Poll Loop (Asynchronous IO)

[chsalvia@gmail.com]

I'm trying to implement a simple poll loop which asynchronously
fetches a list of URLs. Since I'm used to working with multiple
threads, I have little experience using single-threaded IO
multiplexing. I wrote a small program to try to get it to work, but
I'm having difficulty.

I connect to a bunch of non-blocking sockets, then poll them for
activity. On POLLOUT, I send an HTTP request. On POLLIN, I recv
incoming data. But the loop doesn't work. The POLLOUT even occurs
over and over again, on each socket, and POLLIN never occurs.

pollfd* pfd = (pollfd*) malloc(nsock * sizeof(pollfd)) ;
for (int i = 0; i < nsock; ++i) {
pfd[i].fd = sock[i];
pfd[i].events = POLLOUT | POLLIN;
pfd[i].revents = 0;
}

for (int i = 0; i < nsock; ++i) {
connect(sock[i], (sockaddr*) &m_addr[i], sizeof(m_addr)) ;
}

dbuffer buffer;

int timeout = -1;
cout << "Polling... " << endl;
for(;;) {
if (poll(pfd, nsock, timeout) 0) {
for (int i = 0; i < nsock; ++i) {
if (pfd[i].revents & POLLOUT) {
send(sock[i], request, request_length, 0);
}
if (pfd[i].revents & POLLIN) {
cout << "Found POLL IN EVENT" << endl;
int status;
do {
if (status = buffer.recv(soc k[i], buf, maxrecv, 0) {
if (errno != EWOULDBLOCK) break;
}
} while (status != 0);
}
}
}
else {
if (errno == EINTR) continue;
perror("poll()" );
}
}

[Ian Collins]

Re: Poll Loop (Asynchronous IO)

chsalvia@gmail. com wrote:

I'm trying to implement a simple poll loop which asynchronously
fetches a list of URLs. Since I'm used to working with multiple
threads, I have little experience using single-threaded IO
multiplexing. I wrote a small program to try to get it to work, but
I'm having difficulty.
>

Try comp.unix.progr ammer.

--
Ian Collins.