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While attached to debugger it runs just fine. The Periodic Task is invoked and runs over and over, but when I deploy it to my device It seems to run 1-2 times and then stops.

What It does is setting the live tile background image from isolated storage. The images are created in the application and then saved to isolated storage. As mentioned it works well while attached to the debugger.

The only constraint I could think that could break it would be the memory cap. The application creates and saves 40 images of ~25kB each, and that isn't 1 MB! The application is maybe <4 MB, so that is 5 MB... a lot less than the 11 MB minimal requirement.

So it can't be the memory cap kicking in. Two consecutive unhandled crashes should also break the task, but I've thrown all the code in the task's OnInvoke() in a try/catch.

Now I'm out of ideas what stopping my periodic task when running without being connected to visual studio running in debugger. Any clues?

Jason94
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  • Do you always invoke [NotifyComplete](http://msdn.microsoft.com/en-us/library/windowsphone/develop/microsoft.phone.backgroundagent.notifycomplete.aspx) method? – Ulugbek Umirov May 27 '14 at 07:52
  • NotifyComplete is defined outside, and after the try/catch and is always called – Jason94 May 29 '14 at 16:51
  • Did you fix it? You didn't reply to my answer. Does the background agent get blocked or does it just not work? Also, are you creating the images in the background agent? If so, 4MB memory seems unrealistically low. Is that the peak memory? – yasen May 31 '14 at 12:54
  • You said you are creating 40 images. That is a lot of images to create. How are these being created? – Shawn Kendrot Jun 04 '14 at 16:07

3 Answers3

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Firstly are you using Windows 8.1 phone by any chance? Since there is an issue with Periodic tasks do not run on windows phone 8.1 devices as you can see on this forum

Background agent can’t use more than 6MB of memory. You can get the current memory usage using the following snippet :

var memory = DeviceStatus.ApplicationMemoryUsageLimit  
- DeviceStatus.ApplicationCurrentMemoryUsage;


automatically executed by the OS each 30 minutes
the operation can’t exceed 25 seconds per run
if the phone switch to battery saver mode the background agent may not be executed
on some devices only 6 background agents may be planned simultaneously
agents can’t use more that 6MB of memory
agents have to be re-planned each 2 weeks
an agent that crashes two times is automatically disabled by the system

Jerin
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Periodic tasks are unscheduled after two consecutive crashes. You need to make sure that this doesn't happen (check internet connectivity if required, set a timeout on web requests, etc.).

You should place your code in a try/catch block and log exceptions in the Isolated Storage to see what happened afterwards.

Here is the list of constraints that apply on scheduled agents (MSDN): Constraints for all Scheduled Task Types

Here is also a series of blog posts that could help you: Windows Phone: Background Agents Pitfalls

Olivier Payen
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  • thank you for your reply! I've added the memory checks and printed my running times. My Periodic task uses 4mb, and runs for 66 ms! Well inside the requirements... everything should be nice and dandy! Everything is also placed in a try/catch so there is no unhandled exceptions either... – Jason94 May 27 '14 at 18:23
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Have you actually measured and logged the memory that's being used? What you're saying isn't very correct:

  1. When the background agent starts it has already taken 5-6MB to load what it needs from the .NET framework.
  2. If you mean that the compressed files are 25KB each, you should know that the images in the memory are not compressed (at least not that much).

There are two things you can try:

  1. Use this property and check the peak memory usage: DeviceStatus.ApplicationPeakMemoryUsage. Write it to some file (maybe every 5 images or so) and check if it's okay. Paste the results, please.

    Note: When testing the memory usage, it's best to build the app in "Release" and run it without debugging on a device. That's most accurate. There are some minor variations, so you should run the agent several times to be sure it's working within the limits. You can force start it from the app using ScheduledActionService.LaunchForTest.

  2. Also, I'd suggest you subscribe to the Application.Current.UnhandledException event and mark all exceptions as handled (and log them, so that you can fix them). That's for extra safety.

P.S. When the background agent stops executing, is it "blocked" in the list of background tasks on the device?

yasen
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