memcached.c

memcached是一个高性能的分布式的内存对象缓存系统

            if (!update_event(c, EV_WRITE | EV_PERSIST)) {
                if (settings.verbose > 0)
                    fprintf(stderr, "Couldn't update event\n");
                conn_set_state(c, conn_closing);
                return TRANSMIT_HARD_ERROR;
            }
            return TRANSMIT_SOFT_ERROR;
        }
        /* if res==0 or res==-1 and error is not EAGAIN or EWOULDBLOCK,
           we have a real error, on which we close the connection */
        if (settings.verbose > 0)
            perror("Failed to write, and not due to blocking");

        if (c->udp)
            conn_set_state(c, conn_read);
        else
            conn_set_state(c, conn_closing);
        return TRANSMIT_HARD_ERROR;
    } else {
        return TRANSMIT_COMPLETE;
    }
}

static void drive_machine(conn *c) {
    bool stop = false;
    int sfd, flags = 1;
    socklen_t addrlen;
    struct sockaddr addr;
    int res;

    assert(c != NULL);

    while (!stop) {

        switch(c->state) {
        case conn_listening:
            addrlen = sizeof(addr);
            if ((sfd = accept(c->sfd, &addr, &addrlen)) == -1) {
                if (errno == EAGAIN || errno == EWOULDBLOCK) {
                    /* these are transient, so don't log anything */
                    stop = true;
                } else if (errno == EMFILE) {
                    if (settings.verbose > 0)
                        fprintf(stderr, "Too many open connections\n");
                    accept_new_conns(false);
                    stop = true;
                } else {
                    perror("accept()");
                    stop = true;
                }
                break;
            }
            if ((flags = fcntl(sfd, F_GETFL, 0)) < 0 ||
                fcntl(sfd, F_SETFL, flags | O_NONBLOCK) < 0) {
                perror("setting O_NONBLOCK");
                close(sfd);
                break;
            }
            dispatch_conn_new(sfd, conn_read, EV_READ | EV_PERSIST,
                                     DATA_BUFFER_SIZE, false);
            break;

        case conn_read:
            if (try_read_command(c) != 0) {
                continue;
            }
            if ((c->udp ? try_read_udp(c) : try_read_network(c)) != 0) {
                continue;
            }
            /* we have no command line and no data to read from network */
            if (!update_event(c, EV_READ | EV_PERSIST)) {
                if (settings.verbose > 0)
                    fprintf(stderr, "Couldn't update event\n");
                conn_set_state(c, conn_closing);
                break;
            }
            stop = true;
            break;

        case conn_nread:
            /* we are reading rlbytes into ritem; */
            if (c->rlbytes == 0) {
                complete_nread(c);
                break;
            }
            /* first check if we have leftovers in the conn_read buffer */
            if (c->rbytes > 0) {
                int tocopy = c->rbytes > c->rlbytes ? c->rlbytes : c->rbytes;
                memcpy(c->ritem, c->rcurr, tocopy);
                c->ritem += tocopy;
                c->rlbytes -= tocopy;
                c->rcurr += tocopy;
                c->rbytes -= tocopy;
                break;
            }

            /*  now try reading from the socket */
            res = read(c->sfd, c->ritem, c->rlbytes);
            if (res > 0) {
                STATS_LOCK();
                stats.bytes_read += res;
                STATS_UNLOCK();
                c->ritem += res;
                c->rlbytes -= res;
                break;
            }
            if (res == 0) { /* end of stream */
                conn_set_state(c, conn_closing);
                break;
            }
            if (res == -1 && (errno == EAGAIN || errno == EWOULDBLOCK)) {
                if (!update_event(c, EV_READ | EV_PERSIST)) {
                    if (settings.verbose > 0)
                        fprintf(stderr, "Couldn't update event\n");
                    conn_set_state(c, conn_closing);
                    break;
                }
                stop = true;
                break;
            }
            /* otherwise we have a real error, on which we close the connection */
            if (settings.verbose > 0)
                fprintf(stderr, "Failed to read, and not due to blocking\n");
            conn_set_state(c, conn_closing);
            break;

        case conn_swallow:
            /* we are reading sbytes and throwing them away */
            if (c->sbytes == 0) {
                conn_set_state(c, conn_read);
                break;
            }

            /* first check if we have leftovers in the conn_read buffer */
            if (c->rbytes > 0) {
                int tocopy = c->rbytes > c->sbytes ? c->sbytes : c->rbytes;
                c->sbytes -= tocopy;
                c->rcurr += tocopy;
                c->rbytes -= tocopy;
                break;
            }

