RFR: 8212827: GlobalCounter should support nested critical sections

[Robbin Ehn]

Hi Kim,

On 23/10/2018 19:07, Kim Barrett wrote:
> Please review this change to GlobalCounter to support nested critical
> sections.

Great!

> 
> While in the area, cleaned up a few things:
> - Improved comments for GlobalCounter API.
> - Cleaned up write_synchronize global counter increment.
> - Removed a useless acquire barrier in critical_section_begin.

Thanks for doing that!

> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8212827
> 
> Webrev:
> http://cr.openjdk.java.net/~kbarrett/8212827/open.00/

Looks good, ship it, below is just some notes.

I would like the return value here:
inline uintx GlobalCounter::critical_section_begin(Thread *thread) {
And thus the parameter here:
46 inline void GlobalCounter::critical_section_end(Thread *thread, uintx 
begin_value) {
be an opaque type so we don't leak out the implementation, but as long as the
GlobalCounter have the implementation as name, that doesn't help much.

I'm thinking of something like:
inline RCUContext RCU::critical_section_begin(Thread *thread) {
inline void RCU::critical_section_end(Thread *thread, RCUContext context) {
Or
inline CSContext CriticalSection::begin(Thread *thread) {
inline void CriticalSection::end(Thread *thread, CSContext context) {

Thanks, Robbin

> 
> Testing:
> mach5 tier1-5
> New gtest directly testing nested critical sections.
> 
>