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  1. hopmedic's Avatar
    Step 1: Tap the Start button.
    Step 2: Sit back and bask in the glow of a phone that doesn't require you to manage apps running in the background.*
    That's it.

    *The only apps that can continue to run in the background are location tracking (e.g. Here Drive+), and background audio (e.g. Pandora).

    So you're looking for more detail? Read on.

    Application Lifecycle

    Windows Phone uses an application life cycle that only allows one application to run at a time, and only if it is in the foreground, with the exception of the app types above. When you start an app, it becomes THE running app. If you back out of it, it is gone. If you tap the start button (or switch apps due to a toast, reminder, phone call, text message, etc.), the app is placed on the "back stack" and its state is "suspended." The back stack is the list of apps (up to 7) that you can get to by hitting the back button.

    A suspended app is still in memory, but uses no CPU cycles. It is still in memory, but it has stopped doing anything at all. It is just there. If you hit the back button, it will be just as you left it. Depending on how the developer wrote the app, it may look like it kept running, but it didn't. One example that comes to mind is a timer. If you leave the app, and come back to it, it looks like time kept ticking. That's because the developer wrote it such that it tracked the time at which the app was suspended, and it looked at the system clock when reactivated and compensated for the time that it wasn't running. I've done this in one of my own apps.

    If you keep going, starting another app and hitting the start button, the original app will move further down the back stack. The OS can take memory from apps in the back stack if needed by the foreground app, or for other reasons, and take that app out of memory. In this case, its state becomes "Tombstoned". If an app is tombstoned, you may see varying results when you go back into the app, because the developer has to actually program the app to accomodate being tombstoned. It may end up looking wrong going back to it, if the app wasn't developed with tombstoning in mind. I can't think of any cases off the top of my head where I've seen this, but I'm sure it's out there.

    When an app is tombstoned, it calls a method - or a procedure - where it runs whatever steps the developer has defined for the tombstoning process. This would most likely be to save the data that was on the screen into the app's isolated storage (this is a whole different subject that I won't go into right now). The app can still be returned to from the back button, but it may take a couple seconds as it reloads the saved data, since it is no longer in memory.

    If a different app is in the foreground, and there is enough memory use that the OS needs to take more, you can actually see an app removed from the back stack without it being bumped past the 7th.

    Background Tasks

    Background agents (or tasks) can be set up by the developer, and they can also be blocked by the user (from the Settings | Applications | Background Tasks). For this reason the developer should always write his app such that background agents enhance the user experience, but are not necessary for a good user experience.

    Background agents come in a couple different varieties. There is the Periodic Task (which I would venture to guess is most common), and the Resource Intensive Agent. The periodic task typically runs approximately every 30 minutes, but can be scheduled to run with other system processes, so this time can drift by up to 10 minutes. The battery saver mode can disable periodic tasks as well, and so can the user (mentioned above). A periodic task is limited to 25 seconds, can consume no more than 11 MB (audio agents can consume 15 MB) of memory, they expire after 14 days (if you don't use an app for 14 days, its live background agents - which could be updating live tiles - will no longer run until you run the app again), and if the background agent has an error that causes it to fail two times consecutively, it will be disabled. Also, there is a limit to the number of background agents that can be enabled, and that limit varies by phone. Low-memory devices cannot have background agents.

    Something to think about: Rarely, there can be instances where a background agent will have an excessively detrimental effect on battery life. I say rare, because most background agents run for a very short time, often less than a second, occasionally a few seconds, and rarely for the full 25 seconds that they are allowed. Since periodic tasks run every 30 +/- 10 minutes, theoretically you can have the agents running every 20 minutes. Three times an hour. That means that theoretically a task can use up to 30 minutes of processing time per day. Since you can have up to 15 background agents active (that's the most I've seen, but I've also seen the limit lower than that), assuming the worst case scenario, where you have 15 tasks that use 25 seconds of processing per execution, and the tasks run every 20 minutes, we're talking about up to 7.5 hours of processing time. Of course, this is the perfect storm of background tasks, and is highly unlikely, but given the constraints, it is theoretically possible.

    Resource Intensive Agents are for doing things that require more resources, such as downloading podcasts or music in the background. Resource Intensive Agents can run for 10 minutes, but some conditions can cause them to terminate early. External power is required, as is a WiFi connection (or connection through a PC), and these agents will not run unless the battery is at least 90% charged and the screen is locked, and will not run during an active phone call. The external power and WiFi requirements can be bypassed by the developer, though I believe this requires specific (one-time) permission from the user in order to pass certification. In any case, there is a hard limit to the file size that can be transferred. While under cellular, that limit is 20 MB. On WiFi and without external power it is 100 MB, and to download more than 100 MB, external power is required.

