What's the difference if I call System.exit() vs. killProcess().
I am interested in difference only
I dont think There is any difference. although with System.exit(), you should call runFinalizersOnExit first
What should we use?
No one, read this Is quitting an application frowned upon?
It looks like System.exit() is just as good in every respect as kill -- but much simpler and less dependent on other things.
Some have suggested that runFinalizersOnExit be set but according to the docs that is considered unsafe and is phased out as of 1.0 -- so I guess ignore that part.
Contrary to other suggestions, finish() does not end the Linux process which is running the app and does not free up all the memory used by the app.
Granted, android is designed so that for many cases there's no particular need to actually exit an app (At the cost of a slight pause later, android will kill your old apps when it needs their memory) -- however if you do want for any reason to kill your app System.exit() seems to be the idea way. It shuts down the java virtual machine which is running your app - so all resources, memory, and threads will be completely flushed out.
(Note that you can specify in your manifest file that some threads should run in different linux processes -- in which case System.exit() would probably only kill part of your app - but that's more advanced stuff.)
As a matter of fact, I just ran adb shell ps|grep app and I see the com.example.android.lunarlander sample app which I haven't run in about a week -- still in memory, still taking up almost 100000 bytes of memory.
Neither. Use finish(). See this, and the link aromero recommended. Let Android do what what it is meant to do: manage your activity life-cycle. It was designed this way for a reason.
Related
I am developing an android application in which i need to perform an action when other apps are closed / force stopped. This detection has to be made from a service which is been running in the background once started. Making the service to run continuously is not a problem but making detection when other apps are closed is the problem. Please do anyone have any solution.....
I don't believe it's possible to detect when an app is force stopped. Even the app being stopped doesn't get that information. You can detect if an app is currently closed by using the BroadcastReceiver. Here's a pretty decent tutorial on using that: http://saigeethamn.blogspot.com/2009/10/android-developer-tutorial-part-11.html
I am not aware of any official way in which Android allows apps to listen in on when other apps are forced to close. So you’d have to poke around under the hood.
Disclaimer: Doing so is unsupported. While just reading information is unlikely to cause any harm, there’s no guarantee that it will work universally. If you get it to work on your particular build of Android, may still fail on different builds. Also, Google keeps locking down features in Android with every new version, so there’s a high likelihood a future update may break things.
I haven’t actually tried any of the below, hence there is a possibility they will fail to produce the expected result.
That being said, here are a few things you can try. You may need to combine them to get something useful out of them.
Processes
Since Android is based on a (somewhat) modified Linux kernel, it generally supports most Unix mechanisms for working with processes.
Apps are launched by a process called zygote. A quick run of ps on an Android device shows me that all user apps (as well as the higher-level system apps) seem to be children of the zygote process. Thus you could get a list of all processes, find the PID for zygote and grab all its child processes.
Then you might be able to waitpid() on each process and examine its exit status. You may want to experiment around with this a bit and see if the exit codes tell you anything about how the process ended.
Also take a look at ptrace(). You might be able to monitor zygote directly with an option such as PTRACE_O_TRACEFORK, which should basically notify you each time a new app is launched, allowing you to monitor its PID as well.
Downside: You probably need to be root to do any of this. Linux doesn’t let users see other users’ processes (which is an essential security feature), and Android harnesses (or abuses) the user model by running each app with a separate Linux UID.
Logcat
Looking at various logcat apps (e.g. aLogcat), you might be able to monitor the logcat for events like this:
12-26 10:01:27.670 I/ActivityManager( 774): Process org.openbmap (pid 21647) has died.
There are a few events that may occur when an app crashes—ActivityManager will tell you when an app has died, or you might watch for unhandled exceptions.
Note: While this doesn’t seem to require root (aLogcat works fine without), it may not work under all conditions. I have seen devices where aLogcat sees next to no entries, though I didn't investigate why. In those cases, the above approach would not work as it depends on being able to read the logcat.
This discussion (in the comments) raised an interesting question :
What is the result of calling exit in an Android app (with regards to the android life-cycle) and can that damage the OS ?
