Introduction

For asynchronous WCF calls, the preferred modern style is the task-based async pattern with Task and await. Older patterns such as Begin and End methods or event-based async proxies still exist in older codebases, but they are harder to compose and maintain.

The main reason to prefer task-based async is not fashion. It gives cleaner error handling, easier composition, and code that reads like normal control flow instead of nested callbacks and manual completion bookkeeping.

Prefer Task-Based Service Methods

If you control the service contract or client generation, aim for async methods that return Task or Task<T>.

1using System.ServiceModel;
2using System.Threading.Tasks;
3
4[ServiceContract]
5public interface IOrderService
6{
7    [OperationContract]
8    Task<string> SubmitOrderAsync(string orderId);
9}

On the client side, consume it with await:

1public async Task RunAsync(IOrderService client)
2{
3    string result = await client.SubmitOrderAsync("A-1001");
4    Console.WriteLine(result);
5}

This is the style that fits naturally with modern .NET code. It is easier to read, and exceptions propagate in a way that matches the rest of async and await.

Why Older Patterns Are Less Attractive

Classic WCF code often exposed the Asynchronous Programming Model, sometimes called Begin and End.

IAsyncResult pending = client.BeginSubmitOrder("A-1001", null, null);
string result = client.EndSubmitOrder(pending);

This works, but it is awkward to compose. If you need timeouts, retries, cancellation coordination, or multiple concurrent calls, the code becomes harder to reason about.

Event-based async patterns have a similar problem. They split success and failure handling into callback-style code that is more error-prone than a straightforward await.

Do Not Block on Async Calls

If you adopt asynchronous WCF calls, keep the whole path asynchronous where possible. Blocking on .Result or .Wait() defeats much of the benefit and can cause deadlocks in UI or request-thread environments.

1public async Task<string> GetOrderAsync(IOrderService client, string id)
2{
3    return await client.SubmitOrderAsync(id);
4}

That is usually better than this:

string value = client.SubmitOrderAsync("A-1001").Result;

Even when it seems to work, blocking code is more fragile under real synchronization contexts.

Think About Timeouts and Faulted Channels

Asynchronous syntax does not remove the normal WCF concerns. You still need to think about timeouts, channel faults, and exception handling.

1public async Task<string> SafeCallAsync(IOrderService client, string id)
2{
3    try
4    {
5        return await client.SubmitOrderAsync(id);
6    }
7    catch (TimeoutException ex)
8    {
9        Console.WriteLine($"Timed out: {ex.Message}");
10        throw;
11    }
12    catch (CommunicationException ex)
13    {
14        Console.WriteLine($"Communication failed: {ex.Message}");
15        throw;
16    }
17}

If a channel faults, you usually should not keep using it. Recreate the client or channel rather than repeatedly calling through a broken communication object.

Wrapping Legacy Async APIs

In older systems, you may have a generated proxy that exposes Begin and End methods but not task-based methods. In that case, wrapping the legacy API into a Task can be a reasonable transition strategy.

The important point is that your application code should still prefer a task-based boundary. That keeps the legacy complexity isolated in one place instead of leaking across the whole codebase.

Common Pitfalls

• Continuing to use Begin and End everywhere even though the rest of the application uses async and await.
• Blocking on .Result or .Wait() and creating deadlock-prone code paths.
• Assuming async syntax alone solves WCF timeout and fault-handling concerns.
• Reusing a faulted channel after a communication failure.
• Mixing multiple async styles in the same code path and making error handling inconsistent.

Summary

• Prefer task-based async WCF calls with Task and await.
• Older Begin and End or event-based patterns still work, but they are harder to maintain.
• Keep the calling code asynchronous instead of blocking on task results.
• Handle timeouts and communication faults explicitly.
• If legacy proxies expose older async patterns, wrap them so the rest of your code can stay task-based.