    Summary

    I've put this together because I repeatedly see new users coming from other phones asking questions like "Is there a better way to exit an application?" The fact is that you don't need a better way with Windows Phone. The Windows Phone OS manages memory and battery life for you. You can do things like back out of all apps (if you're OCD like me), or you can just hit Start and let the app die in the background. Hopefully this post will help people to better understand not just that you don't need a task manager, but why you don't need one.

    Sources:
    App activation and deactivation for Windows Phone
    Background agents for Windows Phone

    Edit:
    Applications Running Under Lockscreen
    Another situation is that developers can set their apps to run under lockscreen. This means that if the lockscreen is on, or the phone is in the "standby" mode (screen off), the application can still run. This would be the case with such an app if you do NOT leave the app by using either the back button or pressing Start to get back to the start screen, before your phone either times out and shuts the screen off, or you turn the screen off with the power button. If I remember correctly, it used to be a requirement that the app notify you before doing this, but apparently either that requirement was dropped or I don't remember correctly. All I can find at the moment is this:

    1. [Optional] To have a great user experience with user in control, you should prompt the user so they opt-in into running under lock.
    2. [Optional] You should expose as part of your application configuration settings an option for the user to change their mind or simply want to disable it and conserve power.

    (http://blogs.msdn.com/b/jaimer/archi...ck-screen.aspx)

    I had an instance where I was playing one of the Angry Birds games, my wife called me to do something, and a half an hour later when I turned my screen back on to continue playing, the phone was in battery saver mode, where it had more than 50% battery before I'd shut it off. Since then I don't trust the Rovio brand to not run under lock. Keep in mind that the only thing you have to do to avoid this problem is hit the start button.

    Debugging Battery Life Problems:
    While there is no way currently to tell what app(s) is using the most battery power, you can use Data Sense (if available) to help. Consider that most of the time if an app is using a lot of juice, it is probably also using a lot of data. This isn't always the case - an example would be a graphics intensive game that doesn't use data, or a video that isn't streaming - but for the most part, given the connectedness of our phones, if it's using a lot of power, it's probably using a lot of data. Use Data Sense to see how much data apps are using, and sometimes you'll find yourself wondering, "Why in the world does THIS app use so much data?" In the case of apps using a lot of data and you wouldn't expect them to, try blocking a background agent or not using the app, or even uninstalling it, and see if your battery life improves.


    Edit:
    Live Tiles

    I've seen questions about tile updates, so I thought I'd add a little snippet about that here. There are three ways that a tile can be updated. First, and probably most common (though I'm guesstimating here), would be through a background agent, where the background agent runs every 30 +/- 10 minutes as explained above, maybe goes to the web and grabs some data, or maybe it generates its own data to update with, and updates a live tile. A background agent can also pop-up a toast notification in addition to other things it can do, too.

    The second way is that the tile can be updated while the app is running. An example of this is say you have a tile that has a number on it, with notifications. You tap the tile to see what's new. When you back out of the app, the tile no longer has a number. The tile was updated while the app was running. It doesn't have to be a number of notifications that is updated - the app can change the tile image, text, whatever. Just as if it had been run by a background agent.