What is the result of calling exit in an Android app (with regards to the android life-cycle)
The Android documentation for System.exit() says that it "Causes the VM to stop running and the program to exit." I just tried it and it seems to kill the process for the app that called System.exit().
In the Android Developers thread named Activity.finish() x System.exit, someone corroborates that "System.exit() kills your entire process."
Dianne Hackborn aka hackbod goes further "To be clear: using System.exit() is strongly recommended against, and can cause some poor interactions with the system. Please don't design your app to need it."
and can that damage the OS ?
It should not damage the OS. Android will just let your app kill its process, not any other process on the system. It will keep the rest of the system running while your app ends.
I also verified this by running two applications and making one of them call System.exit(). The other was unaffected.
I couldn't find any good application for streaming MP3s from a URL that can run in the background that meets my requirements so I decided to write one myself. It turns out its incredibly easy to stream an MP3 with the native MediaPlayer if you're running Froyo or better, and I am.
But my problem is if I switch applications and try to keep the stream going (some of them last 2-4 hours) and play a game or something while i'm listening to it, it sometimes just dies. I'm not sure exactly what the problem is, my guess is that the Android system decided it was OK to kill that process... but it wasn't.
So is there something I can do to make it kill other processes if resources are needed instead of my streaming mp3 app?
What I have tried:
android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_AUDIO);
But it's no good.
You need to make the service a foreground service, if you haven't already. Foreground services have to display an icon in the notification bar, and the Android system will not kill them unless under extreme memory pressure.
Check out the documents for startForeground()
I found that after my Droid Incredible was updated to Gingerbread (2.3.4) all of a sudden it works. I made no changes at all, it just doesn't die in Gingerbread like it did in Froyo. I know there were media player improvements in Gingerbread so I'm going to have to assume there was a bug in Froyo that was fixed in Gingerbread.
As far as i know, a program can't be running forever, at some point the OS will kill it. But what you can try is to have a service and make it generate notifications once in a while with useful information. Then, start the activity again.
This is due to an activity Lifecycle. The OS might kill your app if it need memory. You might have to consider a service
I have had problems with memory management in my Android phone, which terminated processes like you described. You may consider installing a program like Android Booster to monitor available memory and close programs that are using too much memory, so that the programs you would like to keep open have enough memory to run.
I've seen that if you kill some process, it restarts immediately and keep running. How this implemented? How to inform system that my service should not be killed and if that happened - restart it.
Android just does it. As an OS, Android is specifically designed to run with ram full at all times. So if you kill, or an app force closes it will, if their is room in ram for it be restarted by Android to fill the ram back up.
It does this because even the "fastest" phones are snails to even the most average of desktops and keeping as many programs that you use loaded in ram as possible enables it to simply "resume" the program instead of having to go through the slooooow, time wasting process of having to reload it back into ram and then running it from the beginning.
Android kernels have their own task manager. This means that it will be more efficient than any app-based task manager as it is run at the kernel level, and it should be left up to that task killer to decide when to free up memory or not free up memory. Let Android do what it was designed to do. Anything you do to try and force it to rerun a program or stop a program will, in the long run, slow it down more and possibly even cause stability issues.
However the short answer to your question is that there is no way to tell the "system" that your process should not be killed or to restart when it is closed. That is a choice made entirely by the kernel level task manager.
BTW, why would you want to? I ask this because I don't think you have thought this through very well. Remember, unlike IOS owners who are used to and expect total control over their device to be in the hands of Apple(for good or ill) Android owners expect, and will have control over their device. If you try to take that away from them, you will likely find most people uninstalling your service. And demanding their money back if you charge a fee for it.
I hope this has helped.
Not sure this is something that's good, but I've seen malware processes that have "buddy" processes that revive each other when one or more go down.
I hope whatever you're doing is ethical :-)
I want to make startup cleaner application for Android 1.6. My query is how to manage application that starts while phone boot or starts.
Thanks
I may be wrong but I don't believe you're going to be able to do this in the way described. You could certainly kill off apps that area already running [with the appropriate permissions] but I don't think there's any way to manage when other apps start due to the individual sandbox-style architecture - At least not without rooting the phone