Netty中NioEventLoopGroup的建立原始碼分析

鬆餅人發表於2019-05-26
NettyOOP原始碼

NioEventLoopGroup的無參構造：

1 public NioEventLoopGroup() {
2     this(0);
3 }

呼叫了單參的構造：

1 public NioEventLoopGroup(int nThreads) {
2     this(nThreads, (Executor)null);
3 }

繼續看到雙參構造：

1 public NioEventLoopGroup(int nThreads, Executor executor) {
2     this(nThreads, executor, SelectorProvider.provider());
3 }

在這裡是使用JDK中NIO的原生API：SelectorProvider的provider，產生了一個SelectorProvider物件呼叫，繼續呼叫三參構造。
關於SelectorProvider在我前面的部落格中有介紹過：【Java】NIO中Selector的建立原始碼分析，在Windows下預設建立了WindowsSelectorProvider物件。

繼續看三參構造：

1 public NioEventLoopGroup(int nThreads, ThreadFactory threadFactory, SelectorProvider selectorProvider) {
2     this(nThreads, threadFactory, selectorProvider, DefaultSelectStrategyFactory.INSTANCE);
3 }

在這裡建立了一個單例的DefaultSelectStrategyFactory 物件：

 1 public final class DefaultSelectStrategyFactory implements SelectStrategyFactory {
 2     public static final SelectStrategyFactory INSTANCE = new DefaultSelectStrategyFactory();
 3 
 4     private DefaultSelectStrategyFactory() {
 5     }
 6 
 7     public SelectStrategy newSelectStrategy() {
 8         return DefaultSelectStrategy.INSTANCE;
 9     }
10 }

DefaultSelectStrategyFactory實現的是SelectStrategyFactory 介面：

1 public interface SelectStrategyFactory {
2     SelectStrategy newSelectStrategy();
3 }

該介面提供一個用來產生Select策略的方法，SelectStrategy介面如下：

1 public interface SelectStrategy {
2     int SELECT = -1;
3     int CONTINUE = -2;
4 
5     int calculateStrategy(IntSupplier var1, boolean var2) throws Exception;
6 }

根據IntSupplier 和一個boolean值為Select策略提供了一個計算策略的方法。
在Netty中只提供了DefaultSelectStrategy這一種預設實現：

 1 final class DefaultSelectStrategy implements SelectStrategy {
 2     static final SelectStrategy INSTANCE = new DefaultSelectStrategy();
 3 
 4     private DefaultSelectStrategy() {
 5     }
 6 
 7     public int calculateStrategy(IntSupplier selectSupplier, boolean hasTasks) throws Exception {
 8         return hasTasks ? selectSupplier.get() : -1;
 9     }
10 }


其中IntSupplier :

1 public interface IntSupplier {
2     int get() throws Exception;
3 }

結合上面的來看，最終的選擇策略主要是根據IntSupplier的get值來得到的。

再回到構造：

1 public NioEventLoopGroup(int nThreads, ThreadFactory threadFactory, SelectorProvider selectorProvider, SelectStrategyFactory selectStrategyFactory) {
2     super(nThreads, threadFactory, new Object[]{selectorProvider, selectStrategyFactory, RejectedExecutionHandlers.reject()});
3 }

這裡產生了一個拒絕策略：

 1 public static RejectedExecutionHandler reject() {
 2     return REJECT;
 3 }
 4 
 5 private static final RejectedExecutionHandler REJECT = new RejectedExecutionHandler() {
 6     public void rejected(Runnable task, SingleThreadEventExecutor executor) {
 7         throw new RejectedExecutionException();
 8     }
 9 };
10 
11 public interface RejectedExecutionHandler {
12     void rejected(Runnable var1, SingleThreadEventExecutor var2);
13 }

將selectorProvider、selectStrategyFactory以及這個拒絕策略封裝在一個Object陣列裡，再呼叫了父類MultithreadEventLoopGroup的構造：

1 protected MultithreadEventLoopGroup(int nThreads, ThreadFactory threadFactory, Object... args) {
2     super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, threadFactory, args);
3 }

在這裡對nThreads的大小進行了調整：

1 private static final int DEFAULT_EVENT_LOOP_THREADS = Math.max(1, SystemPropertyUtil.getInt("io.netty.eventLoopThreads", NettyRuntime.availableProcessors() * 2));

SystemPropertyUtil.getInt是根據key值"io.netty.eventLoopThreads"，獲取系統配置值，在沒用設定時使用NettyRuntime.availableProcessors() * 2的值
NettyRuntime的availableProcessors實現如下：

1 synchronized int availableProcessors() {
2     if (this.availableProcessors == 0) {
3         int availableProcessors = SystemPropertyUtil.getInt("io.netty.availableProcessors", Runtime.getRuntime().availableProcessors());
4         this.setAvailableProcessors(availableProcessors);
5     }
6 
7     return this.availableProcessors;
8 }

還是一樣，根據key值"io.netty.availableProcessors"，獲取系統配置值，在沒用設定時使用Runtime.getRuntime().availableProcessors()，是用來獲取處理器的個數。

這樣保證了在預設情況下nThreads的大小是總是cpu個數的2倍。

繼續回到構造，MultithreadEventLoopGroup繼續呼叫父類MultithreadEventExecutorGroup的構造：

1 protected MultithreadEventExecutorGroup(int nThreads, Executor executor, Object... args) {
2     this(nThreads, executor, DefaultEventExecutorChooserFactory.INSTANCE, args);
3 }

在這裡又初始化了一個單例的DefaultEventExecutorChooserFactory物件：

1 public static final DefaultEventExecutorChooserFactory INSTANCE = new DefaultEventExecutorChooserFactory();

DefaultEventExecutorChooserFactory 實現的是EventExecutorChooserFactory介面：

1 public interface EventExecutorChooserFactory {
2     EventExecutorChooserFactory.EventExecutorChooser newChooser(EventExecutor[] var1);
3 
4     public interface EventExecutorChooser {
5         EventExecutor next();
6     }
7 }

DefaultEventExecutorChooserFactory 的具體實現：

1 public EventExecutorChooser newChooser(EventExecutor[] executors) {
2     return (EventExecutorChooser)(isPowerOfTwo(executors.length) ? new DefaultEventExecutorChooserFactory.PowerOfTwoEventExecutorChooser(executors) : new DefaultEventExecutorChooserFactory.GenericEventExecutorChooser(executors));
3 }
4 
5 private static boolean isPowerOfTwo(int val) {
6     return (val & -val) == val;
7 }

isPowerOfTwo是用來檢查executors的大小是否是二的整數次方，若是二的整數次方，產生PowerOfTwoEventExecutorChooser，反之產生GenericEventExecutorChooser：

