Are these some made up terms? Does cold mean app was killed. And warm means app was in memory?
From docs on Reducing Your App’s Launch Time
For example, on iOS, if you swipe back to the home screen and immediately re-enter the app, that is the fastest activation possible. It’s also likely to be a resume. When the system requires a launch is required, it is commonly referred to as a “warm launch.”
Conversely, if a user just played a memory-intensive game, and they then re-enter your app, for example, it may be significantly slower than your average activation. On iOS, your app typically was evicted from memory to allow the foreground application more memory. Frameworks and daemons that your app depends on to launch might also require re-launching and paging in from disk. This scenario, or a launch immediately after boot, is often referred to as a “cold launch.”
Think of warm and cold launches as a spectrum. In real use, your users will experience a range of performance based on the state of the device. This spectrum is why testing in a variety of conditions is essential to predicting your real world performance.
From WWDC:
So, let's take a look at those launches I talked about before, there's a cold launch, a warm launch, and something is often referred to as launch, but isn't quite a launch, a resume.
Cold launches occur after reboot, or when your app has not been launched for very long time.
In order to launcher app, we need to bring it from disk into memory, startup system-side services that support your app, and then spawn your process.
As you'd expect, this can take a little time, but fortunately, once it's happened once, you'll experience a warm launch. In this case, your app still needs to be spawned, but we've already brought your app into memory and started up some of those system-side services. So, this will be a little bit faster and a little bit more consistent.
Finally, there's that resume. This occurs when a user reenters your app from either the home screen or the app switcher. As you know, the app is already launched at this point, so it's going to be very fast.
What you need to remember from this is not to confuse resumes with launches when you're taking measurements
tldr:
every time you hit the app icon, it can be one of the 4 following states:
app wasn't launched for a long long time or it was just launched after a reboot
app was launched and killed before. But launched again. So some system services are still in memory.
app was launched before, but got suspended to reduce memory, it's process is still ongoing. Hitting the app icon won't trigger an app launch
app was launched, but then only backgrounded. It's still in memory. e.g. you've had app put in background while listening to music or location tracking. So tapping on the app on the app icon, won't trigger another app launch. (this scenario wasn't mentioned in the above docs, but was worth mentioning)
Related
I'm running location updates in the background. All works well:
On significant location the app is launched in the background
- appDidFinishLaunching(options:) is called as expected.
I start LocationManager startUpdatingLocation() and startMonitoringSignificantLocationChanges()
Locations are collected correctly.
After some time, I call stopUpdatingLocation()
My program at this stage doesn't need to do anything and no further code is executed
At this point the program stays idle. applicationWillTerminate is never called again. Is this expected? I'd hoped the app will shut down again as no location updates are required.
What's the expected behaviour? Should the app shut down or should it stay idle forever?
Once this happens, then if a user user opens the app or a significant location is received again, then appDidFinishLaunching(options:) is NOT called, but instead applicationDidBecomeActive.
Is there any documentation I can follow that supports the expected behaviour?
Yes, everything here is expected. There's a deleted answer from J.D. Wooder that correctly linked the documentation: "Managing Your App's Life Cycle." As a rule, background iOS apps are not proactively killed. They are only killed when system resources are needed. This is unpredictable, and the app typically will not receive a applicationWillTerminate message when it happens (because the app typically is not running at that point, and it won't be woken up just to kill it). Your app should handled both a cold launch (appDidFinishLaunching) and a warm launch (applicationDidBecomeActive).
Restarting an app from scratch is expensive, so iOS prefers to keep recently used thing in memory if there's no resource pressure. Apps that are doing nothing are very cheap. to keep around.
Note that iOS 13 has grown much more aggressive in killing apps in the background, and that the large cameras on new phones are leading to memory pressures that kill apps more quickly as well, so don't get too comfortable with running in the background for a long time. But it's also very normal.
Please see the iOS app Life Cycle,
appDidFinishLaunching will call only when app Launch,
applicationWillTerminate - called when app terminate from background
applicationDidBecomeActive - Called when app comes to foreground from background
Suppose I am using one App (no other App is active). Now I lock the iPad by simply clicking the lock button or may be I put it in background mode and put my iPad somewhere.
After what amount of time, the App will get killed automatically by system if I don't use that App? Is there any specification by Apple or we cannot say anything that App will launch from scratch in some scenarios.
Note that in any scenario, I don't kill my App manually.
iOS generally (at least in current versions) doesn't kill apps after some arbitrary time. It kills them when it needs to free up resources. Since modern iPads have quite a bit of memory, that means that apps can stay in the background for a very long time depending on how the iPad is used. As Andreas notes, however, there are no promises about that.
I'm building an iOS app for iOS 8 & 9 and I am facing the problem that when the app goes to background the system is terminating it after just 2 or 3 minutes.
My testing is easy:
I kill all running apps from my iPhone.
I restart my iPhone (to ensure no other apps are taking memory).
