[jira] [Created] (HDFS-4522) LightWeightGSet expects incrementing a volatile to be atomic

["Colin Patrick McCabe (JIRA)" <ji...@apache.org>]

Colin Patrick McCabe created HDFS-4522:
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             Summary: LightWeightGSet expects incrementing a volatile to be atomic
                 Key: HDFS-4522
                 URL: https://issues.apache.org/jira/browse/HDFS-4522
             Project: Hadoop HDFS
          Issue Type: Bug
    Affects Versions: 2.0.4-beta
            Reporter: Colin Patrick McCabe
            Assignee: Colin Patrick McCabe
            Priority: Minor


LightWeightGSet uses a volatile integer to track the current modification number (kind of an epoch number).

Unfortunately, it includes code like this, that increments this volatile int:
{code}
     //insert the element to the head of the linked list
     modification++;
     size++;
{code}

The bug here is that in between reading the value of modification, incrementing it, and storing it back in the variable, another thread may have modified it.  This could lead to lost updates.

We should use {{AtomicInteger}} for these cases.

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