Lately I’ve been trying to include a call to a REST service using the WebAPI client to a library already used from inside both an ASP.NET page and a WCF service.

The problem with mixing sync and async

Of course I started with an async/await code:

HttpResponseMessage response = await client.PostAsJsonAsync(GetUpdateUri(), payload);

Unfortunately both consumers were synchronous, so I had to wait for the async to complete before going on with the execution: so I did something that proved to be wrong (the following methods calls the line above):


Deadlock: this never completes as ASP.NET is blocking the context thread waiting for the webapi call to complete, which waits for the thread to be free so it can complete.

How to make a synchronous web api call

What I should have done, instead, would have been to change the ASP.NET page to be an async page (using the Page.RegisterAyncTask) and also change the WCF service to be async, and use the async/await from top to bottom as is best practice. In my case it was too complex and would have required touching code developer by others and already working, so I simply avoided starting the “async chain”:

HttpResponseMessage response = client.PostAsJsonAsync(GetUpdateUri(), payload).Result;

Async/Await resources

On the other end I realized I don’t know enough about the async way of coding, and I spent some time reading some good references, mostly by “async-guru” Stephen Cleary.