cat /proc/sys/net/ipv4/ip_local_port_range

// Netty對(duì)應(yīng)實(shí)現(xiàn)方式：創(chuàng)建io線程組是，boss和worker，使用同一個(gè)線程組，并且線程數(shù)為1
EventLoopGroup ioGroup = new NioEventLoopGroup(1);
b.group(ioGroup, ioGroup)
        .channel(NioServerSocketChannel.class)
        .childHandler(initializer);
ChannelFuture f = b.bind(portNumner);
cf = f.sync();
f.get();

// Netty對(duì)應(yīng)實(shí)現(xiàn)方式：創(chuàng)建io線程組是，boss和worker，使用同一個(gè)線程組，并且線程數(shù)為1，把邏輯運(yùn)算部分投遞到用戶自定義線程處理
EventLoopGroup ioGroup = new NioEventLoopGroup(1);
b.group(ioGroup, ioGroup)
        .channel(NioServerSocketChannel.class)
        .childHandler(initializer);
ChannelFuture f = b.bind(portNumner);
cf = f.sync();
f.get();

// Netty對(duì)應(yīng)實(shí)現(xiàn)方式：創(chuàng)建io線程組boss和worker，boss線程數(shù)為1，work線程數(shù)為cpu*2(一般IO密集可設(shè)置為2倍cpu核數(shù))
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
b.group(bossGroup, workerGroup)
        .channel(NioServerSocketChannel.class)
        .childHandler(initializer);
ChannelFuture f = b.bind(portNumner);
cf = f.sync();
f.get();

// 1.構(gòu)造參數(shù)不傳或傳0，默認(rèn)取系統(tǒng)參數(shù)配置，沒(méi)有參數(shù)配置，取CPU核數(shù)*2
super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, executor, args);
private static final int DEFAULT_EVENT_LOOP_THREADS;
static {
    DEFAULT_EVENT_LOOP_THREADS = Math.max(1, SystemPropertyUtil.getInt(
            "io.netty.eventLoopThreads", NettyRuntime.availableProcessors() * 2));
}
// 2.不同版本的JDK會(huì)有不同版本的SelectorProvider實(shí)現(xiàn)，Windows下的是WindowsSelectorProvider
public NioEventLoopGroup(int nThreads, Executor executor) {
    //默認(rèn)selector,最終實(shí)現(xiàn)類似：https://github.com/frohoff/jdk8u-jdk/blob/master/src/macosx/classes/sun/nio/ch/DefaultSelectorProvider.java
    //basic flow: 1 java.nio.channels.spi.SelectorProvider 2 META-INF/services 3 default
    this(nThreads, executor, SelectorProvider.provider());
}
// 3.創(chuàng)建nThread個(gè)EventExecutor，并封裝到選擇器chooser，chooser會(huì)根據(jù)線程數(shù)分別有兩種實(shí)現(xiàn)（GenericEventExecutorChooser和PowerOfTwoEventExecutorChooser，算法不同，但實(shí)現(xiàn)邏輯一樣，就是均勻的分配線程處理）
EventExecutorChooserFactory.EventExecutorChooser chooser;
children = new EventExecutor[nThreads];
for (int i = 0; i < nThreads; i ++) {
    // ...
    children[i] = newChild(executor, args);
    // ...
}
chooser = chooserFactory.newChooser(children);

// 兩種方式設(shè)置group
// parent和child使用同一個(gè)group，調(diào)用仍然是分別設(shè)置parent和child
@Override
public ServerBootstrap group(EventLoopGroup group) {
    return group(group, group);
}
ServerBootstrap.group(EventLoopGroup parentGroup, EventLoopGroup childGroup){
    // 具體代碼略，可直接參考源碼
    // 里面實(shí)現(xiàn)內(nèi)容是把parentGroup綁定到this.group，把childGroup綁定到this.childGroup
}

