多线程和委托调用

Question

Supose I have a method that runs in several threads and a delegate.

public delegate void Del(string threadId, string value, ref string result);

public event Del Analyze= null;  // The external world can plug in a method


// this method runs simultanioulsy in several threads
private void threaded()
{
   string s= null;
   // yadayada s gets a value and I want a result back
   // from the external world
   string result = null;

   is (Analyze != null)
      Analyze("some thread id", s, ref result);
}

I am aware that the method used as an event must synchronize in order to be thread safe, etc, but what happens if

Analyze("some thread id", s, ref result);

gets called at the same time? Is that OK? Or do I need to synchronize Analyze like:

lock(someobj)
{
    Analyze("some thread id", s, ref result);
}

So the question is more like: is an "event" like this thread safe from the point of view of the calling class (I know I must guarantee the thread safety of plugged in method)

Answer 1

The class that raises the event can do so simultaneously on multiple threads if that is the behaviour you want. An "event" is like a list of methods that get called in order.

Each separate thread will be raising a separate event and as you say it is the event handlers duty to deal with the possibility of being called on multiple threads by separate events if that is how that event is designed.

Thread safety from the point of view of the class raising the event is not a good description of what you are asking because you are mixing terms. Thread safety is about whether a class can be called to do its work safely in a multithreaded situation, that those threads don't interact via the classes state.