C#内部关于绑定事件Event的线程安全
private EventHandler _FieldsChanged;
public event EventHandler FieldsChanged
{
add
{
EventHandler handler2;
EventHandler fieldsChanged = this._FieldsChanged;
do
{
handler2 = fieldsChanged;
EventHandler handler3 = (EventHandler)Delegate.Combine(handler2, value);
fieldsChanged = Interlocked.CompareExchange<EventHandler>(ref this._FieldsChanged, handler3, handler2);
}
while (fieldsChanged != handler2);
}
remove
{
EventHandler handler2;
EventHandler fieldsChanged = this._FieldsChanged;
do
{
handler2 = fieldsChanged;
EventHandler handler3 = (EventHandler)Delegate.Remove(handler2, value);
fieldsChanged = Interlocked.CompareExchange<EventHandler>(ref this._FieldsChanged, handler3, handler2);
}
while (fieldsChanged != handler2);
}
}
下面是我最后的理解，也许是错的：
EventHandler handler2;
EventHandler fieldsChanged = this._FieldsChanged;
do
{
// 两个本地变量都保存着_FieldsChanged的本地引用
handler2 = fieldsChanged;
// 事件绑定。这是唯一一句业务代码
EventHandler handler3 = (EventHandler)Delegate.Combine(handler2, value);
// 如果_FieldsChanged等于handler2，就执行_FieldsChanged=handler3，这里是原子操作，线程安全
// 如果不等，很明显，有线程冲突存在，数据被别的线程修改过了，这里返回_FieldsChanged到fieldsChanged中去
fieldsChanged = Interlocked.CompareExchange<EventHandler>(ref this._FieldsChanged, handler3, handler2);
}
while (fieldsChanged != handler2);
// 实际上，整个过程，如果不考虑线程安全，可以直接这么写
_FieldsChanged = (EventHandler)Delegate.Combine(_FieldsChanged, value);
// 这段代码的精妙之处就在于这个线程安全，如果Combine后，别的线程也进来，那就出现了数据丢失
// 当然，常规做法可以是Lock住这段代码，但是，线程冲突的可行性不到1%，为此损失了99%的性能，悲哀呀！
补充：综合编程 , 安全编程 ,
