Netty源码分析第二章: NioEventLoop
第二节: NioEventLoopGroup之NioEventLoop的创建
回到上一小节的MultithreadEventExecutorGroup类的构造方法:
protected MultithreadEventExecutorGroup(int nThreads, Executor executor,
EventExecutorChooserFactory chooserFactory, Object... args) {
//代码省略
if (executor == null) {
//创建一个新的线程执行器(1)
executor = new ThreadPerTaskExecutor(newDefaultThreadFactory());
}
//构造NioEventLoop(2)
children = new EventExecutor[nThreads];
for (int i = 0; i < nThreads; i ++) {
boolean success = false;
try {
children[i] = newChild(executor, args);
success = true;
} catch (Exception e) {
throw new IllegalStateException("failed to create a child event loop", e);
} finally {
//代码省略
}
}
//创建线程选择器(3)
chooser = chooserFactory.newChooser(children);
//代码省略
}
我们来看第二步构造NioEventLoop:
这里通过 children = new EventExecutor[nThreads] 初始化了children属性, 看下这个属性的定义:
private final EventExecutor[] children
这里的children是EventExecutor类型的数组, 其实就是NioEventLoop的集合, 因为NioEventLoop也是EventExecutor的子类
所以这里初始化了children数组, 大小为参数nThreads传入的线程数量, 默认为cpu核数的两倍
后面就是通过for循环来创建NioEventLoop线程,
在循环体里通过 children[i] = newChild(executor, args) 创建NioEventLoop, 我们跟newChild(executor, args)方法
因为是NioEventLoopGroup调用的,所以跟到NioEventLoop的newChild方法中:
protected EventLoop newChild(Executor executor, Object... args) throws Exception {
return new NioEventLoop(this, executor, (SelectorProvider) args[0],
((SelectStrategyFactory) args[1]).newSelectStrategy(), (RejectedExecutionHandler) args[2]);
}这里我们看到创建了一个NioEventLoop对象, 其中this是NioEventLoopGroup自身, executor就是上一小节讲到的线程执行器
我们继续跟到NioEventLoop的构造方法:
NioEventLoop(NioEventLoopGroup parent, Executor executor, SelectorProvider selectorProvider,
SelectStrategy strategy, RejectedExecutionHandler rejectedExecutionHandler) {
super(parent, executor, false, DEFAULT_MAX_PENDING_TASKS, rejectedExecutionHandler);
//代码省略
provider = selectorProvider;
selector = openSelector();
selectStrategy = strategy;
}
首先看到了调用了父类的构造方法, 然后初始化了几个属性:
selector = openSelector() 这种方式创建个NioEventLoop绑定的selector对象, 有关创建过程, 之后会讲到
跟进父类SingleThreadEventLoop类构造方法:
protected SingleThreadEventLoop(EventLoopGroup parent, Executor executor,
boolean addTaskWakesUp, int maxPendingTasks,
RejectedExecutionHandler rejectedExecutionHandler) {
super(parent, executor, addTaskWakesUp, maxPendingTasks, rejectedExecutionHandler);
tailTasks = newTaskQueue(maxPendingTasks);
}
再跟到父类SingleThreadEventExecutor构造方法:
protected SingleThreadEventExecutor(EventExecutorGroup parent, Executor executor,
boolean addTaskWakesUp, int maxPendingTasks,
RejectedExecutionHandler rejectedHandler) {
super(parent);
this.addTaskWakesUp = addTaskWakesUp;
this.maxPendingTasks = Math.max(16, maxPendingTasks);
this.executor = ObjectUtil.checkNotNull(executor, "executor");
taskQueue = newTaskQueue(this.maxPendingTasks);
rejectedExecutionHandler = ObjectUtil.checkNotNull(rejectedHandler, "rejectedHandler");
}
this.executor = ObjectUtil.checkNotNull(executor, "executor") 这里初始化了线程执行器
taskQueue = newTaskQueue(this.maxPendingTasks) 是创建一个任务队列, 这个任务队列可以将不属于NioEventLoop线程的任务放到这个任务队列中, 通过NioEventLoop线程执行, 具体使用场景之后我们会看到
跟到父类AbstractScheduledEventExecutor的构造方法中:
protected AbstractScheduledEventExecutor(EventExecutorGroup parent) {
super(parent);
}继续跟进去, 最后跟到AbstractEventExecutor类的构造方法:
protected AbstractEventExecutor(EventExecutorGroup parent) {
this.parent = parent;
}这里初始化了parent, 这个parent就NioEventLoop所属的线程组NioEventLoopGroup对象
至此, NioEventLoop创建完成