Catch exception thrown from an async lambda

Question

I am trying to write a method that tries to execute an action but swallows any exceptions that are raised.

My first attempt is the following:

public static void SafeExecute(Action actionThatMayThrowException) {
    try {
        actionThatMayThrowException();
    } catch {
        // noop
    }
}

Which works when called with a synchronous action:

SafeExecute(() => { 
    throw new Exception(); 
});

However fails when called with an asynchronous action:

SafeExecute(async () => { 
    await Task.FromResult(0);
    throw new Exception(); 
});

Is is possible to write a method that handles both scenarios?

Answer 1

To correctly handle async delegates you shouldn't use Action (this will cause the lambda expression to be async void which is dangerous and should be avoided), you should use Func<Task> to be able to await it:

public static async Task SafeExecute(Func<Task> asyncActionThatMayThrowException)
{
    try
    {
        await asyncActionThatMayThrowException();
    }
    catch
    {
        // noop
    }
}

This will solve the async case, but not the synchronous case. You can't do both with a single method. To do that you would need a different method, but it can still call the async one to enable reuse:

private static readonly Task<object> _completedTask = Task.FromResult<object>(null);

public static void SafeExecute(Action actionThatMayThrowException)
{
    SafeExecute(() =>
    {
        actionThatMayThrowException();
        return _completedTask;
    });
}

---

I wouldn't actually recommend disregarding unhandled exceptions in this way. You should consider at least logging the exception.