Memcached源码分析之memcached.h

1.  //memcached.h
2.  
3. //返回在item中data字段key的地址，即把指针指向key
4. #define ITEM_key(item) (((char*)&((item)->data))
5.          + (((item)->it_flags & ITEM_CAS) ? sizeof(uint64_t) : 0))
6. //返回在item中data字段suffix的地址，即把指针指向suffix
7. #define ITEM_suffix(item) ((char*) &((item)->data) + (item)->nkey + 1
8.          + (((item)->it_flags & ITEM_CAS) ? sizeof(uint64_t) : 0))
9.  //返回在item中data字段value的地址，即把指针指向value
10. #define ITEM_data(item) ((char*) &((item)->data) + (item)->nkey + 1
11.          + (item)->nsuffix
12.          + (((item)->it_flags & ITEM_CAS) ? sizeof(uint64_t) : 0))
13. //item总字节数
14. #define ITEM_ntotal(item) (sizeof(struct _stritem) + (item)->nkey + 1
15.          + (item)->nsuffix + (item)->nbytes
16.          + (((item)->it_flags & ITEM_CAS) ? sizeof(uint64_t) : 0))
17. //conn结构体中state字段的枚举，代表连接状态
18. enum conn_states {
19.     conn_listening, /**< the socket which listens for connections */
20.     conn_new_cmd, /**< Prepare connection for next command */
21.     conn_waiting, /**< waiting for a readable socket */
22.     conn_read, /**< reading in a command line */
23.     conn_parse_cmd, /**< try to parse a command from the input buffer */
24.     conn_write, /**< writing out a simple response */
25.     conn_nread, /**< reading in a fixed number of bytes */
26.     conn_swallow, /**< swallowing unnecessary bytes w/o storing */
27.     conn_closing, /**< closing this connection */
28.     conn_mwrite, /**< writing out many items sequentially */
29.     conn_closed, /**< connection is closed */
30.     conn_max_state /**< Max state value (used for assertion) */
31. };
32. //item保存结果枚举
33. enum store_item_type {
34.     NOT_STORED=0, STORED, EXISTS, NOT_FOUND
35. };
36. //item结构体
37. typedef struct _stritem {
38.     struct _stritem *next; //链表中下一个，这个链表有可能是slots链表，也有可能是LRU链表，但一个item不可能同时这两个链表中，所以复用一个指针。
39.     struct _stritem *prev; //链表中上一个。
40.     struct _stritem *h_next;  //相同hash值中链表的下一个。
41.     rel_time_t time;   //最近访问时间
42.     rel_time_t exptime;  //过期时间
43.     int nbytes;  //value的字节数
44.     unsigned short refcount; //引用计数
45.     uint8_t nsuffix;  //后缀长度
46.     uint8_t it_flags;  //标记
47.     uint8_t slabs_clsid;  //item所在的slabclass的id值
48.     uint8_t nkey; //键长
49.     /* this odd type prevents type-punning issues when we do
50.      * the little shuffle to save space when not using CAS. */
51.     union {
52.         uint64_t cas;
53.         char end;
54.     } data[]; //数据，这个数据不仅仅包括key对应的value，还有key、CAS、后缀等等数据也存在此，所以它有4部分“拼”成：CAS(可选)，KEY，后缀，VALUE。
55.     /* if it_flags & ITEM_CAS we have 8 bytes CAS */
56.     /* then null-terminated key */
57.     /* then " flags length " (no terminating null) */
58.     /* then data with terminating (no terminating null; it's binary!) */
59. } item;
60. /**
61. worker线程结构体
62. */
63. typedef struct {
64.     pthread_t thread_id; //线程id
65.     struct event_base *base; //每个线程自己独立的event_base，监听的就是下面的notify_event事件对象
66.     struct event notify_event; //事件对象，fd即为下面的notify_receive_fd
67.     int notify_receive_fd; //管道接收fd
68.     int notify_send_fd; //管道写入fd
69.     struct thread_stats stats; //线程的一些统计
70.     struct conn_queue *new_conn_queue; //连接参数对象CQ_ITEM队列
71.     cache_t *suffix_cache;
72.     uint8_t item_lock_type; //控制线程锁的粒度
73. } LIBEVENT_THREAD;
74. /**
75. 主线程结构体
76. */
77. typedef struct {
78.     pthread_t thread_id; //线程id
79.     struct event_base *base; //event_base
80. } LIBEVENT_DISPATCHER_THREAD;
81. typedef struct conn conn;
82. struct conn {
83.     int sfd; //连接的socket fd
84.     sasl_conn_t *sasl_conn;
85.     bool authenticated;
