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Editorial Team
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Asked: 2026-06-13T12:19:53+00:00

I am trying to create a WCF service that supports asynchronous calls. I followed

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I am trying to create a WCF service that supports asynchronous calls. I followed all samples and tutorials I could find, and all of them have the customary pattern of one synchronous method, and the async Begin and End such as:

[OperationContract(AsyncPattern = false)]
string GetData(int value);

[OperationContract(AsyncPattern = true)]
IAsyncResult BeginGetData(int value, AsyncCallback callback, object asyncState);

string EndGetData(IAsyncResult result);

However, only the synchronous GetData gets called, no matter what I do on the client side. Fiddler tells me that the message is always the same:

 <s:Envelope
 xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Body><GetData
 xmlns="http://tempuri.org/"><value>0</value></GetData></s:Body></s:Envelope>

When I remove the synchronous GetData interface, the async method now is properly called.

Is this normal behavior? Is there anything else I should do to support sync and async versions of a method?

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1 Answer

  1. Editorial Team

    This is a common misconception. You assume that you need to make the server asynchronous in order for the client to be able to make async calls. This is not true. Server and client are 100% independent. They are separated by a binary wire protocol.

    The message that you see in Fiddler is always the same because SOAP does not know anything about sync or async. At the SOAP level your decision does not manifest itself. For that reason the client cannot observe your server-side decision, either.

    This means you can just make the server synchronous in still have a truely async client, or the other way around.

    In any case, you should only implement one pattern on the server: Either sync or async. Never both. Get rid of one of your implementations. From a functional standpoint it doesn’t matter which one stays.

    I’m pulling up important information from the comments here:

    It is hard to fit an explanation about when to use server-side async
    into this comment box. In short, don’t use it on the server by
    default. Use it if special circumstances make it attractive or
    necessary.

    On a meta-level let me point out that async IO has become
    a fad that should not be followed lightly. The community is in a very
    unfortunate state of misinformation about this right now.

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