Sunil G commented on YARN-3136:

Hi [~rohithsharma]

*getLiveContainers()* is giving a copy as you mentioned. Earlier I was looking 
for getter method to fetch FicaSchedulerApp from *applications* with schedule 
lock. But that also not needed.
Map<ApplicationId, SchedulerApplication<T>> applications

this.applications =
         new ConcurrentHashMap<ApplicationId,
*applications* is a concurrent hash map. Hence synchronized can be removed from 
*getTransferredContainers* without any change in the method itself. Also as 
mentioned by [~jianhe], a check will be added on *registerApplicationMaster()*.

> getTransferredContainers can be a bottleneck during AM registration
> -------------------------------------------------------------------
>                 Key: YARN-3136
>                 URL: https://issues.apache.org/jira/browse/YARN-3136
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: scheduler
>    Affects Versions: 2.6.0
>            Reporter: Jason Lowe
>            Assignee: Sunil G
> While examining RM stack traces on a busy cluster I noticed a pattern of AMs 
> stuck waiting for the scheduler lock trying to call getTransferredContainers. 
>  The scheduler lock is highly contended, especially on a large cluster with 
> many nodes heartbeating, and it would be nice if we could find a way to 
> eliminate the need to grab this lock during this call.  We've already done 
> similar work during AM allocate calls to make sure they don't needlessly grab 
> the scheduler lock, and it would be good to do so here as well, if possible.

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