code: @Override
    public synchronized boolean offer(Runnable runnable) {
      int allWorkingThreads = this.executor.getActiveCount() + super.size();
      return allWorkingThreads < this.executor.getPoolSize() && super.offer(runnable);
    }
docs: Inserts the specified element at the tail of this queue if there is at least one available thread to run the
  current task. If all pool threads are actively busy, it rejects the offer.
  
  @param runnable the element to add.
  @return true if it was possible to add the element to this queue, else false
  @see ThreadPoolExecutor#execute(Runnable)