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(In reply to lei xu from comment #0)
> Two buggy sites may raise NullPointerException in HostTracker module if
> concurrent remove operation occurs.
>
> The first case is for "transHost" variable, if a concurrent remove upon
> "hostsDB" variable. The corresponding snippets are attached:
>
> HostNodeConnector transHost = hostsDB.get(networkAddr);
> transHost.setStaticHost(true);
>
> The second case is for "existinghost" variable. The following are snippets:
>
> HostNodeConnector existinghost = hostsDB.get(id);
> existinghost.initArpSendCountDown();
>
> To solve the issue, the simplest way is to add a null checker for these
> variable since we cannot guarantee the result from hostsDB is not NULL.

Hi,

I would like to take up this bug, so could you please provide me the more details.

Thanks,
Suvitha Balu

Hi Suvitha Balu,

I have checked the latest sorce code of HostTracker.java in
https://nexus.opendaylight.org/content/repositories/opendaylight.snapshot/org/opendaylight/controller/hosttracker.implementation/0.6.5-SNAPSHOT/

It seems the concurrency bugs are still there.

First, in the line of 547 and 548,
545: if (hostExists(host)) {
...
547: HostNodeConnector existinghost = hostsDB.get(id);
548:　existinghost.initArpSendCountDown();
The Line 545 cannot guarantee the id is in hostsDB, in the case, I think we can use the same reference in line 545 and 547, for example,
h = hostsDB.get(id)
545: if (h != null){

Hi Lei,
Thanks for the information.

I have checked-out the ODL Origin/master controller and L2switch code and could not find the HostTracker.java file. Is the part of any new feature or specific to any release?

This appears to be referring to the now-defunct HostTracker that used to be in the controller using the AD-SAL. The AD-SAL was completely removed in Beryllium and the recommendation is to use the Host Tracker in the l2switch project as described here:
https://wiki.opendaylight.org/view/L2_Switch:HostTracker

You should be able to install it by installing the Karaf feature for odl-l2switch-hosttracker.