RFR: 8251850: Simplify ResourceMark constructors using delegation

[Ioi Lam]

Hi Kim,

This looks good overall.


I found the following function a little confusing:

  108   static Thread* current_thread_or_null() {
  109     return DEBUG_ONLY(Thread::current_or_null()) NOT_DEBUG(nullptr);

In usual HotSpot code, xxx_or_null() means "if there's no xxx, use". 
However, in this case, we do have a current thread, but we are just not 
using it in product build.

I think it's clearer to changed the constructor

   88   ResourceMark(ResourceArea* area, Thread* thread) :

to

   88   ResourceMark(NOT_PRODUCT_ARG(Thread* thread) ResourceArea* area) :

and then use

  119   explicit ResourceMark(ResourceArea* area)
  120     : ResourceMark(NOT_PRODUCT_ARG(Thread::current()) area) {}


Also, these can be changed to NOT_PRODUCT_ARG -- but you need to move 
the corresponding field declarations up a few lines

   94     DEBUG_ONLY(COMMA _thread(thread))
   95     DEBUG_ONLY(COMMA _previous_resource_mark(nullptr))

Thanks
- Ioi

On 8/14/20 7:29 PM, Kim Barrett wrote:
> Please review this simplification of the constructors for ResourceMark,
> accomplished using delegating constructors.
>
> Also made the constructors "explicit" and the class non-copyable.
>
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8251850
>
> Webrev:
> https://cr.openjdk.java.net/~kbarrett/8251850/open.00/
>
> Testing:
> mach5 tier1
>