[jira] Commented: (SM-512) sendsync from a service to another service seems to cause a deadlock under load

["Krzysztof Sobolewski (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/activemq/browse/SM-512?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=43889#action_43889 ] 

Krzysztof Sobolewski commented on SM-512:
-----------------------------------------

I don't really agree there is no real bug here, because it violates the principle of least surprise. I tripped on the same problem and spent about two days of investigation before I found the cause and reached this report. I think that a deadlock resulting from a compliant use is a bug no matter what.

But I agree that it might be tricky to fix. How about, for example, setting the exchage state to SYNC_STATE_SYNC_SENT before returning if the same thread is executing both sides of the conversation (let's call it super-synchronous)?

I'm basing it on the observation that in org.apache.servicemix.jbi.messaging.DeliveryChannelImpl.sendSync(MessageExchange, long) there is:
                if (me.getSyncState() != MessageExchangeImpl.SYNC_STATE_SYNC_RECEIVED) {
                    waitForExchange(me, me, timeout, "sendSync");
                } else {
and the call to waitForExchange() calls me.wait() which waits for itself (and thus deadlocks).

> sendsync from a service to another service seems to cause a deadlock under load
> -------------------------------------------------------------------------------
>
>                 Key: SM-512
>                 URL: https://issues.apache.org/activemq/browse/SM-512
>             Project: ServiceMix
>          Issue Type: Bug
>    Affects Versions: 3.0-M2
>         Environment: Windows 2003, Intel 2.8 xeon processor. Java 1.5 3.0-M2
>            Reporter: anand somani
>            Assignee: Guillaume Nodet
>             Fix For: 3.0
>
>         Attachments: test.zip
>
>
> We have 2 services A and B. A makes sync requests to B. We have a JMS client that feeds requests to A and that triggers a sync request to B. We are trying to push some 5000 requests (not sequential). Now
>      With st flow - A gets all the responses from B and we are good
>      with Seda flow -  A gets some responses from B (sometimes none) and then all the threads are blocked (seen using JMX) on syncsend(), looks like B has no threads to service requests.
>      with JMS flow ( A and B on different VMs), we see the similar behavior as with seda flow
> With async requests everything works just fine. We have tried increasing seda capacity and workmanager thread count, that did not help.  I am attaching service A and B code along with configuration files
> Also it would be nice to have all the tunable features documented with some explaination somewhere ( I could not find it anywhere)

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