WCF异步服务器端处理

Question

I need to create a WCF service that accept client request and internally connect to a remote machine to do the job. The remote machine has a very good processing capacity but not a good processing speed. This means that can process for example 1000 transactions per second but each transaction can take 1 second, so the only way is to have 1.000 concurrent transactions running in the same second.

The remote machine handle very well this situation, but I am worried about WCF, if each transaction is internally (I dont care the client side model (sync or async)) waiting and blocking a thread inside the server for 1 or 2 seconds this could represent a 1.000 working threads live and that could be very dangerous, or maybe WCF use the thread pool and just put others request in a waiting state and that is bad too.

So, my question is about the possibility of processing the request asynchronously in the server side. So the transaction flow must be like this:

1. Cliente initialize a request (in his side is a synchronous request)
2. Server recive the request and put this request in a Transaction Queue and release the thread
3. When the task finish, the server complete the request sending HTTP 200 and result to the client.

Thanks!

Answer 1

You can use the WCF async pattern to achieve this. When you mark your operationContract with the async attribute, WCF uses the IO CompletionPort threads to process the request.

so it works the following way. Your request is handleded by a thread in IIS and once it reaches WCF it goes to sleep and then the IO CompletionPort thread takes the request process it and then sends back the response to the IIS thread that returns the response to the client.

IO CompletionPort threads are much faster and also doesnt slow down your server in terms of performance or resources.

Look at the following link for more information.

Answer 2

In the middle tier server, declare and implement your operation according to the async pattern:

[OperationContract(Action = "DoSomething", AsyncPattern = true)]
IAsyncResult BeginDoSomething(AsyncCallback asyncCallback, object asyncState);
void EndDoSomething(IAsyncResult iar);

The implementation of BeginDoSomething should send the request to the remote machine and return immediately. When you call DoSomething() on the client side, WCF in the middle tier will realize that this operation is implemented as an asynchronous Begin/End pair and invoke it appropriately.