 1 private static final class GenericEventExecutorChooser implements EventExecutorChooser {
 2     private final AtomicInteger idx = new AtomicInteger();
 3     private final EventExecutor[] executors;
 4 
 5     GenericEventExecutorChooser(EventExecutor[] executors) {
 6         this.executors = executors;
 7     }
 8 
 9     public EventExecutor next() {
10         return this.executors[Math.abs(this.idx.getAndIncrement() % this.executors.length)];
11     }
12 }
13 
14 private static final class PowerOfTwoEventExecutorChooser implements EventExecutorChooser {
15     private final AtomicInteger idx = new AtomicInteger();
16     private final EventExecutor[] executors;
17 
18     PowerOfTwoEventExecutorChooser(EventExecutor[] executors) {
19         this.executors = executors;
20     }
21 
22     public EventExecutor next() {
23         return this.executors[this.idx.getAndIncrement() & this.executors.length - 1];
24     }
25 }

這兩種其實都是用了取模運算，只不過因為二的整數次方的特殊性而使用位運算。

回到構造，MultithreadEventExecutorGroup繼續呼叫本省的構造：

 1 private final EventExecutor[] children;
 2 private final Set<EventExecutor> readonlyChildren;
 3 private final AtomicInteger terminatedChildren;
 4 private final Promise<?> terminationFuture;
 5 private final EventExecutorChooser chooser;
 6 
 7 protected MultithreadEventExecutorGroup(int nThreads, Executor executor, EventExecutorChooserFactory chooserFactory, Object... args) {
 8     this.terminatedChildren = new AtomicInteger();
 9     this.terminationFuture = new DefaultPromise(GlobalEventExecutor.INSTANCE);
10     if (nThreads <= 0) {
11         throw new IllegalArgumentException(String.format("nThreads: %d (expected: > 0)", nThreads));
12     } else {
13         if (executor == null) {
14             executor = new ThreadPerTaskExecutor(this.newDefaultThreadFactory());
15         }
16 
17         this.children = new EventExecutor[nThreads];
18 
19         int j;
20         for(int i = 0; i < nThreads; ++i) {
21             boolean success = false;
22             boolean var18 = false;
23 
24             try {
25                 var18 = true;
26                 this.children[i] = this.newChild((Executor)executor, args);
27                 success = true;
28                 var18 = false;
29             } catch (Exception var19) {
30                 throw new IllegalStateException("failed to create a child event loop", var19);
31             } finally {
32                 if (var18) {
33                     if (!success) {
34                         int j;
35                         for(j = 0; j < i; ++j) {
36                             this.children[j].shutdownGracefully();
37                         }
38 
39                         for(j = 0; j < i; ++j) {
40                             EventExecutor e = this.children[j];
41 
42                             try {
43                                 while(!e.isTerminated()) {
44                                     e.awaitTermination(2147483647L, TimeUnit.SECONDS);
45                                 }
46                             } catch (InterruptedException var20) {
47                                 Thread.currentThread().interrupt();
48                                 break;
49                             }
50                         }
51                     }
52 
53                 }
54             }
55 
56             if (!success) {
57                 for(j = 0; j < i; ++j) {
58                     this.children[j].shutdownGracefully();
59                 }
60 
61                 for(j = 0; j < i; ++j) {
62                     EventExecutor e = this.children[j];
63 
64                     try {
65                         while(!e.isTerminated()) {
66                             e.awaitTermination(2147483647L, TimeUnit.SECONDS);
67                         }
68                     } catch (InterruptedException var22) {
69                         Thread.currentThread().interrupt();
70                         break;
71                     }
72                 }
73             }
74         }
75 
76         this.chooser = chooserFactory.newChooser(this.children);
77         FutureListener<Object> terminationListener = new FutureListener<Object>() {
78             public void operationComplete(Future<Object> future) throws Exception {
79                 if (MultithreadEventExecutorGroup.this.terminatedChildren.incrementAndGet() == MultithreadEventExecutorGroup.this.children.length) {
80                     MultithreadEventExecutorGroup.this.terminationFuture.setSuccess((Object)null);
81                 }
82 
83             }
84         };
85         EventExecutor[] var24 = this.children;
86         j = var24.length;
87 
88         for(int var26 = 0; var26 < j; ++var26) {
89             EventExecutor e = var24[var26];
90             e.terminationFuture().addListener(terminationListener);
91         }
92 
93         Set<EventExecutor> childrenSet = new LinkedHashSet(this.children.length);
94         Collections.addAll(childrenSet, this.children);
95         this.readonlyChildren = Collections.unmodifiableSet(childrenSet);
96     }
97 }

首先是對terminatedChildren的初始化，沒什麼好說的，對terminationFuture的初始化使用DefaultPromise，用來非同步處理終止事件。executor初始化產生一個執行緒池。

接下來就是對children的操作，根據nThreads的大小，產生一個EventExecutor陣列，然後遍歷這個陣列，呼叫newChild給每一個元素初始化。

newChild是在NioEventLoopGroup中實現的：

1 protected EventLoop newChild(Executor executor, Object... args) throws Exception {
2     return new NioEventLoop(this, executor, (SelectorProvider)args[0], ((SelectStrategyFactory)args[1]).newSelectStrategy(), (RejectedExecutionHandler)args[2]);
3 }

在這裡直接使用executor，和之前放在args陣列中的SelectorProvider、SelectStrategyFactory（newSelectStrategy方法產生DefaultSelectStrategy）和RejectedExecutionHandler產生了一個NioEventLoop物件：

 1 private Selector selector;
 2 private Selector unwrappedSelector;
 3 private SelectedSelectionKeySet selectedKeys;
 4 private final SelectorProvider provider;
 5 private final AtomicBoolean wakenUp = new AtomicBoolean();
 6 private final SelectStrategy selectStrategy;
 7 
 8 NioEventLoop(NioEventLoopGroup parent, Executor executor, SelectorProvider selectorProvider, SelectStrategy strategy, RejectedExecutionHandler rejectedExecutionHandler) {
 9    super(parent, executor, false, DEFAULT_MAX_PENDING_TASKS, rejectedExecutionHandler);
10     if (selectorProvider == null) {
11         throw new NullPointerException("selectorProvider");
12     } else if (strategy == null) {
13         throw new NullPointerException("selectStrategy");
14     } else {
15         this.provider = selectorProvider;
16         NioEventLoop.SelectorTuple selectorTuple = this.openSelector();
17         this.selector = selectorTuple.selector;
18         this.unwrappedSelector = selectorTuple.unwrappedSelector;
19         this.selectStrategy = strategy;
20     }
21 }

