Poll Back

• poll()与select()實現的功能相似, 能監聽多個文件描述符. poll()能監聽特定的某個文件描述符其返回事件
• poll()比select()更具有細緻的分類
• poll()效率要比select()高

method

/* select */
unsigned int poll(struct pollfd* __fds, nfds_t __nfds, int __timeout)

/* pollfd */
struct pollfd
{
    int fd;
    short int events;    //expected events     
    short int revents;    //return events
}

parameters

• pollfd: 設置監聽的文件描述符和期待的事件
• nfds: 文件描述符的個數
• timeout: 指定測試時間閾值上界
  • NULL: forever
  • >0: time
  • 0: return immediately after check, without waiting

return value

• num: the number of ready descriptors
• 0: timeout but none is ready
• -1: failure
• errno: wrong code