netty 多线程事件执行器组: http://donald-draper.iteye.com/blog/2391270
netty 多线程事件循环组: http://donald-draper.iteye.com/blog/2391276
netty 抽象调度事件执行器: http://donald-draper.iteye.com/blog/2391379
netty 单线程事件执行器初始化: http://donald-draper.iteye.com/blog/2391895
netty 单线程事件执行器执行任务与graceful方式关闭: http://donald-draper.iteye.com/blog/2392051
引言:
上一篇文章看了单线程事件执行器的任务执行与执行器关闭,先来回顾一下:
单线程事件执行器,执行任务,首先判断任务是否为null,为空抛出空指针异常,否则,判断线程是否在当前事件循环中,在则添加任务到任务队列,否则开启当前单线程事件执行器,并添加任务到任务队列,如果此时事件执行器已关闭,并可以移除任务,则抛出拒绝执行器任务异常;如果需要启动事件执行器唤醒线程,则添加唤醒线程到任务队列。
添加,移除,poll任务操作,实际委托给任务队列,添加,移除hook线程操作委托给关闭hooks线程集合。
单线程事件执行器take任务,首先从调度任务队列peek头部调度任务,如果任务不为空,则获取调度任务延时时间,如果延时时间大于0,则从任务队列超时poll任务,否则从调度任务队列抓取调度任务,添加到任务队列,并从任务队列poll任务;如果调度任务为空,则从任务队列take一个任务,如果是唤醒任务,则忽略。
关闭单线程执行器,首先检查间隔、超时时间,时间单元参数,并且间隔时间要小于超时时间,如果已经关闭,则返回异步关闭任务结果,否则检查线程是否在当前事务循环中,如果是则更新状态为正在关闭,并计算计算关闭间隔和超时时间。
今天来看一下单线程事件循环SingleThreadEventLoop:
package io.netty.channel; import io.netty.util.concurrent.RejectedExecutionHandler; import io.netty.util.concurrent.RejectedExecutionHandlers; import io.netty.util.concurrent.SingleThreadEventExecutor; import io.netty.util.internal.ObjectUtil; import io.netty.util.internal.SystemPropertyUtil; import io.netty.util.internal.UnstableApi; import java.util.Queue; import java.util.concurrent.Executor; import java.util.concurrent.ThreadFactory; /** * Abstract base class for {@link EventLoop}s that execute all its submitted tasks in a single thread. 单线程事件循环在单个线程中执行所有提交的任务 * */ public abstract class SingleThreadEventLoop extends SingleThreadEventExecutor implements EventLoop { protected static final int DEFAULT_MAX_PENDING_TASKS = Math.max(16, SystemPropertyUtil.getInt("io.netty.eventLoop.maxPendingTasks", Integer.MAX_VALUE)); //当前循环任务队列 private final Queue<Runnable> tailTasks; //下面几个构造方法与单线程事件执行器基本相同,就不说了 protected SingleThreadEventLoop(EventLoopGroup parent, ThreadFactory threadFactory, boolean addTaskWakesUp) { this(parent, threadFactory, addTaskWakesUp, DEFAULT_MAX_PENDING_TASKS, RejectedExecutionHandlers.reject()); } protected SingleThreadEventLoop(EventLoopGroup parent, Executor executor, boolean addTaskWakesUp) { this(parent, executor, addTaskWakesUp, DEFAULT_MAX_PENDING_TASKS, RejectedExecutionHandlers.reject()); } protected SingleThreadEventLoop(EventLoopGroup parent, ThreadFactory threadFactory, boolean addTaskWakesUp, int maxPendingTasks, RejectedExecutionHandler rejectedExecutionHandler) { super(parent, threadFactory, addTaskWakesUp, maxPendingTasks, rejectedExecutionHandler); tailTasks = newTaskQueue(maxPendingTasks); } protected SingleThreadEventLoop(EventLoopGroup parent, Executor executor, boolean addTaskWakesUp, int maxPendingTasks, RejectedExecutionHandler rejectedExecutionHandler) { super(parent, executor, addTaskWakesUp, maxPendingTasks, rejectedExecutionHandler); tailTasks = newTaskQueue(maxPendingTasks); } //获取所属事件循环组 @Override public EventLoopGroup