創(chuàng)建兩個進(jìn)程(實(shí)時進(jìn)程)并在它們之間傳送一個令牌，如此往返傳送一定的次數(shù)。其中一個進(jìn)程在讀取令牌時就會引起阻塞。另一個進(jìn)程發(fā)送令牌后等待其返回時也處于阻塞狀態(tài)。發(fā)送令牌帶來的開銷與上下文切換帶來的開銷相比，可以忽略不計(jì)（經(jīng)測試，一次管道傳遞約用時3ns左右）。 (利用管道傳遞令牌)?

方法一：使用gettimeofday()

[cpp]?view plaincopy

//方法一：使用gettimeofday()獲取當(dāng)前時間??

??

#include?<stdio.h>??

#include?<stdlib.h>??

#include?<sys/time.h>??

#include?<time.h>??

#include?<sched.h>??

#include?<sys/types.h>??

#include?<unistd.h>??????//pipe()??

??

int?main()??

{??

????int?x,?i,?fd[2],?p[2];??

????int?tv[2];??//用于進(jìn)程間數(shù)據(jù)通信??

????char?send????=?'s';??

????char?receive;??

????pipe(fd);??

????pipe(p);??

????pipe(tv);??

????struct?timeval?tv_start,tv_end;??

????struct?sched_param?param;??

????param.sched_priority?=?0;??

??

????while?((x?=?fork())?==?-1);??

????if?(x==0)?{?????????//子進(jìn)程??

????????sched_setscheduler(getpid(),?SCHED_FIFO,?&param);??

????????gettimeofday(&tv_start,?NULL);??

????????write(tv[1],?&tv_start,?sizeof(tv_start));//保存數(shù)據(jù)，以便傳遞到父進(jìn)程中進(jìn)行計(jì)算??

????????//printf("Before?Context?Switch?Time1.sec?%u?s\n",?tv_start.tv_sec);??

????????//printf("Before?Context?Switch?Time1.usec?%u?us\n",?tv_start.tv_usec);???????

????????for?(i?=?0;?i?<?10000;?i++)?{??

????????????read(fd[0],?&receive,?1);??

????????????//printf("Child?read!\n");??

????????????write(p[1],?&send,?1);??

????????????//printf("Child?write!\n");??

????????}??

????????exit(0);??

????}??

????else?{??????//父進(jìn)程??

????????sched_setscheduler(getpid(),?SCHED_FIFO,?&param);??

????????for?(i?=?0;?i?<?10000;?i++)?{??

????????????write(fd[1],?&send,?1);??

????????????//printf("Parent?write!\n");??

????????????read(p[0],?&receive,?1);??

????????????//printf("Parent?read!\n");??

????????}??

????????gettimeofday(&tv_end,?NULL);??

????????//printf("After?Context?SWitch?Time1.sec?%u?s\n",?tv_end.tv_sec);??

????????//printf("After?Context?SWitch?Time1.usec?%u?us\n",?tv_end.tv_usec);??

??????????

????}??

????read(tv[0],?&tv_start,?sizeof(tv_start));?????

????//printf("Before?Context?Switch?Time2.sec?%u?s\n",?tv_start.tv_sec);??

????//printf("Before?Context?Switch?Time2.usec?%u?us\n",?tv_start.tv_usec);??

????//printf("Before?Context?Switch?Time?%u?us\n",?tv_start.tv_usec);??

????//printf("After?Context?SWitch?Time2.sec?%u?s\n",?tv_end.tv_sec);??

????//printf("After?Context?SWitch?Time2.usec?%u?us\n",?tv_end.tv_usec);??

????printf("Task?Switch?Time:?%f?us\n",?(1000000*(tv_end.tv_sec-tv_start.tv_sec)?+?tv_end.tv_usec?-?tv_start.tv_usec)/20000.0);???

????return?0;??

} ?

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