    The third way is that a tile can get an update through push notifications. There doesn't have to be a scheduled agent running to receive this kind of update. The push server can send data to the app if it is registered with the server, and when the app receives that notification, it can update a tile, pop-up a toast notification, or even save data changes into the isolated storage of the app.
    Last edited by hopmedic; 01-21-2014 at 09:19 AM. Reason: Added section: Live Tiles
    05-25-2013 10:22 AM
  2. OberstDanjeje's Avatar
    Good idea this post, I'm new to the WP but I know all this, anyway it's very usefull for all.
    Thanks
    05-25-2013 10:47 AM
  3. Muessig's Avatar
    Very useful, thanks for posting - I definitely learnt something new!
    05-26-2013 02:36 AM
  4. keylex90's Avatar
    Just a quick question, will battery drain be reduced if I close some background task for some apps?
    05-26-2013 02:59 AM
  5. Muessig's Avatar
    Just a quick question, will battery drain be reduced if I close some background task for some apps?
    When an app is suspended it is stored in memory as mentioned above. It only exists in memory and takes up no cpu and therefore it shouldn't affect your battery life at all. It should make a difference if you back out of an app or suspend it in terms of battery life.
    05-26-2013 06:28 AM
  6. edoug's Avatar
    So hoe do timers/alarms work in 3rd party apps where I want to be reminded in 45 minutes? Can I rely on it?
    05-26-2013 07:20 AM
  7. mary beth hale's Avatar
    to the point and so informative, thank you so much!
    05-26-2013 01:08 PM
  8. hopmedic's Avatar
    So hoe do timers/alarms work in 3rd party apps where I want to be reminded in 45 minutes? Can I rely on it?
    The third party timers I've used (Timer, Timer Tools) seem to be quite reliable. I don't know for sure how they work, whether they can set an alarm, or if there's a third background agent that I can't seem to find info on. I can think of one workaround, which I've read would cause an exception if you use this method in a published app, as this method is there for testing apps, so you can set them to run at a certain time, but I wonder if you catch the exception and ignore it, if this method would work anyway. I'm sorry, but I can't answer your question.
    edoug likes this.
    05-26-2013 06:47 PM
  9. a5cent's Avatar
    So how do timers/alarms work in 3rd party apps where I want to be reminded in 45 minutes? Can I rely on it?
    Although apps are entirely suspended, the OS itself obviously is not. Your scenario is solved by having 3rd party apps register Alarms or Reminders with the OS. Both alarms and reminders are scheduled notifications, which WP will fire at the predetermined time. The app isn't required to be in memory for a scheduled notification to fire reliably, because it is handled entirely by the OS. In fact, this is exactly how the 1st party alarm and calendar apps work. In this regard, there is no difference between 1st and 3rd party apps.

    The scheduled notification page always includes a text element that can be used to resume/restart the scheduling app.

    This approach is more reliable than if each app were to fire such notifications autonomously.

    Just a quick question, will battery drain be reduced if I close some background task for some apps?
    Background agents can't be closed, they can be deactivated however.

    Most background agents typically complete their periodic duties in well under two seconds. Over a 24h period, deactivating such an agent would save you less than two minutes of processing and communications time. If you had five such background agents and deactivated all of them, that would save you no more than 8 minutes worth of processing and communications time per day. I'd say those 8 minutes of activity won't cause a noticeable difference in terms of battery drain.

    On the other hand, if you've got a "funky" background agent that makes use of its entire 25 second activation period, things will be different. Over a 24h period, that agent alone could use up to 20 minutes of processing and communications time.

    So, to answer your question, yes, deactivating a background agent will reduce battery drain, but it typically won't make a noticeable difference. If you have one or more very intensive agents that use a large portion of their 25 second long processing window, then you likely will notice a difference. I'm unaware of any such background agent. I would likely uninstall the app if I ever encountered one.
    05-27-2013 10:26 AM
  10. hopmedic's Avatar
    Added section: Applications Running Under Lockscreen
    06-12-2013 07:02 AM
  11. dipankar_mitra's Avatar
    Good to know. Maybe this is the reason why the WhatsApp experience is not good on Windows Phone.
    It must be using a background agent to check for new messages, and that may run way after someone sends an IM.
    06-25-2013 02:47 AM
  12. a5cent's Avatar
    Good to know. Maybe this is the reason why the WhatsApp experience is not good on Windows Phone.
    It must be using a background agent to check for new messages, and that may run way after someone sends an IM.
    No, that is not how WhatsApp works on WP. The problems with WhatsApp have been analysed in other threads. It's problems are primarily related to a very funky use of the background audio API.
    anon(8657436) likes this.
    06-25-2013 03:17 AM
  13. gbold3's Avatar
    I'm new to Windows Phone 8, moving from an S3 to a 920. I don't seem to have the option of "applications" under the settings list to control my background tasks? Is there a switch I need to turn on?Thanks
    08-11-2013 01:26 PM
  14. Josh Browning's Avatar
    Really cool post! I've never thought about a phone from this perspective before, but it's quite fascinating...

    One question: I'm using AT&T locker to upload photos from my Nokia Lumia. The pictures are high-res, so the uploading takes a while... If I try to do something else while uploading, or if I let the phone go into sleep mode, will the uploading automatically stop? It unfortunately seems like it would, given the design you discussed. Quite a handy phone from a lot of perspectives, but there's a few little gotcha's too...
    08-12-2013 05:29 PM
  15. a5cent's Avatar
    Hopmedic, you should PM Daniel Rubino and tell him to read your post!

    He wrote this in a recent article:

    "The best part? All of the app’s timers and stopwatch features run in the background, even when the app has been exited or, according to the app description, if the device is even turned off. That’s obviously crucial if you’re running a 4 hour countdown or timing something for longer than normal."
    The above is incorrect, because nothing like that can run in the background. Your post explains exactly what is actually happening:

    Depending on how the developer wrote the app, it may look like it kept running, but it didn't. One example that comes to mind is a timer. If you leave the app, and come back to it, it looks like time kept ticking. That's because the developer wrote it such that it tracked the time at which the app was suspended, and it looked at the system clock when reactivated and compensated for the time that it wasn't running. I've done this in one of my own apps.


