src/share/vm/gc/g1/g1CollectedHeap.cpp

rev 10739 : 8153745: Avoid spawning G1ParPreserveCMReferentsTask when there is no work to be done
Reviewed-by:
rev 10740 : [mq]: check-during-cycle

*** 4460,4470 ****
    // objects discovered by the STW ref processor in case one of these
    // referents points to another object which is also referenced by an
    // object discovered by the STW ref processor.
    double preserve_cm_referents_time = 0.0;
  
!   if (_ref_processor_cm->has_discovered_references()) {
      double preserve_cm_referents_start = os::elapsedTime();
      uint no_of_gc_workers = workers()->active_workers();
      G1ParPreserveCMReferentsTask keep_cm_referents(this,
                                                     per_thread_states,
                                                     no_of_gc_workers,
--- 4460,4474 ----
    // objects discovered by the STW ref processor in case one of these
    // referents points to another object which is also referenced by an
    // object discovered by the STW ref processor.
    double preserve_cm_referents_time = 0.0;
  
!   // To avoid spawning task when there is no work to do, check that
!   // a concurrent cycle is active and that some references have been
!   // discovered.
!   if (concurrent_mark()->cmThread()->during_cycle() &&
!       ref_processor_cm()->has_discovered_references()) {
      double preserve_cm_referents_start = os::elapsedTime();
      uint no_of_gc_workers = workers()->active_workers();
      G1ParPreserveCMReferentsTask keep_cm_referents(this,
                                                     per_thread_states,
                                                     no_of_gc_workers,