数据结构

//变量kcf typedef struct { ngx_uint_t max_cached; //keepalive参数，有多少ngx_http_upstream_keepalive_cache_t ngx_uint_t requests; //每个连接处理多少请求 ngx_msec_t timeout; //空闲超时 ngx_queue_t cache; //ngx_http_upstream_keepalive_cache_t链表,有connection ngx_queue_t free; //ngx_http_upstream_keepalive_cache_t链表,空闲的 ngx_http_upstream_init_pt original_init_upstream; ngx_http_upstream_init_peer_pt original_init_peer; } ngx_http_upstream_keepalive_srv_conf_t; //变量kp，connection cache，串在free/cache上 typedef struct { ngx_http_upstream_keepalive_srv_conf_t *conf; ngx_queue_t queue; //串在cache/free上 ngx_connection_t *connection; socklen_t socklen; ngx_sockaddr_t sockaddr; } ngx_http_upstream_keepalive_cache_t; //request选择server的方法，串在负载均衡算法之前 typedef struct { ngx_http_upstream_keepalive_srv_conf_t *conf; ngx_http_upstream_t *upstream; void *data; ngx_event_get_peer_pt original_get_peer; ngx_event_free_peer_pt original_free_peer; #if (NGX_HTTP_SSL) ngx_event_set_peer_session_pt original_set_session; ngx_event_save_peer_session_pt original_save_session; #endif } ngx_http_upstream_keepalive_peer_data_t;

算法

关键的两个函数

ngx_http_upstream_get_keepalive_peer()

遍历ngx_http_upstream_keepalive_srv_conf_t.cache链表，通过比较地址，选出对应的connection

 

ngx_http_upstream_free_keepalive_peer()

把connection归还到ngx_http_upstream_keepalive_srv_conf_t.free中

关闭

ngx_http_upstream_free_keepalive_peer（） { ... //设置超时 ngx_add_timer(c->read, kp->conf->timeout); if (c->write->timer_set) { ngx_del_timer(c->write); } //空操作 c->write->handler = ngx_http_upstream_keepalive_dummy_handler; //如果有错误、数据，就关闭连接 c->read->handler = ngx_http_upstream_keepalive_close_handler; ... }

总结

nginx的把所有空闲连接，放在一个链表中，需要时，从链表中遍历查找，这是O(n)算法，当后端连接数比较多时、空闲连接数很多时，需要优化为O(1)算法。