I launch my app.
I do nothing inside my app.
I press the "Home" button, moving my app to background.
I wait doing nothing else for 2 or 3 minutes.
I open my app again and surprise, the system has terminated it and now it is restarting as a new launch.
Some comments:
The app does not use CoreLocation in background neither any other service.
I've profiled the app, trying to understand if it is consuming too much memory. When moving to background, it consumes around 25Mb of RAM memory. I'm attaching a screenshot below.
This behavior has been tested on iPhone 5, 5s, 6, 6+.
In iPhone 6s and 6s+ seems to take a bit more time to happen, but still happens.
My question is: Do you know why would this be happening? anything I might not be considering or just forgetting?
I don't want to force my app to run in background by using CoreLocation or something similar. And I'm ok if the system kills my app eventually. What I don't want is that everytime I move my app to background the system terminates it.
Any hint or help will be appreciated.
Thanks,
All applications are automatically killed by the system
According the Apple documentation:
App Termination
Apps must be prepared for termination to happen at any time and should not >wait to save user data or perform other critical tasks. System-initiated >termination is a normal part of an app’s life cycle. The system usually >terminates apps so that it can reclaim memory and make room for other apps >being launched by the user, but the system may also terminate apps that >are misbehaving or not responding to events in a timely manner.
Suspended apps receive no notification when they are terminated; the >system kills the process and reclaims the corresponding memory. If an app >is currently running in the background and not suspended, the system calls >the applicationWillTerminate: of its app delegate prior to termination. >The system does not call this method when the device reboots.
In addition to the system terminating your app, the user can terminate >your app explicitly using the multitasking UI. User-initiated termination >has the same effect as terminating a suspended app. The app’s process is >killed and no notification is sent to the app.
https://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/TheAppLifeCycle/TheAppLifeCycle.html#//apple_ref/doc/uid/TP40007072-CH2-SW1
You can track position but you will certainly see a blue status bar to indicate that an application use GPS tracking.
Maybe you can try to "wake up" your app in background with silent notification...
If it is not necessary to keep your app alive, trust the system...
Some error in inside your code. Please select debug Navigator before run your app... Now you can able to find your error..
Or too much memory also it will terminated..
Apps which are running in the background drain battery life faster, It gives you a bad perception of the device, instead of the app, because the average consumer has no idea that it's an app draining battery.
Thus iOS won't allow your app to run in the background, more than a few seconds. But there are some exception, an app can request extension to this by declaring that its starting a Background Task.
for more info you can check below links:
http://blog.dkaminsky.info/2013/01/27/keep-your-ios-app-running-in-background-forever/
http://www.speirs.org/blog/2012/1/2/misconceptions-about-ios-multitasking.html
This question might have been asked before but i couldn't find an answer. If i open an app and press home button it goes in background and if i open it again it calls app delegate methods such as "applicationWillEnterForeground". How long it will take me to be in background so app calls didFinishLaunchingWithOptions and starts the fresh app?
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
Thanks
There are many factors that are taken under consideration to remove your app from the memory (kill the process).
The most simple one is rebooting the device. All apps are off after a reboot. Apps with Voip however are launched automatically into the background after a reboot.
The second and most common one is memory pressure. If your app is in the background and system runs out of RAM, it kills the suspended apps starting from the one that consumes the most RAM and keeps killing them until it reclaims enough memory.
Another, quite common one is something known as the watchdog. There are specific scenarios when your app's main thread has a limited time to finish the task. For example, when you app returns from the background or when the user presses the home button, you have about 10s to free the main thread. (Keep in mind there are situations such as background tasks, music playback and other, that grant your app more execution time in the background).
But, a typical app will be killed if the runloop does not return in about 10.
Another case worth mentioning is if your app uses very little RAM. It was mentioned in one of WWDC sessions, that if your application consumes no more than 16MB of RAM, it will be dumped to flash storage, and restored back to the memory on reopening, rather than being killed. So in this case your app may never be killed (I'm not sure about the reboot, but I assume the dumped image is ignored after a reboot and a normal launch process happens).
Next one is the user's explicit action, that is entering the multitasking UI and swiping the app upwards, which will kill the application.
I think that sums up the most common scenarios.
And of course you might also want to have a look at the docs: https://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/TheAppLifeCycle/TheAppLifeCycle.html#//apple_ref/doc/uid/TP40007072-CH2-SW1
How much RAM does the device have? Have much RAM was your app using? Are you following best practices when your app receives didReceiveMemoryWarning:? Are you opening other apps before going back to yours? This is such a "it depends" question.
What's the larger question here? Why do you want to know when your app will get purged from memory?
Is there a any chance that an in memory data might be lost when an iOS app goes to background?
for example if the OS give notice to the app with
didReceiveMemoryWarning and the app didn't take any action to release some space.
so far I have never notice this.
Not instantly, but the app may be terminated at any point, if other apps are used and the system decides, that it needs the memory blocked by your app.