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https://issues.apache.org/jira/browse/HADOOP-17462?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17261741#comment-17261741
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David Mollitor commented on HADOOP-17462:
-----------------------------------------
Let me review [~sjlee0]'s comments before pushing into the project.
> 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: 20m
> 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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