select.c

/*  $OpenBSD: select.c,v 1.2 2002/06/25 15:50:15 mickey Exp $   */

/*
 * Copyright 2000-2002 Niels Provos <provos@citi.umich.edu>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <sys/types.h>
#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#else
#include <sys/_libevent_time.h>
#endif
#ifdef HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif
#include <sys/queue.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#ifdef CHECK_INVARIANTS
#include <assert.h>
#endif

#include "event.h"
#include "evutil.h"
#include "event-internal.h"
#include "evsignal.h"
#include "log.h"

#ifndef howmany
#define        howmany(x, y)   (((x)+((y)-1))/(y))
#endif

#ifndef _EVENT_HAVE_FD_MASK
/* This type is mandatory, but Android doesn't define it. */
#undef NFDBITS
//32个bit位
#define NFDBITS (sizeof(long)*8)
typedef unsigned long fd_mask;
#endif

struct selectop {
    //select函数中最大的socket值
    int event_fds;      /* Highest fd in fd set */

    // 集合中的字节数，1个字节表示8位能存储8个socket，下面四个结合大小都一样
    int event_fdsz;
    // select输出集合
    fd_set* event_readset_in;
    fd_set* event_writeset_in;
    // select结果结合
    fd_set* event_readset_out;
    fd_set* event_writeset_out;
    //文件描述符作为索引,获取与该文件描述相关的event
    struct event** event_r_by_fd;
    struct event** event_w_by_fd;
};

static void* select_init    (struct event_base*);
static int select_add       (void*, struct event*);
static int select_del       (void*, struct event*);
static int select_dispatch  (struct event_base*, void*, struct timeval*);
static void select_dealloc     (struct event_base*, void*);

const struct eventop selectops = {
    "select",
    select_init,
    select_add,
    select_del,
    select_dispatch,
    select_dealloc,
    0
};

static int select_resize(struct selectop* sop, int fdsz);

static void*
select_init(struct event_base* base)
{
    struct selectop* sop;

    /* Disable select when this environment variable is set */
    if (evutil_getenv("EVENT_NOSELECT"))
        return (NULL);

    if (!(sop = calloc(1, sizeof(struct selectop))))
        return (NULL);

    select_resize(sop, howmany(32 + 1, NFDBITS)*sizeof(fd_mask));

    evsignal_init(base);

    return (sop);
}

#ifdef CHECK_INVARIANTS
static void
check_selectop(struct selectop* sop)
{
    int i;
    for (i = 0; i <= sop->event_fds; ++i) {
        if (FD_ISSET(i, sop->event_readset_in)) {
            assert(sop->event_r_by_fd[i]);
            assert(sop->event_r_by_fd[i]->ev_events & EV_READ);
            assert(sop->event_r_by_fd[i]->ev_fd == i);
        } else {
            assert(! sop->event_r_by_fd[i]);
        }
        if (FD_ISSET(i, sop->event_writeset_in)) {
            assert(sop->event_w_by_fd[i]);
            assert(sop->event_w_by_fd[i]->ev_events & EV_WRITE);
            assert(sop->event_w_by_fd[i]->ev_fd == i);
        } else {
            assert(! sop->event_w_by_fd[i]);
        }
    }

}
#else
#define check_selectop(sop) do { (void) sop; } while (0)
#endif

static int
select_dispatch(struct event_base* base, void* arg, struct timeval* tv)
{
    int res, i, j;
    struct selectop* sop = arg;

    check_selectop(sop);

    memcpy(sop->event_readset_out, sop->event_readset_in,
           sop->event_fdsz);
    memcpy(sop->event_writeset_out, sop->event_writeset_in,
           sop->event_fdsz);

    res = select(sop->event_fds + 1, sop->event_readset_out,
                 sop->event_writeset_out, NULL, tv);

    check_selectop(sop);

    if (res == -1) {
        if (errno != EINTR) {
            event_warn("select");
            return (-1);
        }

        evsignal_process(base);
        return (0);
    } else if (base->sig.evsignal_caught) {
        evsignal_process(base);
    }

    event_debug(("%s: select reports %d", __func__, res));

    check_selectop(sop);
    i = random() % (sop->event_fds + 1);
    for (j = 0; j <= sop->event_fds; ++j) {
        struct event* r_ev = NULL, *w_ev = NULL;
        if (++i >= sop->event_fds + 1)
            i = 0;

        res = 0;
        if (FD_ISSET(i, sop->event_readset_out)) {
            r_ev = sop->event_r_by_fd[i];
            res |= EV_READ;
        }
        if (FD_ISSET(i, sop->event_writeset_out)) {
            w_ev = sop->event_w_by_fd[i];
            res |= EV_WRITE;
        }
        if (r_ev && (res & r_ev->ev_events)) {
            event_active(r_ev, res & r_ev->ev_events, 1);
        }
        if (w_ev && w_ev != r_ev && (res & w_ev->ev_events)) {
            event_active(w_ev, res & w_ev->ev_events, 1);
        }
    }
    check_selectop(sop);

    return (0);
}


// 将集合调整到fdsz大小
static int
select_resize(struct selectop* sop, int fdsz)
{
    int n_events, n_events_old;

    fd_set* readset_in = NULL;
    fd_set* writeset_in = NULL;
    fd_set* readset_out = NULL;
    fd_set* writeset_out = NULL;
    struct event** r_by_fd = NULL;
    struct event** w_by_fd = NULL;
    // select中使用bit来表示socket是否加入到集合中，如果bits[socket] == 1说明socket
    // 在select集合当中，libevent没有使用默认的fd_set_t结构体，而是自己实现一个