            /*  now try reading from the socket */
            res = read(c->sfd, c->rbuf, c->rsize > c->sbytes ? c->sbytes : c->rsize);
            if (res > 0) {
                STATS_LOCK();
                stats.bytes_read += res;
                STATS_UNLOCK();
                c->sbytes -= res;
                break;
            }
            if (res == 0) { /* end of stream */
                conn_set_state(c, conn_closing);
                break;
            }
            if (res == -1 && (errno == EAGAIN || errno == EWOULDBLOCK)) {
                if (!update_event(c, EV_READ | EV_PERSIST)) {
                    if (settings.verbose > 0)
                        fprintf(stderr, "Couldn't update event\n");
                    conn_set_state(c, conn_closing);
                    break;
                }
                stop = true;
                break;
            }
            /* otherwise we have a real error, on which we close the connection */
            if (settings.verbose > 0)
                fprintf(stderr, "Failed to read, and not due to blocking\n");
            conn_set_state(c, conn_closing);
            break;

        case conn_write:
            /*
             * We want to write out a simple response. If we haven't already,
             * assemble it into a msgbuf list (this will be a single-entry
             * list for TCP or a two-entry list for UDP).
             */
            if (c->iovused == 0 || (c->udp && c->iovused == 1)) {
                if (add_iov(c, c->wcurr, c->wbytes) != 0 ||
                    (c->udp && build_udp_headers(c) != 0)) {
                    if (settings.verbose > 0)
                        fprintf(stderr, "Couldn't build response\n");
                    conn_set_state(c, conn_closing);
                    break;
                }
            }

            /* fall through... */

        case conn_mwrite:
            switch (transmit(c)) {
            case TRANSMIT_COMPLETE:
                if (c->state == conn_mwrite) {
                    while (c->ileft > 0) {
                        item *it = *(c->icurr);
                        assert((it->it_flags & ITEM_SLABBED) == 0);
                        item_remove(it);
                        c->icurr++;
                        c->ileft--;
                    }
                    conn_set_state(c, conn_read);
                } else if (c->state == conn_write) {
                    if (c->write_and_free) {
                        free(c->write_and_free);
                        c->write_and_free = 0;
                    }
                    conn_set_state(c, c->write_and_go);
                } else {
                    if (settings.verbose > 0)
                        fprintf(stderr, "Unexpected state %d\n", c->state);
                    conn_set_state(c, conn_closing);
                }
                break;

            case TRANSMIT_INCOMPLETE:
            case TRANSMIT_HARD_ERROR:
                break;                   /* Continue in state machine. */

            case TRANSMIT_SOFT_ERROR:
                stop = true;
                break;
            }
            break;

        case conn_closing:
            if (c->udp)
                conn_cleanup(c);
            else
                conn_close(c);
            stop = true;
            break;
        }
    }

    return;
}

void event_handler(const int fd, const short which, void *arg) {
    conn *c;

    c = (conn *)arg;
    assert(c != NULL);

    c->which = which;

    /* sanity */
    if (fd != c->sfd) {
        if (settings.verbose > 0)
            fprintf(stderr, "Catastrophic: event fd doesn't match conn fd!\n");
        conn_close(c);
        return;
    }

    drive_machine(c);

    /* wait for next event */
    return;
}

static int new_socket(const bool is_udp) {
    int sfd;
    int flags;

    if ((sfd = socket(AF_INET, is_udp ? SOCK_DGRAM : SOCK_STREAM, 0)) == -1) {
        perror("socket()");
        return -1;
    }

    if ((flags = fcntl(sfd, F_GETFL, 0)) < 0 ||
        fcntl(sfd, F_SETFL, flags | O_NONBLOCK) < 0) {
        perror("setting O_NONBLOCK");
        close(sfd);
        return -1;
    }
    return sfd;
}


/*
 * Sets a socket's send buffer size to the maximum allowed by the system.
 */
static void maximize_sndbuf(const int sfd) {
    socklen_t intsize = sizeof(int);
    int last_good = 0;
    int min, max, avg;
    int old_size;

    /* Start with the default size. */
    if (getsockopt(sfd, SOL_SOCKET, SO_SNDBUF, &old_size, &intsize) != 0) {
        if (settings.verbose > 0)
            perror("getsockopt(SO_SNDBUF)");
        return;
    }

