David Mollitor created HADOOP-17462:
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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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