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https://issues.apache.org/jira/browse/DIRMINA-845?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13072938#comment-13072938
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Ilya Ivanov commented on DIRMINA-845:
-------------------------------------
"The only reason you might send those message in the wrong order is that they
are read from the queue by two different threads"
Exactly this case! flush itself read sequentially but two concurrent flush(es)
are run at the moment because two threads writing to session 3.
> 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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