在上一篇中的简单代码中开头的两行代码是
1 eventloopgroup boss = new nioeventloopgroup(1); 2 eventloopgroup worker = new nioeventloopgroup();
服务端应用要创建首先要创建两个eventloopgroup ，为什么是两个eventloopgroup ，这就涉及netty的核心设计思想——主从reactor模型。这里不展开说，内容比较多，可以自行学习。每个eventloopgroup 可以包含一个或多个eventloop，每一个eventloop简单来说的就是一个死循环的线程，这个线程循环监听一个通道的所有事件，这个模式下面其他流程中也会反复提到。下面开始追代码。
说明一下，上面的两个构造函数一个有参数一个无参数，无参数的通过获取本机cpu的核数（注意是核数不是个数，例如我的电脑4个cpu，每个cpu都是双核的，所以无参的时候应该创建8个eventloop）来决定创建线程的个数，有参数就是指定在这个eventloopgroup 中创建具体个数的eventloop。
我要评论 protected multithreadeventloopgroup(int nthreads, threadfactory threadfactory, object... args) {
super(nthreads == 0 ? default_event_loop_threads : nthreads, threadfactory, args);
}
static {
default_event_loop_threads = math.max(1, systempropertyutil.getint(
"io.netty.eventloopthreads", runtime.getruntime().availableprocessors() * 2)); //获取本机cup核数
if (logger.isdebugenabled()) {
logger.debug("-dio.netty.eventloopthreads: {}", default_event_loop_threads);
}
}
protected multithreadeventexecutorgroup(int nthreads, executor executor, object... args) {
this(nthreads, executor, defaulteventexecutorchooserfactory.instance, args);
}
protected multithreadeventexecutorgroup(int nthreads, executor executor,
eventexecutorchooserfactory chooserfactory, object... args) {
if (nthreads <= 0) {
throw new illegalargumentexception(string.format("nthreads: %d (expected: > 0)", nthreads));
}
if (executor == null) {
executor = new threadpertaskexecutor(newdefaultthreadfactory()); //创建默认的线程执行器
}
children = new eventexecutor[nthreads]; //创建保存eventloop的数组
for (int i = 0; i < nthreads; i ++) {
boolean success = false;
try {
children[i] = newchild(executor, args); //循环填充数组，在这里实例化每一个eventloop
success = true;
} catch (exception e) {
// todo: think about if this is a good exception type
throw new illegalstateexception("failed to create a child event loop", e);
} finally {
if (!success) {
for (int j = 0; j < i; j ++) {
children[j].shutdowngracefully();
}
for (int j = 0; j < i; j ++) {
eventexecutor e = children[j];
try {
while (!e.isterminated()) {
e.awaittermination(integer.max_value, timeunit.seconds);
}
} catch (interruptedexception interrupted) {
// let the caller handle the interruption.
thread.currentthread().interrupt();
break;
}
}
}
}
}
chooser = chooserfactory.newchooser(children); //将创建好的eventloop数组注册到选择器工厂
final futurelistener<object> terminationlistener = new futurelistener<object>() {
@override
public void operationcomplete(future<object> future) throws exception {
if (terminatedchildren.incrementandget() == children.length) {
terminationfuture.setsuccess(null);
}
}
};
for (eventexecutor e: children) {
e.terminationfuture().addlistener(terminationlistener);
}
set<eventexecutor> childrenset = new linkedhashset<eventexecutor>(children.length);
collections.addall(childrenset, children);
readonlychildren = collections.unmodifiableset(childrenset);
}
eventexecutor是一个接口，是eventloop接口的子接口，当children[i] = newchild(executor, args)执行时，实际上执行的是nioeventloopgroup中重写的，可以发现创建的nioeventloop的实例，而nioeventloop间接实现了eventloop
@override
protected eventloop newchild(executor executor, object... args) throws exception {
return new nioeventloop(this, executor, (selectorprovider) args[0],
((selectstrategyfactory) args[1]).newselectstrategy(), (rejectedexecutionhandler) args[2]);
}
至此eventloopgroup以及包含的多个eventloop创建完成，这里只是在eventloopgroup中创建了多个nioeventloop，nioeventloop并没有run起来，需要在注册通道后才能run起来监控通道的事件和执行task。后面章节还会介绍nioeventloop类中的在其他方法。ok，这个部分就到这。
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