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, the write operation, the write operation is complete again call the times function to record the time of the end of the output, and then at different times