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https://issues.apache.org/activemq/browse/SM-1858?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Freeman Fang reassigned SM-1858:
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Assignee: Freeman Fang
> Deadlock On Component Uninstall (using Seda Flow)
> -------------------------------------------------
>
> Key: SM-1858
> URL: https://issues.apache.org/activemq/browse/SM-1858
> Project: ServiceMix
> Issue Type: Bug
> Components: servicemix-core
> Affects Versions: 3.3
> Environment: SunOS 5.10 Generic_137111-06 sun4u sparc
> SUNW,Sun-Fire-880
> Java(TM) SE Runtime Environment (build 1.6.0_01-b06)
> Java HotSpot(TM) 64-Bit Server VM (build 1.6.0_01-b06, mixed mode)
> ServiceMix 3.3
> Reporter: Corey Baswell
> Assignee: Freeman Fang
> Attachments: stacktraces.txt
>
>
> I've recently updated servicemix from 3.1 to 3.3 and have started seeing a
> deadlock condition when we attempt to reinstall a component on a running
> system. Not sure if this bug was present prior to 3.3 but I've never seen it
> in 3.1. I'll try to explain the scenario. There are two components involved A
> & B. Component A calls B and returns a response to its caller. The situation
> that causes the deadlock is if I try to do an uninstall component A (first
> step in a reinstall) while component A is waiting for a response from
> component B.
> The time line for the locks that cause this deadlock are:
> # Component A send a synchronous request to component B through the
> SedaFlow. A read lock is established on the flow.
> # Since the request is synchronous the Component A request thread waits on
> the MessageExchange object (to be notified when a response is ready).
> # A reinstall of component A is triggered. The
> org.apache.servicemix.jbi.framework.InstallationService.unloadInstaller is
> called to first remove this component. The first thing thing the
> InstallationService does is to suspend the broker which in turn suspends the
> SedaFlow. Before the Seda Flow can be suspended a write lock must be acquired
> on the flow however this write lock cannot be acquired until the read lock
> from step 1. is released.
> # Component B finishes its request and is now ready to return the response.
> Before it calls notify on the MessaeExchange lock in step 2. (allowing
> Component A to finish its request) it first must acquire a read lock on the
> SedaFlow lock. However it can't acquire this read lock because of the waiting
> write lock in step 3.
> # Deadlock
> I'm not sure what the best way to fix this is but since I don't understand
> the interaction of ServiceMix's internals enough to dork with the
> synchronization I'm going to change the write lock attempt in the suspend()
> method of AbstractFlow to timeout after a couple of seconds. Something like:
> {code}
> public synchronized void suspend() {
> if (log.isDebugEnabled()) {
> log.debug("Called Flow suspend");
> }
> try
> {
> lock.writeLock().tryLock(10, TimeUnit.SECONDS);
> }
> catch (InterruptedException iexc)
> {
> throw new RuntimeException("Unable to suspend flow because write
> lock could not be acquired.");
> }
> suspendThread = Thread.currentThread();
> }
> {code}
> I think this will work in my scenario because I'm only using one flow (seda).
> If multiple flows were being used however it would be possible for some to be
> suspended before this exception would be thrown and that could leave
> everything in a bad state (i.e. this is definitely a hack).
> I've also attached the stack traces from the time line above.
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