[YARN-7051] Avoid concurrent modification exception in FifoIntraQueuePreemptionPlugin

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 2.9.0, 2.8.1, 3.0.0-alpha3
• Fix Version/s: 2.9.0, 3.0.0-beta1, 2.8.2
• Component/s: capacity scheduler, scheduler preemption, yarn
• Target Version/s: 2.8.2
• Hadoop Flags: Reviewed
• Assignee: Eric Payne
• Reporter: Eric Payne
• Created: 18/Aug/17 21:13
• Updated: 14/Oct/19 15:37
• Resolved: 28/Aug/17 07:14

Description

FifoIntraQueuePreemptionPlugin#calculateUsedAMResourcesPerQueue has the following code:

    Collection<FiCaSchedulerApp> runningApps = leafQueue.getApplications();
    Resource amUsed = Resources.createResource(0, 0);

    for (FiCaSchedulerApp app : runningApps) {

runningApps is unmodifiable but not concurrent. This caused the preemption monitor thread to crash in the RM in one of our clusters.