<AWT Dev> numAppContexts in AppContext modified in not-thread-safe way.

David Holmes David.Holmes at oracle.com
Thu Aug 18 17:44:39 PDT 2011

Hi Clemens,

On 19/08/2011 10:34 AM, Clemens Eisserer wrote:
> Hi David,
>       Part of the missing picture here is how AppContexts get created and
>     dispose()'d as it may be that the way AppContext is used you can't
>     actually get concurrent modification of numAppContexts. But there's no
>     way to discern that from the AppContext code so it would be safer to use
>     the AtomicInteger.
> I had a look how AppContexts are created, and at least the IcedTea plugin
> calls SunToolkit.createNewAppContext() in a fresh thread without any
> synchronization (as does caciocavallo-web).
> I don't this with all the code the non-atomicity of operations on
> numAppContexts is a real-world problem, but on the other hand - it wouldn't
> hurt to have this replaced with correct code ;)


Though it is also interesting to note that the only use of numAppContexts is 
for the shortcut lookup of the main app context when numAppContexts==1. It's 
not clear to me why this case needs to be handled specially. I also can't 
tell what code would be calling getAppContext under those conditions.

Anyway, use of AtomicInteger is correct and should be "harmless".


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