Netty-NioEventLoop

Netty 事件循环主逻辑在 NioEventLoop.run 中的 processSelectedKeys函数中

protected void run() {
　　　　　　　//主循环不断读取IO事件和task，因为 EventLoop 也是 juc 的 ScheduledExecutorService 实现
        for (;;) {
            try {
                switch (selectStrategy.calculateStrategy(selectNowSupplier, hasTasks())) {
                    case SelectStrategy.CONTINUE:
                        continue;
                    case SelectStrategy.SELECT:
                        select(wakenUp.getAndSet(false));

                        

                        if (wakenUp.get()) {
                            selector.wakeup();
                        }
                        // fall through
                    default:
                }

                cancelledKeys = 0;
                needsToSelectAgain = false;
　　　　　　　　　　   // IO事件占总执行时间的百分比 */
                final int ioRatio = this.ioRatio;
                if (ioRatio == 100) {
                    try {
                        processSelectedKeys();
                    } finally {
                        // Ensure we always run tasks.
                        runAllTasks();
                    }
                } else {
                    final long ioStartTime = System.nanoTime();
                    try {
                        processSelectedKeys();
                    } finally {
                        // Ensure we always run tasks.
                        final long ioTime = System.nanoTime() - ioStartTime;
                        runAllTasks(ioTime * (100 - ioRatio) / ioRatio);
                    }
                }
            } catch (Throwable t) {
                handleLoopException(t);
            }
            // Always handle shutdown even if the loop processing threw an exception.
            try {
                if (isShuttingDown()) {
                    closeAll();
                    if (confirmShutdown()) {
                        return;
                    }
                }
            } catch (Throwable t) {
                handleLoopException(t);
            }
        }
    }

processSelectedKeys 函数 执行时会判断是否执行优化的版本，即判断 SelectedSelectionKeySet 是否为空。

是否开启优化取决于是否设置了环境变量  io.netty.noKeySetOptimization ，默认是 false 代表开启

private static final boolean DISABLE_KEYSET_OPTIMIZATION =
            SystemPropertyUtil.getBoolean("io.netty.noKeySetOptimization", false);

原理是通过反射的方式设置 eventLoop绑定的selector中的 selectKeys属性 为 SelectedSelectionKeySet ，好处是不用 迭代  selector.selectedKeys()

注入时机为初始化 EventLoop 的时候

private SelectorTuple openSelector() {
        12 　　　　　//注入逻辑40 
        Object maybeException = AccessController.doPrivileged(new PrivilegedAction<Object>() {
            @Override
            public Object run() {
                try {
                    Field selectedKeysField = selectorImplClass.getDeclaredField("selectedKeys");
                    Field publicSelectedKeysField = selectorImplClass.getDeclaredField("publicSelectedKeys");

                    Throwable cause = ReflectionUtil.trySetAccessible(selectedKeysField);
                    if (cause != null) {
                        return cause;
                    }
                    cause = ReflectionUtil.trySetAccessible(publicSelectedKeysField);
                    if (cause != null) {
                        return cause;
                    }

                    selectedKeysField.set(unwrappedSelector, selectedKeySet);
                    publicSelectedKeysField.set(unwrappedSelector, selectedKeySet);
                    return null;
                } catch (NoSuchFieldException e) {
                    return e;
                } catch (IllegalAccessException e) {
                    return e;
                }
            }
        });

        ........78     }

处理读事件  主要在    processSelectedKey 中 ，分别对 读、写、连接事件进行了处理。

private void processSelectedKeysOptimized() {
        for (int i = 0; i < selectedKeys.size; ++i) {
            final SelectionKey k = selectedKeys.keys[i];
            // null out entry in the array to allow to have it GC'ed once the Channel close
            // See https://github.com/netty/netty/issues/2363
            selectedKeys.keys[i] = null;

            final Object a = k.attachment();

            if (a instanceof AbstractNioChannel) {
                //分别处理每个channel的事件
                processSelectedKey(k, (AbstractNioChannel) a);
            } else {
                @SuppressWarnings("unchecked")
                NioTask<SelectableChannel> task = (NioTask<SelectableChannel>) a;
                processSelectedKey(k, task);
            }

            if (needsToSelectAgain) {
                // null out entries in the array to allow to have it GC'ed once the Channel close
                // See https://github.com/netty/netty/issues/2363
                selectedKeys.reset(i + 1);

                selectAgain();
                i = -1;
            }
        }
    }

    private void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {
        final AbstractNioChannel.NioUnsafe unsafe = ch.unsafe();
        if (!k.isValid()) {
            final EventLoop eventLoop;
            try {
                eventLoop = ch.eventLoop();
            } catch (Throwable ignored) {
                // If the channel implementation throws an exception because there is no event loop, we ignore this
                // because we are only trying to determine if ch is registered to this event loop and thus has authority
                // to close ch.
                return;
            }
            // Only close ch if ch is still registered to this EventLoop. ch could have deregistered from the event loop
            // and thus the SelectionKey could be cancelled as part of the deregistration process, but the channel is
            // still healthy and should not be closed.
            // See https://github.com/netty/netty/issues/5125
            if (eventLoop != this || eventLoop == null) {
                return;
            }
            // close the channel if the key is not valid anymore
            unsafe.close(unsafe.voidPromise());
            return;
        }

        try {
            int readyOps = k.readyOps();
            // We first need to call finishConnect() before try to trigger a read(...) or write(...) as otherwise
            // the NIO JDK channel implementation may throw a NotYetConnectedException.
            if ((readyOps & SelectionKey.OP_CONNECT) != 0) {
                // remove OP_CONNECT as otherwise Selector.select(..) will always return without blocking
                // See https://github.com/netty/netty/issues/924
                int ops = k.interestOps();
                ops &= ~SelectionKey.OP_CONNECT;
                k.interestOps(ops);
　　　　　　　　　　//处理了连接事件
                unsafe.finishConnect();
            }

            // Process OP_WRITE first as we may be able to write some queued buffers and so free memory.
            if ((readyOps & SelectionKey.OP_WRITE) != 0) {
                // Call forceFlush which will also take care of clear the OP_WRITE once there is nothing left to write

　　　　　　　　　　
　　　　　　　　　　//将要写入的buffer flush掉
　　　　　　　　　　ch.unsafe().forceFlush();

            }

            // Also check for readOps of 0 to workaround possible JDK bug which may otherwise lead
            // to a spin loop
            if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
　　　　　　　　   //回调 pipeline 上所有的 ChannelInboundHandler 的 fireChannelRead  和 channelReadComplete 函数
                unsafe.read();
            }
        } catch (CancelledKeyException ignored) {
            unsafe.close(unsafe.voidPromise());
        }
    }

注意 ： NioServerSocketChannel 和 NioSocketChannel 都是 同样的 处理逻辑， 不同的是  前者 只关注 OP_ACCEPT 和 OP_READ事件， 后者 关注  OP_READ、OP_WRITE、OP_CONNECT事件

当NioServerSocketChannel 发生 OP_ACCEPT事件时 会 触发 AbstractNioChannel.NioUnsafe.read ->  NioSctpServerChannel.doReadMessages(List<Object>)  -> ServerBootstrapAcceptor.channelRead ，将受到的 NioSocketChannel 注册到 childEventLoop 。