src/hotspot/share/gc/shared/workgroup.hpp

*** 200,209 ****
--- 200,230 ----
  
  protected:
    virtual AbstractGangWorker* allocate_worker(uint which);
  };
  
+ // Temporarily try to set the number of active workers.
+ // It's not guaranteed that it succeeds, and users need to
+ // query the number of active workers.
+ class WithUpdatedActiveWorkers : public StackObj {
+ private:
+   AbstractWorkGang* const _gang;
+   const uint              _old_active_workers;
+ 
+ public:
+   WithUpdatedActiveWorkers(AbstractWorkGang* gang, uint requested_num_workers) :
+       _gang(gang),
+       _old_active_workers(gang->active_workers()) {
+     uint capped_num_workers = MIN2(requested_num_workers, gang->total_workers());
+     gang->update_active_workers(capped_num_workers);
+   }
+ 
+   ~WithUpdatedActiveWorkers() {
+     _gang->update_active_workers(_old_active_workers);
+   }
+ };
+ 
  // Several instances of this class run in parallel as workers for a gang.
  class AbstractGangWorker: public WorkerThread {
  public:
    AbstractGangWorker(AbstractWorkGang* gang, uint id);