利用多线程优化

现在都是多核 cpu，设计时要充分考虑别让 cpu 的力量被白白浪费

前面的代码只有一个选择器，没有充分利用多核 cpu，如何改进呢？

分两组选择器

• 单线程配一个选择器，专门处理 accept 事件
• 创建 cpu 核心数的线程，每个线程配一个选择器，轮流处理 read 事件

public class ChannelDemo7 { public static void main(String[] args) throws IOException { new BossEventLoop().register(); }

@Slf4j
static class BossEventLoop implements Runnable {
    private Selector boss;
    private WorkerEventLoop[] workers;
    private volatile boolean start = false;
    AtomicInteger index = new AtomicInteger();

    public void register() throws IOException {
        if (!start) {
            ServerSocketChannel ssc = ServerSocketChannel.open();
            ssc.bind(new InetSocketAddress(8080));
            ssc.configureBlocking(false);
            boss = Selector.open();
            SelectionKey ssckey = ssc.register(boss, 0, null);
            ssckey.interestOps(SelectionKey.OP_ACCEPT);
            workers = initEventLoops();
            new Thread(this, "boss").start();
            log.debug("boss start...");
            start = true;
        }
    }

    public WorkerEventLoop[] initEventLoops() {

// EventLoop[] eventLoops = new EventLoop[Runtime.getRuntime().availableProcessors()]; WorkerEventLoop[] workerEventLoops = new WorkerEventLoop[2]; for (int i = 0; i < workerEventLoops.length; i++) { workerEventLoops[i] = new WorkerEventLoop(i); } return workerEventLoops; }

    @Override
    public void run() {
        while (true) {
            try {
                boss.select();
                Iterator<SelectionKey> iter = boss.selectedKeys().iterator();
                while (iter.hasNext()) {
                    SelectionKey key = iter.next();
                    iter.remove();
                    if (key.isAcceptable()) {
                        ServerSocketChannel c = (ServerSocketChannel) key.channel();
                        SocketChannel sc = c.accept();
                        sc.configureBlocking(false);
                        log.debug("{} connected", sc.getRemoteAddress());
                        workers[index.getAndIncrement() % workers.length].register(sc);
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

@Slf4j
static class WorkerEventLoop implements Runnable {
    private Selector worker;
    private volatile boolean start = false;
    private int index;

    private final ConcurrentLinkedQueue<Runnable> tasks = new ConcurrentLinkedQueue<>();

    public WorkerEventLoop(int index) {
        this.index = index;
    }

    public void register(SocketChannel sc) throws IOException {
        if (!start) {
            worker = Selector.open();
            new Thread(this, "worker-" + index).start();
            start = true;
        }
        tasks.add(() -> {
            try {
                SelectionKey sckey = sc.register(worker, 0, null);
                sckey.interestOps(SelectionKey.OP_READ);
                worker.selectNow();
            } catch (IOException e) {
                e.printStackTrace();
            }
        });
        worker.wakeup();
    }

    @Override
    public void run() {
        while (true) {
            try {
                worker.select();
                Runnable task = tasks.poll();
                if (task != null) {
                    task.run();
                }
                Set<SelectionKey> keys = worker.selectedKeys();
                Iterator<SelectionKey> iter = keys.iterator();
                while (iter.hasNext()) {
                    SelectionKey key = iter.next();
                    if (key.isReadable()) {
                        SocketChannel sc = (SocketChannel) key.channel();
                        ByteBuffer buffer = ByteBuffer.allocate(128);
                        try {
                            int read = sc.read(buffer);
                            if (read == -1) {
                                key.cancel();
                                sc.close();
                            } else {
                                buffer.flip();
                                log.debug("{} message:", sc.getRemoteAddress());
                                debugAll(buffer);
                            }
                        } catch (IOException e) {
                            e.printStackTrace();
                            key.cancel();
                            sc.close();
                        }
                    }
                    iter.remove();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

}

💡 如何拿到 cpu 个数

• Runtime.getRuntime().availableProcessors() 如果工作在 docker 容器下，因为容器不是物理隔离的，会拿到物理 cpu 个数，而不是容器申请时的个数
• 这个问题直到 jdk 10 才修复，使用 jvm 参数 UseContainerSupport 配置， 默认开启