code: @Override
      public final void clear() {
          int spin = 0;
          for(;;) {
              final long writeLock = seqLock.tryWriteLock();
              if(writeLock > 0L) {
                  final int stackTop = this.stackTop.get();
                  if(stackTop>0) {
                      try {
                          for(int i = 0; i<stackTop; i++) {
                              stack.set(i, null);
                          }
                          stackNotFullCondition.signal();
                          return;
                      } finally {
                          this.stackTop.set(0);
                      }
                  } else {
                      return;
                  }
              }
  
              spin = Condition.progressiveYield(spin);
          }
      }
docs: clear the stack - does not null old references