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

["David Mollitor (Jira)" <ji...@apache.org>]

David Mollitor created HADOOP-17462:
---------------------------------------

             Summary: 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


{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.

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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