[jira] [Created] (SLING-7447) Race condition in ThreadLocalCleaner initialization code

["Robert Munteanu (JIRA)" <ji...@apache.org>]

Robert Munteanu created SLING-7447:
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             Summary: Race condition in ThreadLocalCleaner initialization code
                 Key: SLING-7447
                 URL: https://issues.apache.org/jira/browse/SLING-7447
             Project: Sling
          Issue Type: Bug
          Components: Commons
    Affects Versions: Commons Threads 3.2.14
            Reporter: Robert Munteanu
            Assignee: Robert Munteanu
             Fix For: Commons Threads 3.2.16


There is a race condition in the {{ThreadLocalCleaner}} initialization code that can lead to the fields not being fully initialized when read.

The stack trace is similar to

{noformat}Exception in thread "sling-oak-observation-2" java.lang.NullPointerException
        at org.apache.sling.commons.threads.impl.ThreadLocalCleaner.copy(ThreadLocalCleaner.java:110)
        at org.apache.sling.commons.threads.impl.ThreadLocalCleaner.saveOldThreadLocals(ThreadLocalCleaner.java:230)
        at org.apache.sling.commons.threads.impl.ThreadLocalCleaner.<init>(ThreadLocalCleaner.java:155)
        at org.apache.sling.commons.threads.impl.ThreadPoolExecutorCleaningThreadLocals.beforeExecute(ThreadPoolExecutorCleaningThreadLocals.java:58)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1139)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:748){noformat}

Assume that two threads, _T1_ and _T2_ enter the constructor at more or less the same time. The following events can then occur, leading to the above invalid access


||T1||T2||
|check threadLocalsField (is null)| - |
|invoke initReflectionFields, load threadLocalsField| - |
| - | check threadLocalsField (is not null) |
| - | invoke saveOldTreadLocals |
| - | invoke copy |

At this point, the {{tableField}} field is null since {{initReflectionFields}} has not yet completed, which leads to the above NPE.




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