Github user kiszk commented on a diff in the pull request:

    https://github.com/apache/spark/pull/22001#discussion_r208950122
  
    --- Diff: core/src/main/scala/org/apache/spark/scheduler/DAGScheduler.scala 
---
    @@ -929,6 +955,28 @@ class DAGScheduler(
           // HadoopRDD whose underlying HDFS files have been deleted.
           finalStage = createResultStage(finalRDD, func, partitions, jobId, 
callSite)
         } catch {
    +      case e: Exception if e.getMessage ==
    +          
DAGScheduler.ERROR_MESSAGE_BARRIER_REQUIRE_MORE_SLOTS_THAN_CURRENT_TOTAL_NUMBER 
=>
    +        logWarning("The job requires to run a barrier stage that requires 
more slots than the " +
    +          "total number of slots in the cluster currently.")
    +        jobIdToNumTasksCheckFailures.putIfAbsent(jobId, 0)
    +        val numCheckFailures = jobIdToNumTasksCheckFailures.get(jobId) + 1
    --- End diff --
    
    Is it OK while this increment is not atomic?
    In the following scenario, the value may not be correct
    1. We assume `jobIdToNumTasksCheckFailures(jobId) = 1`
    1. Thread A executes L963, then `numCheckFailures = 2`
    1. Thread B executes L963, then `numCheckFailures = 2`
    1. Thread B executes L964 and L965, then 
`jobIdToNumTasksCheckFailures(jobId)` has 2.
    1. Thread A executes L964 and L965, then 
`jobIdToNumTasksCheckFailures(jobId)` has 2.
    
    Since two threads detected failure, we expect `3`. But, it is `2`.


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