86.     enum conn_states state; //当前的连接状态
87.     enum bin_substates substate;
88.     rel_time_t last_cmd_time;
89.     struct event event; // 监听的事件
90.     short ev_flags; //监听的事件 类型
91.     short which; /** which events were just triggered */ //刚触发的事件
92.     /**
93.         读buffer会涉及两个方向上的“读”：
94.         一个是从socket读进来到rbuf里面
95.         一个是从rbuf里面把数据读出去解析，读buffer相当于一个中介，从socket读进来最终还是得被别人读出去解析，而
96.         rcurr工作指针与rbytes就是在rbuf数据被读出去解析的时候用到，用来控制可以读出去被解析的数据还剩余多少。
97.     */
98.     char *rbuf; /** buffer to read commands into */ //读buffer
99.     char *rcurr; /** but if we parsed some already, this is where we stopped */ //读buffer的当前指针
100.     int rsize; /** total allocated size of rbuf */ //读buffer大小
101.     int rbytes; /** how much data, starting from rcur, do we have unparsed */ //剩余buffer字节数
102.     //下面4个属性和上面4个类似
103.     char *wbuf;
104.     char *wcurr;
105.     int wsize;
106.     int wbytes;
107.     /** which state to go into after finishing current write */
108.     enum conn_states write_and_go; //完成当前写操作后，连接状态将会置为此状态
109.     void *write_and_free; /** free this memory after finishing writing */
110.     char *ritem; /** when we read in an item's value, it goes here */ //这个指针指向item结构体中data中的value地址
111.     int rlbytes; //尚未读完item的data的value的字节数
112.     void *item; /* for commands set/add/replace */ //当执行set/add/replace 命令时，此指针用于指向分配的item空间
113.     /* data for the swallow state */
114.     int sbytes; /* how many bytes to swallow */
115.     //下面是往socket写出数据时用的字段
116.     struct iovec *iov; //iovec结构体数组
117.     int iovsize; //*iov数组大小
118.     int iovused; //*iov数组已被使用的元素个数
119.     struct msghdr *msglist; //msghdr结构体数组，表示sendmsg要发送的消息列表
120.     int msgsize; //*msglist数组大小
121.     int msgused; //*msglist数组已使用的元素个数
122.     int msgcurr; //当前要发送的msghdr
123.     int msgbytes; //当前msghdr的字节数
124.     item **ilist; //get key1 key2命令时，要发送给客户端的item列表
125.     int isize; //列表大小
126.     item **icurr; //当前要发送的item
127.     int ileft; //剩余数目
128.     char **suffixlist;
129.     int suffixsize;
130.     char **suffixcurr;
131.     int suffixleft;
132.     enum protocol protocol; /* which protocol this connection speaks */
133.     enum network_transport transport; /* what transport is used by this connection */
134.     //UDP相关的字段
135.     int request_id; /* Incoming UDP request ID, if this is a UDP "connection" */
136.     struct sockaddr_in6 request_addr; /* udp: Who sent the most recent request */
137.     socklen_t request_addr_size;
138.     unsigned char *hdrbuf; /* udp packet headers */
139.     int hdrsize; /* number of headers' worth of space is allocated */
140.     bool noreply; /* True if the reply should not be sent. */
141.     /* current stats command */
142.     struct {
143.         char *buffer;
144.         size_t size;
145.         size_t offset;
146.     } stats;
147.     // 二进制相关的字段
148.     protocol_binary_request_header binary_header;
149.     uint64_t cas; /* the cas to return */
150.     short cmd; /* current command being processed */
151.     int opaque;
152.     int keylen;
153.     conn *next; /* Used for generating a list of conn structures */
154.     LIBEVENT_THREAD *thread; /* Pointer to the thread object serving this connection */
155. };
156. //非阻塞方式获取互斥锁
157. static inline int mutex_lock(pthread_mutex_t *mutex)
158. {
159.     while (pthread_mutex_trylock(mutex));
160.     return 0;
161. }
162. //释放锁
163. #define mutex_unlock(x) pthread_mutex_unlock(x)
164. #include "stats.h"
165. #include "slabs.h"
166. #include "assoc.h"
167. #include "items.h"
168. #include "trace.h"
169. #include "hash.h"
170. #include "util.h"