[jira] [Created] (YARN-2983) NPE possible in ClientRMService#getQueueInfo

["Varun Saxena (JIRA)" <ji...@apache.org>]

Varun Saxena created YARN-2983:
----------------------------------

             Summary: NPE possible in ClientRMService#getQueueInfo
                 Key: YARN-2983
                 URL: https://issues.apache.org/jira/browse/YARN-2983
             Project: Hadoop YARN
          Issue Type: Bug
          Components: resourcemanager
    Affects Versions: 2.5.1
            Reporter: Varun Saxena
            Assignee: Varun Saxena


While going through code for checking YARN-2978 , found one issue. 
During construction GetQueueInfoResponse in {{ClientRMService#getQueueInfo}}, we first collect application attempts from scheduler and then get apps from a ConcurrentHashMap in {{RMContext}}. Although the operation(get/put/remove,etc) itself on a ConcurrentHashMap is thread-safe, but a series of multiple ConcurrentHashMap#get (say, in a for loop) is not. 

For instance, in code below, we are calling rmContext.getRMApps()#get in a loop. Now a ConcurrentHashMap#get can return null if the key doesnt exist. But there is no null check inside this for loop before dereferencing the value returned i.e. rmApp. Although all the applicationattempts  have been fetched for the queue just above the for loop, but as this block of code is not synchronized, there is a possibility that another thread may delete RMApp from the ConcurrentHashMap at the same time. This can happen when an app finishes/completes and number of completed apps exceed the config  {{yarn.resourcemanager.max-completed-applications}}.
I think there should be a null check inside this for loop, otherwise a NPE can occur.

{code:title=ClientRMService#getQueueInfo}
public GetQueueInfoResponse getQueueInfo(GetQueueInfoRequest request)
      throws YarnException {
  .....
  if (request.getIncludeApplications()) {
    List<ApplicationAttemptId> apps =
    scheduler.getAppsInQueue(request.getQueueName());
    appReports = new ArrayList<ApplicationReport>(apps.size());
    for (ApplicationAttemptId app : apps) {
      RMApp rmApp = rmContext.getRMApps().get(app.getApplicationId());
      appReports.add(rmApp.createAndGetApplicationReport(null, true));
    }
  }
  ......
}
{code}



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