S3168 — "async" methods should not return "void"

Why is this an issue?

An async method with a void return type does not follow the task asynchronous programming (TAP) model since the return type should be Task or Task<TResult>

Doing so prevents control over the asynchronous execution, such as:

• waiting for the execution to complete
• catching any exception that might occur during execution
• testing execution behavior

Exceptions

• Methods implementing an interface
• Methods overriding a base class method
• Virtual methods
• Methods with the EventHandler delegate signature Using void for EventHandler is compliant with the TAP model.

  
  public async void button1_Click(object sender, EventArgs e)
  {
    await DoSomethingAsync();
  }
  

• Methods name matching On[A-Z]\w* pattern Some frameworks may not use the same EventHandler method signature.

  
  public async void OnClick(EventContext data)
  {
    await DoSomethingAsync();
  }
  

How to fix it

Update the return type of the method from void to Task.

Code examples

Noncompliant code example

private async void ThrowExceptionAsync() // Noncompliant: async method return type is 'void'
{
  throw new InvalidOperationException();
}

public void Method()
{
  try
  {
    ThrowExceptionAsync();
  }
  catch (Exception)
  {
    // The exception is never caught here
    throw;
  }
}

Compliant solution

private async Task ThrowExceptionAsync() // Compliant: async method return type is 'Task'
{
  throw new InvalidOperationException();
}

public async Task Method()
{
  try
  {
    await ThrowExceptionAsync();
  }
  catch (Exception)
  {
    // The exception is caught here
    throw;
  }
}

Resources

Documentation

• Microsoft Learn - async (C# Reference)
• Microsoft Learn - Asynchronous programming
• Microsoft Learn - Task asynchronous programming model
• Microsoft Learn - Task Class
• Microsoft Learn - Task<TResult> Class
• Microsoft Learn - EventHandler Delegate