[ACCEPTED]-c++ how to use select to see if a socket has closed-select
Accepted answer
The below snippet first checks if the socket 3 is marked readable (which it is when closed) and 2 then if there's actually anything to be 1 read.
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/ioctl.h>
bool isclosed(int sock) {
fd_set rfd;
FD_ZERO(&rfd);
FD_SET(sock, &rfd);
timeval tv = { 0 };
select(sock+1, &rfd, 0, 0, &tv);
if (!FD_ISSET(sock, &rfd))
return false;
int n = 0;
ioctl(sock, FIONREAD, &n);
return n == 0;
}
You don't need to do a select() followed by ioctl(). You 2 can instead do a non-blocking peek on the 1 socket to see if it returns 0.
bool isclosed (int sock) {
char x;
interrupted:
ssize_t r = ::recv(sock, &x, 1, MSG_DONTWAIT|MSG_PEEK);
if (r < 0) {
switch (errno) {
case EINTR: goto interrupted;
case EAGAIN: break; /* empty rx queue */
case ETIMEDOUT: break; /* recv timeout */
case ENOTCONN: break; /* not connected yet */
default: throw(errno);
}
}
return r == 0;
}
If you get a read notification and the read 2 returns 0 bytes the client has exited cleanly. If 1 not you will get an exception notification.
Source:
stackoverflow.com
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