Everyone knows that in Silverlight all wcf service calls are asynchronous. But what can we say about the timing of the requests? For the following code, is it always true that "Hello A" will be received by the server before "Hello B"?
ServiceClient proxy = new ServiceClient();
ServiceClient proxy2 = new ServiceClient();
proxy.SayHelloAsync("Hello A");
proxy2.SayHelloAsync("Hello B");
I ran the code repeatedly and the server always received "Hello A" first. Was it just by luck?
Yes, if you have two async calls, you can have any of them finishing first.
If you need to wait any to finish, you should take a look on WaitHandle
It was just luck. I've run almost exactly the same test, and had them finish in a variety of diferent orders. This is especially true in real-world scenarios, where you might have a large number of outstanding calls going on simultaneously (for instance, in a chat application). If you need call A to finish before call B, you'll need to chain them in some fashion, and none of the mechanisms for doing so are very clean. The recommendation to use a WaitHandle of some sort can be dangerous, in my experience. Your mileage may vary, but what I've found is that if you're not very careful, using a WaitHandle to manage the timing of WCF calls can stop critical threads from functioning. It's better, though more complicated, to make your call to "B" from a method that's called when "A" is completed.