IO多路复用

1.Selector

当执行IO读写操作时，通过先将数据放入缓冲区，然后由一个统一selelctor来监控缓冲区，等缓冲区就绪后会通知我们的程序

public static void main(String[] args) throws Exception{
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        ServerSocket serverSocket = serverSocketChannel.socket();
        serverSocketChannel.configureBlocking(false);
        serverSocket.bind(new InetSocketAddress("127.0.0.1", 8088));
        Selector selector = Selector.open();
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        while(true) {
            selector.select();
            Iterator iter = selector.selectedKeys().iterator();
            while(iter.hasNext()) {
                SelectionKey key = (SelectionKey) iter.next();
                if(key.isAcceptable()) {
                    ServerSocketChannel server =  (ServerSocketChannel) key.channel();
                    SocketChannel channel = server.accept();
                    channel.configureBlocking(false);
                    channel.register(selector, SelectionKey.OP_READ);
                    System.out.println("Connected: " + channel.socket().getRemoteSocketAddress());
                }
                if(key.isReadable()) {
                    ByteBuffer byteBuffer = ByteBuffer.allocate(512);
                    SocketChannel socketChannel = (SocketChannel) key.channel();
                    socketChannel.read(byteBuffer);
                    byteBuffer.flip();
                    System.out.println("server received message: " + getString(byteBuffer));
                    byteBuffer.clear();
                    String message = "server sending message " + System.currentTimeMillis();
                    System.out.println("server sending message: " + message);
                    byteBuffer.put(message.getBytes());
                    byteBuffer.flip();
                    socketChannel.write(byteBuffer);
                }
                iter.remove();
            }
        }
    }

2.epoll

epoll是linux下io一种处理方式，用户首先创建一个epoll的fd(文件描述符)，然后将要关注的io的fd注册进我们刚创建的epoll的fd中，然后执行epoll_wati

int main(void)

{

　　int epfd,nfds;

　　struct epoll_event ev,events[2]; //ev用于注册事件，数组用于返回要处理的事件

　　epfd = epoll_create(1); //只需要监听一个描述符——标准输入

　　ev.data.fd = STDIN_FILENO;

　　ev.events = EPOLLIN|EPOLLET; //监听读状态同时设置ET模式

　　epoll_ctl(epfd, EPOLL_CTL_ADD, STDIN_FILENO, &ev); //注册epoll事件

　　for(;;)

　　{

　　　　nfds = epoll_wait(epfd, events, 2, -1);

　　　　for(int i = 0; i < nfds; i++)

　　　　{

　　　　　　if(events[i].data.fd==STDIN_FILENO)

　　　　　　　　printf("ok ok ok!\n");

　　　　}

　　}

}

3.kqueue

用法上跟epoll类似

struct kevent changes[FD_NUM];
struct kevent events[FD_NUM];

EV_SET(&changes[0], STDIN_FILENO, EVFILT_READ, EV_ADD | EV_ENABLE, 0, 0, &STDIN_FILENO); 
EV_SET(&changes[1], STDIN_FILENO, EVFILT_WRITE, EV_ADD | EV_ENABLE, 0, 0, &STDIN_FILENO);

int nev = kevent(kq, changes, FD_NUM, events, FD_NUM, NULL); // 已经就绪的文件描述符数量
for(int i=0; i<nev; i++){
    struct kevent event = events[i];

    int ready_fd = *((int *)event.udata); 
    if(ready_fd == STDIN_FILENO){
        
    }

}