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

[Aleksey Shipilev]

On 03/07/2018 11:26 AM, Roman Kennke wrote:
> In some cases I actually question why we are waiting at all, and don't
> we want to SpinPause() instead? E.g:

SpinPause is for very short busy-waits. We cannot afford busy-waiting on most of those paths.

>>    // 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? ^^

Fixed with ShenandoahControlLoopInterval.


>> @@ -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).

It does exist. It does not exist with your OOM-during-evac changes.


>> 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?

It waits for concurrent thread to react on cancellation, mostly for logging purposes.

Thanks,
-Aleksey