NioEventLoop首先在繼承鏈上呼叫父類的構造，都是一些成員的賦值操作，簡單看一看：

 1 protected SingleThreadEventLoop(EventLoopGroup parent, Executor executor, boolean addTaskWakesUp, int maxPendingTasks, RejectedExecutionHandler rejectedExecutionHandler) {
 2     super(parent, executor, addTaskWakesUp, maxPendingTasks, rejectedExecutionHandler);
 3     this.tailTasks = this.newTaskQueue(maxPendingTasks);
 4 }
 5 
 6 protected SingleThreadEventExecutor(EventExecutorGroup parent, Executor executor, boolean addTaskWakesUp, int maxPendingTasks, RejectedExecutionHandler rejectedHandler) {
 7     super(parent);
 8     this.threadLock = new Semaphore(0);
 9     this.shutdownHooks = new LinkedHashSet();
10     this.state = 1;
11     this.terminationFuture = new DefaultPromise(GlobalEventExecutor.INSTANCE);
12     this.addTaskWakesUp = addTaskWakesUp;
13     this.maxPendingTasks = Math.max(16, maxPendingTasks);
14     this.executor = (Executor)ObjectUtil.checkNotNull(executor, "executor");
15     this.taskQueue = this.newTaskQueue(this.maxPendingTasks);
16     this.rejectedExecutionHandler = (RejectedExecutionHandler)ObjectUtil.checkNotNull(rejectedHandler, "rejectedHandler");
17 }
18 
19 protected AbstractScheduledEventExecutor(EventExecutorGroup parent) {
20     super(parent);
21 }
22 
23 protected AbstractEventExecutor(EventExecutorGroup parent) {
24     this.selfCollection = Collections.singleton(this);
25     this.parent = parent;
26 }

在經過這繼承鏈上的一系列呼叫後，給provider成員賦值selectorProvider，就是之前建立好的WindowsSelectorProvider，然後使用openSelector方法，最終建立JDK原生的Selector：

 1 private NioEventLoop.SelectorTuple openSelector() {
 2     final AbstractSelector unwrappedSelector;
 3     try {
 4         unwrappedSelector = this.provider.openSelector();
 5     } catch (IOException var7) {
 6         throw new ChannelException("failed to open a new selector", var7);
 7     }
 8 
 9     if (DISABLE_KEYSET_OPTIMIZATION) {
10         return new NioEventLoop.SelectorTuple(unwrappedSelector);
11     } else {
12         final SelectedSelectionKeySet selectedKeySet = new SelectedSelectionKeySet();
13         Object maybeSelectorImplClass = AccessController.doPrivileged(new PrivilegedAction<Object>() {
14             public Object run() {
15                 try {
16                     return Class.forName("sun.nio.ch.SelectorImpl", false, PlatformDependent.getSystemClassLoader());
17                 } catch (Throwable var2) {
18                     return var2;
19                 }
20             }
21         });
22         if (maybeSelectorImplClass instanceof Class && ((Class)maybeSelectorImplClass).isAssignableFrom(unwrappedSelector.getClass())) {
23             final Class<?> selectorImplClass = (Class)maybeSelectorImplClass;
24             Object maybeException = AccessController.doPrivileged(new PrivilegedAction<Object>() {
25                 public Object run() {
26                     try {
27                         Field selectedKeysField = selectorImplClass.getDeclaredField("selectedKeys");
28                         Field publicSelectedKeysField = selectorImplClass.getDeclaredField("publicSelectedKeys");
29                         Throwable cause = ReflectionUtil.trySetAccessible(selectedKeysField, true);
30                         if (cause != null) {
31                             return cause;
32                         } else {
33                             cause = ReflectionUtil.trySetAccessible(publicSelectedKeysField, true);
34                             if (cause != null) {
35                                 return cause;
36                             } else {
37                                 selectedKeysField.set(unwrappedSelector, selectedKeySet);
38                                 publicSelectedKeysField.set(unwrappedSelector, selectedKeySet);
39                                 return null;
40                             }
41                         }
42                     } catch (NoSuchFieldException var4) {
43                         return var4;
44                     } catch (IllegalAccessException var5) {
45                         return var5;
46                     }
47                 }
48             });
49             if (maybeException instanceof Exception) {
50                 this.selectedKeys = null;
51                 Exception e = (Exception)maybeException;
52                 logger.trace("failed to instrument a special java.util.Set into: {}", unwrappedSelector, e);
53                 return new NioEventLoop.SelectorTuple(unwrappedSelector);
54             } else {
55                 this.selectedKeys = selectedKeySet;
56                 logger.trace("instrumented a special java.util.Set into: {}", unwrappedSelector);
57                 return new NioEventLoop.SelectorTuple(unwrappedSelector, new SelectedSelectionKeySetSelector(unwrappedSelector, selectedKeySet));
58             }
59         } else {
60             if (maybeSelectorImplClass instanceof Throwable) {
61                 Throwable t = (Throwable)maybeSelectorImplClass;
62                 logger.trace("failed to instrument a special java.util.Set into: {}", unwrappedSelector, t);
63             }
64 
65             return new NioEventLoop.SelectorTuple(unwrappedSelector);
66         }
67     }
68 }

可以看到在一開始就使用provider的openSelector方法，即WindowsSelectorProvider的openSelector方法，建立了WindowsSelectorImpl物件（【Java】NIO中Selector的建立原始碼分析 ）

然後根據DISABLE_KEYSET_OPTIMIZATION判斷：

1 private static final boolean DISABLE_KEYSET_OPTIMIZATION = SystemPropertyUtil.getBoolean("io.netty.noKeySetOptimization", false);

可以看到這個系統配置在沒有設定預設是false，如果設定了則直接建立一個SelectorTuple物件返回：

 1 private static final class SelectorTuple {
 2     final Selector unwrappedSelector;
 3     final Selector selector;
 4 
 5     SelectorTuple(Selector unwrappedSelector) {
 6         this.unwrappedSelector = unwrappedSelector;
 7         this.selector = unwrappedSelector;
 8     }
 9 
10     SelectorTuple(Selector unwrappedSelector, Selector selector) {
11         this.unwrappedSelector = unwrappedSelector;
12         this.selector = selector;
13     }
14 }

可以看到僅僅是將unwrappedSelector和selector封裝了，unwrappedSelector對應的是JDK原生Selector沒有經過更改的，而selector對應的是經過更改修飾操作的。

在沒有系統配置下，就對Selector進行更改修飾操作：
首先建立SelectedSelectionKeySet物件，這個SelectedSelectionKeySet繼承自AbstractSet：

1 final class SelectedSelectionKeySet extends AbstractSet<SelectionKey> {
2     SelectionKey[] keys = new SelectionKey[1024];
3     int size;
4     
5     SelectedSelectionKeySet() {
6     }
7     ......
8 }

後面是通過反射機制，使得WindowsSelectorImpl的selectedKeys和publicSelectedKeys成員直接賦值為SelectedSelectionKeySet物件。

WindowsSelectorImpl的這兩個成員是在SelectorImpl中定義的：

1 protected Set<SelectionKey> selectedKeys = new HashSet();
2 private Set<SelectionKey> publicSelectedKeys;

從這裡就可以明白，在JDK原生的Selector中，selectedKeys和publicSelectedKeys這兩個Set的初始化大小都為0，而在這裡僅僅就是使其初始化大小變為1024。
後面就是對一些異常的處理，沒什麼好說的。

openSelector結束後，就可以分別對包裝過的Selector和未包裝過的Selector，即selector和unwrappedSelector成員賦值，再由selectStrategy儲存剛才產生的選擇策略，用於Selector的輪詢。

