src/hotspot/share/gc/shenandoah/shenandoahRootProcessor.hpp

rev 59533 : 8246097: Shenandoah: limit parallelism in CLDG root handling
Reviewed-by: XXX

*** 224,236 ****
  };
  
  template <bool CONCURRENT, bool SINGLE_THREADED>
  class ShenandoahClassLoaderDataRoots {
  private:
    ShenandoahPhaseTimings::Phase _phase;
  public:
!   ShenandoahClassLoaderDataRoots(ShenandoahPhaseTimings::Phase phase);
    ~ShenandoahClassLoaderDataRoots();
  
    void always_strong_cld_do(CLDClosure* clds, uint worker_id);
    void cld_do(CLDClosure* clds, uint worker_id);
  };
--- 224,245 ----
  };
  
  template <bool CONCURRENT, bool SINGLE_THREADED>
  class ShenandoahClassLoaderDataRoots {
  private:
+   ShenandoahSharedSemaphore     _semaphore;
    ShenandoahPhaseTimings::Phase _phase;
+ 
+   static uint worker_count(uint n_workers) {
+     // Limit concurrency a bit, otherwise it wastes resources when workers are tripping
+     // over each other. This also leaves free workers to process other parts of the root
+     // set, while admitted workers are busy with doing the CLDG walk.
+     return MAX2(1u, MIN2(ShenandoahSharedSemaphore::max_tokens(), n_workers / 2));
+   }
+ 
  public:
!   ShenandoahClassLoaderDataRoots(ShenandoahPhaseTimings::Phase phase, uint n_workers);
    ~ShenandoahClassLoaderDataRoots();
  
    void always_strong_cld_do(CLDClosure* clds, uint worker_id);
    void cld_do(CLDClosure* clds, uint worker_id);
  };