3-2-1.Netty源码:避免空轮循的bug

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 //NioEventLoop.java
//重新构造个selector
private void rebuildSelector0() {
  final Selector oldSelector = selector;
  final SelectorTuple newSelectorTuple;
  ...
  try {
    newSelectorTuple = openSelector();
  }
  ...
  
  //获取这个selector上所有注册的channelkey
  for (SelectionKey key : oldSelector.keys()) {
    Object a = key.attachment();
    try {
        if (!key.isValid() || key.channel().keyFor(newSelectorTuple.unwrappedSelector) != null) {
            continue;
        }
        //这个select上所有感兴趣事件
        int interestOps = key.interestOps();
        key.cancel();
        
        SelectionKey newKey = key.channel().register(newSelectorTuple.unwrappedSelector, interestOps, a);
        if (a instanceof AbstractNioChannel) {
            ((AbstractNioChannel) a).selectionKey = newKey;
        }
        nChannels++;
    } catch (Exception e) {
        ...
    }
  }

  selector = newSelectorTuple.selector;
  unwrappedSelector = newSelectorTuple.unwrappedSelector;

  try {
      // time to close the old selector as everything else is registered to the new one
      oldSelector.close();
  } 
  ...
}

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 //NioEventLoop.java
 private SelectorTuple openSelector() {
    final Selector unwrappedSelector;
    
    try {
        unwrappedSelector = provider.openSelector();
    } catch (IOException e) {
        throw new ChannelException("failed to open a new selector", e);
    }
    if (DISABLE_KEYSET_OPTIMIZATION) {
        return new SelectorTuple(unwrappedSelector);
    }

    Object maybeSelectorImplClass = AccessController.doPrivileged(new PrivilegedAction<Object>() {
        @Override
        public Object run() {
            try {
                return Class.forName(
                        "sun.nio.ch.SelectorImpl",
                        false,
                        PlatformDependent.getSystemClassLoader());
            } catch (Throwable cause) {
                return cause;
            }
        }
    });

    if (!(maybeSelectorImplClass instanceof Class) ||
            !((Class<?>) maybeSelectorImplClass).isAssignableFrom(unwrappedSelector.getClass())) {
        if (maybeSelectorImplClass instanceof Throwable) {
            Throwable t = (Throwable) maybeSelectorImplClass;
            logger.trace("failed to instrument a special java.util.Set into: {}", unwrappedSelector, t);
        }
        return new SelectorTuple(unwrappedSelector);
    }

    final Class<?> selectorImplClass = (Class<?>) maybeSelectorImplClass;

    final SelectedSelectionKeySet selectedKeySet = new SelectedSelectionKeySet();

    Object maybeException = AccessController.doPrivileged(new PrivilegedAction<Object>() {
        @Override
        public Object run() {
            try {
                
                Field selectedKeysField = selectorImplClass.getDeclaredField("selectedKeys");
                Field publicSelectedKeysField = selectorImplClass.getDeclaredField("publicSelectedKeys");

                if (PlatformDependent.javaVersion() >= 9 && PlatformDependent.hasUnsafe()) {
                    long selectedKeysFieldOffset = PlatformDependent.objectFieldOffset(selectedKeysField);
                    long publicSelectedKeysFieldOffset = PlatformDependent.objectFieldOffset(publicSelectedKeysField);

                    if (selectedKeysFieldOffset != -1 && publicSelectedKeysFieldOffset != -1) {
                        PlatformDependent.putObject(
                                unwrappedSelector, selectedKeysFieldOffset, selectedKeySet);
                        PlatformDependent.putObject(
                                unwrappedSelector, publicSelectedKeysFieldOffset, selectedKeySet);
                        return null;
                    }
                }
                
                Throwable cause = ReflectionUtil.trySetAccessible(selectedKeysField, true);
                if (cause != null) {
                    return cause;
                }
                cause = ReflectionUtil.trySetAccessible(publicSelectedKeysField, true);
                if (cause != null) {
                    return cause;
                }
                
                selectedKeysField.set(unwrappedSelector, selectedKeySet);
                publicSelectedKeysField.set(unwrappedSelector, selectedKeySet);
                return null;
            } catch (NoSuchFieldException e) {
                return e;
            } catch (IllegalAccessException e) {
                return e;
            }
        }
    });

    if (maybeException instanceof Exception) {
        selectedKeys = null;
        Exception e = (Exception) maybeException;
        logger.trace("failed to instrument a special java.util.Set into: {}", unwrappedSelector, e);
        return new SelectorTuple(unwrappedSelector);
    }
    selectedKeys = selectedKeySet;
    logger.trace("instrumented a special java.util.Set into: {}", unwrappedSelector);
    return new SelectorTuple(unwrappedSelector,
            new SelectedSelectionKeySetSelector(unwrappedSelector, selectedKeySet));
}