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From "Sylvain Legault (JIRA)" <j...@apache.org>
Subject [jira] Created: (BEANUTILS-318) Many threads are stuck in infinite loops in MethodUtils because static WeakHashMap is not thread safe
Date Thu, 12 Jun 2008 20:46:45 GMT
Many threads are stuck in infinite loops in MethodUtils  because static WeakHashMap is not
thread safe
------------------------------------------------------------------------------------------------------

                 Key: BEANUTILS-318
                 URL: https://issues.apache.org/jira/browse/BEANUTILS-318
             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: Sylvain Legault


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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