Are you sure? From your desription it would seem that the reason
loadClassInternal is syncronized is to stop this case from happening.
The way you are describing it it would not make any differnce, and the
resolve_instance_class_or_null is not thread safe.
On Fri, 2002-05-31 at 12:13, Bordet, Simone wrote:
> Hi,
>
> so I dug into the hotspot code for JDK 131, and I found the problem. I am too tired
>now to think for a solution, this is for you brave guys :)
>
> The problems arises from a 20 lines of code in
>src/share/vm/memory/systemDictionary.cpp (attached), method
>resolve_instance_class_or_null(...).
> The loading mechanism of the JVM is done in 2 steps:
>
> 1- look in a dictionary, if not found, put there a placeholder, then
> 2- load the class, calling loadClassInternal().
>
> Thread A comes in asking for class "cls1" with classloader cl1, the class has never
>been loaded, put a placeholder in the dictionary, and call loadClassInternal.
> Thread B comes in asking for class "cls1" with classloader cl1, there is already a
>placeholder, throw CCE.
>
> The key is to ask for the same class with the same classloader.
>
> I think this may happen with the UnifiedClassLoader scheme in several occasions, a
>simple example being:
>
> class Base {}
> class Derived1 extends Base {}
> class Derived2 extends Base {}
>
> If Base is loaded by classloader1, and we have 2 threads trying to load one Derived1
>and one Derived2 (and both need Base), we end up with 2 thread using the same
>classloader to load the same class, and the JVM code throws CCE.
>
> I wrote a simple testcase (attached), but it does not use JBoss classloaders,
>however should be trivial to code it against JBoss codebase. If someone can take care
>of it... thanks :P
>
> As I said I did not think enough to find a solution, but at least we all know where
>to start.
>
> Cheers
>
> Simon
>
> PS: it seems attachments are not allowed ?
>
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>
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