RFR (M) 8195099: Concurrent safe-memory-reclamation mechanism

[Kim Barrett]

> On Apr 10, 2018, at 10:42 AM, Robbin Ehn <robbin.ehn at oracle.com> wrote:
> 
> Full: http://cr.openjdk.java.net/~rehn/8195099/v2/webrev/
> Inc : http://cr.openjdk.java.net/~rehn/8195099/v2/inc/webrev/

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GlobalCounter describes its implementation, but is not the least bit
evocative of its purpose.  I don't have a good name suggestion though.

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This is being put in utilities.  Similarly we put SpinYield in
utilities.  But I'm not sure either of those are properly placed
there.  These are synchronization building blocks, and all other
synchronization stuff is in runtime.

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src/hotspot/share/utilities/globalCounter.hpp 

Consider just forward declaring Thread (at namespace scope).

Consider just forward declaring CounterThreadCheck at class scope,
with the definition in the .cpp file.

With those changes, don't need to #include thread.hpp in this header.
Although globalCounter.inline.hpp still needs to #include thread.hpp,
so maybe this doesn't matter so much?

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src/hotspot/share/utilities/globalCounter.hpp 

Although CriticalSection is fully defined in this header, I think it
can't be instantiated without including globalCounter.inline.hpp.
Consider just forward declaring in the GlobalCounter definition, with
the definition in the .inline.hpp.

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src/hotspot/share/utilities/globalCounter.inline.hpp 

Missing #include globalCounter.hpp.

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src/hotspot/share/utilities/globalCounter.inline.hpp 
  36   OrderAccess::release_store_fence(thread->get_rcu_counter(), gbl_cnt + 1);

"gbl_cnt + 1" => "gbl_cnt | COUNTER_ACTIVE".

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src/hotspot/share/utilities/globalCounter.hpp

  74   // Must be called after finished accessing the data.
  75   // Do not provide fence, allows load/stores moving into the critical section.
  76   static void critical_section_end(Thread *thread);

Both begin and end should have descriptions of their ordering
behavior.  I'm thinking something similar to the descriptions we have
for Atomic operations.

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