Netty原始碼分析NioEventLoop處理IO事件相關邏輯

protected void run() {
    for (;;) {
        try {
            switch (selectStrategy.calculateStrategy(selectNowSupplier, hasTasks())) {
                case SelectStrategy.CONTINUE:
                    continue;
                case SelectStrategy.SELECT:
                    //輪詢io事件(1)
                    select(wakenUp.getAndSet(false));
                    if (wakenUp.get()) {
                        selector.wakeup();
                    }
                default:
            }
            cancelledKeys = 0;
            needsToSelectAgain = false;
            //預設是50
            final int ioRatio = this.ioRatio; 
            if (ioRatio == 100) {
                try {
                    processSelectedKeys();
                } finally {
                    runAllTasks();
                }
            } else {
                //記錄下開始時間
                final long ioStartTime = System.nanoTime();
                try {
                    //處理輪詢到的key(2)
                    processSelectedKeys();
                } finally {
                    //計算耗時
                    final long ioTime = System.nanoTime() - ioStartTime;
                    //執行task(3)
                    runAllTasks(ioTime * (100 - ioRatio) / ioRatio);
                }
            }
        } catch (Throwable t) {
            handleLoopException(t);
        }
        //程式碼省略
    }
}

private void processSelectedKeys() { 
    if (selectedKeys != null) {
        //flip()方法會直接返回key的陣列
        processSelectedKeysOptimized(selectedKeys.flip());
    } else {
        processSelectedKeysPlain(selector.selectedKeys());
    }
}

private void processSelectedKeysOptimized(SelectionKey[] selectedKeys) {
    //通過for迴圈遍歷陣列
    for (int i = 0;; i ++) {
        //拿到當前的selectionKey
        final SelectionKey k = selectedKeys[i];
        if (k == null) {
            break;
        }
        //將當前參照設定為null
        selectedKeys[i] = null;
        //獲取channel(NioSeverSocketChannel)
        final Object a = k.attachment();
        //如果是AbstractNioChannel, 則呼叫processSelectedKey()方法處理io事件
        if (a instanceof AbstractNioChannel) {
            processSelectedKey(k, (AbstractNioChannel) a);
        } else {
            @SuppressWarnings("unchecked")
            NioTask<SelectableChannel> task = (NioTask<SelectableChannel>) a;
            processSelectedKey(k, task);
        }

        //程式碼省略
    }
}

private void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {
    //獲取到channel中的unsafe
    final AbstractNioChannel.NioUnsafe unsafe = ch.unsafe();
    //如果這個key不是合法的, 說明這個channel可能有問題
    if (!k.isValid()) {
        //程式碼省略
    }
    try {
        //如果是合法的, 拿到key的io事件
        int readyOps = k.readyOps();
        //連結事件
        if ((readyOps & SelectionKey.OP_CONNECT) != 0) {
            int ops = k.interestOps();
            ops &= ~SelectionKey.OP_CONNECT;
            k.interestOps(ops);
            unsafe.finishConnect();
        }
        //寫事件
        if ((readyOps & SelectionKey.OP_WRITE) != 0) {
            ch.unsafe().forceFlush();
        }
        //讀事件和接受連結事件
        //如果當前NioEventLoop是work執行緒的話, 這裡就是op_read事件
        //如果是當前NioEventLoop是boss執行緒的話, 這裡就是op_accept事件
        if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
            unsafe.read();
            if (!ch.isOpen()) {
                return;
            }
        }
    } catch (CancelledKeyException ignored) {
        unsafe.close(unsafe.voidPromise());
    }
}