Experiment: Merging hs-rt and hs-gc

Mikael Vidstedt mikael.vidstedt at oracle.com
Wed Jun 3 14:28:08 UTC 2015

Given that the feedback on this has been positive we're going to move 
ahead with this experiment. The plan is to do a final integration from 
jdk9/hs-gc up to jdk9/hs *tomorrow* and then lock down hs-gc. More 
detailed information will be sent out in separate emails.

If you have feedback on how the experiment is working out please let us 


On 2015-05-29 10:31, Mikael Vidstedt wrote:
> All,
> As you all know the JDK 9 development of Hotspot is done in three 
> different mercurial forests: hs-rt[1], hs-gc[2] and hs-comp[3]. This 
> division has served as a way of isolating changes from each other in 
> order to get more testing done on them before they are shared to other 
> forests. However, as a side effect of this the propagation time of 
> fixes is also impacted, and in some cases we have seen fixes stuck for 
> several weeks waiting for the respective forests to stabilize.
> We would like to propose an experiment, which will merge the hs-rt and 
> hs-gc forests, having hs-rt be the forest through which all the hs-rt 
> and hs-gc changes are integrated. For the duration of the experiment 
> the hs-gc forest will be locked down so that no accidental 
> integrations are made to it. This change would mean that the combined 
> hs-rt gets more testing faster, and that the fix propagation time goes 
> to zero for changes between hs-rt and hs-gc. The hs-comp forest will 
> not be affected.
> We suggest that the experiment starts June 4th and goes on for at 
> least two weeks (giving us some time to adapt in case of issues). 
> Monitoring and evaluation of the new structure will take place 
> continuously, with an option to revert back if things do not work out. 
> This will remain an experiment for at least a few months, after which 
> we will evaluate it and depending on the results consider making it 
> the new standard. If so, the hs-gc forest will eventually be retired, 
> with an option of looking at further reduction of forests going forward.
> It's worth pointing out explicitly that if you have any changes based 
> on the hs-gc forest those changes would have to be rebased on top of 
> hs-rt instead once the hs-gc forest has been locked down.
> Please let us know if you have any feedback or questions!
> Cheers,
> Mikael
> [1] http://hg.openjdk.java.net/jdk9/hs-rt
> [2] http://hg.openjdk.java.net/jdk9/hs-gc
> [3] http://hg.openjdk.java.net/jdk9/hs-comp

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