parent() { return (EventLoopGroup) super.parent(); } //获取当前事件循环 @Override public EventLoop next() { return (EventLoop) super.next(); } //注册通道 @Override public ChannelFuture register(Channel channel) { return register(new DefaultChannelPromise(channel, this)); } //注册通道 @Override public ChannelFuture register(final ChannelPromise promise) { ObjectUtil.checkNotNull(promise, "promise"); //委托给通道关联的UnSafe,这个具体我们在后面再说 promise.channel().unsafe().register(this, promise); return promise; } //此注册方法已丢弃 @Deprecated @Override public ChannelFuture register(final Channel channel, final ChannelPromise promise) { if (channel == null) { throw new NullPointerException("channel"); } if (promise == null) { throw new NullPointerException("promise"); } channel.unsafe().register(this, promise); return promise; } /** * Adds a task to be run once at the end of next (or current) {@code eventloop} iteration. *在事件循环迭代后,运行指定任务 * @param task to be added. */ @UnstableApi public final void executeAfterEventLoopIteration(Runnable task) { ObjectUtil.checkNotNull(task, "task"); if (isShutdown()) { //事件循环关闭,则抛出拒绝执行异常 reject(); } //如果添加任务到任务队列失败,则拒绝执行任务 if (!tailTasks.offer(task)) { reject(task); } //如果需要为任务,启动唤醒线程,则添加唤醒线程到任务队列 if (wakesUpForTask(task)) { wakeup(inEventLoop()); } } /** * Removes a task that was added previously via {@link #executeAfterEventLoopIteration(Runnable)}. *在在事件循环迭代后,移除指定任务 * @param task to be removed. * * @return {@code true} if the task was removed as a result of this call. */ @UnstableApi final boolean removeAfterEventLoopIterationTask(Runnable task) { return tailTasks.remove(ObjectUtil.checkNotNull(task, "task")); } //是否启动唤醒任务线程 @Override protected boolean wakesUpForTask(Runnable task) { return !(task instanceof NonWakeupRunnable); } //在运行所有任务结束后,执行tailTasks任务队列中的任务 @Override protected void afterRunningAllTasks() { runAllTasksFrom(tailTasks); } //判断tailTasks任务队列中是否有任务 @Override protected boolean hasTasks() { return super.hasTasks() || !tailTasks.isEmpty(); } //获取任务队列中的任务数 @Override public int pendingTasks() { return super.pendingTasks() + tailTasks.size(); } /** * Marker interface for {@link Runnable} that will not trigger an {@link #wakeup(boolean)} in all cases. 标记线程不会触发唤醒线程 */ interface NonWakeupRunnable extends Runnable { } }
从上面来看,单线程事件循环SingleThreadEventLoop,继承了单线程事件执行器,实现了事件循环接口,内部一个事件循环任务队列,我们可以把单线程事件循环看为一个简单的事件执行器,单线程事件循环中多了一个通道注册的方法,实际注册工作委托给通道关联的UnSafe。
再来看一下Nio事件循环的定义:
/** * {@link SingleThreadEventLoop} implementation which register the {@link Channel}'s to a * {@link Selector} and so does the multi-plexing of these in the event loop. * */ public final class NioEventLoop extends SingleThreadEventLoop {
nio事件循环实际为一个单线程事件循环,这样做的目的是,事件循环关联的通道注册到一个
选择器,可以复用循环事件,即保证通道的IO操作线程安全。
总结:
单线程事件循环SingleThreadEventLoop,继承了单线程事件执行器,实现了事件循环接口,
内部一个事件循环任务队列,我们可以把单线程事件循环看为一个简单的事件执行器,单线程事件循环中多了一个通道注册的方法,实际注册工作委托给通道关联的UnSafe。