RFR: ShConcurrentThread races with set_gc_state_bit

[Aleksey Shipilev]

On 01/16/2018 08:33 PM, Zhengyu Gu wrote:
> 661 void ShenandoahHeap::set_gc_state_bit_concurrently(uint bit, bool value) {
> 1662   _gc_state.set_cond(bit, value);
> 1663   MutexLocker mu(Threads_lock);
> 1664   JavaThread::set_gc_state_all_threads(_gc_state.raw_value());
> 
> 
> I wonder if you want to move _gc_state.set_cond(bit, value) into locked section? In case that global
> state is set, then we hit a safepoint ... not sure if it is matter.

Does not really matter: the Threads_lock is here to capture all threads. The GC state manipulation
is MT-safe in itself.

Thanks,
-Aleksey