Using the async CTP from Microsoft for .NET,
is it possible to catch an exception thrown by an async method in the calling method?
public async void Foo()
{
var x = await DoSomethingAsync();
/* Handle the result, but sometimes an exception might be thrown.
For example, DoSomethingAsync gets data from the network
and the data is invalid... a ProtocolException might be thrown. */
}
public void DoFoo()
{
try
{
Foo();
}
catch (ProtocolException ex)
{
/* The exception will never be caught.
Instead when in debug mode, VS2010 will warn and continue.
The deployed the app will simply crash. */
}
}
So basically I want the exception from the async code to bubble up into my calling code
if that is even possible at all.
Best Answer
It's somewhat weird to read but yes, the exception will bubble up to the calling code - but only if you
await
orWait()
the call toFoo
.As Stephen Cleary wrote in Async/Await - Best Practices in Asynchronous Programming:
Note that using
Wait()
may cause your application to block, if .NET decides to execute your method synchronously.This explanation http://www.interact-sw.co.uk/iangblog/2010/11/01/csharp5-async-exceptions is pretty good - it discusses the steps the compiler takes to achieve this magic.