Memcached源码分析之memcached.h

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