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From "Ilya Ivanov (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DIRMINA-845) ProtocolEncoderOutputImpl isn't thread-safe
Date Fri, 29 Jul 2011 02:48:09 GMT
ProtocolEncoderOutputImpl isn't thread-safe
-------------------------------------------

                 Key: DIRMINA-845
                 URL: https://issues.apache.org/jira/browse/DIRMINA-845
             Project: MINA
          Issue Type: Bug
          Components: Filter
    Affects Versions: 2.0.4
            Reporter: Ilya Ivanov


ProtocolEncoderOutputImpl uses ConcurrentLinkedQueue and at first look it seems to be thread-safe.
But really concurrent execution of flush method isn't thread-safe (and write-mergeAll also).

E.g. in RTMP several channels multiplexed in single connection. According protocol specification
it's possible to write to different channels concurrently. But it doesn't work with MINA.
I've synchronized channel writing, but it doesn't prevent concurrent run of flushing (in 2.0.4
it's done directly in ProtocolCodecFilter.filterWrite, but ProtocolEncoderOutputImpl.flush
has the same problem).

Here the fragment of flushing code:

while (!bufferQueue.isEmpty()) {
  Object encodedMessage = bufferQueue.poll();
                
  if (encodedMessage == null) {
    break;
  }

  // Flush only when the buffer has remaining.
  if (!(encodedMessage instanceof IoBuffer) || ((IoBuffer) encodedMessage).hasRemaining())
{
    SocketAddress destination = writeRequest.getDestination();
    WriteRequest encodedWriteRequest = new EncodedWriteRequest(encodedMessage, null, destination);


    nextFilter.filterWrite(session, encodedWriteRequest);
  }
} 

Suppose original packets sequence is A, B, ...
Concurrent run of flushing may proceed as following:

thread-1: Object encodedMessage = bufferQueue.poll(); // gets A packet
thread-2: Object encodedMessage = bufferQueue.poll(); // gets B packet
...
thread-2: nextFilter.filterWrite(...); // writes B packet
thread-1: nextFilter.filterWrite(...); // writes A packet

so, resulting sequence will B, A

It's quite confusing result especially when documentation doesn't contain any explanation
about such behavior.

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