twemproxy源码分析之五：zero copy

先给出msg的数据结构：

 

truct msg {

    TAILQ_ENTRY(msg)     c_tqe;          

    TAILQ_ENTRY(msg)     s_tqe;          

    TAILQ_ENTRY(msg)     m_tqe;          

 

    uint64_t             id;              

    int                  route_idx;      

    struct msg           *peer;          

    struct conn          *owner;          

 

    struct rbnode        tmo_rbe;        

 

    struct mhdr          mhdr;            

    uint32_t             mlen;            

 

    int                  state;          

    uint8_t              *pos;            

    uint8_t              *token;          

 

    msg_parse_t          parser;          

    msg_parse_result_t   result;          

 

    mbuf_copy_t          pre_splitcopy;  

    msg_post_splitcopy_t post_splitcopy;  

    msg_coalesce_t       pre_coalesce;    

    msg_coalesce_t       post_coalesce;  

 

    msg_type_t           type;            

 

    uint8_t              *key_start;      

    uint8_t              *key_end;        

 

    uint32_t             vlen;            

    uint8_t              *end;            

 

    uint8_t              *narg_start;    

    uint8_t              *narg_end;      

    uint32_t             narg;            

    uint32_t             rnarg;          

    uint32_t             rlen;            

    uint32_t             integer;        

 

    struct msg           *frag_owner;    

    uint32_t             nfrag;          

    uint64_t             frag_id;        

 

    err_t                err;            

    unsigned             error:1;        

    unsigned             ferror:1;        

    unsigned             request:1;      

    unsigned             quit:1;          

    unsigned             noreply:1;      

    unsigned             done:1;          

    unsigned             fdone:1;        

    unsigned             first_fragment:1;

    unsigned             last_fragment:1;

    unsigned             swallow:1;      

    unsigned             redis:1;        

 

 

看这三个成员   

    TAILQ_ENTRY(msg)     c_tqe;          

    TAILQ_ENTRY(msg)     s_tqe;          

    TAILQ_ENTRY(msg)     m_tqe;          

c_tqe是用来插入到client类型的conn中的输入或者输出队列中

s_tqe是用来插入到server类型的conn（即连接后端redis server的conn）中的输入或者输出队列中

m_tqe是用来插入到发送对列（一个发送队列对应一个远端或是client或是redisinstance）中的输入或者输出队列中

具体的插入删除过程见上一篇。