Question

公共类EventsType { 公共事件EventHandler＆gt; 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);
        }
    }
}

我希望C＃编译器能像这样翻译NewEvent：

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);
    }
}

，但Reflector表示它是以这种方式实现的：

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);
    }
}

拜托，smb解释我为什么会这样？

Answer 1

是的，基本上是C# 4 has made some changes in this area。它使其无需锁定即可保证线程安全。这不是唯一的变化 - 它还会改变对类中类字段事件的引用的解决方式：+ =和 - =现在通过“添加”和“删除”位而不是直接使用支持字段。

请注意，此更改会影响使用C＃4编译器编译的代码，即使是旧框架也是如此;锁定也发生了变化仅影响针对.NET 4编译的代码，因为它使用了一种新方法（Monitor.TryEnter(object, out bool)）。

Answer 2

这个问题的答案在很大程度上取决于您使用的版本。多年来它经过了很多改进。见http://blogs.msdn.com/b/cburrows/archive/2010/03/05/events-get-a-little-overhaul-in-c-4-part-i-locks.aspx

Answer 3

您期望的是一个简单的非线程安全实现。像事件语法这样的字段总是提供线程安全语法（因此是反射器版本）。请参阅此artcile以了解事件＆amp;他们是如何实施的。

C＃事件实现（文章与反射器）

3 个答案: