Running function in background - even while previous call to this function is running

Question

Hi everyone. I have a WPF C# .Net 4.5.2 app, which receives GPS data from tracking devices out in the field via TCP and plots them on a map (using the WPF Bing Maps control). One of the things I do when receiving data from a tracker is to get the street
address at the tracker's coordinates by using Bing's reverse geocoding facility. This can take a few seconds, and because I don't want it to slow down everything, I want to run this function in the background (i.e. in a separate thread). So I thought about
using .Net 4.5's Async/Await feature. This is how it looks:
private async void GetStreetAddress(int trackerId, double lat, double lng)
string streetAddress = await bingMap.ReverseGeocodeAsync(lat, lng);
dal.UpdateTracerAddress(trackerId, streetAddress);
So basically it calls Bing Map's reverse geocoding function, gets a street address, and updates this tracker's address in the database (MySQL database). Just to complete the picture, the ReverseGeocodeAsync shell looks like this:
public async Task<string> ReverseGeocodeAsync(double lat, double lng)
string streetAddress = "";
//Reverse Geocoding code...
return streetAddress;
My question is the following: What happens if the GetAddress() function is called again while it is still running? So, normally the app receives TCP data from one of the trackers, and then calls the GetAddress() function to get the street address.
Now, while that function is running in the background, the app receives another packet of TCP data and again calls that same GetAddress function before the previous instance has finished. Will it just create another instance of that function on the stack?
Thanks
Fabricio Rodriguez - Pretoria, South Africa

Answer 1

If your code is definitely working as expected and is executing ReverseGeocodeAsync on a different thread then you can do that any number of times and they will all just run.
It is quite easy to write async await and find the flippin thing runs synchronously though.
I recommend you put a break point in that method
public async Task<string> ReverseGeocodeAsync(double lat, double lng)
string streetAddress = ""; // Break here
Spin it up and give it a twirl.
When you hit it that break point, open up the Threads window and make 100% certain what thread your break point is on.
https://msdn.microsoft.com/en-us/library/w15yf86f.aspx
I've seen code which looks like it'll run asynchronously just fine which turns out to be running synchronously.
It's dead easy to go wrong.
Hope that helps.
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