回到MultithreadEventExecutorGroup的構造，在呼叫newChild方法時即NioEventLoop建立的過程中可能出現異常情況，就需要遍歷children陣列，將之前建立好的NioEventLoop使用shutdownGracefully優雅地關閉掉：
shutdownGracefully在AbstractEventExecutor中實現：

1 public Future<?> shutdownGracefully() {
2     return this.shutdownGracefully(2L, 15L, TimeUnit.SECONDS);
3 }

這裡設定了超時時間，繼續呼叫SingleThreadEventExecutor的shutdownGracefully方法：

 1 public Future<?> shutdownGracefully(long quietPeriod, long timeout, TimeUnit unit) {
 2     if (quietPeriod < 0L) {
 3         throw new IllegalArgumentException("quietPeriod: " + quietPeriod + " (expected >= 0)");
 4     } else if (timeout < quietPeriod) {
 5         throw new IllegalArgumentException("timeout: " + timeout + " (expected >= quietPeriod (" + quietPeriod + "))");
 6     } else if (unit == null) {
 7         throw new NullPointerException("unit");
 8     } else if (this.isShuttingDown()) {
 9         return this.terminationFuture();
10     } else {
11         boolean inEventLoop = this.inEventLoop();
12 
13         while(!this.isShuttingDown()) {
14             boolean wakeup = true;
15             int oldState = this.state;
16             int newState;
17             if (inEventLoop) {
18                 newState = 3;
19             } else {
20                 switch(oldState) {
21                 case 1:
22                 case 2:
23                     newState = 3;
24                     break;
25                 default:
26                     newState = oldState;
27                     wakeup = false;
28                 }
29             }
30 
31             if (STATE_UPDATER.compareAndSet(this, oldState, newState)) {
32                 this.gracefulShutdownQuietPeriod = unit.toNanos(quietPeriod);
33                 this.gracefulShutdownTimeout = unit.toNanos(timeout);
34                 if (oldState == 1) {
35                     try {
36                         this.doStartThread();
37                     } catch (Throwable var10) {
38                         STATE_UPDATER.set(this, 5);
39                         this.terminationFuture.tryFailure(var10);
40                         if (!(var10 instanceof Exception)) {
41                             PlatformDependent.throwException(var10);
42                         }
43 
44                         return this.terminationFuture;
45                     }
46                 }
47 
48                 if (wakeup) {
49                     this.wakeup(inEventLoop);
50                 }
51 
52                 return this.terminationFuture();
53             }
54         }
55 
56         return this.terminationFuture();
57     }
58 }

前三個判斷沒什麼好說的，isShuttingDown判斷：

1 public boolean isShuttingDown() {
2     return this.state >= 3;
3 }

在之前NioEventLoop建立的時候，呼叫了一系列的繼承鏈，其中state是在SingleThreadEventExecutor的構造方法中實現的，初始值是1，state有如下幾種狀態：

1 private static final int ST_NOT_STARTED = 1;
2 private static final int ST_STARTED = 2;
3 private static final int ST_SHUTTING_DOWN = 3;
4 private static final int ST_SHUTDOWN = 4;
5 private static final int ST_TERMINATED = 5;

可見在NioEventLoop初始化後處於尚未啟動狀態，並沒有Channel的註冊，也就不需要輪詢。

isShuttingDown就必然是false，就進入了else塊：
首先得到inEventLoop的返回值，該方法在AbstractEventExecutor中實現：

1 public boolean inEventLoop() {
2     return this.inEventLoop(Thread.currentThread());
3 }

他傳入了一個當前執行緒，接著呼叫inEventLoop的過載，這個方法是在SingleThreadEventExecutor中實現：

1 public boolean inEventLoop(Thread thread) {
2     return thread == this.thread;
3 }

通過觀察之前的SingleThreadEventExecutor構造方法，發現並沒有對thread成員初始化，此時的this.thread就是null，那麼返回值就是false，即inEventLoop為false。

在while迴圈中又對isShuttingDown進行了判斷，shutdownGracefully當讓不僅僅使用在建立NioEventLoop物件失敗時才呼叫的，無論是在EventLoopGroup的關閉，還是Bootstrap的關閉，都會關閉繫結的NioEventLoop，所以在多執行緒環境中，有可能會被其他執行緒關閉。

在while迴圈中，結合上面可知滿足進入switch塊，在switch塊中令newState為3；
然後呼叫STATE_UPDATER的compareAndSet方法，STATE_UPDATER是用來原子化更新state成員的：

1 private static final AtomicIntegerFieldUpdater<SingleThreadEventExecutor> STATE_UPDATER = AtomicIntegerFieldUpdater.newUpdater(SingleThreadEventExecutor.class, "state");

所以這裡就是使用CAS操作，原子化更新state成員為3，也就是使當前狀態由ST_NOT_STARTED 變為了ST_SHUTTING_DOWN 狀態。

gracefulShutdownQuietPeriod和gracefulShutdownTimeout分別儲存quietPeriod和timeout的納秒級顆粒度。

