WP7 Max HTTPWebRequests

Question

This is kind of a 2 part question

1) Is there a max number of HttpWebRequests that can be run at the same time in WP7?

I'm going to create a ScheduledTaskAgent to run a PeriodicTask. There will be 2 different REST service calls the first one will get a list of IDs for records that need to be downloaded, the second service will be used to download those records one at a time. I don't know how many records there will be my guestimage would be +-50.

2.) Would making all the individual record requests at once be a bad idea? (assuming that its possible) or should I wait for a request to finish before starting another?

Answer 1

I seem to remember (but can't find the reference right now) that the maximum number of requests that the OS can make at once is 7. You should avoid making this many at once though as it will stop other/system apps from being able to make requests.

Answer 2

Having just spent a week and a half working at getting a BackgroundAgent to stay within it's memory limits, I would suggest doing them one at a time.

You lose about half your memory to system libraries and the like, your first web request will take another nearly 20%, but it seems to reuse that memory on subsequent requests.
If you need to store the results into a local database, it is going to take a good chunk more. I have found a CompiledQuery uses less memory, which means holding a single instance of your context.

Between each call I would suggest doing a GC.Collect(), I even add a short Thread.Sleep() just to be sure the process has some time to tidying things up.
Another thing I do is track how much memory I am using and attempt to exit gracefully when I get to around 97 or 98%.

You can not use the debugger to test memory limits as the debug memory is much higher and the limits are not enforced. However, for comparative testing between versions of your code, the debugger does produce very similar result on subsequent runs over the same code.

You can track your memory usage with Microsoft.Phone.Info.DeviceStatus.ApplicationCurrentMemoryUsage and Microsoft.Phone.Info.DeviceStatus.ApplicationMemoryUsageLimit

I write a status log into IsolatedStorage so I can see the result of runs on the phone and use ScheduledActionService.LaunchForTest() to kick the off. I then use ShellToast notifications to let me know when the task runs and also when it completes, that way I can launch my app to read the status log without interrupting it.

Answer 3

1) Your memory limit in a PeriodicTask or ResourceIntensiveTask is 5 MB. So you definitely should control your requests really careful. I dont think there is a limit in the code.

2)You have only 5 MB. So when you start all your requests at the same time it will terminate immediately.

3) I think you should better use a ResourceIntensiveTask because a PeriodicTask should only run 15 seconds.

Good guide for Multitasking features in Mango: http://blogs.infosupport.com/blogs/alexb/archive/2011/05/26/multi-tasking-in-windows-phone-7-1.aspx

Answer 4

Tyler,

My 2 cents here.

1. I don't believe there is any restriction on how mant HTTPWebequests you can spin up. These however have to be async, off course, and may be served from the browser stack. Most modern browsers including IE9 handle over 5 concurrently to the same domain; but you are not guaranteed a request handle immediately. However, it should not matter if you are willing to wait on a separate thread, dump your content on to the request pipe & wait for response on yet another thread. This post (here) has a nice walkthrough of why we need to do this.

2. Nothing wrong with this approach either, IMO. You're just going to have to wait until all the requests have their respective pipelines & then wait for the responses.

Thanks!