static ngx_int_tngx_http_upstream_init_ip_hash(ngx_conf_t *cf, ngx_http_upstream_srv_conf_t *us){    //调用了加权轮询    if (ngx_http_upstream_init_round_robin(cf, us) != NGX_OK) {        return NGX_ERROR;    }    //修改了针对单个请求进行初始化的回调函数    us->peer.init = ngx_http_upstream_init_ip_hash_peer;    return NGX_OK;}

static ngx_int_tngx_http_upstream_init_ip_hash_peer(ngx_http_request_t *r,    ngx_http_upstream_srv_conf_t *us){    struct sockaddr_in                     *sin;    //针对IPv6的支持#if (NGX_HAVE_INET6)    struct sockaddr_in6                    *sin6;#endif    ngx_http_upstream_ip_hash_peer_data_t  *iphp;    iphp = ngx_palloc(r->pool, sizeof(ngx_http_upstream_ip_hash_peer_data_t));    if (iphp == NULL) {        return NGX_ERROR;    }    r->upstream->peer.data = http://www.mamicode.com/&iphp->rrp;    //调用了RR算法中的初始化函数    if (ngx_http_upstream_init_round_robin_peer(r, us) != NGX_OK) {        return NGX_ERROR;    }    //回调函数设置，具体做选择的回调函数    r->upstream->peer.get = ngx_http_upstream_get_ip_hash_peer;    switch (r->connection->sockaddr->sa_family) {    //保存客户端地址    case AF_INET:        sin = (struct sockaddr_in *) r->connection->sockaddr;        iphp->addr = (u_char *) &sin->sin_addr.s_addr;        //转储IPv4只用到了前3个字节，因为在后面的hash计算过程中只用到了3个字节        iphp->addrlen = 3;        break;#if (NGX_HAVE_INET6)    case AF_INET6:        sin6 = (struct sockaddr_in6 *) r->connection->sockaddr;        iphp->addr = (u_char *) &sin6->sin6_addr.s6_addr;        iphp->addrlen = 16;        break;#endif    default:        iphp->addr = ngx_http_upstream_ip_hash_pseudo_addr;        iphp->addrlen = 3;    }    //初始化hash种子    iphp->hash = 89;    //初始化尝试失败次数    iphp->tries = 0;    //做RR选择的函数    iphp->get_rr_peer = ngx_http_upstream_get_round_robin_peer;    return NGX_OK;}

typedef struct {    /* the round robin data must be first */    ngx_http_upstream_rr_peer_data_t   rrp;    //hash种子值    ngx_uint_t                         hash;    //IP地址    u_char                             addrlen;    u_char                            *addr;    //尝试连接的次数    u_char                             tries;    ngx_event_get_peer_pt              get_rr_peer;} ngx_http_upstream_ip_hash_peer_data_t;typedef struct {    //指向所有服务器的指针    ngx_http_upstream_rr_peers_t   *peers;    //当前服务器    ngx_uint_t                      current;    //指向位图的指针    uintptr_t                      *tried;    //位图的实际存储位置    uintptr_t                       data;} ngx_http_upstream_rr_peer_data_t;typedef struct ngx_http_upstream_rr_peers_s  ngx_http_upstream_rr_peers_t;struct ngx_http_upstream_rr_peers_s {    ngx_uint_t                      number;//所有服务器地址总数 /* ngx_mutex_t                    *mutex; */    ngx_uint_t                      total_weight;//所有服务总权重    unsigned                        single:1;//是否只有一个后端服务    unsigned                        weighted:1;//number ！= total_weight ?    ngx_str_t                      *name;    ngx_http_upstream_rr_peers_t   *next;    ngx_http_upstream_rr_peer_t     peer[1];};

static ngx_int_tngx_http_upstream_get_ip_hash_peer(ngx_peer_connection_t *pc, void *data){    ngx_http_upstream_ip_hash_peer_data_t  *iphp = data;    time_t                        now;    ngx_int_t                     w;    uintptr_t                     m;    ngx_uint_t                    i, n, p, hash;    ngx_http_upstream_rr_peer_t  *peer;    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, pc->log, 0,                   "get ip hash peer, try: %ui", pc->tries);    /* TODO: cached */    //如果失败次数太多，或者只有一个后端服务，那么直接做RR选择    if (iphp->tries > 20 || iphp->rrp.peers->single) {        return iphp->get_rr_peer(pc, &iphp->rrp);    }    now = ngx_time();    pc->cached = 0;    pc->connection = NULL;    hash = iphp->hash;    for ( ;; ) {        //计算IP的hash值        for (i = 0; i < iphp->addrlen; i++) {            //113质数，可以让哈希结果更散列            hash = (hash * 113 + iphp->addr[i]) % 6271;        }        //根据哈希结果得到被选中的后端服务器        if (!iphp->rrp.peers->weighted) {            p = hash % iphp->rrp.peers->number;        } else {            w = hash % iphp->rrp.peers->total_weight;            for (i = 0; i < iphp->rrp.peers->number; i++) {                w -= iphp->rrp.peers->peer[i].weight;                if (w < 0) {                    break;                }            }            p = i;        }        //服务器对应在位图中的位置计算        n = p / (8 * sizeof(uintptr_t));        m = (uintptr_t) 1 << p % (8 * sizeof(uintptr_t));        if (!(iphp->rrp.tried[n] & m)) {            ngx_log_debug2(NGX_LOG_DEBUG_HTTP, pc->log, 0,                           "get ip hash peer, hash: %ui %04XA", p, m);            //获取服务器            peer = &iphp->rrp.peers->peer[p];            /* ngx_lock_mutex(iphp->rrp.peers->mutex); */            //服务器未挂掉            if (!peer->down) {                //失败次数已达上限                if (peer->max_fails == 0 || peer->fails < peer->max_fails) {                    break;                }                if (now - peer->checked > peer->fail_timeout) {                    peer->checked = now;                    break;                }            }            //更改位图标记值            iphp->rrp.tried[n] |= m;            /* ngx_unlock_mutex(iphp->rrp.peers->mutex); */            //在连接一个远端服务器时，当前连接异常失败后可以尝试的次数            pc->tries--;        }        //已经尝试的次数超过阈值，采用RR轮询        if (++iphp->tries >= 20) {            return iphp->get_rr_peer(pc, &iphp->rrp);        }    }    //当前服务索引    iphp->rrp.current = p;    //服务器地址及名字保存    pc->sockaddr = peer->sockaddr;    pc->socklen = peer->socklen;    pc->name = &peer->name;    /* ngx_unlock_mutex(iphp->rrp.peers->mutex); */    //位图更新    iphp->rrp.tried[n] |= m;    //保留种子，使下次get_ip_hash_peer的时候能够选到同一个peer上    iphp->hash = hash;    return NGX_OK;}