unix课程实验2，同步与异步write的效率比较，将文件读入缓存，调用times函数进行计时，进行写操作，写操作完全完成后再次调用times函数，记录结束的时间，再将不同时间输出-unix course experiment 2, synchronous and asynchronous write the efficiency comparison, the file is read into the cache, timing of times a function is called,