网络服务器通常都使用epoll进行异步IO处理，而开发者通常使用mac，为了方便开发，我把自己的handy库移植到了mac平台上。移植过程中，网上居然没有搜到kqueue的使用例子，让我惊讶不已。为了让大家不用像我一样再次花费大力气搞定kqueue，我整理了一个简单清晰可运行的kqueue例子，供大家参考。 
kqueue一共有几个函数：

 //类似epoll_create

 int kqueue(void);

 //兼具epoll_ctl及epoll_wait功能

 int kevent(int kq, const struct kevent *changelist, int nchanges, struct kevent *eventlist, int nevents, const struct timespec *timeout);

 //设定kevent参数的宏

 EV_SET(&kev, ident, filter, flags, fflags, data, udata);

 struct kevent {

 uintptr_t ident; /* identifier for this event */

 int16_t filter; /* filter for event */

 uint16_t flags; /* general flags */

 uint32_t fflags; /* filter-specific flags */

 intptr_t data; /* filter-specific data */

 void *udata; /* opaque user data identifier */

 };

函数调用示例：

 //创建kqueue

 int epollfd = kqueue();

 //添加或者修改fd

 struct kevent ev[];

 int n = ;

 if (events & kReadEvent) {

     EV_SET(&ev[n++], fd, EVFILT_READ, EV_ADD|EV_ENABLE, , , (void*)(intptr_t)fd);

 } else if (modify){

     EV_SET(&ev[n++], fd, EVFILT_READ, EV_DELETE, , , (void*)(intptr_t)fd);

 }

 if (events & kWriteEvent) {

     EV_SET(&ev[n++], fd, EVFILT_WRITE, EV_ADD|EV_ENABLE, , , (void*)(intptr_t)fd);

 } else if (modify){

     EV_SET(&ev[n++], fd, EVFILT_WRITE, EV_DELETE, , , (void*)(intptr_t)fd);

 }

 printf("%s fd %d events read %d write %d\n",

        modify ? "mod" : "add", fd, events & kReadEvent, events & kWriteEvent);

 int r = kevent(efd, ev, n, NULL, , NULL);

 //获取ready的fd

 struct timespec timeout;

 timeout.tv_sec = waitms / ;

 timeout.tv_nsec = (waitms % ) *  * ;

 const int kMaxEvents = ;

 struct kevent activeEvs[kMaxEvents];

 int n = kevent(efd, NULL, , activeEvs, kMaxEvents, &timeout);

 //处理IO事件

 for (int i = ; i < n; i ++) {

     int fd = (int)(intptr_t)activeEvs[i].udata;

     int events = activeEvs[i].filter;

     if (events == EVFILT_READ) {

         handleRead(efd, fd);

     } else if (events == EVFILT_WRITE) {

         handleWrite(efd, fd);

     }

 }

注意kevent与epoll最大的不同在于READ/WRITE事件是分开注册并且分开返回的，而Epoll则是一个fd一次返回读和写事件，用标志位来判断。 
可以运行的代码如下：kqueue-example（handy对kqueue提供了封装版本）

 #include <sys/socket.h>

 #include <sys/event.h>

 #include <netinet/in.h>

 #include <arpa/inet.h>

 #include <fcntl.h>

 #include <unistd.h>

 #include <stdio.h>

 #include <errno.h>

 #include <string.h>

 #include <stdlib.h>

 #define exit_if(r, ...) if(r) {printf(__VA_ARGS__); printf("error no: %d error msg %s\n", errno, strerror(errno)); exit(1);}

 const int kReadEvent = ;

 const int kWriteEvent = ;

 void setNonBlock(int fd) {

     int flags = fcntl(fd, F_GETFL, );

     exit_if(flags<, "fcntl failed");

     int r = fcntl(fd, F_SETFL, flags | O_NONBLOCK);

     exit_if(r<, "fcntl failed");

 }

 void updateEvents(int efd, int fd, int events, bool modify) {

     struct kevent ev[];

     int n = ;

     if (events & kReadEvent) {

         EV_SET(&ev[n++], fd, EVFILT_READ, EV_ADD|EV_ENABLE, , , (void*)(intptr_t)fd);