// 調(diào)用順序
ServerBootstrap:bind() -> doBind() -> initAndRegister()
private ChannelFuture doBind(final SocketAddress localAddress) {
    final ChannelFuture regFuture = initAndRegister();
    // ...
    doBind0(regFuture, channel, localAddress, promise);
    // ...
}
final ChannelFuture initAndRegister() {
    // 創(chuàng)建ServerSocketChannel
    Channel channel = channelFactory.newChannel();
    // ...
    // 開始register
    ChannelFuture regFuture = config().group().register(channel);
    // register調(diào)用順序
    // next().register(channel) -> (EventLoop) super.next() -> chooser.next()
    // ...
}

// 啟動(dòng)BossGroup線程并綁定本地SocketAddress
private static void doBind0(
        final ChannelFuture regFuture, final Channel channel,
        final SocketAddress localAddress, final ChannelPromise promise) {
    channel.eventLoop().execute(new Runnable() {
        @Override
        public void run() {
            if (regFuture.isSuccess()) {
                channel.bind(localAddress, promise).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
            } else {
                promise.setFailure(regFuture.cause());
            }
        }
    });
}

// 消息事件讀取
NioEventLoop.run() -> processSelectedKeys() -> ... -> ServerBootstrapAcceptor.channelRead
// ServerBootstrapAcceptor.channelRead處理客戶端連接事件
// 最后一行的childGroup.register的邏輯和上面的代碼調(diào)用處一樣
public void channelRead(ChannelHandlerContext ctx, Object msg) {
    child.pipeline().addLast(childHandler);
    setChannelOptions(child, childOptions, logger);
    setAttributes(child, childAttrs);
    childGroup.register(child)
}

while(1) {
  nready = select(list);
  // 用戶層依然要遍歷，只不過(guò)少了很多無(wú)效的系統(tǒng)調(diào)用
  for(fd <-- fdlist) {
    if(fd != -1) {
      // 只讀已就緒的文件描述符
      read(fd, buf);
      // 總共只有 nready 個(gè)已就緒描述符，不用過(guò)多遍歷
      if(--nready == 0) break;
    }
  }
}

// DefaultSelectorProvider.create方法在不同版本的jdk下有不同實(shí)現(xiàn)，創(chuàng)建不同Selector
// Windows版本的jdk，其實(shí)現(xiàn)中調(diào)用的是native的poll方法
public static SelectorProvider create() {
    return new WindowsSelectorProvider();
}
// Linux版本的jdk
public static SelectorProvider create() {
    String str = (String)AccessController.doPrivileged(new GetPropertyAction("os.name"));
    if (str.equals("SunOS")) {
        return createProvider("sun.nio.ch.DevPollSelectorProvider");
    }
    if (str.equals("Linux")) {
        return createProvider("sun.nio.ch.EPollSelectorProvider");
    }
    return new PollSelectorProvider();
}

// 創(chuàng)建指定的EventLoopGroup
bossGroup = new EpollEventLoopGroup(1, new DefaultThreadFactory("BOSS_LOOP"));
workerGroup = new EpollEventLoopGroup(32, new DefaultThreadFactory("IO_LOOP"));
b.group(bossGroup, workerGroup)
        // 指定channel的class
        .channel(EpollServerSocketChannel.class)
        .childHandler(initializer);
// 其中channel(clz)方法是通過(guò)class來(lái)new一個(gè)反射ServerSocketChannel創(chuàng)建工廠類
public B channel(Class<? extends C> channelClass) {
    if (channelClass == null) {
        throw new NullPointerException("channelClass");
    }
    return channelFactory(new ReflectiveChannelFactory<C>(channelClass));
}
final ChannelFuture initAndRegister() {
    // ...
    Channel channel = channelFactory.newChannel();
    // ...
}

childOption(ChannelOption.SO_KEEPALIVE, true)

option(ChannelOption.SO_REUSEADDR, true)

childOption(ChannelOption.TCP_NODELAY, true)

option(ChannelOption.SO_BACKLOG, 100)

