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From "Niall Pemberton (JIRA)" <>
Subject [jira] Resolved: (BEANUTILS-373) CLONE - MethodUtils is not thread safe because WeakFastHashMap which uses WeakHashMap is not thread-safe.
Date Mon, 22 Mar 2010 15:19:27 GMT


Niall Pemberton resolved BEANUTILS-373.

       Resolution: Fixed
    Fix Version/s: 1.8.3

Doh! Must have had a brain fart when I applied the fix for BEANUTILS-318.

Thanks, this is now fixed:

> CLONE - MethodUtils is not thread safe because WeakFastHashMap which uses WeakHashMap
is not thread-safe.
> ---------------------------------------------------------------------------------------------------------
>                 Key: BEANUTILS-373
>                 URL:
>             Project: Commons BeanUtils
>          Issue Type: Bug
>          Components: Bean / Property Utils
>    Affects Versions: 1.8.2
>         Environment: Weblogic 9.2 on Linux, but should not be relevant
>            Reporter: Andrew Sunde
>            Assignee: Niall Pemberton
>             Fix For: 1.8.3
> The problem lies in the class org.apache.commons.beanutils.MethodUtils. This class is
keeping a global cache in a non synchronized WeakFastHashMap (which claims to be syncronized).
When operating in Fast mode (which is what the WeakFastHashMap is set to after it is created),
it then access the underlining WeakHashMap without synchronization. Therefore this can lead
to a corruption in the underlining HashMap.
> See the description of the WeakHashMap javadoc:
> From Java Sun: "
> Like most collection classes, this class is not synchronized. A synchronized WeakHashMap
may be constructed using the Collections.synchronizedMap  method. 
> ....
> The behavior of the WeakHashMap class depends in part upon the actions of the garbage
collector, so several familiar (though not required) Map invariants do not hold for this class.
Because the garbage collector may discard keys at any time, a WeakHashMap may behave as though
an unknown thread is silently removing entries.
> "
> Therefore even if you are doing a "get" from the hashmap, there is a chance that you
could get a corrupted hashmap because the garbage collector could be changing the hashmap
on the fly. This could lead to threads getting stuck in an infinite loop.
> The modification to make the MethodUtils cache thread safe is a one line change. 
> Before: 
> private static WeakFastHashMap cache = new WeakFastHashMap();
> After: 
> private static Map cache = Collections.synchronizedMap(new WeakHashMap());

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