在linux中使用父进程和子进程中的Pipe

Question

I write a code for pipe in that every time parent die first why it happen there is no rule which process execute first but here parent always die first why, anybody can explain this code.

main() {

int data_pass;
int file_pipes[2];
const char *some_data = "my name is khan";
char buffer[BUFSIZ + 1];
pid_t pid;
memset(buffer,'\0',BUFSIZ);
if(pipe(file_pipes) == 0)
{
    pid = fork();
    switch(pid)
    {

        case -1:
        {
            printf("cant create \n");
            exit(0);
        }
        case 0:
        {
            data_pass = read(file_pipes[0],buffer,BUFSIZ);
            printf("readed data is %s\n",buffer);
            exit(0);
        }
        default:
            {

            sleep(5);
            data_pass = write(file_pipes[1],some_data,strlen(some_data));
            printf("wrote\n");
        }
    }
}
exit(0);

}

o/p-> wrote

 readed data is my name is khan

Answer 1

It depends on scheduler. On some systems child is created in runnable state, but parent can use his whole time quantum. On some other system can be implementation different and parent is stopped and child is chosen to run instantly.

In conclusion you can not rely on execution order of processes that are runnign in parallel without synchronization.

See syscall waitpid or wait .

Also sleep(5) doesn't mean the process will be sleeping for 5 seconds. It can be more if scheduler plans other processes with higher priority instead. It can be less too, if process obtains signal from OS.