RFR: Use os::naked_short_sleep instead of naked Thread events for sleeping

[Roman Kennke]

Hi Aleksey,

that makes a lot of sense.

In some cases I actually question why we are waiting at all, and don't
we want to SpinPause() instead? E.g:



>    // Wait for the actual stop(), can't leave run_service() earlier.
>    while (!should_terminate()) {
> -    Thread::current()->_ParkEvent->park(10);
> +    os::naked_short_sleep(10);
>    }
>  }

And hardcoded 10ms? ^^

> @@ -444,7 +444,7 @@
>                   GCCause::to_string(GCCause::_shenandoah_allocation_failure_evac),
>                   Thread::current()->name());
>      while (heap->is_evacuation_in_progress()) { // wait.
> -      Thread::current()->_ParkEvent->park(1);
> +      os::naked_short_sleep(1);
>      }
>    }
>  }

This loop doesn't exist anymore (in dev repo).

> diff -r 58279d273cc4 src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp
> --- a/src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp	Mon Mar 05 17:05:30 2018 +0100
> +++ b/src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp	Wed Mar 07 11:13:54 2018 +0100
> @@ -2849,7 +2849,7 @@
>  void ShenandoahHeap::try_inject_alloc_failure() {
>    if (ShenandoahAllocFailureALot && !cancelled_concgc() && ((os::random() % 1000) > 950)) {
>      _inject_alloc_failure.set();
> -    Thread::current()->_ParkEvent->park(1);
> +    os::naked_short_sleep(1);
>      if (cancelled_concgc()) {
>        log_info(gc)("Allocation failure was successfully injected");
>      }

What is this waiting for?

Roman