public static ThreadPoolExecutor newFixedThreadPool(int corePoolSize) {
        return new ThreadPoolExecutor(corePoolSize,
            corePoolSize,
            0,
            TimeUnit.MILLISECONDS,
            new SynchronousQueue<Runnable>());
    }
public static ThreadPoolExecutor newFixedThreadPool ( int corePoolSize ) { return new ThreadPoolExecutor ( corePoolSize , corePoolSize , 0 , TimeUnit . MILLISECONDS , new SynchronousQueue < Runnable > ( ) ) ; }
固定大小线程池，无队列

@param corePoolSize 初始化线程池
@return the thread pool executor