    // 4字节即sizeof(fd_mask)可以存储NFDBITS个event
    n_events = (fdsz / sizeof(fd_mask)) * NFDBITS;
    n_events_old = (sop->event_fdsz / sizeof(fd_mask)) * NFDBITS;

    if (sop->event_readset_in)
        check_selectop(sop);

    if ((readset_in = realloc(sop->event_readset_in, fdsz)) == NULL)
        goto error;
    sop->event_readset_in = readset_in;
    if ((readset_out = realloc(sop->event_readset_out, fdsz)) == NULL)
        goto error;
    sop->event_readset_out = readset_out;
    if ((writeset_in = realloc(sop->event_writeset_in, fdsz)) == NULL)
        goto error;
    sop->event_writeset_in = writeset_in;
    if ((writeset_out = realloc(sop->event_writeset_out, fdsz)) == NULL)
        goto error;
    sop->event_writeset_out = writeset_out;
    if ((r_by_fd = realloc(sop->event_r_by_fd,
                           n_events * sizeof(struct event*))) == NULL)
        goto error;
    sop->event_r_by_fd = r_by_fd;
    if ((w_by_fd = realloc(sop->event_w_by_fd,
                           n_events * sizeof(struct event*))) == NULL)
        goto error;
    sop->event_w_by_fd = w_by_fd;

    memset((char*)sop->event_readset_in + sop->event_fdsz, 0,
           fdsz - sop->event_fdsz);
    memset((char*)sop->event_writeset_in + sop->event_fdsz, 0,
           fdsz - sop->event_fdsz);
    memset(sop->event_r_by_fd + n_events_old, 0,
           (n_events - n_events_old) * sizeof(struct event*));
    memset(sop->event_w_by_fd + n_events_old, 0,
           (n_events - n_events_old) * sizeof(struct event*));

    sop->event_fdsz = fdsz;
    check_selectop(sop);

    return (0);

error:
    event_warn("malloc");
    return (-1);
}

//arg 是select_init返回的void*
//ev read、write或者singal，也可以使他们中的任意组合比如ev同时监测某个socket的读/写
static int
select_add(void* arg, struct event* ev)
{
    struct selectop* sop = arg;

    if (ev->ev_events & EV_SIGNAL) //信号事件集成在每一个OS的IO模型模块中
        return (evsignal_add(ev)); //直接调用singnal.c模块

    check_selectop(sop);
    /*
     * Keep track of the highest fd, so that we can calculate the size
     * of the fd_sets for select(2)
     * selectop->event_fds是传给API select的所有文件符fds中的最大值
     */
    if (sop->event_fds < ev->ev_fd) {
        int fdsz = sop->event_fdsz;
        //一个fd_mask有32位，内保存32个文件描述符
        if (fdsz < sizeof(fd_mask))
            fdsz = sizeof(fd_mask);

        //howmany(x,y)将x向上取整y的倍数
        while (fdsz <
               (howmany(ev->ev_fd + 1, NFDBITS) * sizeof(fd_mask)))//加一个ev_fd进来会不会放不下
            fdsz *= 2;

        if (fdsz != sop->event_fdsz) {
            if (select_resize(sop, fdsz)) {//将selectop中的各个set的缓冲区扩充
                check_selectop(sop);
                return (-1);
            }
        }

        //添加进来的fds文件描述符大于当前保存的文件描述符
        //更新sop->event_fds
        sop->event_fds = ev->ev_fd;
    }

    //将不同ev的文件描述符添加到select的不同set中
    //读event添加到readset，写event添加到writeset
    //将文件描述符作为索引，保存到selectop->event_*_by_fd[ev->ev_fd]=ev中
    if (ev->ev_events & EV_READ) {
        FD_SET(ev->ev_fd, sop->event_readset_in);
        sop->event_r_by_fd[ev->ev_fd] = ev;
    }
    if (ev->ev_events & EV_WRITE) {
        FD_SET(ev->ev_fd, sop->event_writeset_in);
        sop->event_w_by_fd[ev->ev_fd] = ev;
    }
    check_selectop(sop);

    return (0);
}

/*
 * Nothing to be done here.
 */

static int
select_del(void* arg, struct event* ev)
{
    struct selectop* sop = arg;

    check_selectop(sop);
    if (ev->ev_events & EV_SIGNAL)
        return (evsignal_del(ev));

    if (sop->event_fds < ev->ev_fd) {
        check_selectop(sop);
        return (0);
    }

    if (ev->ev_events & EV_READ) {
        FD_CLR(ev->ev_fd, sop->event_readset_in);
        sop->event_r_by_fd[ev->ev_fd] = NULL;
    }

    if (ev->ev_events & EV_WRITE) {
        FD_CLR(ev->ev_fd, sop->event_writeset_in);
        sop->event_w_by_fd[ev->ev_fd] = NULL;
    }

    check_selectop(sop);
    return (0);
}

static void
select_dealloc(struct event_base* base, void* arg)
{
    struct selectop* sop = arg;

    evsignal_dealloc(base);
    if (sop->event_readset_in)
        free(sop->event_readset_in);
    if (sop->event_writeset_in)
        free(sop->event_writeset_in);
    if (sop->event_readset_out)
        free(sop->event_readset_out);
    if (sop->event_writeset_out)
        free(sop->event_writeset_out);
    if (sop->event_r_by_fd)
        free(sop->event_r_by_fd);
    if (sop->event_w_by_fd)
        free(sop->event_w_by_fd);

    memset(sop, 0, sizeof(struct selectop));
    free(sop);
}