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。