C fork / exec,带有非阻塞管道IO

int nonBlockingPOpen(char *const argv[]){
    int inpipe;
    pid_t pid;
    /* open both ends of pipe nonblockingly */
    pid = fork();

    switch(pid){
        case 0:         /*child*/
            sleep(1); /*child should open after parent has open for reading*/

            /*redirect stdout to opened pipe*/
            int outpipe = open("./fifo",O_WRONLY);
            /*SHOULD BLOCK UNTIL MAIN PROCESS OPENS FOR WRITinG*/
            dup2(outpipe,1);
            fcntl(1,F_SETFL,fcntl(1,F_GETFL) | O_NONBLOCK);

            printf("HelLO WORLD I AM A CHILD PROCESS\n");
            /*This seems to be written to the pipe immediately,blocking or not.*/
            execvp(*argv,argv);
            /*All output from this program,which outputs "one" sleeps for 1 second
             *outputs "two" sleeps for a second,etc,is captured only after the
             *exec'd program exits!
             */
            break;

        default:        /*parent*/
            inpipe = open("./fifo",O_RDONLY | O_NONBLOCK);
            sleep(2);
            /*no need to do anything special here*/
            break;
    }

    return inpipe;
}@H_874_3@ 
 
为什么子进程每次生成一行时都不会将其stdout写入管道？在execvp或dup2的工作方式中是否有一些我缺少的东西？我知道我对这一切的处理方式有点奇怪,但我找不到另一种以编程方式捕获闭源二进制文件输出的方法.