Sometimes I do wonder how much stupid I can be.
Thanks MJ On 15-Jan-12 22:49, ss griffon wrote:
On Sun, Jan 15, 2012 at 8:48 AM, Manish Jain<invalid.poin...@gmail.com> wrote:Hi All, I was trying to write a small demo code using the select() system call. Here are the sources : #include<sys/types.h> #include<unistd.h> #include<fcntl.h> #include<iostream> #include<cstring> #include<cassert> int nice_child(int * fd, int * fd_close) { close(fd[0]); close(fd_close[0]); close(fd_close[1]); char buffer[32]; while (1) { sleep(3); strcpy(buffer, "I love my wife !"); write(fd[1], buffer, strlen(buffer) + 1); } return 0; } int naughty_child(int * fd, int * fd_close) { close(fd[0]); close(fd_close[0]); close(fd_close[1]); char buffer[32]; while (1) { sleep(4); strcpy(buffer, "I love your wife !"); write(fd[1], buffer, strlen(buffer) + 1); } return 0; } int main() { int fd_nice[2]; int fd_naughty[2]; pipe(fd_nice); pipe(fd_naughty); if (fork() == 0) { return nice_child(fd_nice, fd_naughty); } else { if (fork() == 0) { return naughty_child(fd_naughty, fd_nice); } } close(fd_nice[1]); close(fd_naughty[1]); fd_set fdset; char buffer[64]; int fd = (*fd_naughty> *fd_nice) ? *fd_naughty : *fd_nice; FD_ZERO(&fdset); FD_SET(fd_nice[0],&fdset); FD_SET(fd_naughty[0],&fdset); while (1) { int result = select(fd + 1,&fdset, 0, 0, 0); assert(result> 0); if (FD_ISSET(fd_nice[0],&fdset)) { int result = read(fd, buffer, sizeof(buffer)); buffer[result] = 0; std::cout<< "Nice child sent : "<< buffer<< std::endl; } if (FD_ISSET(fd_naughty[0],&fdset)) { int result = read(fd, buffer, sizeof(buffer)); buffer[result] = 0; std::cout<< "Naughty child sent : "<< buffer<< std::endl; } } return 0; } I was expecting the output to be like : Nice child sent : I love my wife ! Naughty child sent : I love your wife ! Nice child sent : I love my wife ! But what I actually get is : Nice child sent : I love your wife ! Nice child sent : I love your wife ! Nice child sent : I love your wife ! Nice child sent : I love your wife ! Nice child sent : I love your wife ! Nice child sent : I love your wife ! Can somebody throw some light on what might be wrong ? Thank you& Regards Manish Jain invalid.poin...@gmail.com _______________________________________________ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "freebsd-questions-unsubscr...@freebsd.org"It looks like you are always reading from the same file descriptor 'fd'. Instead you should read from fd_naughty[0] or fd_nice[0] based on your FD_ISSET checks. Also, don't forget to wait() for your child processes.
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