use s_contentionCount as additional source of randomness

src/libraries/System.Private.CoreLib/src/System/Threading/Lock.cs

@@ -345,22 +345,22 @@ private void ExitImpl()
 
  // we use this to de-synchronize threads if interlocked operations fail
  // we will pick a random number in exponentially expanding range and spin that many times
- private unsafe void CollisionBackoff(int collisions)
+ private static unsafe void CollisionBackoff(int collisions)
  {
  Debug.Assert(collisions > 0);
 
- // no need for much randomness here, we will just hash the stack address + _wakeWatchDog.
- uint rand = ((uint)&collisions + (uint)_wakeWatchDog) * 2654435769u;
+ // no need for much randomness here, we will just hash the stack address + s_contentionCount.
+ uint rand = ((uint)&collisions + (uint)s_contentionCount) * 2654435769u;
  uint spins = rand >> (byte)(32 - Math.Min(collisions, MaxExponentialBackoffBits));
  Thread.SpinWait((int)spins);
  }
 
  // same idea as in CollisionBackoff, but with guaranteed minimum wait
- private unsafe void IterationBackoff(int iteration)
+ private static unsafe void IterationBackoff(int iteration)
  {
  Debug.Assert(iteration > 0 && iteration < MaxExponentialBackoffBits);
 
- uint rand = ((uint)&iteration + (uint)_wakeWatchDog) * 2654435769u;
+ uint rand = ((uint)&iteration + (uint)s_contentionCount) * 2654435769u;
  // set the highmost bit to ensure minimum number of spins is exponentialy increasing
  // it basically gurantees that we spin at least 1, 2, 4, 8, 16, times, and so on
  rand |= (1u << 31);