Async Pitfalls: void vs Task, ConfigureAwait

Syntax

async Task MethodName() { } // not async void

Examples

// Avoid: exceptions here cannot be caught by the caller
async void RiskyOperation()
{
    throw new InvalidOperationException("This will crash unpredictably");
}

// Prefer: exceptions surface normally when awaited
async Task SaferOperationAsync()
{
    throw new InvalidOperationException("This can be caught properly");
}

try
{
    await SaferOperationAsync();
}
catch (InvalidOperationException e)
{
    Console.WriteLine($"Caught: {e.Message}");
}

// Risky in UI/ASP.NET (classic) contexts - can deadlock
// int result = SomeAsyncMethod().Result;

// Safe: await it properly, all the way up the call chain
async Task<int> GetResultSafelyAsync()
{
    return await SomeAsyncMethod();
}

async Task<int> SomeAsyncMethod()
{
    await Task.Delay(100);
    return 42;
}

public async Task<string> LoadDataAsync()
{
    // In library code (not top-level app code), this avoids resuming
    // on the original context unnecessarily
    await Task.Delay(500).ConfigureAwait(false);
    return "data";
}

Best practices

• Avoid async void entirely except for top-level UI event handlers, which are required to return void by their delegate signature
• Never call .Result or .Wait() on a Task from synchronous code that has a synchronization context - await all the way up the call chain instead
• Use ConfigureAwait(false) in reusable library code that does not need to resume on a specific UI or request context, but skip it in top-level application/UI code where the context often matters
• Wrap awaited calls in try/catch to handle exceptions properly - unlike async void, an awaited async Task lets exceptions propagate normally to the caller

At a glance

Purpose

Applications on the .NET platform

File extension

.cs

Runs in

.NET runtime

Usually used with

.NET SDK and libraries

Specifications & further reading

• C# language reference

Related C# documentation