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From "Ryan Boettcher (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (VFS-309) ThreadLocal memory leak in DefaultFileContent
Date Tue, 22 Apr 2014 14:48:15 GMT

    [ https://issues.apache.org/jira/browse/VFS-309?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13976849#comment-13976849
] 

Ryan Boettcher edited comment on VFS-309 at 4/22/14 2:46 PM:
-------------------------------------------------------------

I tracked down a problem we were having that appears to be this bug.  Turns out the ThreadLocal
class can put more than one value it it's map if the same object in the same thread adds a
value more than once.  

What should fix this is in the close() method instead of calling:
threadData.set(null);

the line should instead look like this:
threadData.remove();

The set(value) method will only set the "exact" key matching value to null, leaving all other
map entries for the owning Object instance in the Thread until the thread ends.  The remove()
method attempts to remove all the entries for the instance, not just the exact match, though
I admit I don't (atm) entirely understand how it does that.


was (Author: golion):
I tracked down a problem we were having that appears to be this bug.  Turns out the ThreadLocal
class can put more than one value it it's map if the same object in the same thread adds a
value more than once.  

What should fix this is in the close() method instead of calling:
threadData.set(null);

the line should instead look like this:
threadData.remove();

The set(Thread) method will only set the "exact" key matching value to null, leaving all other
map entries for the owning Object instance in the Thread until the thread ends.  The remove()
method attempts to remove all the entries for the instance, not just the exact match, though
I admit I don't (atm) entirely understand how it does that.

> ThreadLocal memory leak in DefaultFileContent
> ---------------------------------------------
>
>                 Key: VFS-309
>                 URL: https://issues.apache.org/jira/browse/VFS-309
>             Project: Commons VFS
>          Issue Type: Bug
>    Affects Versions: 2.0
>         Environment: Tomcat servlet container
>            Reporter: jontro
>
> When using commons vfs in a servlet container the ThreadLocal values stored will not
be released once the request finishes.
> There needs to be a method to clear these values otherwise the data will leak into the
next request.
> This was detected with tomcat 6.0.26. Upon undeploying an app that uses commons vfs tomcat
detects the leaks with a huge amount of the following messages:
> A web application created a ThreadLocal with key of type [java.lang.ThreadLocal] (value
[java.lang.ThreadLocal@52fb241d]) and a value of type [org.apache.commons.vfs.provider.FileContentThreadData]
(value [org.apache.commons.vfs.provider.FileContentThreadData@6600167a]) but failed to remove
it when the web application was stopped. To prevent a memory leak, the ThreadLocal has been
forcibly removed.



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