    /* Binary-search for the real maximum. */
    min = old_size;
    max = MAX_SENDBUF_SIZE;

    while (min <= max) {
        avg = ((unsigned int)(min + max)) / 2;
        if (setsockopt(sfd, SOL_SOCKET, SO_SNDBUF, (void *)&avg, intsize) == 0) {
            last_good = avg;
            min = avg + 1;
        } else {
            max = avg - 1;
        }
    }

    if (settings.verbose > 1)
        fprintf(stderr, "<%d send buffer was %d, now %d\n", sfd, old_size, last_good);
}


static int server_socket(const int port, const bool is_udp) {
    int sfd;
    struct linger ling = {0, 0};
    struct sockaddr_in addr;
    int flags =1;

    if ((sfd = new_socket(is_udp)) == -1) {
        return -1;
    }

    setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, (void *)&flags, sizeof(flags));
    if (is_udp) {
        maximize_sndbuf(sfd);
    } else {
        setsockopt(sfd, SOL_SOCKET, SO_KEEPALIVE, (void *)&flags, sizeof(flags));
        setsockopt(sfd, SOL_SOCKET, SO_LINGER, (void *)&ling, sizeof(ling));
        setsockopt(sfd, IPPROTO_TCP, TCP_NODELAY, (void *)&flags, sizeof(flags));
    }

    /*
     * the memset call clears nonstandard fields in some impementations
     * that otherwise mess things up.
     */
    memset(&addr, 0, sizeof(addr));

    addr.sin_family = AF_INET;
    addr.sin_port = htons(port);
    addr.sin_addr = settings.interf;
    if (bind(sfd, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
        perror("bind()");
        close(sfd);
        return -1;
    }
    if (!is_udp && listen(sfd, 1024) == -1) {
        perror("listen()");
        close(sfd);
        return -1;
    }
    return sfd;
}

static int new_socket_unix(void) {
    int sfd;
    int flags;

    if ((sfd = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
        perror("socket()");
        return -1;
    }

    if ((flags = fcntl(sfd, F_GETFL, 0)) < 0 ||
        fcntl(sfd, F_SETFL, flags | O_NONBLOCK) < 0) {
        perror("setting O_NONBLOCK");
        close(sfd);
        return -1;
    }
    return sfd;
}

static int server_socket_unix(const char *path) {
    int sfd;
    struct linger ling = {0, 0};
    struct sockaddr_un addr;
    struct stat tstat;
    int flags =1;

    if (!path) {
        return -1;
    }

    if ((sfd = new_socket_unix()) == -1) {
        return -1;
    }

    /*
     * Clean up a previous socket file if we left it around
     */
    if (lstat(path, &tstat) == 0) {
        if (S_ISSOCK(tstat.st_mode))
            unlink(path);
    }

    setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, (void *)&flags, sizeof(flags));
    setsockopt(sfd, SOL_SOCKET, SO_KEEPALIVE, (void *)&flags, sizeof(flags));
    setsockopt(sfd, SOL_SOCKET, SO_LINGER, (void *)&ling, sizeof(ling));

    /*
     * the memset call clears nonstandard fields in some impementations
     * that otherwise mess things up.
     */
    memset(&addr, 0, sizeof(addr));

    addr.sun_family = AF_UNIX;
    strcpy(addr.sun_path, path);
    if (bind(sfd, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
        perror("bind()");
        close(sfd);
        return -1;
    }
    if (listen(sfd, 1024) == -1) {
        perror("listen()");
        close(sfd);
        return -1;
    }
    return sfd;
}

/* listening socket */
static int l_socket = 0;

/* udp socket */
static int u_socket = -1;

/* invoke right before gdb is called, on assert */
void pre_gdb(void) {
    int i;
    if (l_socket > -1) close(l_socket);
    if (u_socket > -1) close(u_socket);
    for (i = 3; i <= 500; i++) close(i); /* so lame */
    kill(getpid(), SIGABRT);
}

/*
 * We keep the current time of day in a global variable that's updated by a
 * timer event. This saves us a bunch of time() system calls (we really only
 * need to get the time once a second, whereas there can be tens of thousands
 * of requests a second) and allows us to use server-start-relative timestamps
 * rather than absolute UNIX timestamps, a space savings on systems where
 * sizeof(time_t) > sizeof(unsigned int).
 */
volatile rel_time_t current_time;
static struct event clockevent;

/* time-sensitive callers can call it by hand with this, outside the normal ever-1-second timer */
static void set_current_time(void) {
    current_time = (rel_time_t) (time(0) - stats.started);
}

static void clock_handler(const int fd, const short which, void *arg) {
    struct timeval t = {.tv_sec = 1, .tv