario you found this?

> Hadoop Client getRpcResponse May Return Wrong Result
> ----------------------------------------------------
>
>                 Key: HADOOP-17462
>                 URL: https://issues.apache.org/jira/browse/HADOOP-17462
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: common
>            Reporter: David Mollitor
>            Assignee: David Mollitor
>            Priority: Major
>              Labels: pull-request-available
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> {code:java|Title=Client.java}
>   /** @return the rpc response or, in case of timeout, null. */
>   private Writable getRpcResponse(final Call call, final Connection connection,
>       final long timeout, final TimeUnit unit) throws IOException {
>     synchronized (call) {
>       while (!call.done) {
>         try {
>           AsyncGet.Util.wait(call, timeout, unit);
>           if (timeout >= 0 && !call.done) {
>             return null;
>           }
>         } catch (InterruptedException ie) {
>           Thread.currentThread().interrupt();
>           throw new InterruptedIOException("Call interrupted");
>         }
>       }
>  */
>   static class Call {
>     final int id;               // call id
>     final int retry;           // retry count
> ...
>     boolean done;               // true when call is done
> ...
> }
> {code}
> The {{done}} variable is not marked as {{volatile}} so the thread which is checking its status is free to cache the value and never reload it even though it is expected to change by a different thread.  The while loop may be stuck waiting for the change, but is always looking at a cached value.  If that happens, timeout will occur and then return 'null'.
> In previous versions of Hadoop, there was no time-out at this level, so it would cause endless loop.  Really tough error to track down if it happens.



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