[jira] [Commented] (DIRMINA-845) ProtocolEncoderOutputImpl isn't thread-safe

["Dominic Williams (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DIRMINA-845?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13169893#comment-13169893 ] 

Dominic Williams commented on DIRMINA-845:
------------------------------------------

Ilya perhaps we can coordinate to create a solution for Red5.

Take a look at related issue regarding how serialization here can lead to deadlock http://code.google.com/p/red5/issues/detail?id=164
                
> 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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