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https://issues.apache.org/jira/browse/YARN-2983?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14257561#comment-14257561
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Jian He commented on YARN-2983:
-------------------------------
thanks for taking over YARN-2987 too ! Given the change is fairly small and
they are touching the same piece of code, do you mind incorporating this change
as part of that and close this ?
> 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
> Attachments: YARN-2983.patch
>
>
> 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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