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From "Mikhail Markov (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HARMONY-2982) [classlib][net ] java.net.URLClassLoader implementation is not thread safe.
Date Wed, 14 Feb 2007 13:54:05 GMT

    [ https://issues.apache.org/jira/browse/HARMONY-2982?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12473098
] 

Mikhail Markov commented on HARMONY-2982:
-----------------------------------------

In my opinion, the syncronization of resCache is required as get() and put() operations are
not simple and involve a lot of operations (please take a look at IdentityHashMap implementation)
and potentially if they happen sumultaneously for the same key value, the result returned
by get() could be not valid. For example (looking into IdentityHashMap code):
put() method has done these operations:
            ...
            // insert the key and assign the value to null initially
            elementData[index] = _key;
            elementData[index + 1] = null;
            ...
 and at that time get() was called, then it could return null which is not valid.

So, IMO synchronization for resCache is needed.

> [classlib][net ] java.net.URLClassLoader implementation is not thread safe.
> ---------------------------------------------------------------------------
>
>                 Key: HARMONY-2982
>                 URL: https://issues.apache.org/jira/browse/HARMONY-2982
>             Project: Harmony
>          Issue Type: Bug
>          Components: Classlib
>            Reporter: Elena Semukhina
>         Attachments: H-2982.patch, H-2982_1.patch
>
>
> The DRLVM smoke test classloader.StressLoader fails intermittently on both Linux and
Windows.
> To reproduce the failure you should run the test iteratively in the following way:
> while true; do $DRLVM -cp <path to smoke test classes> classloader.StressLoader;
done
> I observe two sorts of intermittent failures: 
> 1. java.lang.NullPointerException
> 	at java.net.URLClassLoader.explore(URLClassLoader.java:1200)
> 	at java.net.URLClassLoader.findResourceImpl(URLClassLoader.java:809)
> 	at java.net.URLClassLoader$5.run(URLClassLoader.java:667)
> 	at java.net.URLClassLoader$5.run(URLClassLoader.java)
> 	at java.security.AccessController.doPrivilegedImpl(Unknown Source)
> 	at java.security.AccessController.doPrivileged(Unknown Source)
> 	at java.net.URLClassLoader.findResource(URLClassLoader.java:665)
> 	at java.lang.ClassLoader$BootstrapLoader.findResource(Unknown Source)
> 	at java.lang.ClassLoader.getResource(Unknown Source)
> 	at java.lang.ClassLoader.getResourceAsStream(Unknown Source)
> 	at java.lang.ClassLoader.getSystemResourceAsStream(Unknown Source)
> 	at classloader.LogLoader.loadClass(Unknown Source)
> 	at classloader.StressLoader.run(Unknown Source)
> 2. java.lang.ArrayIndexOutOfBoundsException
> 	at java.util.IdentityHashMap.rehash(IdentityHashMap.java:501)
> 	at java.util.IdentityHashMap.put(IdentityHashMap.java:463)
> 	at java.net.URLClassLoader.findResourceImpl(URLClassLoader.java:720)
> 	at java.net.URLClassLoader$5.run(URLClassLoader.java:667)
> 	at java.net.URLClassLoader$5.run(URLClassLoader.java)
> 	at java.security.AccessController.doPrivilegedImpl(Unknown Source)
> 	at java.security.AccessController.doPrivileged(Unknown Source)
> 	at java.net.URLClassLoader.findResource(URLClassLoader.java:665)
> 	at java.lang.ClassLoader$BootstrapLoader.findResource(Unknown Source)
> 	at java.lang.ClassLoader.getResource(Unknown Source)
> 	at java.lang.ClassLoader.getResourceAsStream(Unknown Source)
> 	at java.lang.ClassLoader.getSystemResourceAsStream(Unknown Source)
> 	at classloader.LogLoader.loadClass(Unknown Source)
> 	at classloader.StressLoader.run(Unknown Source)
> java.lang.ArrayIndexOutOfBoundsException
> 	at java.util.IdentityHashMap.rehash(IdentityHashMap.java:501)
> 	at java.util.IdentityHashMap.put(IdentityHashMap.java:463)
> 	at java.net.URLClassLoader.findResourceImpl(URLClassLoader.java:720)
> 	at java.net.URLClassLoader$5.run(URLClassLoader.java:667)
> 	at java.net.URLClassLoader$5.run(URLClassLoader.java)
> 	at java.security.AccessController.doPrivilegedImpl(Unknown Source)
> 	at java.security.AccessController.doPrivileged(Unknown Source)
> 	at java.net.URLClassLoader.findResource(URLClassLoader.java:665)
> 	at java.lang.ClassLoader$BootstrapLoader.findResource(Unknown Source)
> 	at java.lang.ClassLoader.getResource(Unknown Source)
> 	at java.lang.ClassLoader.getResourceAsStream(Unknown Source)
> 	at java.lang.ClassLoader.getSystemResourceAsStream(Unknown Source)
> 	at classloader.LogLoader.loadClass(Unknown Source)
> 	at classloader.StressLoader.run(Unknown Source)
> java.lang.ArrayIndexOutOfBoundsException
> 	at java.util.IdentityHashMap.rehash(IdentityHashMap.java:501)
> 	at java.util.IdentityHashMap.put(IdentityHashMap.java:463)
> 	at java.net.URLClassLoader.findResourceImpl(URLClassLoader.java:720)
> 	at java.net.URLClassLoader$5.run(URLClassLoader.java:667)
> 	at java.net.URLClassLoader$5.run(URLClassLoader.java)
> 	at java.security.AccessController.doPrivilegedImpl(Unknown Source)
> 	at java.security.AccessController.doPrivileged(Unknown Source)
> 	at java.net.URLClassLoader.findResource(URLClassLoader.java:665)
> 	at java.lang.ClassLoader$BootstrapLoader.findResource(Unknown Source)
> 	at java.lang.ClassLoader.getResource(Unknown Source)
> 	at java.lang.ClassLoader.getResourceAsStream(Unknown Source)
> 	at java.lang.ClassLoader.getSystemResourceAsStream(Unknown Source)
> 	at classloader.LogLoader.loadClass(Unknown Source)
> 	at classloader.StressLoader.run(Unknown Source)

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