nmethodBucket in instanceKlass.hpp atomic counters

[David Holmes]

Please ignore - #$#@ autocomplete jumped to the wrong GC address.

David

On 2/03/2015 11:28 AM, David Holmes wrote:
> Hi Staffan,
>
> cc'ing gc group as ...
>
> On 28/02/2015 12:07 PM, Staffan Friberg wrote:
>> Hi,
>>
>> Was reading through the code for the nmethodBucket in instanceKlass.hpp
>> and noticed that when we increase the number we simply do a +1, while
>> when we remove the dependency we do a using an atomic.
>>
>> Do we have synchronization else where for the increment and decrement,
>> and we simply use the atomic in the decrement to ensure visibility to
>> non-compiler threads (GC)?
>
>   ... the atomic decrement was added as part of the G1 class unloading
> code:
>
> https://bugs.openjdk.java.net/browse/JDK-804942
>
> The increment is only performed at a safepoint or under the
> CodeCache_lock. However unless there is something else that guarantees
> increments and decrements can not be occurring around the same time,
> then the use of the atomic decrement is not sufficient for thread-safety.
>
> David
>
>> //Staffan