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https://issues.apache.org/jira/browse/YARN-2983?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Varun Saxena updated YARN-2983:
-------------------------------
    Description: 
While going through code for checking YARN-2978 , found one issue. 
During construction of {{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) are 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}

  was:
While going through code for checking YARN-2978 , found one issue. 
During construction of {{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}


> 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 of {{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) are 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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