前面可知oldState使1，呼叫doStartThread方法：

  1 private void doStartThread() {
  2     assert this.thread == null;
  3 
  4     this.executor.execute(new Runnable() {
  5         public void run() {
  6             SingleThreadEventExecutor.this.thread = Thread.currentThread();
  7             if (SingleThreadEventExecutor.this.interrupted) {
  8                 SingleThreadEventExecutor.this.thread.interrupt();
  9             }
 10 
 11             boolean success = false;
 12             SingleThreadEventExecutor.this.updateLastExecutionTime();
 13             boolean var112 = false;
 14 
 15             int oldState;
 16             label1685: {
 17                 try {
 18                     var112 = true;
 19                     SingleThreadEventExecutor.this.run();
 20                     success = true;
 21                     var112 = false;
 22                     break label1685;
 23                 } catch (Throwable var119) {
 24                     SingleThreadEventExecutor.logger.warn("Unexpected exception from an event executor: ", var119);
 25                     var112 = false;
 26                 } finally {
 27                     if (var112) {
 28                         int oldStatex;
 29                         do {
 30                             oldStatex = SingleThreadEventExecutor.this.state;
 31                         } while(oldStatex < 3 && !SingleThreadEventExecutor.STATE_UPDATER.compareAndSet(SingleThreadEventExecutor.this, oldStatex, 3));
 32 
 33                         if (success && SingleThreadEventExecutor.this.gracefulShutdownStartTime == 0L) {
 34                             SingleThreadEventExecutor.logger.error("Buggy " + EventExecutor.class.getSimpleName() + " implementation; " + SingleThreadEventExecutor.class.getSimpleName() + ".confirmShutdown() must be called before run() implementation terminates.");
 35                         }
 36 
 37                         try {
 38                             while(!SingleThreadEventExecutor.this.confirmShutdown()) {
 39                                 ;
 40                             }
 41                         } finally {
 42                             try {
 43                                 SingleThreadEventExecutor.this.cleanup();
 44                             } finally {
 45                                 SingleThreadEventExecutor.STATE_UPDATER.set(SingleThreadEventExecutor.this, 5);
 46                                 SingleThreadEventExecutor.this.threadLock.release();
 47                                 if (!SingleThreadEventExecutor.this.taskQueue.isEmpty()) {
 48                                     SingleThreadEventExecutor.logger.warn("An event executor terminated with non-empty task queue (" + SingleThreadEventExecutor.this.taskQueue.size() + ')');
 49                                 }
 50 
 51                                 SingleThreadEventExecutor.this.terminationFuture.setSuccess((Object)null);
 52                             }
 53                         }
 54 
 55                     }
 56                 }
 57 
 58                 do {
 59                     oldState = SingleThreadEventExecutor.this.state;
 60                 } while(oldState < 3 && !SingleThreadEventExecutor.STATE_UPDATER.compareAndSet(SingleThreadEventExecutor.this, oldState, 3));
 61 
 62                 if (success && SingleThreadEventExecutor.this.gracefulShutdownStartTime == 0L) {
 63                     SingleThreadEventExecutor.logger.error("Buggy " + EventExecutor.class.getSimpleName() + " implementation; " + SingleThreadEventExecutor.class.getSimpleName() + ".confirmShutdown() must be called before run() implementation terminates.");
 64                 }
 65 
 66                 try {
 67                     while(!SingleThreadEventExecutor.this.confirmShutdown()) {
 68                         ;
 69                     }
 70 
 71                     return;
 72                 } finally {
 73                     try {
 74                         SingleThreadEventExecutor.this.cleanup();
 75                     } finally {
 76                         SingleThreadEventExecutor.STATE_UPDATER.set(SingleThreadEventExecutor.this, 5);
 77                         SingleThreadEventExecutor.this.threadLock.release();
 78                         if (!SingleThreadEventExecutor.this.taskQueue.isEmpty()) {
 79                             SingleThreadEventExecutor.logger.warn("An event executor terminated with non-empty task queue (" + SingleThreadEventExecutor.this.taskQueue.size() + ')');
 80                         }
 81 
 82                         SingleThreadEventExecutor.this.terminationFuture.setSuccess((Object)null);
 83                     }
 84                 }
 85             }
 86 
 87             do {
 88                 oldState = SingleThreadEventExecutor.this.state;
 89             } while(oldState < 3 && !SingleThreadEventExecutor.STATE_UPDATER.compareAndSet(SingleThreadEventExecutor.this, oldState, 3));
 90 
 91             if (success && SingleThreadEventExecutor.this.gracefulShutdownStartTime == 0L) {
 92                 SingleThreadEventExecutor.logger.error("Buggy " + EventExecutor.class.getSimpleName() + " implementation; " + SingleThreadEventExecutor.class.getSimpleName() + ".confirmShutdown() must be called before run() implementation terminates.");
 93             }
 94 
 95             try {
 96                 while(!SingleThreadEventExecutor.this.confirmShutdown()) {
 97                     ;
 98                 }
 99             } finally {
100                 try {
101                     SingleThreadEventExecutor.this.cleanup();
102                 } finally {
103                     SingleThreadEventExecutor.STATE_UPDATER.set(SingleThreadEventExecutor.this, 5);
104                     SingleThreadEventExecutor.this.threadLock.release();
105                     if (!SingleThreadEventExecutor.this.taskQueue.isEmpty()) {
106                         SingleThreadEventExecutor.logger.warn("An event executor terminated with non-empty task queue (" + SingleThreadEventExecutor.this.taskQueue.size() + ')');
107                     }
108 
109                     SingleThreadEventExecutor.this.terminationFuture.setSuccess((Object)null);
110                 }
111             }
112 
113         }
114     });
115 }

剛才說過this.thread並沒有初始化，所以等於null成立，斷言可以繼續。

然後直接使executor執行了一個執行緒，這個executor其實就是在剛才的MultithreadEventExecutorGroup中產生的ThreadPerTaskExecutor物件。

線上程中，首先將SingleThreadEventExecutor的thread成員初始化為當前執行緒。

在這裡可能就有疑問了，為什麼會在關閉時會呼叫名為doStartThread的方法，這個方法不因該在啟動時呼叫嗎？
其實doStartThread在啟動時是會被呼叫的，當在啟動時被呼叫的話，每一個NioEventLoop都會被繫結一個執行緒用來處理真正的Selector操作，根據之前的說法就可以知道，每個EventLoopGroup在建立後都會被繫結cpu個數的二倍個NioEventLoop，而每個NioEventLoop都會繫結一個Selector物件，上面又說了在啟動時SingleThreadEventExecutor繫結了一個執行緒，即NioEventLoop繫結了一個執行緒來處理其繫結的Selector的輪詢。
至於關閉時還會啟動Selector的輪詢，就是為了解決註冊了的Channel沒有被處理的情況。

回到doStartThread方法，其實這個doStartThread方法的核心是SingleThreadEventExecutor.this.run()，這個方法就是正真的Selector的輪詢操作，在NioEventLoop中實現：

 1 protected void run() {
 2     while(true) {
 3         while(true) {
 4             try {
 5                 switch(this.selectStrategy.calculateStrategy(this.selectNowSupplier, this.hasTasks())) {
 6                 case -2:
 7                     continue;
 8                 case -1:
 9                     this.select(this.wakenUp.getAndSet(false));
10                     if (this.wakenUp.get()) {
11                         this.selector.wakeup();
12                     }
13                 default:
14                     this.cancelledKeys = 0;
15                     this.needsToSelectAgain = false;
16                     int ioRatio = this.ioRatio;
17                     if (ioRatio == 100) {
18                         try {
19                             this.processSelectedKeys();
20                         } finally {
21                             this.runAllTasks();
22                         }
23                     } else {
24                         long ioStartTime = System.nanoTime();
25                         boolean var13 = false;
26 
27                         try {
28                             var13 = true;
29                             this.processSelectedKeys();
30                             var13 = false;
31                         } finally {
32                             if (var13) {
33                                 long ioTime = System.nanoTime() - ioStartTime;
34                                 this.runAllTasks(ioTime * (long)(100 - ioRatio) / (long)ioRatio);
35                             }
36                         }
37 
38                         long ioTime = System.nanoTime() - ioStartTime;
39                         this.runAllTasks(ioTime * (long)(100 - ioRatio) / (long)ioRatio);
40                     }
41                 }
42             } catch (Throwable var21) {
43                 handleLoopException(var21);
44             }
45 
46             try {
47                 if (this.isShuttingDown()) {
48                     this.closeAll();
49                     if (this.confirmShutdown()) {
50                         return;
51                     }
52                 }
53             } catch (Throwable var18) {
54                 handleLoopException(var18);
55             }
56         }
57     }
58 }

