ePoll not accepting some clients - c

Question

I have implemented a server using epoll, in what I believe to be the standard way, in fact, when I implemented it using the example from the epoll man page I got the same behavior.
This leads me to believe that there must be a problem with my client, and that I'm making assumptions somehow where I shouldn't. The main method of my client forks n number of clients, which then connect to the server. What I'm seeing is that usually a subset of these clients don't trigger the epoll, and never hit the
accept() call. The three-way-handshake completes because there is a listening socket, so the client behaves as if it where accepted, but it never gets served, as the server doesn't know about it. I can't figure out why this is happening, and haven't been able to find similar questions online. Thoughts?
Here's the relevant server code:
// wrapper which binds to port and exits on error
listenFD = tcpSocket(host, port);
SetNonblocking(listenFD);
// wrapper which listens and exits on error
tcpListen(listenFD);
epollFD = epoll_create(EPOLL_QUEUE_LEN);
if (epollFD == -1)
errSystem("epoll_create");
// Add the server socket to the epoll event loop
event.events = EPOLLIN | EPOLLERR | EPOLLHUP | EPOLLET;
event.data.fd = listenFD;
if (epoll_ctl (epollFD, EPOLL_CTL_ADD, listenFD, &event) == -1)
errSystem("epoll_ctl");
while(TRUE){
//struct epoll_event events[MAX_EVENTS];
numFDs = epoll_wait(epollFD, events, EPOLL_QUEUE_LEN, -1);
for (i = 0; i < numFDs; i++){
// Case 1: Error condition
if (events[i].events & (EPOLLHUP | EPOLLERR)){
errMessage("epoll: EPOLLERR");
Close(events[i].data.fd);
printf("Closed connection to %d\n", events[i].data.fd);
fflush(stdout);
continue;
}
// Case 2: Server is receiving a connection request
if (events[i].data.fd == listenFD){
// socketlen_t
clientLen = sizeof(client);
newFD = Accept (listenFD, (SA *)&client, &clientLen);
SetNonblocking(newFD);
// Set receive low water mark to message size
SetSockOpt(newFD, SOL_SOCKET, SO_RCVLOWAT, &lowWater, sizeof(lowWater));
// Add the new socket descriptor to the epoll loop
event.data.fd = newFD;
event.events = EPOLLIN | EPOLLET;
if (epoll_ctl (epollFD, EPOLL_CTL_ADD, newFD, &event) == -1)
errSystem ("epoll_ctl");
printf("Connected to client on socket %d\n", newFD);
// tell the client we're connected and ready
// (this is an attempt to fix my issue. I'd rather not do this...)
Writen(newFD, buffer, CLIENT_MESSAGE_SIZE);
continue;
}
if (events[i].events & EPOLLIN){
//serve the client
}
}
}
And this is the client code. One instance of these works, but if I fork more than 5 or so (sometimes just 2) a number of them won't get accepted.
int Client(const char *host, const int port, const int timeLen, const int clientNum){
long double delta;
PTSTRUCTS ptstructs = (PTSTRUCTS) malloc(sizeof(TSTRUCTS));
size_t result;
stop = FALSE;
cNum = clientNum;
Signal(SIGINT, closeFD);
Signal(SIGALRM, sendMessage);
nsockets = 0;
// wrapper which calls connect() and exits with message on error
connectFD = tcpConnect(host, port);
printf("%d connected to server:\n", clientNum);
fflush(stdout);
bzero(sbuf, CLIENT_MESSAGE_SIZE);
// initialize client message
strcpy(sbuf, CLIENT_MESSAGE);
// get the start time
getStartTime(ptstructs);
getEndTime(ptstructs);
while((delta = getTimeDelta(ptstructs)) < timeLen){
// One or more clients blocks here for ever
if ((result = receiveMessage()) < CLIENT_MESSAGE_SIZE){
break;
}
//sendMessage();
alarm(1);
//delay(USER_DELAY);
getEndTime(ptstructs);
}
stop = TRUE;
Close (connectFD);
getEndTime(ptstructs);
delta = getTimeDelta(ptstructs);
printf("Client %d served %ld bytes in %.6Lf seconds.\n", clientNum, byteCount, delta);
fflush(stdout);
// free heap memory
free(ptstructs);
return (1);
}
I should probably note that I'm seeing the same behavior if I don't set EPOLLET. I originally thought this might be the result of edge-triggering behavior, but nope.

Answer 1

Does your backlog argument of listen() greater than the number of clients?
#some-programmer-dude, sorry for not commentting, the closed fd will be removed from epoll event set automatically http://man7.org/linux/man-pages/man7/epoll.7.html