a look behind the scenes: windows 8 background processing

A look behind the scenes: Windows 8 background

processingGill Cleeren@gillcleeren

About me…

• Gill Cleeren• .NET Architect @Ordina • Pluralsight trainer• Microsoft Regional Director• Client Dev MVP• Speaker • User group lead (www.visug.be) • Author • Blog: www.snowball.be• Email: gill@snowball.be • Twitter: @gillcleeren

See my courses on Pluralsight!

• See my courses at

http://gicl.me/PluralsightCourses

Agenda

• Windows 8 lifecycle explained• Background processing options• Server-side• Background tasks• Lock screen apps• Alarm apps (new in Windows 8.1)• Geofencing (new in Windows 8.1)• Background transfers• Background audio

Q: Why do we need background APIs?A: The process lifecycle of Windows 8

Before Windows 8…

User was in control

Now, since Windows 8…

Windows 8 handles the process lifecycle itself• No dialogs• Give the user the best experience• App should give the impression it has

been running all the time

Typical aspects of the process lifecycle

1 app in the foreground

System of app events exists

User must be unaware

Background processing exists

The process lifecycle

Not running

Running

SuspendedNot running/ Terminated

Launching Suspending

Resuming

TerminationApp CloseApp crash

DemoThe Application-Circle-of-Life

It’s an event thing…

• Launched• Happens when user taps tile• PreviousExecutionState indicates if the app was

• Activation• Most often in combination with a contract

• Search• Share

• Doesn’t trigger the Launched event handler code!

protected override void OnLaunched(LaunchActivatedEventArgs args){ if (args.PreviousExecutionState ==

ApplicationExecutionState.Terminated) { ... }

It’s an event thing…

• Suspending• Last chance to save state• Apps won’t get suspended in critical code blocks• 5 seconds before suspending fires• 5 seconds to execute code

• Resuming• Can only happen is app is suspended, not terminated• Same memory instance• Immediate• Typical use: data-rehydration

App, you are… terminated!

• Termination• Not an event that we see in code• Triggered by Windows

• Low memory resources• Application closed by user• App crash• User logoff

State management

• Application events can be used to manage state• User must think that app has been running all the time

• Options:• SuspensionManager

• Available already in Windows 8• In Windows 8.1, integrated in NavigationHelper

• Application Data API• Local• Roaming

• Service• Time issues possible

DemoApplication events

Q: OK, what background processing options do we have?A: Quite a few actually! Let’s take a look!

Options for background processing

Server-side • Push notifications

Client-side

• Background tasks• Lock screen apps• Alarm apps• Geofencing• Background transfer• Background audio

Push notificationsServer-side

Push notifications

• WNS = Windows Notification Service• Allows delivery of tile and toast XML messages over the wire

• Can arrive when the app isn’t running• Create background processing without processing

• Happens on the server

• Transparent process for the developer• Free services

• Cloud-based so no worries on scalability• Easily updates millions of devices• Register your app in the store

• No need to publish!

• You can use Azure for every component• It’s recommended to do so even!

Push notification architectureWindows 8 Cloud Service

Windows Notification

Service

Modern UI App

NotificationClient Platform

2

3

1 3

1. Request Channel URI2. Register with your Cloud Service3. Authenticate & Push Notification

DemoPush notifications

Background tasksClient-side

Background tasks in general

• Balance between UX and hardware restrictions• Battery, network…

• Windows 8 locks down what apps can do in the background• An app can’t keep running when it’s not in the foreground• Only “small amounts of code” are possible• Constrained environment hard for some scenarios

• Typical uses• Download data from a service• Send notification to the user• …

• Run all the time• Once registered, run when app is running and when it’s not running

Building blocks of a background task

BackgroundTaskBuilder

MyBackgroundTask

IBackgroundTask

Trigger

Condition

TaskEntryPoint: MyBackgroundTask

Your background code

• A class which implements IBackgroundTask

public sealed class MyBackgroundTask: IBackgroundTask{ public void Run(IBackgroundTaskInstance task) { // Insert background code }}

Triggers

• Background task only starts when a trigger is firing• One task, one trigger• Trigger is an “event” that happens in the system

Control Channel

Push Notification Maintenance Timer System Event

27

New background events in Windows 8.1• BackgroundWorkCostChanged• Related to Background Work Costs• Based on what is scheduled, we can decide not to run our background task• This event allows you to change your background API strategy based on

what's currently going on with the system

• NfcStateChange• Allows your app to respond to near field communication (NFC) events for your

device even when the app isn't currently active

New in 8.1!