進入switch塊，首先呼叫之前準備好的選擇策略，其中this.selectNowSupplier在NioEventLoop建立的時候就被建立了：

1 private final IntSupplier selectNowSupplier = new IntSupplier() {
2     public int get() throws Exception {
3         return NioEventLoop.this.selectNow();
4     }
5 };

實際上呼叫了selectNow方法：

 1 int selectNow() throws IOException {
 2     int var1;
 3     try {
 4         var1 = this.selector.selectNow();
 5     } finally {
 6         if (this.wakenUp.get()) {
 7             this.selector.wakeup();
 8         }
 9 
10     }
11 
12     return var1;
13 }

這裡就直接呼叫了JDK原生的selectNow方法。
之前說過的選擇策略：

1 public int calculateStrategy(IntSupplier selectSupplier, boolean hasTasks) throws Exception {
2     return hasTasks ? selectSupplier.get() : -1;
3 }

其中hasTasks是根據hasTasks方法來判斷，而hasTasks方法就是判斷任務佇列是否為空，那麼在一開始初始化，必然是空的，所以這裡calculateStrategy的返回值就是-1；

那麼case為-1條件成立，執行this.select(this.wakenUp.getAndSet(false))，其中wakenUp是一個原子化的Boolean，用來表示是需要喚醒Selector的輪詢阻塞，初始化是為true，這裡通過CAS操作設定為false代表不需要喚醒，後面在select執行完後，又判斷wakenUp是否需要喚醒，說明在select中對Selector的阻塞進行了檢查，若是需要喚醒，就通過Selector的原生API完成喚醒【Java】NIO中Selector的select方法原始碼分析

來看看這裡的select實現：

 1 private void select(boolean oldWakenUp) throws IOException {
 2     Selector selector = this.selector;
 3 
 4     try {
 5         int selectCnt = 0;
 6         long currentTimeNanos = System.nanoTime();
 7         long selectDeadLineNanos = currentTimeNanos + this.delayNanos(currentTimeNanos);
 8 
 9         while(true) {
10             long timeoutMillis = (selectDeadLineNanos - currentTimeNanos + 500000L) / 1000000L;
11             if (timeoutMillis <= 0L) {
12                 if (selectCnt == 0) {
13                     selector.selectNow();
14                     selectCnt = 1;
15                 }
16                 break;
17             }
18 
19             if (this.hasTasks() && this.wakenUp.compareAndSet(false, true)) {
20                 selector.selectNow();
21                 selectCnt = 1;
22                 break;
23             }
24 
25             int selectedKeys = selector.select(timeoutMillis);
26             ++selectCnt;
27             if (selectedKeys != 0 || oldWakenUp || this.wakenUp.get() || this.hasTasks() || this.hasScheduledTasks()) {
28                 break;
29             }
30 
31             if (Thread.interrupted()) {
32                 if (logger.isDebugEnabled()) {
33                     logger.debug("Selector.select() returned prematurely because Thread.currentThread().interrupt() was called. Use NioEventLoop.shutdownGracefully() to shutdown the NioEventLoop.");
34                 }
35 
36                 selectCnt = 1;
37                 break;
38             }
39 
40             long time = System.nanoTime();
41             if (time - TimeUnit.MILLISECONDS.toNanos(timeoutMillis) >= currentTimeNanos) {
42                 selectCnt = 1;
43             } else if (SELECTOR_AUTO_REBUILD_THRESHOLD > 0 && selectCnt >= SELECTOR_AUTO_REBUILD_THRESHOLD) {
44                 logger.warn("Selector.select() returned prematurely {} times in a row; rebuilding Selector {}.", selectCnt, selector);
45                 this.rebuildSelector();
46                 selector = this.selector;
47                 selector.selectNow();
48                 selectCnt = 1;
49                 break;
50             }
51 
52             currentTimeNanos = time;
53         }
54 
55         if (selectCnt > 3 && logger.isDebugEnabled()) {
56             logger.debug("Selector.select() returned prematurely {} times in a row for Selector {}.", selectCnt - 1, selector);
57         }
58     } catch (CancelledKeyException var13) {
59         if (logger.isDebugEnabled()) {
60             logger.debug(CancelledKeyException.class.getSimpleName() + " raised by a Selector {} - JDK bug?", selector, var13);
61         }
62     }
63 
64 }

這個方法雖然看著很長，但核心就是判斷這個存放任務的阻塞佇列是否還有任務，若是有，就直接呼叫Selector的selectNow方法獲取就緒的檔案描述符，若是沒有就緒的檔案描述符該方法也會立即返回；若是阻塞佇列中沒有任務，就呼叫Selector的select(timeout)方法，嘗試在超時時間內取獲取就緒的檔案描述符。

因為現在是在執行NioEventLoopGroup的建立，並沒有Channel的註冊，也就沒有輪詢到任何檔案描述符就緒。
在輪詢結束後，回到run方法，進入default塊：
其中ioRatio是執行IO操作和執行任務佇列的任務用時比率，預設是50。若是ioRatio設定為100，就必須等到tasks阻塞佇列中的所有任務執行完畢才再次進行輪詢；若是小於100，那麼就根據(100 - ioRatio) / ioRatio的比值乘以ioTime計算出的超時時間讓所有任務嘗試在超時時間內執行完畢，若是到達超時時間還沒執行完畢，就在下一輪的輪詢中執行。

processSelectedKeys方法就是獲取Selector輪詢的SelectedKeys結果：

1 private void processSelectedKeys() {
2     if (this.selectedKeys != null) {
3         this.processSelectedKeysOptimized();
4     } else {
5         this.processSelectedKeysPlain(this.selector.selectedKeys());
6     }
7 
8 }

selectedKeys 在openSelector時被初始化過了，若是在openSelector中出現異常selectedKeys才會為null。

processSelectedKeysOptimized方法：

 1 private void processSelectedKeysOptimized() {
 2     for(int i = 0; i < this.selectedKeys.size; ++i) {
 3         SelectionKey k = this.selectedKeys.keys[i];
 4         this.selectedKeys.keys[i] = null;
 5         Object a = k.attachment();
 6         if (a instanceof AbstractNioChannel) {
 7             this.processSelectedKey(k, (AbstractNioChannel)a);
 8         } else {
 9             NioTask<SelectableChannel> task = (NioTask)a;
10             processSelectedKey(k, task);
11         }
12 
13         if (this.needsToSelectAgain) {
14             this.selectedKeys.reset(i + 1);
15             this.selectAgain();
16             i = -1;
17         }
18     }
19 
20 }

