Linux 多路服用 select

 

    #include<fcntl.h>
    #include<stdio.h>
    #include<unistd.h>
    #include<sys/select.h>
    #include<sys/types.h>
    #include<sys/time.h>
    #define PIPENAME "/tmp/p1"
    #define PIPENAME_TWO "/tmp/p2"
    #define MSGCOUNT 10
    #define MSGSIZE 255

    /*管道1,2的文件描述符*/
    int fd1,fd2;
    pid_t pid1,pid2;

int
main(int argc,char *argv[]) {
    char buf[255],buf2[255];
    int len,rfd;
    struct timeval val;
    fd_set set;


        /*創建管道1，並打開*/
 if(mkfifo(PIPENAME,O_CREAT|O_EXCL)<0) /*創建管道1*/
  {
     perror("Create1 error!\n");
     unlink(PIPENAME);/*清除管道1*/
     exit(0);
  }

  fd1=open(PIPENAME,O_RDWR,0);/*打開管道1*/
  if(fd1<0)
  {
     perror("open1 error!\n");
     unlink(PIPENAME);
     exit(0);
  }

        /*創建管道2，並打開*/
 if(mkfifo(PIPENAME_TWO,O_CREAT|O_EXCL)<0) /*創建管道2*/
  {
     perror("Create2 error!\n");
     unlink(PIPENAME_TWO);/*清除管道2*/
     exit(0);
  }

  fd2=open(PIPENAME_TWO,O_RDWR,0);/*打開管道2*/
  if(fd2<0)
  {
     perror("open2 error!\n");
     unlink(PIPENAME_TWO);
     exit(0);
  }


/*******創建2個子進程********/
    pid1=fork();
    if(pid1==0)/*子進程*/
    {
    char msg[]="hello";
    sleep(4);
    printf("write to Pipe2\n");
    write(fd2,msg,sizeof(msg));
    }
      else
    {
        pid2=fork();
        if(pid2==0)/*子進程*/
        {
        char msg[]="hello";
        sleep(5);
        printf("write to Pipe1\n");
        write(fd1,msg,sizeof(msg));
        }



        /*超時時間*/
        val.tv_sec=5;
        val.tv_usec=0;


        while(1)
        {
            /*設置文件描述符集，先清空，再加入管道1,2*/
            /*每次循環都要清空集合，否則不能檢測描述符變化 */
            FD_ZERO(&set);
            FD_SET(fd1,&set);
            FD_SET(fd2,&set);

                rfd=select(FD_SETSIZE,&set,NULL,NULL,&val);

            switch(rfd)
        {
        case -1: exit(-1);break;
        case 0:break;
        default:
            if(FD_ISSET(fd1,&set))  //測試fd1是否可讀，
                 {
                        read(fd1,buf2,sizeof(buf2));
                        printf("[1]Get msg!\n");

                    }
                    if(FD_ISSET(fd2,&set))
                    {
                        read(fd2,buf,sizeof(buf));
                        printf("[2]Get msg!\n");

                    }
        }//switch
      }//while
     }//else

    }  //main

write to Pipe2

[2]Get msg!

write to Pipe1

[1]Get msg!