1 Reply Latest reply on Apr 14, 2008 12:13 PM by David Lloyd

    Out of order message problem (discussion thread for JBREM-96

    David Lloyd Master

      When dealing with a protocol using multiple channels (HTTP for example, and possibly a future multi-channel JRPP variant), sending two messages on two different channels can cause ordering issues if the second message sent arrives first.

      For example, sending a context open on channel A, and a request on channel B, may cause the request to be received before the context open message, resulting in the request being rejected with a "no such context" error. Another example is that stream messages must be handled sequentially.

      There are several possible solutions, including but not limited to:

      * for any message B that must come after A, always send A and B on the same channel (problem: HTTP channels are transient, so this won't work for HTTP) (problem: this could load up one channel while leaving other channels empty, even if load-balancing is used)
      * don't send B until after A is acknowledged (problem: acknowledging A might not be possible within the underlying protocol, like if A is sent in an HTTP reply, requiring a separate ACK message, which can lead to performance problems)
      * if a message comes in seemingly unsolicited (like a request on a nonexistant context) or out of sequence (like in a stream), queue the message for some fixed amount of time to see if the context open message arrives (problem: could be a source of DoS on the server; also this is a duplication of what protocols like TCP already do, which means that all the same problems must be in effect re-solved)

      Please share any ideas you have or comments on the above.

      The JIRA issue is at http://jira.jboss.com/jira/browse/JBREM-963