select, poll và epoll

/* Van de: ban co N socket. recv tren mot socket rong se CHAN.
   Nen ban khong the cu lan luot goi recv tren tung cai.

   Ba loi giai sai:

   1. Mot luong moi socket.
      -> N luong. Bai 46.8 da noi ve gioi han cua no.

   2. Dat socket sang khong chan, roi quay vong hoi tung cai.
      -> Vong lap ban 100% CPU du khong co gi xay ra.
         Duoc goi la "hoi vong", va no la mot phan mem xau.

   3. Khong chan cong voi sleep giua cac vong.
      -> Do tre bang thoi gian sleep. 10 ms sleep nghia la
         moi phan hoi cham them trung binh 5 ms.

   Loi giai dung: hoi HE DIEU HANH.

      "Toi co N socket day. Hay cho toi ngu cho toi khi
       MOT trong so chung co viec, roi danh thuc toi
       va noi la cai nao."

   Do la select, poll, epoll, kqueue, va IOCP. */

SOCKET kh[FD_SETSIZE];
int kh_co = 0;
int xong  = 0;

while (xong < SO_KH) {
    /* 1. Dung lai danh sach MOI VONG. select pha huy no. */
    fd_set doc;
    FD_ZERO(&doc);
    FD_SET(sv, &doc);                           /* socket lang nghe */
    for (int i = 0; i < kh_co; ++i) FD_SET(kh[i], &doc);

    struct timeval tv = { 5, 0 };
    int r = select(0, &doc, NULL, NULL, &tv);
    if (r == 0) { printf("select het gio\n"); break; }
    if (r < 0)  { printf("select loi %d\n", WSAGetLastError()); break; }

    /* 2. Socket lang nghe san sang doc = co ket noi moi */
    if (FD_ISSET(sv, &doc)) {
        SOCKET c = accept(sv, NULL, NULL);
        if (c != INVALID_SOCKET) {
            kh[kh_co++] = c;
            printf("[%4lu ms] server: accept, dang theo doi %d socket\n",
                   tich()-t0, kh_co);
        }
    }

    /* 3. Duyet cac socket client */
    for (int i = 0; i < kh_co; ) {
        if (!FD_ISSET(kh[i], &doc)) { ++i; continue; }

        char dem[64];
        int n = recv(kh[i], dem, 63, 0);
        if (n > 0) {
            dem[n] = 0;
            printf("[%4lu ms] server: doc \"%s\", tra loi ngay\n",
                   tich()-t0, dem);
            send(kh[i], dem, n, 0);
        }
        closesocket(kh[i]);
        ++xong;
        kh[i] = kh[--kh_co];        /* xoa: chuyen phan tu cuoi len */
        /* KHONG ++i o day, vi vi tri i gio la phan tu khac */
    }
}

#include <stdio.h>
#include <winsock2.h>
int main(void) {
    printf("FD_SETSIZE tren Winsock = %d\n", FD_SETSIZE);
    printf("sizeof(fd_set) = %d byte\n", (int)sizeof(fd_set));
    return 0;
}

#include <poll.h>

struct pollfd pfd[1024];
nfds_t so = 0;

pfd[so].fd     = sv;
pfd[so].events = POLLIN;
so++;

for (;;) {
    int r = poll(pfd, so, 5000);        /* thoi gian cho tinh bang MILI GIAY */
    if (r == 0) continue;               /* het gio */
    if (r < 0) {
        if (errno == EINTR) continue;
        break;
    }

    /* Socket lang nghe */
    if (pfd[0].revents & POLLIN) {
        int c = accept(sv, NULL, NULL);
        if (c >= 0 && so < 1024) {
            pfd[so].fd      = c;
            pfd[so].events  = POLLIN;
            pfd[so].revents = 0;
            so++;
        }
    }

    /* Client */
    for (nfds_t i = 1; i < so; ) {
        short re = pfd[i].revents;

        if (re & (POLLHUP | POLLERR | POLLNVAL)) {
            close(pfd[i].fd);
            pfd[i] = pfd[--so];
            continue;
        }
        if (re & POLLIN) {
            char dem[1024];
            ssize_t n = recv(pfd[i].fd, dem, sizeof dem, 0);
            if (n <= 0) {
                close(pfd[i].fd);
                pfd[i] = pfd[--so];
                continue;
            }
            send(pfd[i].fd, dem, (size_t)n, 0);
        }
        ++i;
    }
}

#include <sys/epoll.h>

int ep = epoll_create1(0);
if (ep < 0) { perror("epoll_create1"); return 1; }

/* Dang ky socket lang nghe MOT LAN duy nhat */
struct epoll_event sk;
sk.events  = EPOLLIN;
sk.data.fd = sv;
epoll_ctl(ep, EPOLL_CTL_ADD, sv, &sk);

struct epoll_event sk_ra[64];

for (;;) {
    int n = epoll_wait(ep, sk_ra, 64, -1);      /* -1 = cho mai */
    if (n < 0) {
        if (errno == EINTR) continue;
        break;
    }

    /* CHI duyet nhung cai SAN SANG, khong duyet toan bo */
    for (int i = 0; i < n; ++i) {
        int fd = sk_ra[i].data.fd;

        if (fd == sv) {
            int c = accept(sv, NULL, NULL);
            if (c < 0) continue;
            struct epoll_event e;
            e.events  = EPOLLIN;
            e.data.fd = c;
            epoll_ctl(ep, EPOLL_CTL_ADD, c, &e);
            continue;
        }

        if (sk_ra[i].events & (EPOLLHUP | EPOLLERR)) {
            epoll_ctl(ep, EPOLL_CTL_DEL, fd, NULL);
            close(fd);
            continue;
        }

        char dem[1024];
        ssize_t r = recv(fd, dem, sizeof dem, 0);
        if (r <= 0) {
            epoll_ctl(ep, EPOLL_CTL_DEL, fd, NULL);
            close(fd);
            continue;
        }
        send(fd, dem, (size_t)r, 0);
    }
}
close(ep);