C＃的活动实施（第VS反射镜） [英] The C# events implementation (articles vs reflector)

问题描述

public class EventsType
{
    public event EventHandler<MyEventArgs<Object>> NewEvent;

    public void SmthHappened(string data)
    {
        MyEventArgs<Object> eventArgs = new MyEventArgs<Object>(data);
        OnNewEvent(eventArgs);
    }

    private void OnNewEvent(MyEventArgs<Object> eventArgs)
    {
        EventHandler<MyEventArgs<Object>> tempEvent = NewEvent;

        if (tempEvent != null)
        {                
            tempEvent(this, eventArgs);
        }
    }
}

我预计，C＃编译器将翻译NewEvent是这样的：

I expected that the C# compiler will translate the NewEvent like this:

private EventHandler<MyEventArgs<object>> _newEvent;

public event EventHandler<MyEventArgs<object>> NewEvent
{
    [MethodImpl(MethodImplOptions.Synchronized)]
    add
    {
    _newEvent = (EventHandler<MyEventArgs<object>>)Delegate.Combine(_newEvent, value);
    }
    [MethodImpl(MethodImplOptions.Synchronized)]
    remove
    {
    _newEvent = (EventHandler<MyEventArgs<object>>)Delegate.Remove(_newEvent, value);
    }
}

，而反射器是说，它是这样实现

, but the Reflector says that it is implemented this way:

public event EventHandler<MyEventArgs<object>> NewEvent
{
    add
    {
        EventHandler<MyEventArgs<object>> handler2;
        EventHandler<MyEventArgs<object>> newEvent = this.NewEvent;
        do
        {
            handler2 = newEvent;
            EventHandler<MyEventArgs<object>> handler3 = (EventHandler<MyEventArgs<object>>) Delegate.Combine(handler2, value);
            newEvent = Interlocked.CompareExchange<EventHandler<MyEventArgs<object>>>(ref this.NewEvent, handler3, handler2);
        }
        while (newEvent != handler2);
    }
    remove
    {
        EventHandler<MyEventArgs<object>> handler2;
        EventHandler<MyEventArgs<object>> newEvent = this.NewEvent;
        do
        {
            handler2 = newEvent;
            EventHandler<MyEventArgs<object>> handler3 = (EventHandler<MyEventArgs<object>>) Delegate.Remove(handler2, value);
            newEvent = Interlocked.CompareExchange<EventHandler<MyEventArgs<object>>>(ref this.NewEvent, handler3, handler2);
        }
        while (newEvent != handler2);
    }
}

请，SMB解释我为什么会这样？

Please, smb explain me why is it so?

推荐答案

烨：的 C＃4已经在这方面作出一些变化，基本上是这样。这使得它线程安全的无锁。这不是唯一的改变 - 这也改变了类中如何引用到现场般的事件解析：+ =和 - =现在通过添加和删除位，而不是直接与背领域工作

Yup: C# 4 has made some changes in this area, basically. It makes it thread-safe without locking. That's not the only change - it also changes how references to field-like events within the class are resolved: += and -= now go through the "add" and "remove" bits rather than working directly with the backing field.

请注意，这一变化将影响与C＃编译器4编译代码，甚至对老年人框架;也有变为锁定其中的只有的影响对.NET 4编译的代码，因为它使用的新方法（的Monitor.TryEnter(object，出布尔） ）。

Note that this change affects code compiled with the C# 4 compiler even against older frameworks; there are also changes to locking which only affect code compiled against .NET 4, as it uses a new method (Monitor.TryEnter(object, out bool)).

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