這裡就通過遍歷在openSelector中注入進Selector的SelectedKeys，得到SelectionKey 物件。
在這裡可以看到Netty很巧妙地通過SelectionKey的attachment附件，將JDK中的Channel和Netty中的Channel聯絡了起來。
根據得到的附件Channel的型別，執行不同的processSelectedKey方法，去處理IO操作。

processSelectedKey(SelectionKey k, AbstractNioChannel ch)方法：

 1 private void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {
 2     NioUnsafe unsafe = ch.unsafe();
 3     if (!k.isValid()) {
 4         NioEventLoop eventLoop;
 5         try {
 6             eventLoop = ch.eventLoop();
 7         } catch (Throwable var6) {
 8             return;
 9         }
10 
11         if (eventLoop == this && eventLoop != null) {
12             unsafe.close(unsafe.voidPromise());
13         }
14     } else {
15         try {
16             int readyOps = k.readyOps();
17             if ((readyOps & 8) != 0) {
18                 int ops = k.interestOps();
19                 ops &= -9;
20                 k.interestOps(ops);
21                 unsafe.finishConnect();
22             }
23 
24             if ((readyOps & 4) != 0) {
25                 ch.unsafe().forceFlush();
26             }
27 
28             if ((readyOps & 17) != 0 || readyOps == 0) {
29                 unsafe.read();
30             }
31         } catch (CancelledKeyException var7) {
32             unsafe.close(unsafe.voidPromise());
33         }
34 
35     }
36 }

這裡的主要核心就是根據SelectedKey的readyOps值來判斷，處理不同的就緒事件，有如下幾種事件：

1 public static final int OP_READ = 1 << 0;
2 public static final int OP_WRITE = 1 << 2;
3 public static final int OP_CONNECT = 1 << 3;
4 public static final int OP_ACCEPT = 1 << 4;

結合來看上面的判斷就對應：連線就緒、寫就緒、偵聽或者讀就緒，交由Netty的AbstractNioChannel的NioUnsafe去處理不同事件的byte資料，NioUnsafe會將資料再交由ChannelPipeline雙向連結串列去處理。
關於ChannelPipeline會在後續的部落格中詳細介紹。

processSelectedKey(SelectionKey k, NioTask<SelectableChannel> task)這個方法的實現細節需要由使用者實現NioTask<SelectableChannel>介面，就不說了。

回到processSelectedKeys方法，在this.selectedKeys等於null的情況下：

 1 private void processSelectedKeysPlain(Set<SelectionKey> selectedKeys) {
 2     if (!selectedKeys.isEmpty()) {
 3         Iterator i = selectedKeys.iterator();
 4 
 5         while(true) {
 6             SelectionKey k = (SelectionKey)i.next();
 7             Object a = k.attachment();
 8             i.remove();
 9             if (a instanceof AbstractNioChannel) {
10                 this.processSelectedKey(k, (AbstractNioChannel)a);
11             } else {
12                 NioTask<SelectableChannel> task = (NioTask)a;
13                 processSelectedKey(k, task);
14             }
15 
16             if (!i.hasNext()) {
17                 break;
18             }
19 
20             if (this.needsToSelectAgain) {
21                 this.selectAgain();
22                 selectedKeys = this.selector.selectedKeys();
23                 if (selectedKeys.isEmpty()) {
24                     break;
25                 }
26 
27                 i = selectedKeys.iterator();
28             }
29         }
30 
31     }
32 }

這是在openSelector中注入進Selector的SelectedKeys失敗的情況下，直接遍歷Selector本身的SelectedKeys，和processSelectedKeysOptimized沒有差別。

繼續回到run方法，在呼叫完processSelectedKeys方法後，就需要呼叫runAllTasks處理任務佇列中的任務：
runAllTasks（）方法：

 1 protected boolean runAllTasks() {
 2     assert this.inEventLoop();
 3 
 4     boolean ranAtLeastOne = false;
 5 
 6     boolean fetchedAll;
 7     do {
 8         fetchedAll = this.fetchFromScheduledTaskQueue();
 9         if (this.runAllTasksFrom(this.taskQueue)) {
10             ranAtLeastOne = true;
11         }
12     } while(!fetchedAll);
13 
14     if (ranAtLeastOne) {
15         this.lastExecutionTime = ScheduledFutureTask.nanoTime();
16     }
17 
18     this.afterRunningAllTasks();
19     return ranAtLeastOne;
20 }

首先呼叫fetchFromScheduledTaskQueue方法：

 1 private boolean fetchFromScheduledTaskQueue() {
 2     long nanoTime = AbstractScheduledEventExecutor.nanoTime();
 3 
 4     for(Runnable scheduledTask = this.pollScheduledTask(nanoTime); scheduledTask != null; scheduledTask = this.pollScheduledTask(nanoTime)) {
 5         if (!this.taskQueue.offer(scheduledTask)) {
 6             this.scheduledTaskQueue().add((ScheduledFutureTask)scheduledTask);
 7             return false;
 8         }
 9     }
10 
11     return true;
12 }

這裡就是通過pollScheduledTask不斷地從延時任務佇列獲取到期的任務，將到期的任務新增到taskQueue任務佇列中，為上面的runAllTasksFrom執行做準備；若是新增失敗，再把它放進延時任務佇列。

pollScheduledTask方法：

 1 protected final Runnable pollScheduledTask(long nanoTime) {
 2     assert this.inEventLoop();
 3 
 4     Queue<ScheduledFutureTask<?>> scheduledTaskQueue = this.scheduledTaskQueue;
 5     ScheduledFutureTask<?> scheduledTask = scheduledTaskQueue == null ? null : (ScheduledFutureTask)scheduledTaskQueue.peek();
 6     if (scheduledTask == null) {
 7         return null;
 8     } else if (scheduledTask.deadlineNanos() <= nanoTime) {
 9         scheduledTaskQueue.remove();
10         return scheduledTask;
11     } else {
12         return null;
13     }
14 }

從延時任務佇列中獲取隊首的任務scheduledTask，若是scheduledTask的deadlineNanos小於等於nanoTime，說明該任務到期。

回到runAllTasks，將到期了的延時任務放在了任務佇列，由runAllTasksFrom執行這些任務：

 1 protected final boolean runAllTasksFrom(Queue<Runnable> taskQueue) {
 2     Runnable task = pollTaskFrom(taskQueue);
 3     if (task == null) {
 4         return false;
 5     } else {
 6         do {
 7             safeExecute(task);
 8             task = pollTaskFrom(taskQueue);
 9         } while(task != null);
10 
11         return true;
12     }
13 }

不斷地從任務佇列隊首獲取任務，然後執行，直到沒有任務。

pollTaskFrom是獲取隊首任務：

1 protected static Runnable pollTaskFrom(Queue<Runnable> taskQueue) {
2     Runnable task;
3     do {
4         task = (Runnable)taskQueue.poll();
5     } while(task == WAKEUP_TASK);
6 
7     return task;
8 }

其中WAKEUP_TASK，是用來巧妙地控制迴圈：

1 private static final Runnable WAKEUP_TASK = new Runnable() {
2     public void run() {
3     }
4 };


safeExecute是執行任務：

1 protected static void safeExecute(Runnable task) {
2     try {
3         task.run();
4     } catch (Throwable var2) {
5         logger.warn("A task raised an exception. Task: {}", task, var2);
6     }
7 
8 }

