netty之NioEventLoopGroup源码分析二
大家好,今天我准备死磕NioEventLoopGroup的源码，首先讲下概念，NioEventLoopGroup 它是一个线程池，存放NioEventLoop，一个数组，今天打算先看下这行代码的初始化
EventLoopGroup bossGroup = new NioEventLoopGroup();
一、初始化
1、时序图：
2.类的关系
3.源码说明：
步骤1：
1 EventLoopGroup bossGroup = new NioEventLoopGroup(); 2 //调用链1 3 public NioEventLoopGroup() { 4 this(0); 5 } 6 //调用链2 7 public NioEventLoopGroup(int nThreads) { 8 this(nThreads, (Executor) null); 9 } 10 //调用链3 11 public NioEventLoopGroup(int nThreads, Executor executor) { 12 this(nThreads, executor, SelectorProvider.provider()); 13 } 14 //调用链4 15 public NioEventLoopGroup( 16 int nThreads, Executor executor, final SelectorProvider selectorProvider) { 17 super(nThreads, executor, selectorProvider); 18 }
如上四个方法是NioEventLoopGroup类的四个构造函数，首先会执行第3行的无参构造函数，然后调用第7行的构造函数，再继续调用第11行的构造函数，这里需要获取一个SelectorProvider,见步骤2，再继续调用第15行的构造函数，这里内部实现调用父类MultithreadEventLoopGroup的构造函数。
步骤2：
1 public static SelectorProvider provider() { 2 synchronized (lock) { 3 if (provider != null) 4 return provider; 5 return AccessController.doPrivileged( 6 new PrivilegedAction<SelectorProvider>() { 7 public SelectorProvider run() { 8 if (loadProviderFromProperty()) 9 return provider; 10 if (loadProviderAsService()) 11 return provider; 12 provider = sun.nio.ch.DefaultSelectorProvider.create(); 13 return provider; 14 } 15 }); 16 } 17 }
这里SelectorProvider的静态方法provider获取一个SelectorProvider，全局唯一的，有加锁，依赖底层系统的实现provider不一样，后续另开专题分析；
步骤3：
1 protected MultithreadEventLoopGroup(int nThreads, Executor executor, Object... args) { 2 super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, executor, args); 3 }
如上是MultithreadEventLoopGroup的构造函数，内部又调用了父类MultithreadEventExecutorGroup的构造函数，继续往下看；
步骤4：
1 protected MultithreadEventExecutorGroup(int nThreads, Executor executor, Object... args) { 2 if (nThreads <= 0) { 3 throw new IllegalArgumentException(String.format("nThreads: %d (expected: > 0)", nThreads)); 4 } 5 6 if (executor == null) { 7 executor = new ThreadPerTaskExecutor(newDefaultThreadFactory()); 8 } 9 10 children = new EventExecutor[nThreads]; 11 for (int i = 0; i < nThreads; i ++) { 12 boolean success = false; 13 try { 14 children[i] = newChild(executor, args); 15 success = true; 16 } catch (Exception e) { 17 // TODO: Think about if this is a good exception type 18 throw new IllegalStateException("failed to create a child event loop", e); 19 } finally { 20 if (!success) { 21 for (int j = 0; j < i; j ++) { 22 children[j].shutdownGracefully(); 23 } 24 25 for (int j = 0; j < i; j ++) { 26 EventExecutor e = children[j]; 27 try { 28 while (!e.isTerminated()) { 29 e.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS); 30 } 31 } catch (InterruptedException interrupted) { 32 Thread.currentThread().interrupt(); 33 break; 34 } 35 } 36 } 37 } 38 } 39 40 final FutureListener<Object> terminationListener = new FutureListener<Object>() { 41 @Override 42 public void operationComplete(Future<Object> future) throws Exception { 43 if (terminatedChildren.incrementAndGet() == children.length) { 44 terminationFuture.setSuccess(null); 45 } 46 } 47 }; 48 49 for (EventExecutor e: children) { 50 e.terminationFuture().addListener(terminationListener); 51 } 52 53 Set<EventExecutor> childrenSet = new LinkedHashSet<EventExecutor>(children.length); 54 Collections.addAll(childrenSet, children); 55 readonlyChildren = Collections.unmodifiableSet(childrenSet); 56 }
如上是核心实现的构造函数，代码比较多，我们分段来看下都做了哪些事？
为了方便查看，把代码又粘贴了一遍
if (nThreads <= 0) { throw new IllegalArgumentException(String.format("nThreads: %d (expected: > 0)", nThreads)); }
判断线程数是否小于等于0，否则抛出异常。
if (executor == null) { executor = new ThreadPerTaskExecutor(newDefaultThreadFactory()); }
