反编译组件 - 寻常code

问题描述

我反编译使用ILSpy的组件，特别是一级了我的注意：

I decompiled an assembly using ILSpy, and one class in particular got my attention:

public class CustomTextStream : NetworkStream
{
    private EventHandler<CustomEventArgs> someEvent;
    public event EventHandler<CustomEventArgs> SomePublicEvent
    {
        add
        {
            EventHandler<CustomEventArgs> eventHandler = this.someEvent;
            EventHandler<CustomEventArgs> eventHandler2;
            do
            {
                eventHandler2 = eventHandler;
                EventHandler<CustomEventArgs> value2 =
                    (EventHandler<CustomEventArgs>)Delegate.Combine(eventHandler2, value);
                eventHandler =
                    Interlocked.CompareExchange<EventHandler<CustomEventArgs>>(
                    ref this.someEvent, value2, eventHandler2);
            }
            while (eventHandler != eventHandler2);
        }
        remove
        {
            // similar stuff...
        }
    }
}

此外，在code，恍如私人委托来触发一个真实的事件：

Further in the code, seems like private delegate is used to fire an actual event:

if (something != null && somethingElse != 0)
{
    this.someEvent(this, new CustomEventArgs(someArg));
}

这样的问题：一个人能猜到可能是这背后的自定义访问的想法，假设一些编译/反编译神奇未能成行？我没有太多熟悉的白细胞介素，顺便说一句...

The question: Can someone guess what could be the idea behind this custom accessors, assuming that some "compile/decompile magic" didn't take place? I'm not much familiar with IL, btw...

（边注：该应用程序是多线程的，并利用网络，很明显）

(Side note: the application is multi-threaded and utilizes networking, obviously.)

推荐答案

这是由编译器生成一个新的事件处理程序code。它在C＃4（C＃3的版本是不同的）

This is a new event handler code generated by compiler. It was introduced in C# 4 (C# 3 version was different)

Interlocked.CompareExchange比较第一个参数与第三，如果他们是平等的，替换第二个第一个参数。这是一个线程安全的操作。循环用于为变量赋值时eventHandler2和检查之前之后，另一个线程改变了这一委托的情况。在这种情况下，Interlocked.CompareExchange不执行交换，循环条件不计算为真，下一个尝试。

Interlocked.CompareExchange compares first argument with third, and if they are equal, replaces first argument with second. This is a thread-safe operation. Loop is used for a case when after assigning a variable eventHandler2 and before check, another thread changes this delegate. In this case, Interlocked.CompareExchange does not perform exchange, loop condition does not evaluate to true and next attempt is made.

C＃3的事件处理程序生成的简单code：

C# 3 generated simple code in event handlers:

add { lock(this) { changed = changed + value; } }

其中有较低的性能，并可能引入死锁。

Which had lower performance and could introduce deadlocks.

有关于这个问题的一个伟大的系列文章：

There is a great series of articles on this subject:

Events得到一个小大修在C＃4

Events得到一个小大修在C＃4，第II部分

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