     } else if (modify){

         EV_SET(&ev[n++], fd, EVFILT_READ, EV_DELETE, , , (void*)(intptr_t)fd);

     }

     if (events & kWriteEvent) {

         EV_SET(&ev[n++], fd, EVFILT_WRITE, EV_ADD|EV_ENABLE, , , (void*)(intptr_t)fd);

     } else if (modify){

         EV_SET(&ev[n++], fd, EVFILT_WRITE, EV_DELETE, , , (void*)(intptr_t)fd);

     }

     printf("%s fd %d events read %d write %d\n",

            modify ? "mod" : "add", fd, events & kReadEvent, events & kWriteEvent);

     int r = kevent(efd, ev, n, NULL, , NULL);

     exit_if(r, "kevent failed ");

 }

 void handleAccept(int efd, int fd) {

     struct sockaddr_in raddr;

     socklen_t rsz = sizeof(raddr);

     int cfd = accept(fd,(struct sockaddr *)&raddr,&rsz);

     exit_if(cfd<, "accept failed");

     sockaddr_in peer, local;

     socklen_t alen = sizeof(peer);

     int r = getpeername(cfd, (sockaddr*)&peer, &alen);

     exit_if(r<, "getpeername failed");

     printf("accept a connection from %s\n", inet_ntoa(raddr.sin_addr));

     setNonBlock(cfd);

     updateEvents(efd, cfd, kReadEvent|kWriteEvent, false);

 }

 void handleRead(int efd, int fd) {

     char buf[];

     int n = ;

     while ((n=::read(fd, buf, sizeof buf)) > ) {

         printf("read %d bytes\n", n);

         int r = ::write(fd, buf, n); //写出读取的数据

         //实际应用中，写出数据可能会返回EAGAIN，此时应当监听可写事件，当可写时再把数据写出

         exit_if(r<=, "write error");

     }

     if (n< && (errno == EAGAIN || errno == EWOULDBLOCK))

         return;

     exit_if(n<, "read error"); //实际应用中，n<0应当检查各类错误，如EINTR

     printf("fd %d closed\n", fd);

     close(fd);

 }

 void handleWrite(int efd, int fd) {

     //实际应用应当实现可写时写出数据，无数据可写才关闭可写事件

     updateEvents(efd, fd, kReadEvent, true);

 }

 void loop_once(int efd, int lfd, int waitms) {

     struct timespec timeout;

     timeout.tv_sec = waitms / ;

     timeout.tv_nsec = (waitms % ) *  * ;

     const int kMaxEvents = ;

     struct kevent activeEvs[kMaxEvents];

     int n = kevent(efd, NULL, , activeEvs, kMaxEvents, &timeout);

     printf("epoll_wait return %d\n", n);

     for (int i = ; i < n; i ++) {

         int fd = (int)(intptr_t)activeEvs[i].udata;

         int events = activeEvs[i].filter;

         if (events == EVFILT_READ) {

             if (fd == lfd) {

                 handleAccept(efd, fd);

             } else {

                 handleRead(efd, fd);

             }

         } else if (events == EVFILT_WRITE) {

             handleWrite(efd, fd);

         } else {

             exit_if(, "unknown event");

         }

     }

 }

 int main() {

     short port = ;

     int epollfd = kqueue();

     exit_if(epollfd < , "epoll_create failed");

     int listenfd = socket(AF_INET, SOCK_STREAM, );

     exit_if(listenfd < , "socket failed");

     struct sockaddr_in addr;

     memset(&addr, , sizeof addr);

     addr.sin_family = AF_INET;

     addr.sin_port = htons(port);

     addr.sin_addr.s_addr = INADDR_ANY;

     int r = ::bind(listenfd,(struct sockaddr *)&addr, sizeof(struct sockaddr));

     exit_if(r, "bind to 0.0.0.0:%d failed %d %s", port, errno, strerror(errno));

     r = listen(listenfd, );

     exit_if(r, "listen failed %d %s", errno, strerror(errno));

     printf("fd %d listening at %d\n", listenfd, port);

     setNonBlock(listenfd);

     updateEvents(epollfd, listenfd, kReadEvent, false);

     for (;;) { //实际应用应当注册信号处理函数，退出时清理资源

         loop_once(epollfd, listenfd, );

     }

     return ;

 }

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