RFR: 8085903: New fix for memory leak in ProtectionDomain cache

[Sean Mullan]

I received a private comment that there may be cases where the map's 
value is reclaimed by the garbage collector, but the key still exists. 
If that ProtectionDomain is subsequently used for permission checks, a 
Map.putIfAbsent method will not replace the value.

So, I have added an additional check for this case in the PDCache.put 
method, and it instead uses the Map.replace method. Updated webrev:

http://cr.openjdk.java.net/~mullan/webrevs/8085903/webrev.01/

--Sean

On 01/08/2016 03:06 PM, Sean Mullan wrote:
> Please review this fix for a memory leak in the ProtectionDomain cache
> (which maps each ProtectionDomain to their granted
> PermissionCollection). The memory leak only occurs if custom permissions
> are used in a policy file.
>
> http://cr.openjdk.java.net/~mullan/webrevs/8085903/webrev.00/
>
> Custom permissions cause a chain of strong references that link back to
> the ProtectionDomain key used in the map, preventing it from being
> removed (and also preventing the custom permission's URLClassLoader from
> being garbage collected). This fix wraps the PermissionCollection in a
> SoftReference which allows the objects to be garbage collected in
> response to memory demand.
>
> Thanks,
> Sean