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New background triggers in Windows 8.1• DeviceUseTrigger• Represents an event that an application can trigger to initiate a fixed-length,

long-running operation (content transfer, sync) with a device

• DeviceServicingTrigger• Represents an event that an application can trigger to initiate a long-running

update (firmware or settings) of a device

• … LocationTrigger (later)

New in 8.1!

Conditions

• Can be added on trigger• Trigger only fires when condition is true• Can help not to waste valuable resources

Internet Available /

Unavailable

Session Connected /

Disconnected

User Present / Not Present

Preparing your solution

• Registering a background task is done using Package manifest

Preparing your solution

One last thing before I’m deferred…

• If you have async code in the Run() of IBackgroundTask, you’ll need a deferral

public void Run(IBackgroundTaskInstance taskInstance){ BackgroundTaskDeferral deferral = taskInstance.GetDeferral();

// be awesome asynchronally

deferral.Complete();}

Constraints

• Background tasks are limited in the usage of• CPU

- Network- Not constrained when running on AC power- Modeled as the amount of energy the network is used to transfer bytes

- Not based on throughput

• Critical tasks receive guaranteed application resource quotas

CPU resource quota Refresh period

Lock screen app 2 CPU seconds 15 minutes

Non-lock screen app 1 CPU second 2 hours

Demo:Working in the background

Tomorrow in the office…Debugging background tasks is time consuming, boss. I have to toggle my

internet connection every time.

What? Didn’t you attend the user group talk on background tasks in WinRT??

Can’t say I did…(leaves the room quietly…)

Clearly this is not a conversation

you’ll have!

Debugging background tasks

Make sure the names match!

Manually trigger from Visual Studio

Demo:Working Debugging in the background

The

screen

The lock screen and lock screen apps• A set of APIs only available when the user puts the app on the lock

screen• WNS (Push Notifications): RAW notification that can trigger code execution• Network Trigger: constant connection• Time trigger: execute code at specific intervals

• Less constraints• Apps can become a lock screen only by using these triggers• Not every app should be on the lock screen!• An app can only ask once• User can enable/disable it through Permissions settings pane

The lock screen and lock screen apps• Only 7 apps can be on the lock screen• User-managed• App should be able to function if not on the lock screen too

• When on the lock screen:• Can update the badge• Display tile if promoted• Display toast that opens the app after login

Demo:Take a loOk at the loCk screen

Creating a lock screen app

• Step 1: Include a background task that requires lock screen permission

Creating a lock screen app

• Step 2: add required logos (manifest)• Lock screen badge logo• Wide logo for the app

• Step 3: enable lock screen notifications in manifest

Demo:Creating a lock screen app

Available triggers for lock screen apps

Push notification trigger

Control channel trigger

Time trigger

Push notification trigger

• WNS: allows sending push updates• Templated XML only

• Push Notification Trigger enables triggering a background task AND receiving just any string• RAW notification• 5K max

• All apps use same open connection• Efficient• No extra open sockets• App can still update lock screen or trigger code

• Delivered on best-effort basis

Steps to enable the Push Notification trigger• On the client• Channel URI• Background task• Push Notification trigger

• On the server• Authenticate• Send any string to client (raw notification)

PushNotificationTrigger pushNotificationTrigger = new PushNotificationTrigger();

When would you use this?

• Notify the client that action is required

Email is availableIncoming

communication message

Notify client that it needs to sync

data

Demo: Raw notifications

Network trigger

• If server-side can’t use WNS, we need to fall back on sockets• Open connection in the background• Complex to create• Not good for battery• Guaranteed delivery

Network trigger

• 2 types exist• Control channel trigger

• Required• Persistent connection between client and server• Initiated by the client• Maintained by Windows even when the app is in the background

• Keep-alive trigger • Optional• Client can send keep-alive messages even when in background

Time trigger

• Can run code based on time interval• Minimum is 15 minutes

• Requires app to be on the lock screen• Code ignored if not

• Requires manifest change to use Timer• Useful for POP3 mail checks, perform a service call

DemoTime trigger

Windows 8 and alarms

• In Windows 8, it’s not possible to build an alarm app…• Background process?• Lock screen?• Time trigger?

Windows 8.1 now has the Alarms App• Can be an alarm clock, timer and stopwatch

New in 8.1!

