Catch Async Method exception in Azure function

Question

I have written Azure function v1 using C# (library project) with Aspect (AOP) for Logging. I'm not getting exception in catch block.

Catch an exception thrown by an async method

I have same problem discussed above, however, Azure Function Run method is Async Task and its exception handling same as async void. Not sure where is a problem? assuming this is function SDK issue.

Azure Function

public static class PingFunction
{
    [LoggerAspect]
    [FunctionName("PingFunction")]
    public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)]HttpRequestMessage req, TraceWriter log)
    {
        string name = string.Empty;
        log.Info("C# HTTP trigger function processed a request.");

            SomeService someService = new SomeService();
            await someService.DoSomething();

        return req.CreateResponse(HttpStatusCode.OK, "Hello " + name);
    }
}

public class SomeService
{
    public async Task DoSomething()
    {
        await Task.Delay(1000);
        throw new Exception("Exception from Service");
    }
}

Logger Aspect (MrAdvise)

public class LoggerAspectAttribute : Attribute, IMethodAdvice
{
    public void Advise(MethodAdviceContext context)
    {
        //Logger initilizer here
        Console.WriteLine($"{context.TargetType.Name} started...");
        try
        {
            context.Proceed(); // this calls the original method
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }
        finally
        {
            Console.WriteLine($"{context.TargetType.Name} completed...");
        }
    }
}

Workaround When I removed Async-await from Azure function and call async method by "GetAwaiter().GetResult()", then it works.

public static HttpResponseMessage Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)]HttpRequestMessage req, TraceWriter log)
    {
        string name = string.Empty;
        log.Info("C# HTTP trigger function processed a request.");

        SomeService someService = new SomeService();
        someService.DoSomething().GetAwaiter().GetResult();

        return req.CreateResponse(HttpStatusCode.OK, "Hello " + name);
    }

Task.GetAwaiter().GetResult() methods cause the potential for deadlock issues and should be avoided in favor of async/await.

My function process millions for events per-day. Is it the right solution if this is FunctionSDK issue or something else?

This is mostly to do with MrAdvice AOP framework support for Async calls, try using Postsharp, that would work as expected. GetAwaiter().GetResult() is not a good solution as that is making calls Synchronous — Mrinal Kamboj
If you are only keen for the free version, then please try github.com/Virtuoze/NConcern — Mrinal Kamboj

picrap picrap · Accepted Answer · 2019-01-09T10:27:10

you need to write an async advice, such as:

public class LoggerAspectAttribute : Attribute, IMethodAsyncAdvice
{
    public async Task Advise(MethodAsyncAdviceContext context)
    {
        //Logger initilizer here
        Console.WriteLine($"{context.TargetType.Name} started...");
        try
        {
            await context.ProceedAsync(); // this calls the original method
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }
        finally
        {
            Console.WriteLine($"{context.TargetType.Name} completed...");
        }
    }
}

EDIT : and yes, it works with Mr Advice :)

Catch Async Method exception in Azure function

1 Answers