Selector#wakeup()

看thrift源码发现selector.wakeup()方法，通常在selector.select()后线程会阻塞。使用wakeup()方法，线程会立即返回。源码分析应该是用的线程中断实现的。下面是个小demo

public class TestSelector {
    private static Selector selector;

    public static void main(String[] args) throws IOException, InterruptedException {
        startSelectorThread();
        Thread.sleep(2000);
        selector.wakeup();
    }

    private static void startSelectorThread(){
        Runnable selectorTask = () -> {
            try{
                String host = "127.0.0.1";
                int port = 8888;
                ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
                serverSocketChannel.configureBlocking(false);
                SocketAddress socketAddress = new InetSocketAddress(host, port);
                serverSocketChannel.bind(socketAddress);
                selector = Selector.open();
                while(true){
                    serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
                    System.out.println("selector start select .....");
                    Set<SelectionKey> selectionKeySet =  selector.selectedKeys();
                    for(Iterator<SelectionKey> iterator = selectionKeySet.iterator(); iterator.hasNext(); ){
                        SelectionKey selectionKey = iterator.next();
                        System.out.println(selectionKey.toString());
                        selectionKeySet.remove(selectionKey);
                        ServerSocketChannel serverSocketChannel1 = (ServerSocketChannel) selectionKey.channel();
                        SocketChannel clientChannel = serverSocketChannel1.accept();
                        clientChannel.configureBlocking(false);
                        clientChannel.register(selector, SelectionKey.OP_READ | SelectionKey.OP_WRITE);
                        iterator.remove();
                    }

                    System.out.println("selector end select ....");
                }
            }catch (Exception e){
                e.printStackTrace();
            }
        }; //task
        Thread thread = new Thread(selectorTask);
        thread.start();
    }
}

我们看下wakeup()注释

/**
     * Causes the first selection operation that has not yet returned to return
     * immediately.
     *
     * <p> If another thread is currently blocked in an invocation of the
     * {@link #select()} or {@link #select(long)} methods then that invocation
     * will return immediately.  If no selection operation is currently in
     * progress then the next invocation of one of these methods will return
     * immediately unless the {@link #selectNow()} method is invoked in the
     * meantime.  In any case the value returned by that invocation may be
     * non-zero.  Subsequent invocations of the {@link #select()} or {@link
     * #select(long)} methods will block as usual unless this method is invoked
     * again in the meantime.
     *
     * <p> Invoking this method more than once between two successive selection
     * operations has the same effect as invoking it just once.  </p>
     *
     * @return  This selector
     */
    public abstract Selector wakeup();

可以看出，这个方法会让阻塞的线程立即返回。跟进poll实现的selector的wakeup()方法

public Selector wakeup() {
        Object var1 = this.interruptLock;
        synchronized(this.interruptLock) {
            if (!this.interruptTriggered) {
                this.pollWrapper.interrupt();
                this.interruptTriggered = true;
            }

            return this;
        }
    }

上面可以看出使用的是interrupt()给线程发个中断信号实现的