Question

I’m new to both WCF and threading, so please bear with me. I have a WCF service set up. The service has multiple threads, all of which act upon a single array. This works without a problem so far. However, this service has a method, which, when called, will return the array. My questions:

1. The array is serialized when it is transferred to the client by WCF. Is this a thread safe operation? In other words, can I count on WCF to block all threads from accessing this array while it’s being serialized?

2. If I can’t count on WCF to do this, then how can I implement it manually? I don’t really understand how WCF would facilitate this since the serialization happens after I return from my method call. How can I guarantee a thread will not modify the array after it’s been returned by my method but before WCF serializes it?

Answer 1

No, the WCF runtime won’t lock the data for you. Even if it would, it can’t keep you of from accessing the array in another thread.

I think the only possibilty to get this threadsafe is to copy the data you return in a private variable before leaving the function:

string[] Servicemethod()
{
  lock(myLock)
  {
      byte[] localCopy = new byte[myData.Length]; 
      Array.Copy(myData, localCopy, myData.Length);
      return localCopy;
  }
}

EDIT

If its not an option to copy large datastructures another option might be to not return an array but an instance of a custom class which implements ISerializable.

That way you can write a threadsafe serialization of your data yourself.

But before doing that, i would measure the impact of the extra copy.