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https://issues.apache.org/jira/browse/HADOOP-10487?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13966628#comment-13966628
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Daryn Sharp commented on HADOOP-10487:
--------------------------------------
s/need for a final/need for a volatile/
> Racy code in UserGroupInformation#ensureInitialized()
> -----------------------------------------------------
>
> Key: HADOOP-10487
> URL: https://issues.apache.org/jira/browse/HADOOP-10487
> Project: Hadoop Common
> Issue Type: Bug
> Reporter: Haohui Mai
> Assignee: Haohui Mai
>
> UserGroupInformation#ensureInitialized() uses the double-check-locking
> pattern to reduce the synchronization cost:
> {code}
> private static void ensureInitialized() {
> if (conf == null) {
> synchronized(UserGroupInformation.class) {
> if (conf == null) { // someone might have beat us
> initialize(new Configuration(), false);
> }
> }
> }
> }
> {code}
> As [~tlipcon] pointed out in the original jira (HADOOP-9748). This pattern is
> incorrect. Please see more details in
> http://en.wikipedia.org/wiki/Double-checked_locking and
> http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html
> This jira proposes to use the static class holder pattern to do it correctly.
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