int epoll_create(int size);// 建立epoll 例項
int epoll_ctl(int epfd,int op,int fd,struct epoll_event* event) // 

op為列舉型別，可選擇的引數有

EPOLL_CTL_ADD // register the target descriptor fd on epoll instance
EPOLL_CTL_MOD // change the event associated with the target file descriptor fd
EPOLL_CTL_DEL // remove the target file descriptor fd from epoll instance

epoll_event 結構體成員

typedef union epoll_data {
    void *ptr;
    int fd;
    uint32_t u32;
    uint64_t u64;      
} epoll_data_t;

struct epoll_event {
    uint32_t events;
    epoll_data_t data;
};

常用的event types:

EPOLLIN // the associated file is available for read operations;
EPOLLOUT // the associated file is available for write operations;
EPOLLERR // error condition happened on the associated file desciptor
EPOLLET // sets the edge triggered behavior for the associated file descriptor

epoll_wait 函式

int epoll_wait(int epfd,struct epoll_event *events,int maxevents,int timeout);

檢測新增到epoll樹上的節點是不是處於就緒狀態，如果沒有就緒的檔案描述符會阻塞

如果有節點處於就緒狀態，通過引數events 把對應的fd傳出。