cat /proc/sys/net/ipv4/tcp_max_syn_backlog

cat /proc/sys/net/core/somaxconn

SOMAXCONN = AccessController.doPrivileged(new PrivilegedAction<Integer>() {
    @Override
    public Integer run() {
        // 1.設(shè)置默認(rèn)值
        int somaxconn = PlatformDependent.isWindows() ? 200 : 128;
        File file = new File("/proc/sys/net/core/somaxconn");
        if (file.exists()) {
            // 2.文件存在，讀取操作系統(tǒng)配置
            in = new BufferedReader(new FileReader(file));
            somaxconn = Integer.parseInt(in.readLine());
        } else {
            // 3.文件不存在，從各個(gè)參數(shù)中讀取
            if (SystemPropertyUtil.getBoolean("io.netty.net.somaxconn.trySysctl", false)) {
                tmp = sysctlGetInt("kern.ipc.somaxconn");
                if (tmp == null) {
                    tmp = sysctlGetInt("kern.ipc.soacceptqueue");
                    if (tmp != null) {
                        somaxconn = tmp;
                    }
                } else {
                    somaxconn = tmp;
                }
            }
        }
    }
}

static {
    //以io.netty.allocator.type為準(zhǔn)，沒(méi)有的話，安卓平臺(tái)用非池化實(shí)現(xiàn)，其他用池化實(shí)現(xiàn)
    String allocType = SystemPropertyUtil.get(
            "io.netty.allocator.type", PlatformDependent.isAndroid() ? "unpooled" : "pooled");
    allocType = allocType.toLowerCase(Locale.US).trim();
    ByteBufAllocator alloc;
    if ("unpooled".equals(allocType)) {
        alloc = UnpooledByteBufAllocator.DEFAULT;
        logger.debug("-Dio.netty.allocator.type: {}", allocType);
    } else if ("pooled".equals(allocType)) {
        alloc = PooledByteBufAllocator.DEFAULT;
        logger.debug("-Dio.netty.allocator.type: {}", allocType);
    } else {
        //io.netty.allocator.type設(shè)置的不是"unpooled"或者"pooled"，就用池化實(shí)現(xiàn)。
        alloc = PooledByteBufAllocator.DEFAULT;
        logger.debug("-Dio.netty.allocator.type: pooled (unknown: {})", allocType);
    }
    DEFAULT_ALLOCATOR = alloc;
}

public class DefaultChannelConfig implements ChannelConfig {
    // ...
    public DefaultChannelConfig(Channel channel) {
        this(channel, new AdaptiveRecvByteBufAllocator());
    }
    // ...
}

/**
 * Shortcut method for {@link #shutdownGracefully(long, long, TimeUnit)} with sensible default values.
 *
 * @return the {@link #terminationFuture()}
 */
Future<?> shutdownGracefully();
/**
 * Signals this executor that the caller wants the executor to be shut down.  Once this method is called,
 * {@link #isShuttingDown()} starts to return {@code true}, and the executor prepares to shut itself down.
 * Unlike {@link #shutdown()}, graceful shutdown ensures that no tasks are submitted for <i>'the quiet period'</i>
 * (usually a couple seconds) before it shuts itself down.  If a task is submitted during the quiet period,
 * it is guaranteed to be accepted and the quiet period will start over.
 *
 * @param quietPeriod the quiet period as described in the documentation
                     靜默期：在此期間，仍然可以提交任務(wù)
 * @param timeout     the maximum amount of time to wait until the executor is {@linkplain #shutdown()}
 *                    regardless if a task was submitted during the quiet period
                     超時(shí)時(shí)間：等待所有任務(wù)執(zhí)行完的最大時(shí)間
 * @param unit        the unit of {@code quietPeriod} and {@code timeout}
 *
 * @return the {@link #terminationFuture()}
 */
Future<?> shutdownGracefully(long quietPeriod, long timeout, TimeUnit unit);
// 抽象類中的實(shí)現(xiàn)
static final long DEFAULT_SHUTDOWN_QUIET_PERIOD = 2;
static final long DEFAULT_SHUTDOWN_TIMEOUT = 15;
@Override
public Future<?> shutdownGracefully() {
    return shutdownGracefully(DEFAULT_SHUTDOWN_QUIET_PERIOD, DEFAULT_SHUTDOWN_TIMEOUT, TimeUnit.SECONDS);
}