Re: [rvm-research] Scheduling a new Garbage Collection Phase

On 09/07/13 09:48, Nathan Ricci wrote:
>     I'm implementing a garbage collector, called (for now) the
> "Control Collector". I've based it on the mark sweep collector, and
> the classes are called "GCControl", GCControlCollector, etc.  
>
>     As part of this, I'm trying to add a new collection phase, and I
> want to divide some of the work between multiple threads. I seem to
> have misunderstood how to do this, however, since in the
> GCControlCollector#collectionPhase, I see the same worker ordinal
> enter the new phase multiple times in a garbage collection. 
>
>      Do I even have the right idea? Is it the case that in a
> Collector, I should only see a given phaseID once per worker ordinal
> (as returned by ParallelCollector#parallelWorkerOrdinal()), and the
> worker ordinals have a one-to-one correspondence to threads?
You have the right idea - this is the intention. 

Bear in mind that the phase CLOSURE is invoked 3 times in a Simple
collection, so you should see your control closure invoked 3 times per
GC thread. 

What do you see at GC verbosity level 7 with 1 GC thread ?  Two threads ?

The logic for scheduling phases is in org.mmtk.plan.Phase - it might be
helpful to write a pretty-printer for complex phases so that you can
statically check the resulting structure after your modification.  Some
if the login in the Phase class is pretty byzantine, but
processPhaseStack is where most of it happens, and this is fairly
straightforward.

Hope this helps,
Robin
>
>      Some code is below. Thanks for any help.
>
>            --Nathan Ricci
>               Tufts University
>
> I create and schedule the phase in the plan:
>
> public class GCControl extends MS {
> ...
>   public static final short CONTROL_CLOSURE =
> Phase.createSimple("GCControl.control_closure");
>   protected static final short controlClosurePhase =
> Phase.createComplex("GCControl.control_closure_complex",
>                                                                      
>     null,
>                                                                      
>     Phase.scheduleGlobal(CONTROL_CLOSURE),
>                                                                      
>     Phase.scheduleCollector(CONTROL_CLOSURE));
>
> public GCControl() {
>     super();
>   this.insertPhaseAfter(Phase.scheduleCollector(PREPARE),            
>    i                         Phase.scheduleComplex(controlPhase));
>
>     this.insertPhaseAfter(Phase.scheduleCollector(CLOSURE),  
> Phase.scheduleComplex(controlClosurePhase));
>  
>        ...
> }
>
> Here is the collectionPhase method from the GCControlCollector:
>
> public void collectionPhase(short phaseId, boolean primary) {
>     
>  if (phaseId == GCControl.CONTROL_CLOSURE) {
>    Log.write("GCControlCollector: collectionPhase: CONTROL_CLOSURE
> phase: ordinal ");
>    Log.write(parallelWorkerOrdinal());
>   ...
>    return;
>  }
>   ...
>  super.collectionPhase(phaseId, primary);
>   }
>
>
> I end up seeing from those log messages that the CONTROL_CLOSURE phase
> comes up multiple times with the same worker ordinal, even within a
> garbage collection. 
>
>
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