抓到Netty一个Bug，聊一下Netty是如何高效接收网络连接的（二）

public final class NioEventLoop extends SingleThreadEventLoop {

    private void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {
        final AbstractNioChannel.NioUnsafe unsafe = ch.unsafe();
        ..............省略.................

        try {
            int readyOps = k.readyOps();

            if ((readyOps & SelectionKey.OP_CONNECT) != 0) {
               ..............处理OP_CONNECT事件.................
            }


            if ((readyOps & SelectionKey.OP_WRITE) != 0) {
              ..............处理OP_WRITE事件.................
            }


            if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
                //本文重点处理OP_ACCEPT事件
                unsafe.read();
            }
        } catch (CancelledKeyException ignored) {
            unsafe.close(unsafe.voidPromise());
        }
    }

}
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public abstract class AbstractNioMessageChannel extends AbstractNioChannel {

  private final class NioMessageUnsafe extends AbstractNioUnsafe {

        //存放连接建立后，创建的客户端SocketChannel
        private final List<Object> readBuf = new ArrayList<Object>();

        @Override
        public void read() {
            //必须在Main Reactor线程中执行
            assert eventLoop().inEventLoop();
            //注意下面的config和pipeline都是服务端ServerSocketChannel中的
            final ChannelConfig config = config();
            final ChannelPipeline pipeline = pipeline();
            //创建接收数据Buffer分配器（用于分配容量大小合适的byteBuffer用来容纳接收数据）
            //在接收连接的场景中，这里的allocHandle只是用于控制read loop的循环读取创建连接的次数。
            final RecvByteBufAllocator.Handle allocHandle = unsafe().recvBufAllocHandle();
            allocHandle.reset(config);

            boolean closed = false;
            Throwable exception = null;
            try {
                try {
                    do {
                        //底层调用NioServerSocketChannel->doReadMessages 创建客户端SocketChannel
                        int localRead = doReadMessages(readBuf);

                        //已无新的连接可接收则退出read loop
                        if (localRead == 0) {
                            break;
                        }
                        if (localRead < 0) {
                            closed = true;
                            break;
                        }
                        //统计在当前事件循环中已经读取到得Message数量（创建连接的个数）
                        allocHandle.incMessagesRead(localRead);
                    } while (allocHandle.continueReading());//判断是否已经读满16次
                } catch (Throwable t) {
                    exception = t;
                }

                int size = readBuf.size();
                for (int i = 0; i < size; i ++) {
                    readPending = false;
                    //在NioServerSocketChannel对应的pipeline中传播ChannelRead事件
                    //初始化客户端SocketChannel，并将其绑定到Sub Reactor线程组中的一个Reactor上
                    pipeline.fireChannelRead(readBuf.get(i));
                }
                //清除本次accept 创建的客户端SocketChannel集合
                readBuf.clear();
                allocHandle.readComplete();
                //触发readComplete事件传播
                pipeline.fireChannelReadComplete();
                ....................省略............
            } finally {
                ....................省略............
            }
        }
    }
  }
}
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    public NioServerSocketChannel(ServerSocketChannel channel) {
        //父类AbstractNioChannel中保存JDK NIO原生ServerSocketChannel以及要监听的事件OP_ACCEPT
        super(null, channel, SelectionKey.OP_ACCEPT);
        //DefaultChannelConfig中设置用于Channel接收数据用的buffer->AdaptiveRecvByteBufAllocator
        config = new NioServerSocketChannelConfig(this, javaChannel().socket());
    }
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    public static SocketChannel accept(final ServerSocketChannel serverSocketChannel) throws IOException {
        try {
            return AccessController.doPrivileged(new PrivilegedExceptionAction<SocketChannel>() {
                @Override
                public SocketChannel run() throws IOException {
                    return serverSocketChannel.accept();
                }
            });
        } catch (PrivilegedActionException e) {
            throw (IOException) e.getCause();
        }
    }
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  private final class NioMessageUnsafe extends AbstractNioUnsafe {

        //存放连接建立后，创建的客户端SocketChannel
        private final List<Object> readBuf = new ArrayList<Object>();
}
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                int size = readBuf.size();
                for (int i = 0; i < size; i ++) {
                    readPending = false;
                    //NioServerSocketChannel对应的pipeline中传播read事件
                    //io.netty.bootstrap.ServerBootstrap.ServerBootstrapAcceptor.channelRead
                    //初始化客户端SocketChannel，并将其绑定到Sub Reactor线程组中的一个Reactor上
                    pipeline.fireChannelRead(readBuf.get(i));
                }
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