實際上就是執行Runnable 的run方法。

繼續回到runAllTasks方法，當所有到期任務執行完畢後，根據ranAtLeastOne判斷是否需要修改最後一次執行時間lastExecutionTime，最後呼叫afterRunningAllTasks方法，該方法是在SingleThreadEventLoop中實現的：

1 protected void afterRunningAllTasks() {
2     this.runAllTasksFrom(this.tailTasks);
3 }

這裡就僅僅執行了tailTasks佇列中的任務。runAllTasks到這裡執行完畢。

再來看看runAllTasks(timeoutNanos)方法：

 1 protected boolean runAllTasks(long timeoutNanos) {
 2     this.fetchFromScheduledTaskQueue();
 3     Runnable task = this.pollTask();
 4     if (task == null) {
 5         this.afterRunningAllTasks();
 6         return false;
 7     } else {
 8         long deadline = ScheduledFutureTask.nanoTime() + timeoutNanos;
 9         long runTasks = 0L;
10 
11         long lastExecutionTime;
12         while(true) {
13             safeExecute(task);
14             ++runTasks;
15             if ((runTasks & 63L) == 0L) {
16                 lastExecutionTime = ScheduledFutureTask.nanoTime();
17                 if (lastExecutionTime >= deadline) {
18                     break;
19                 }
20             }
21 
22             task = this.pollTask();
23             if (task == null) {
24                 lastExecutionTime = ScheduledFutureTask.nanoTime();
25                 break;
26             }
27         }
28 
29         this.afterRunningAllTasks();
30         this.lastExecutionTime = lastExecutionTime;
31         return true;
32     }
33 }

這個方法前面的runAllTasks方法類似，先通過fetchFromScheduledTaskQueue將所有到期了的延時任務放在taskQueue中，然後不斷從taskQueue隊首獲取任務，但是，若是執行到了到超過了63個任務，判斷是否達到了超時時間deadline，若是達到結束迴圈，留著下次執行，反之繼續迴圈執行任務。

 

回到run方法，在輪詢完畢，並且執行完任務後，通過isShuttingDown判斷當前狀態，在之前的CAS操作中，state已經變為了3，所以isShuttingDown成立，就需要呼叫closeAll方法

 1 private void closeAll() {
 2     this.selectAgain();
 3     Set<SelectionKey> keys = this.selector.keys();
 4     Collection<AbstractNioChannel> channels = new ArrayList(keys.size());
 5     Iterator var3 = keys.iterator();
 6 
 7     while(var3.hasNext()) {
 8         SelectionKey k = (SelectionKey)var3.next();
 9         Object a = k.attachment();
10         if (a instanceof AbstractNioChannel) {
11             channels.add((AbstractNioChannel)a);
12         } else {
13             k.cancel();
14             NioTask<SelectableChannel> task = (NioTask)a;
15             invokeChannelUnregistered(task, k, (Throwable)null);
16         }
17     }
18 
19     var3 = channels.iterator();
20 
21     while(var3.hasNext()) {
22         AbstractNioChannel ch = (AbstractNioChannel)var3.next();
23         ch.unsafe().close(ch.unsafe().voidPromise());
24     }
25 
26 }

在這裡首先呼叫selectAgain進行一次輪詢：

 1 private void selectAgain() {
 2     this.needsToSelectAgain = false;
 3 
 4     try {
 5         this.selector.selectNow();
 6     } catch (Throwable var2) {
 7         logger.warn("Failed to update SelectionKeys.", var2);
 8     }
 9 
10 }

通過這次的輪詢，將當前仍有事件就緒的JDK的SelectionKey中繫結的Netty的Channel新增到channels集合中，遍歷這個集合，通過unsafe的close方法關閉Netty的Channel。

之後呼叫confirmShutdown方法：

 1 protected boolean confirmShutdown() {
 2     if (!this.isShuttingDown()) {
 3         return false;
 4     } else if (!this.inEventLoop()) {
 5         throw new IllegalStateException("must be invoked from an event loop");
 6     } else {
 7         this.cancelScheduledTasks();
 8         if (this.gracefulShutdownStartTime == 0L) {
 9             this.gracefulShutdownStartTime = ScheduledFutureTask.nanoTime();
10         }
11 
12         if (!this.runAllTasks() && !this.runShutdownHooks()) {
13             long nanoTime = ScheduledFutureTask.nanoTime();
14             if (!this.isShutdown() && nanoTime - this.gracefulShutdownStartTime <= this.gracefulShutdownTimeout) {
15                 if (nanoTime - this.lastExecutionTime <= this.gracefulShutdownQuietPeriod) {
16                     this.wakeup(true);
17 
18                     try {
19                         Thread.sleep(100L);
20                     } catch (InterruptedException var4) {
21                         ;
22                     }
23 
24                     return false;
25                 } else {
26                     return true;
27                 }
28             } else {
29                 return true;
30             }
31         } else if (this.isShutdown()) {
32             return true;
33         } else if (this.gracefulShutdownQuietPeriod == 0L) {
34             return true;
35         } else {
36             this.wakeup(true);
37             return false;
38         }
39     }
40 }

首先呼叫cancelScheduledTasks，取消所有的延時任務：

 1 protected void cancelScheduledTasks() {
 2     assert this.inEventLoop();
 3 
 4     PriorityQueue<ScheduledFutureTask<?>> scheduledTaskQueue = this.scheduledTaskQueue;
 5     if (!isNullOrEmpty(scheduledTaskQueue)) {
 6         ScheduledFutureTask<?>[] scheduledTasks = (ScheduledFutureTask[])scheduledTaskQueue.toArray(new ScheduledFutureTask[scheduledTaskQueue.size()]);
 7         ScheduledFutureTask[] var3 = scheduledTasks;
 8         int var4 = scheduledTasks.length;
 9 
10         for(int var5 = 0; var5 < var4; ++var5) {
11             ScheduledFutureTask<?> task = var3[var5];
12             task.cancelWithoutRemove(false);
13         }
14 
15         scheduledTaskQueue.clearIgnoringIndexes();
16     }
17 }

遍歷scheduledTasks這個延時任務對立中所有的任務，通過cancelWithoutRemove將該任務取消。

至此輪詢的整個生命週期完成。

回到SingleThreadEventExecutor的doStartThread方法，在run方法執行完畢後，說明Selector輪詢結束，呼叫SingleThreadEventExecutor.this.cleanup()方法關閉Selector：

1 protected void cleanup() {
2     try {
3         this.selector.close();
4     } catch (IOException var2) {
5         logger.warn("Failed to close a selector.", var2);
6     }
7 
8 }

這次終於可以回到MultithreadEventExecutorGroup的構造，在children建立完畢後，用chooserFactory根據children的大小建立chooser，前面說過。

然後產生terminationListener非同步中斷監聽物件，給每個NioEventLoop設定中斷監聽，然後對children進行了備份處理，通過readonlyChildren儲存。


至此NioEventLoopGroup的建立全部結束。

 

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