RFR: 8168914: Crash in ClassLoaderData/JNIHandleBlock::oops_do during concurrent marking

[Kim Barrett]

> On Feb 20, 2017, at 5:52 PM, David Holmes <david.holmes at oracle.com> wrote:
>> 02 -> 03:
>> - Only use load_acquire when reading the size for the "head" chunk
> 
> Sorry but I don't like the way this is done - the conditional may end up being more expensive than the unnecessary load-acquire. Unrolling the first loop iteration, as per the email discussion, is a better way to go IMO.

+1

> And as Kim indicated you shouldn't need any casts for the OrderAccess ops as you should be using the "void*" versions.
> 
>> - Fix grammar in comment
>> - Refer to the correct lock in comment
>> 
>> AFAICS (scanning through all the emails) there are now only three
>> remaining comments:
>> - Thomas: can we assert in ChunkedHandeList::add that the correct mutex
>>          is locked?
>> - Then we would have to pass the mutex along as a parameter to `add`,
> 
> Why do you need to pass it in?
> 
> oop* ClassLoaderData::ChunkedHandleList::add(oop o) {
>  assert(ClassLoaderData::metaspace_lock()->owned_by_self(), "should own lock");

The metaspace_lock() is per-CLD, so that doesn’t work.