第6-8行，会调用子类MultithreadEventLoopGroup的newDefaultThreadFactory方法生成ThreadFactory,这里涉及到java继承初始化的知识，不是调用MultithreadEventExecutorGroup的newDefaultThreadFactory方法，需要注意一下；
//调用链1,此方法是MultithreadEventLoopGroup类的
1 protected ThreadFactory newDefaultThreadFactory() { 2 return new DefaultThreadFactory(getClass(), Thread.MAX_PRIORITY); 3 } 4 5 //调用链2 6 public DefaultThreadFactory(Class<?> poolType, int priority) { 7 this(poolType, false, priority); 8 } 9 //调用链3 10 public DefaultThreadFactory(Class<?> poolType, boolean daemon, int priority) { 11 this(toPoolName(poolType), daemon, priority); 12 } 13 14 //调用链4 15 private static String toPoolName(Class<?> poolType) { 16 if (poolType == null) { 17 throw new NullPointerException("poolType"); 18 } 19 String poolName; 20 Package pkg = poolType.getPackage(); 21 if (pkg != null) { 22 poolName = poolType.getName().substring(pkg.getName().length() + 1); 23 } else { 24 poolName = poolType.getName(); 25 } 26 27 switch (poolName.length()) { 28 case 0: 29 return "unknown"; 30 case 1: 31 return poolName.toLowerCase(Locale.US); 32 default: 33 if (Character.isUpperCase(poolName.charAt(0)) && Character.isLowerCase(poolName.charAt(1))) { 34 return Character.toLowerCase(poolName.charAt(0)) + poolName.substring(1); 35 } else { 36 return poolName; 37 } 38 } 39 } 40 41 //调用链5 42 public DefaultThreadFactory(String poolName, boolean daemon, int priority) { 43 if (poolName == null) { 44 throw new NullPointerException("poolName"); 45 } 46 if (priority < Thread.MIN_PRIORITY || priority > Thread.MAX_PRIORITY) { 47 throw new IllegalArgumentException( 48 "priority: " + priority + " (expected: Thread.MIN_PRIORITY <= priority <= Thread.MAX_PRIORITY)"); 49 } 50 51 prefix = poolName + '-' + poolId.incrementAndGet() + '-'; 52 this.daemon = daemon; 53 this.priority = priority; 54 }
如上依次从调用链到调用链5，完成DefaultThreadFactory初始化；
再继续初始化ThreadPerTaskExecutor类
1 public ThreadPerTaskExecutor(ThreadFactory threadFactory) { 2 if (threadFactory == null) { 3 throw new NullPointerException("threadFactory"); 4 } 5 this.threadFactory = threadFactory; 6 }
这里就是new 一个线程工程；
1 children = new EventExecutor[nThreads]; 2 for (int i = 0; i < nThreads; i ++) { 3 boolean success = false; 4 try { 5 children[i] = newChild(executor, args); 6 success = true; 7 } catch (Exception e) { 8 // TODO: Think about if this is a good exception type 9 throw new IllegalStateException("failed to create a child event loop", e); 10 } finally { 11 if (!success) { 12 for (int j = 0; j < i; j ++) { 13 children[j].shutdownGracefully(); 14 } 15 16 for (int j = 0; j < i; j ++) { 17 EventExecutor e = children[j]; 18 try { 19 while (!e.isTerminated()) { 20 e.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS); 21 } 22 } catch (InterruptedException interrupted) { 23 Thread.currentThread().interrupt(); 24 break; 25 } 26 } 27 } 28 } 29 }
上面初始化了8个(默认，可修改)NioEventLoop, NioEventLoop另外专题分析；
final FutureListener<Object> terminationListener = new FutureListener<Object>() { @Override public void operationComplete(Future<Object> future) throws Exception { if (terminatedChildren.incrementAndGet() == children.length) { terminationFuture.setSuccess(null); } } };
创建了一个监听器
for (EventExecutor e: children) { e.terminationFuture().addListener(terminationListener); }
这里循环调用增加这个监听器；
Set<EventExecutor> childrenSet = new LinkedHashSet<EventExecutor>(children.length); Collections.addAll(childrenSet, children);
readonlyChildren = Collections.unmodifiableSet(childrenSet);
这里创建一个LinkedHashSet,在把children中的元素全部加进去，然后调用unmodifiableSet,返回一个只读的Chidren，readOnlyChildren;
好了，暂时先分析这么多。