So, there’s a way now!

• Windows 8.1 adds the ability to make an app the Alarm app• Can show toasts (including sound) at specific time

• Precise to the second

• When the app is the alarm app, it can show special toast messages

New in 8.1!

Steps to Become an Alarm App

• Make the app lock-screen enabled• Select the Timer, Control channel

or Push Notification

• Make the app Toast capable• Define a badge logo

New in 8.1!

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Steps to Become an Alarm App

• Edit the manifest XML• No option to do this from the manifest designer

<Extensions> <Extension Category="windows.backgroundTasks" EntryPoint="App"> <BackgroundTasks> <Task Type="timer" /> </BackgroundTasks> </Extension> <m2:Extension Category="windows.alarm" /></Extensions>

New in 8.1!

Steps to Become an Alarm App

• Request alarm access from the app• Use the AlarmApplicationManager.RequestAccessAsync()

• Create the scheduled toast notification• Set Duration to Long• Add custom commands (snooze and dismiss)

• Specify the snooze interval

New in 8.1!

Demo: ALAAAARM!!!

Geofencing

Coffeehouse

Works with GPS, Wi-Fi or IP address

New in 8.1!

Usages for geofencing

• “Remember the milk!”• Let the user know about delays at his (train)station• Check in on FourSquare automatically• Coupon-codes for stores• Virtual tour guide• …

New in 8.1!

Steps to Enable Geofencing in Your App • App must have required permissions• In the manifest, app must have a Location task• Containing a background task is therefore required• Must have lock-screen permissions

• Can prompt the user, only once though• Afterwards, still possible from Settings

• Setting up the geofence• Only circular fences are supported

• Contains latitude, longitude and radius• Get in notifications when entering or leaving the geofence

New in 8.1!

Demo:Geofencing

BackgroundTransfer API

• Allows uploading and downloading (large) files from outside the app• Runs when app is suspended

• Download is performed in a separate process• BackgroundTransferHost.exe

• Lives in Windows.Networking.BackgroundTransfer namespace• BackgroundDownloader & BackgroundUploader

Protocol Upload Download

HTTP X XHTTPS X XFTP X

BackgroundTransfer API

• Handles network status changes and glitches• Auto recovery

• Other supported features

Basic server credentials Proxy credentials Cookies Custom HTTP

headers

Flow to transfer files

BackgroundDownloader

Download Operation

Progress

ControlStartPause

ResumeStartAsync()

Transferring a file

private async void DownloadFile(Uri source, StorageFile destinationFile){ var downloader = new BackgroundDownloader(); var dl = downloader.CreateDownload(source, destinationFile);

await dl.StartAsync();}

Background Transfer Updates

• BackgroundTransferGroup allows apps to group transfer and change their priority• Do downloads in parallel or serial

• Possible to use a tile or toast update with the status of the transfer• BackgroundDownloader and BackgroundUploader have been extended

• FailureTileNotification • FailureToastNotification • SuccessToastNotification • SuccessTileNotification

New in 8.1!

Demo:Transferring files

Playing audio in the background

• Audio can be played using the MediaElement• Pauses the playback when app is suspended

• MediaElement defines AudioCategory property• 2 options exist to enable

background audio public enum AudioCategory{ Other = 0, ForegroundOnlyMedia = 1, BackgroundCapableMedia = 2, Communications = 3, Alerts = 4, SoundEffects = 5, GameEffects = 6, GameMedia = 7,}

Register from transport controls

Play / Pause

Next / Previous Track

Sound Level

Audio Information

Register for transport controls

• In Windows 8: • Register for MediaControl events

• PlayPauseTogglePressed• PlayPressed• PausePressed• StopPressed • (optional) SoundLevelChanged

• Option will probably be discontinued after Windows 8.1

Register for transport controls

• In Windows 8.1• Use the SystemMediaTransportControls

• Not a static class that exposes events• Can be accessed through the GetForCurrentView static method• All events are processed through the single ButtonPressed event• Offers more options

• Record, rewind…

Demo:Playing music in the background

Summary

• Background processing in Windows 8 is limited and constrained• Different approach than in previous editions• Background tasks and lock screen apps allow to run small blocks of

code• Downloading in the background and playing audio is supported

More info?

• Check out my Pluralsight course on this topic

http://gicl.me/PSWin8BGProc

Q&A

Thanks!

A look behind the scenes: Windows 8 background

processingGill Cleeren@gillcleeren