code: @Override
      public final N peek() {
          // read the current cursor
          int spin = 0;
          for(;;) {
              final long readLock = seqLock.readLock();
              final int stackTop = this.stackTop.get();
              if(stackTop > 0) {
                  final N  n = stack.get(stackTop-1);
                  if(seqLock.readLockHeld(readLock)) {
                      return n;
                  } // else loop again
              } else {
                  return null;
              }
  
              spin = Condition.progressiveYield(spin);
          }
      }
docs: peek at the top of the stack
  
  @return N - the object at the top of the stack