RFR (S): JDK-8046518: G1: Double calls to register_concurrent_cycle_end()

[Stefan Karlsson]

On 2014-06-11 12:33, Bengt Rutisson wrote:
>
> Hi all,
>
> Can I have a review for this change?
>
> http://cr.openjdk.java.net/~brutisso/8046518/webrev.00/
>
> https://bugs.openjdk.java.net/browse/JDK-8046518
>
> Background:
> When we abort a concurrent cycle due to a Full GC in G1 we call 
> ConcurrentMark::abort(). That will set _has_aborted flag and then call 
> register_concurrent_cycle_end().
>
> The concurrent marking thread will see the _has_aborted flag in its 
> ConcurrentMarkThread::run() method, abort the execution and then call 
> register_concurrent_cycle_end().
>
> Currently this works since the code inside 
> register_concurrent_cycle_end() is guarded by 
> _concurrent_cycle_started which it then resets. So, the double calls 
> will not necessarily result in too much extra work being done. But one 
> of the things that register_concurrent_cycle_end() does is to call 
> report_gc_end() on the concurrent GC tracer. That prevents further use 
> of it for this GC. This means that inside the 
> ConcurrentMarkThread::run() method we can not rely on the tracer.
>
> Removing the call to register_concurrent_cycle_end() in 
> ConcurrentMark::abort() and relying on the call in 
> ConcurrentMarkThread::run() seems to be a reasonable approach.

The double call was deliberately put there to make sure that we end the 
tracing of the concurrent GC before starting to trace teh Full GC. Why 
do you need to change this? I guess it has to do with your other GCId 
changes?

thanks,
StefanK

>
> Thanks,
> Bengt

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