Issue
I am trying to write a program where i need to monitor ends of unnamed pipe for certain events. Can I use unnamed pipes with poll function?
If yes, can you please show me the syntax for poll function with functional descriptors
Solution
An example of poll
To use poll
to check if readfd
is readable or writefd
is writable:
int readfd;
int writefd;
// initialize readfd & writefd, ...
// e.g. with: open(2), socket(2), pipe(2), dup(2) syscalls
struct pollfd fdtab[2];
memset (fdtab, 0, sizeof(fdtab)); // not necessary, but I am paranoid
// first slot for readfd polled for input
fdtab[0].fd = readfd;
fdtab[0].events = POLLIN;
fdtab[0].revents = 0;
// second slot with writefd polled for output
fdtab[1].fd = writefd;
fdtab[1].events = POLLOUT;
fdtab[1].revents = 0;
// do the poll(2) syscall with a 100 millisecond timeout
int retpoll = poll(fdtab, 2, 100);
if (retpoll > 0) {
if (fdtab[0].revents & POLLIN) {
/* read from readfd,
since you can read from it without being blocked */
}
if (fdtab[1].revents & POLLOUT) {
/* write to writefd,
since you can write to it without being blocked */
}
}
else if (retpoll == 0) {
/* the poll has timed out, nothing can be read or written */
}
else {
/* the poll failed */
perror("poll failed");
}
Answered By - Basile Starynkevitch Answer Checked By - David Goodson (WPSolving Volunteer)