nonblocking socketchannel是否准备好?

[gadmyth]

下面是客户端的代码, 用的nonblocking模式, 将一个能读能写的socketChannel注册到一个selector上, 且将这个channel绑定到一个ByteBuffer上. 现在出现的问题是, 当这个channel与服务器端连接好后, selector会select到这个channel已经准备好, 于是让channel把数据写给服务器端; 但后面循环中, selector还是select到这个channel是准备好的状态, 但是我已经把数据都写给服务器端了, 凭什么selector又判断channel的状态是准备好写的呢, 不解! 另外, 这个channel是能读能写的, 为什么seletor没有判断出channel是能读的呢?(在if(key.isReadable()){...}里的打印语句没有出来)

不知道selector的select的原理到底是什么, java i/o这本书上也只是说它可以判断出channel是否准备好, 但具体的细节又是什么呢? 谢谢

public class SocketChannelClient {
	public static void main(String... args) {
		try {
			final Selector selector = Selector.open();
			SocketAddress address = new InetSocketAddress("127.0.0.1", 8888);
			final SocketChannel channelI = SocketChannel.open(address);
			channelI.configureBlocking(false);
			ByteBuffer buff = ByteBuffer.wrap("123456".getBytes());
			channelI.register(selector, SelectionKey.OP_READ | SelectionKey.OP_WRITE, buff);

			/*
			new Thread() {
				public void run(){
					try{Thread.sleep(5000);}catch(Exception e){e.printStackTrace();}
					System.out.println("fuck");
					channelI.keyFor(selector).interestOps(SelectionKey.OP_WRITE | SelectionKey.OP_READ);
				}
			}.start();*/
			
			while(true) {
				selector.select();
				Set keys = selector.selectedKeys();
				System.out.println("keys size: " + keys.size());
				Iterator it = keys.iterator();
				while(it.hasNext()) {
					SelectionKey key = (SelectionKey)it.next();
					System.out.println("\tkeys size: " + keys.size());
					if(key.isWritable()){
						//System.out.println("writable " + Math.random());
						SocketChannel channel = (SocketChannel)key.channel();
						ByteBuffer buffer = (ByteBuffer)key.attachment();
						if(!buffer.hasRemaining()) {
							buffer.rewind();
							//buffer.position(0);
							/buffer.limit(0);
						}
						else {
							channel.write(buffer);
							//key.interestOps(SelectionKey.OP_READ);
							//buffer.clear();
							//key.cancel();
						}
					}
					if(key.isReadable()){
						System.out.println("readable");
						SocketChannel channel = (SocketChannel)key.channel();
						ByteBuffer buffer = ByteBuffer.allocate(6);
						channel.read(buffer);
						System.out.println(new String(buffer.array()));
					}
					it.remove();
				}
				//System.out.println("out of inner loop: " + Math.random());
			}
		}
		catch(Exception e){e.printStackTrace();}
	}
}

[gadmyth]

看来这帖要沉了

[KKluxKlan]

我测试了下关于非阻塞通信程序,发现selection.isReadable()只有在客户端发送数据过来才为true;而selectionKey.iswritable()在客户端与服务器联通后,一直是为true的. 这里可能就是表示连接的客户端socket通道支持写入,所以它一直为true.