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Date: Fri, 19 Mar 2010 18:54:27 +0000 (UTC)
From: "Andrew Sunde (JIRA)" <jira@apache.org>
To: issues@commons.apache.org
Subject: [jira] Created: (BEANUTILS-373) CLONE - MethodUtils is not thread
 safe because WeakFastHashMap which uses WeakHashMap is not thread-safe.
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CLONE - MethodUtils is not thread safe because WeakFastHashMap which uses WeakHashMap is not thread-safe.
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                 Key: BEANUTILS-373
                 URL: https://issues.apache.org/jira/browse/BEANUTILS-373
             Project: Commons BeanUtils
          Issue Type: Bug
          Components: Bean / Property Utils
    Affects Versions: 1.7.0
         Environment: Weblogic 9.2 on Linux, but should not be relevant
            Reporter: Andrew Sunde
            Assignee: Niall Pemberton
             Fix For: 1.8.0


The problem lies in the class org.apache.commons.beanutils.MethodUtils. This class is keeping a global cache in a non synchronized WeakHashMap. WeakHashMap is not thread safe and required external synchronization. The lack of synchronization can cause corruption and the WeakHashMap.get() method to go into an infinite loop.

Googling "WeakHashMap infinite loop" returns many cases of similar problem with WeakHashMap. The solution is to decorate the WeakHashMap in a synchronized Map as described in this thread:
http://dev.eclipse.org/mhonarc/lists/aspectj-users/msg08824.html

The modification to make the MethodUtils cache thread safe is a one line change. 
Before: 
private static WeakHashMap cache = new WeakHashMap();

After: 
private static Map cache = Collections.synchronizedMap(new WeakHashMap());

Example of thread dump

"ExecuteThread: '0' for queue: 'weblogic.kernel.Default'" id=13 idx=0x3c tid=5905 prio=5 alive, daemon
    at org/apache/commons/beanutils/MethodUtils$MethodDescriptor.equals(MethodUtils.java:828)[optimized]
    at java/util/WeakHashMap.eq(WeakHashMap.java:254)[inlined]
    at java/util/WeakHashMap.get(WeakHashMap.java:345)[optimized]
    at org/apache/commons/beanutils/MethodUtils.getMatchingAccessibleMethod(MethodUtils.java:530)[optimized]
    at org/apache/commons/beanutils/MethodUtils.invokeMethod(MethodUtils.java:209)[inlined]
::::

"ExecuteThread: '1' for queue: 'weblogic.kernel.Default'" id=14 idx=0x40 tid=5906 prio=5 alive, daemon
    at org/apache/commons/beanutils/MethodUtils$MethodDescriptor.equals(MethodUtils.java:833)[optimized]
    at java/util/WeakHashMap.eq(WeakHashMap.java:254)[inlined]
    at java/util/WeakHashMap.get(WeakHashMap.java:345)[optimized]
    at org/apache/commons/beanutils/MethodUtils.getMatchingAccessibleMethod(MethodUtils.java:530)[optimized]
    at org/apache/commons/beanutils/MethodUtils.invokeMethod(MethodUtils.java:209)[inlined]
:::
"ExecuteThread: '2' for queue: 'weblogic.kernel.Default'" id=15 idx=0x44 tid=5907 prio=5 alive, daemon
    at org/apache/commons/beanutils/MethodUtils$MethodDescriptor.equals(MethodUtils.java:833)[optimized]
    at java/util/WeakHashMap.eq(WeakHashMap.java:254)[inlined]
    at java/util/WeakHashMap.get(WeakHashMap.java:345)[optimized]
    at org/apache/commons/beanutils/MethodUtils.getMatchingAccessibleMethod(MethodUtils.java:530)[optimized]
    at org/apache/commons/beanutils/MethodUtils.invokeMethod(MethodUtils.java:209)[inlined]


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