src/hotspot/share/gc/shenandoah/shenandoahLock.cpp

*** 44,10 ***
--- 44,11 ---
  template<bool ALLOW_BLOCK>
  void ShenandoahLock::contended_lock_internal(JavaThread* java_thread) {
    assert(!ALLOW_BLOCK || java_thread != nullptr, "Must have a Java thread when allowing block.");
    // Spin this much, but only on multi-processor systems.
    int ctr = os::is_MP() ? 0xFF : 0;
+   int yields = 0;
    // Apply TTAS to avoid more expensive CAS calls if the lock is still held by other thread.
    while (Atomic::load(&_state) == locked ||
           Atomic::cmpxchg(&_state, unlocked, locked) != unlocked) {
      if (ctr > 0 && !SafepointSynchronize::is_synchronizing()) {
        // Lightly contended, spin a little if no safepoint is pending.

*** 66,21 ***
          // To avoid it, we wait here until local poll is armed and then proceed
          // to TBVIM exit for blocking. We do not SpinPause, but yield to let
          // VM thread to arm the poll sooner.
          while (SafepointSynchronize::is_synchronizing() &&
                 !SafepointMechanism::local_poll_armed(java_thread)) {
!           os::naked_yield();
          }
        } else {
!         os::naked_yield();
        }
      } else {
!       os::naked_yield();
      }
    }
  }
  
  ShenandoahSimpleLock::ShenandoahSimpleLock() {
    assert(os::mutex_init_done(), "Too early!");
  }
  
  void ShenandoahSimpleLock::lock() {
--- 67,33 ---
          // To avoid it, we wait here until local poll is armed and then proceed
          // to TBVIM exit for blocking. We do not SpinPause, but yield to let
          // VM thread to arm the poll sooner.
          while (SafepointSynchronize::is_synchronizing() &&
                 !SafepointMechanism::local_poll_armed(java_thread)) {
!           yield_or_sleep(yields);
          }
        } else {
!         yield_or_sleep(yields);
        }
      } else {
!       yield_or_sleep(yields);
      }
    }
  }
  
+ void ShenandoahLock::yield_or_sleep(int &yields) {
+   // Simple yield-sleep policy: do one 100us sleep after every N yields.
+   // Tested with different values of N, and chose 3 for best performance.
+   if (yields < 3) {
+     os::naked_yield();
+     yields++;
+   } else {
+     os::naked_short_nanosleep(100000);
+     yields = 0;
+   }
+ }
+ 
  ShenandoahSimpleLock::ShenandoahSimpleLock() {
    assert(os::mutex_init_done(), "Too early!");
  }
  
  void ShenandoahSimpleLock::lock() {