RFR(S): 8149834: gc/shared/gcTimer.cpp:88 assert(_is_concurrent_phase_active) failed: A concurrent phase is not active

[Jon Masamitsu]

Sangheon,

Change looks good.

One  issue for you consideration.

http://cr.openjdk.java.net/~sangheki/8149834/webrev.00/src/share/vm/gc/g1/g1ConcurrentMark.cpp.frames.html

1042 void G1ConcurrentMark::register_concurrent_phase_end() {
1043 register_concurrent_phase_end_common(false);
1044 }
1045
1046 void G1ConcurrentMark::register_concurrent_gc_end() {
1047 register_concurrent_phase_end_common(true);
1048 }

I understand that adding these functions is a style and
I've used  that style before but in this case it confuses
me.  Having register_concurrent_phase_end()
call register_concurrent_phase_end_common() makes sense
since their names are similar but I'm less clear
about register_concurrent_gc_end() calling
register_concurrent_phase_end_common().

Maybe register_concurrent_gc_end() should be renamed
register_concurrent_phase_end_and_stop_timer().

Or have two statics
static const bool StopTimer = true;
static const bool DontStopTime = false;

and then call

register_concurrent_phase_end_common(StopTimer)

register_concurrent_phase_end_common(DontStopTimer)

You could drop the "_common" part of the name.


As I said, it's a matter of style so you can choose.

Jon



On 03/02/2016 11:41 PM, sangheon wrote:
> Hi all,
>
> Could I have a couple of reviews for this quick fix?
>
> There is a race between VMThread and ConcurrentMarkThread for 
> ConcurrentGCTimer.
> At the end of abort, VMThread is trying to end concurrent timer and if 
> ConcurrentMarkThread is trying to start or end concurrent phase, timer 
> related asserts will be fired.
> (Only ConcurrentMarkThread starts a concurrent phase)
> We have 3 different cases but the root cause is same[1].
>
> This proposal is introducing 3 phases of started, not started and 
> stopping for concurrent phase status.
> And the status is updated by cmpxchg.
>
> However, I think more proper fix would be eliminating the race.
> Currently G1CollectedHeap has ConcurrentGCTimer but it is mostly used 
> from ConcurrentMarkThread.
> So moving the timer and related routines to ConcurrentMark seems better.
> I filed a new RFE for this[2].
>
> Many thanks to Jon, Bengt(base patch as well) and StefanK for the 
> discussion.
>
> CR: https://bugs.openjdk.java.net/browse/JDK-8151085
> Webrev: http://cr.openjdk.java.net/~sangheki/8149834/webrev.00
> Testing: JPRT, local test with adding some sleep at vm code.
>
> [1] Related bugs:
> https://bugs.openjdk.java.net/browse/JDK-8145996
> https://bugs.openjdk.java.net/browse/JDK-8150819
>
> [2] RFE for proper fix:
> https://bugs.openjdk.java.net/browse/JDK-8151085
>
> Thanks,
> Sangheon
>
>
>
>