    One question: I'm using AT&T locker to upload photos from my Nokia Lumia. The pictures are high-res, so the uploading takes a while... If I try to do something else while uploading, or if I let the phone go into sleep mode, will the uploading automatically stop? It unfortunately seems like it would, given the design you discussed. Quite a handy phone from a lot of perspectives, but there's a few little gotcha's too...
    WP actually does have the ability to upload or download files in the background, but how or even if that ability is used will differ from one app to another. I don't know how AT&T handles the situation you described, but technically WP8 could upload your pictures in the background if the corresponding app is developed to do so. As it is now, if we really want to know, we must test each individual app to find out how it transfers files.

    This is another one of those areas where WP needs improvement. IMHO all file transfers should always occur asynchronously and in the background. The current situation is far too inconsistent.

    P.S. Hopmedic did a really good job explaining the situation, but no matter how much anyone writes on a subject like this, there will always remain some edge cases that don't get covered, like the background file transfer capability you asked about. Forum posts aren't really up to the task of being entirely comprehensive on such matters.
    08-12-2013 08:55 PM
  16. hopmedic's Avatar
    Thanks for the complement, A5cent. I did message Daniel, though reading his article, it doesn't look to me like it really matters, for the most part. To a lay person, they want to know that the alarms will work if they leave the app, and I think that's the message he's trying to get across. Since his article isn't directed necessarily at developers, I think it meets the need - with one slight exception. That being that if a person is concerned about background tasks draining the battery, they may incorrectly place blame on this app or apps like it.

    Also, the post that you quoted from me would refer to the stopwatch portion of the app. This is how it works when there will be no alarm. Actually, your post above better addresses timers where there are alarms - where the alarm is actually hooked into the OS alarm system.
    Although apps are entirely suspended, the OS itself obviously is not. Your scenario is solved by having 3rd party apps register Alarms or Reminders with the OS. Both alarms and reminders are scheduled notifications, which WP will fire at the predetermined time. The app isn't required to be in memory for a scheduled notification to fire reliably, because it is handled entirely by the OS. In fact, this is exactly how the 1st party alarm and calendar apps work. In this regard, there is no difference between 1st and 3rd party apps.
    Now if the article was directed at developers, that would be a different story...
    anon(8657436) likes this.
    08-14-2013 12:20 PM
  17. a5cent's Avatar
    I did message Daniel, though reading his article, it doesn't look to me like it really matters, for the most part. To a lay person, they want to know that the alarms will work if they leave the app, and I think that's the message he's trying to get across.
    IMHO we should expect effective communication and technical correctness from WPC (this is the only such error I recall, so 99.9% of the time they nail both aspects). Particularly because the technicalities can always be omitted if they get too involved.

    Anyway, great that you PM'd him!!! Hope he reads and learns ;-)
    08-14-2013 03:40 PM
  18. mvmsk's Avatar
    Thanks for the info. I'm feeling totally uncomfortable seeing some apps in the multitasking window.!!
    09-23-2013 01:52 AM
  19. menotu123's Avatar
    Thank you... excellent explanation ... much appreciated..
    12-04-2013 08:29 AM
  20. pirateman1966's Avatar
    what he said.
    03-29-2014 06:29 AM
  21. sahib lopez's Avatar
    I wonder if this will have to be updated when 8.1 is in our hands ?
    04-08-2014 12:03 AM
  22. prasath1234's Avatar
    Hey it was indeed very useful info. Thank you buddy:thumbup::p:sly:

    Sent from my C2305 using WPCentral Forums mobile app
    04-30-2014 12:44 AM
  23. a5cent's Avatar
    I wonder if this will have to be updated when 8.1 is in our hands ?
    Yes, it will require a huge update! It's probably best to leave this thread as it is and create an entirely new thread, because just comparing the differences could prove interesting. I don't envy the person who takes on that task though. There is a lot more to explain than there was for WP8.0, and it's also quite a bit more complicated.
    Lola Cathrine and sahib lopez like this.
    04-30-2014 12:48 AM
  24. Lola Cathrine's Avatar
    Excellent ! Really helpful, thank you !
    02-22-2015 01:59 PM
  25. Duy Nguyen 8s's Avatar
    Thanks you. I like it.
    05-01-2015 10:04 AM

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