> On 2011-11-15 16:41:28, Gordon Sim wrote: > > http://svn.apache.org/repos/asf/qpid/trunk/qpid/java/client/src/main/java/org/apache/qpid/client/AMQSession_0_10.java, > > line 787 > > <https://reviews.apache.org/r/2832/diff/1/?file=58392#file58392line787> > > > > Are there any other locks acquired as part of the block here? If so are > > there any lock ordering issues where you could be introducing a deadlock? > > rajith attapattu wrote: > Not that I could think of. The message-delivery-lock is taken to ensure > that no messages are being served while we start pulling them out of the > queue. > In my tests so far, I haven't encountered any issues. However I plan to > have more manual tests - ex. Trying to stop the connection while the message > consumers are in full flight. > > Gordon Sim wrote: > What about the failover mutex? Could the release trigger a codepath that > attempts to acquire that? What about an asynchronous exception occurring > concurrently; would that ever need to acquire the message-delivery-lock?
Certainly possible as mentioned in the comment below. The failover and the synchronous exceptions are things that could trigger a deadlock. Testing is the best way to eliminate these possibilities. However IMO acquiring the message-delivery-lock is a must to ensure unwanted interaction between messages delivery & releasing. > On 2011-11-15 16:41:28, Gordon Sim wrote: > > http://svn.apache.org/repos/asf/qpid/trunk/qpid/java/client/src/main/java/org/apache/qpid/client/AMQSession_0_10.java, > > line 796 > > <https://reviews.apache.org/r/2832/diff/1/?file=58392#file58392line796> > > > > You are syncing here while holding the delivery lock, could that cause > > any problems? > > rajith attapattu wrote: > So far I haven't encountered any issues. However things like failover, > session exceptions etc..could cause issues. I'm planning more thorough longer > running tests. > Another thing I am considering is to not use a sync() at all. I'm not > quite convinced that it's of much value here. > > I've noticed that the client continues to get messages into it's queue > even after the code returns from the sync call. Hence the code snippet to > release any messages received after the connection is stopped. I was > expecting the brokers response to the sync command to be received after the > client has got all the messages that were in flight. So after I sync I could > just release the messages in the queue and be done with it. But that's not > the case. > > It seems that the dispatcher thread takes a bit of time to process the > UnprocessedMessages into the correct JMSMessages and put them onto the queue. > So the sync() really doesn't add much value here. > > Gordon Sim wrote: > It sounds like it is necessary but not sufficient. You need to know that > the stop has been processed by the broker and it will not send any further, > but you also need to synchronise with the thread actually processing incoming > messages(?). I looked at it the other way :). Since it's not sufficient, it's not necessary. All though it sounds wrong, not having the sync doesn't influence the outcome of the patch at all (Bcos we release any messages we receive after the connection is stopped). It's not ideal, but with the absence of a proper mechanism to synchronize with the message processing dispatcher thread this seems a reasonable approach. Another reason why I shied away from attempting that was due to the nasty interactions we may have with threading. The dispatcher thread does use the message delivery lock and that route could increase the potential for a deadlock. > On 2011-11-15 16:41:28, Gordon Sim wrote: > > http://svn.apache.org/repos/asf/qpid/trunk/qpid/java/client/src/main/java/org/apache/qpid/client/BasicMessageConsumer_0_10.java, > > line 126 > > <https://reviews.apache.org/r/2832/diff/1/?file=58393#file58393line126> > > > > What case(s) is this code required for? You are releasing a message you > > have just received, right? When is that required? > > rajith attapattu wrote: > See the above for an explanation for why this is needed. > > Gordon Sim wrote: > You mean this is here because of the lack of synchronization with the > dispatcher thread? If so that seems a little nasty to me... anyway to do this > more cleanly? That is precisely the reason. This also makes the sync call redundant. I started with the sync() and realized that it wasn't sufficient, hence added this. As explained above, I'm not sure if there is a reasonable way to synchronize with the message delivery thread. One possible approach might be is to do something like the syncDispatchQueue() method. Where we push a certain marker message into the queue and then we get that we know there are no more messages in the pipeline. But I'm concerned about the safety and feasibility of such an approach. Robbie I believe is one person who have looked at this code more extensively in the last little while. So waiting to hear from him about his ideas as well. I'm open to suggestions on this area. Lets see if we can collectively figure out a better solution. - rajith ----------------------------------------------------------- This is an automatically generated e-mail. To reply, visit: https://reviews.apache.org/r/2832/#review3264 ----------------------------------------------------------- On 2011-11-15 15:36:36, rajith attapattu wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > https://reviews.apache.org/r/2832/ > ----------------------------------------------------------- > > (Updated 2011-11-15 15:36:36) > > > Review request for qpid, Gordon Sim, Robbie Gemmell, Weston Price, and > Oleksandr Rudyy. > > > Summary > ------- > > This attempts to fix one of the issues related to the handling of Message > credits. See QPID-3602 for an overall picture of the various issues. > > This particular patch does the following. > 1. When the connection is stopped, it sends message.stop() & releases all > messages in the prefetch buffer. > 2. It will also release any messages (that were in flight) that comes after > the connection is stopped. (*) > > (*) This interferes with the immediate_prefetch feature. However I don't know > if immediate prefetch is really required in the 0-10 path. > > As always comments, suggestions & criticisms are equally welcomed. > > > This addresses bug QPID-3604. > https://issues.apache.org/jira/browse/QPID-3604 > > > Diffs > ----- > > > http://svn.apache.org/repos/asf/qpid/trunk/qpid/java/client/src/main/java/org/apache/qpid/client/AMQSession_0_10.java > 1202228 > > http://svn.apache.org/repos/asf/qpid/trunk/qpid/java/client/src/main/java/org/apache/qpid/client/BasicMessageConsumer_0_10.java > 1202228 > > http://svn.apache.org/repos/asf/qpid/trunk/qpid/java/systests/src/main/java/org/apache/qpid/client/prefetch/PrefetchBehaviourTest.java > 1202228 > > http://svn.apache.org/repos/asf/qpid/trunk/qpid/java/client/src/main/java/org/apache/qpid/client/AMQConnection.java > 1202228 > > Diff: https://reviews.apache.org/r/2832/diff > > > Testing > ------- > > See PrefetchBehaviourTest#testConnectionStop for more details. > > > Thanks, > > rajith > >
