Netty源码分析第二章: NioEventLoop
第七节:处理IO事件
上一小节我们了解了执行select()操作的相关逻辑, 这一小节我们继续学习select()之后, 轮询到io事件的相关逻辑:
回到NioEventLoop的run()方法:
protected void run() { ???for (;;) { ???????try { ???????????switch (selectStrategy.calculateStrategy(selectNowSupplier, hasTasks())) { ???????????????case SelectStrategy.CONTINUE: ???????????????????continue; ???????????????case SelectStrategy.SELECT: ???????????????????//轮询io事件(1) ???????????????????select(wakenUp.getAndSet(false)); ???????????????????if (wakenUp.get()) { ???????????????????????selector.wakeup(); ???????????????????} ???????????????default: ???????????} ???????????cancelledKeys = 0; ???????????needsToSelectAgain = false; ???????????//默认是50 ???????????final int ioRatio = this.ioRatio; ????????????if (ioRatio == 100) { ???????????????try { ???????????????????processSelectedKeys(); ???????????????} finally { ???????????????????runAllTasks(); ???????????????} ???????????} else { ???????????????//记录下开始时间 ???????????????final long ioStartTime = System.nanoTime(); ???????????????try { ???????????????????//处理轮询到的key(2) ???????????????????processSelectedKeys(); ???????????????} finally { ???????????????????//计算耗时 ???????????????????final long ioTime = System.nanoTime() - ioStartTime; ???????????????????//执行task(3) ???????????????????runAllTasks(ioTime * (100 - ioRatio) / ioRatio); ???????????????} ???????????} ???????} catch (Throwable t) { ???????????handleLoopException(t); ???????} ???????//代码省略 ???}}我们首先看if (ioRatio == 100)这个判断, ioRatio主要是用来控制processSelectedKeys()方法执行时间和任务队列执行时间的比例, 其中ioRatio默认是50, 所以会走到下一步else
首先通过final long ioStartTime = System.nanoTime()记录下开始时间, 再通过processSelectedKeys()方法处理轮询到的key, 我们跟到processSelectedKeys()方法中:
private void processSelectedKeys() { ????if (selectedKeys != null) { ???????//flip()方法会直接返回key的数组 ???????processSelectedKeysOptimized(selectedKeys.flip()); ???} else { ???????processSelectedKeysPlain(selector.selectedKeys()); ???}}我们知道selector通过netty优化之后, 会初始化 selectedKeys这个属性, 所以这个属性不为空就会走到processSelectedKeysOptimized(selectedKeys.flip())方法, 这个方法就是对应优化过的selector进行操作的, 如果是优化的selector, 则会进入processSelectedKeysPlain(selector.selectedKeys())方法
selectedKeys.flip()为selectedKey中绑定的数组, 我们之前小节讲过selectedKeys其实是通过数组存储的, 所以经过select()操作如果监听到事件selectedKeys的数组就会有值
跟进到processSelectedKeysOptimized(selectedKeys.flip())方法中:
private void processSelectedKeysOptimized(SelectionKey[] selectedKeys) { ???//通过for循环遍历数组 ???for (int i = 0;; i ++) { ???????//拿到当前的selectionKey ???????final SelectionKey k = selectedKeys[i]; ???????if (k == null) { ???????????break; ???????} ???????//将当前引用设置为null ???????selectedKeys[i] = null; ???????//获取channel(NioSeverSocketChannel) ???????final Object a = k.attachment(); ???????//如果是AbstractNioChannel, 则调用processSelectedKey()方法处理io事件 ???????if (a instanceof AbstractNioChannel) { ???????????processSelectedKey(k, (AbstractNioChannel) a); ???????} else { ???????????@SuppressWarnings("unchecked") ???????????NioTask<SelectableChannel> task = (NioTask<SelectableChannel>) a; ???????????processSelectedKey(k, task); ???????} ???????//代码省略 ???}}首先通过for循环遍历数组中的每一个key, 获得key之后首先将数组中对应的下标清空, 因为selector不会自动清空, 这与我们使用原生selector时候, 通过遍历selector.selectedKeys()的set的时候, 拿到key之后要执行remove()是一个意思
之后获取注册在key上的channel, 判断channel是不是AbstractNioChannel, 通常情况都是AbstractNioChannel, 所以这里会执行rocessSelectedKey(k, (AbstractNioChannel) a)
跟到rocessSelectedKey(k, (AbstractNioChannel) a)方法中:
private void processSelectedKey(SelectionKey k, AbstractNioChannel ch) { ???//获取到channel中的unsafe ???final AbstractNioChannel.NioUnsafe unsafe = ch.unsafe(); ???//如果这个key不是合法的, 说明这个channel可能有问题 ???if (!k.isValid()) { ???????//代码省略 ???} ???try { ???????//如果是合法的, 拿到key的io事件 ???????int readyOps = k.readyOps(); ???????//链接事件 ???????if ((readyOps & SelectionKey.OP_CONNECT) != 0) { ???????????int ops = k.interestOps(); ???????????ops &= ~SelectionKey.OP_CONNECT; ???????????k.interestOps(ops); ???????????unsafe.finishConnect(); ???????} ???????//写事件 ???????if ((readyOps & SelectionKey.OP_WRITE) != 0) { ???????????ch.unsafe().forceFlush(); ???????} ???????//读事件和接受链接事件 ???????//如果当前NioEventLoop是work线程的话, 这里就是op_read事件 ???????//如果是当前NioEventLoop是boss线程的话, 这里就是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()); ???}}我们首先获取和channel绑定的unsafe, 之后拿到channel注册的事件
我们关注if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0)这个判断, 这个判断相信注释上写的很明白, 如果当前NioEventLoop是work线程的话, 这里就是op_read事件, 如果是当前NioEventLoop是boss线程的话, 这里就是op_accept事件
然后会通过channel绑定的unsafe对象执行read()方法用于处理链接或者读写事件
以上就是NioEventLoop对io事件的处理过程, 有关read()方法执行逻辑, 会在以后的章节中详细剖析
Netty源码分析第2章(NioEventLoop)---->第7节: 处理IO事件
原文地址：https://www.cnblogs.com/xiangnan6122/p/10203152.html