Develop Reference

How to detect process foreground for Android O

On our application there's a service that is normally started during Application.OnCreate (directly calling context.startService) and also later on via AlarmManager (refactor is in progress to migrate some of its work to JobScheduler).
Our application also have a BroadcastReceiver that gets launched with its direct intent.
Given the new limitations in Android Oreo (https://developer.android.com/about/versions/oreo/android-8.0-changes.html) we're having an issue as follows:
app/process is in background/dead
BroadcastReceiver gets fired by the OS
Application.onCreate() executes before the BroadcastReceiver
Application.onCreate() code tries to run the Service
this leads to crash with "IllegalStateException: Not allowed to start service Intent".
I'm aware of the new recommended ways of launching a Service as answered by CommonsWare here https://stackoverflow.com/a/44505719/906362, but for this specific case, I simply want to have if(process in foreground) { startService }. I'm currently using the following method and it seems to work:
#TargetApi(Build.VERSION_CODES.LOLLIPOP)
private static boolean isProcessInForeground_V21(Context context) {
ActivityManager am = (ActivityManager) context.getSystemService(ACTIVITY_SERVICE);
List<ActivityManager.AppTask> tasks = am.getAppTasks();
return tasks.size() > 0;
}
But I can't find the exact checks Android Oreo is doing (I got as far as here https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/app/ContextImpl.java on the startServiceCommon method, but from there requireForeground flag seems to go to some native implementation)
So my question:
For the specific purpose of Android Oreo new limitations, how to check if my process is foreground before calling startService?

To continue your investigation: (TL;DR: see between horizontal lines at the bottom)
Disclaimer, I don't know too much about Android, I just like digging in the source code.
Note: you can also navigate the code in Android Studio if you jump to file instead of class:
or searching for text in Project and Libraries.
IActivityManager is defined by AIDL, that's why there are no sources for it:
https://android.googlesource.com/platform/frameworks/base/+/refs/heads/master/core/java/android/app/IActivityManager.aidl#145
Based on how AIDL needs to be implemented I found that ActivityManagerService extends IActivityManager.Stub (God bless Google indexing).
Note I also found this, which might be an interesting read if you're really interested how things work internally.
https://programmer.group/android-9.0-source-app-startup-process.html
ActivityManagerService sources reveal that in Oreo startService is forwarded to ActiveServices which is located in the same package.
Assuming we're looking for an exception like this:
java.lang.IllegalStateException: Not allowed to start service Intent {...}: app is in background uid UidRecord{af72e61 u0a229 CAC bg:+3m52s273ms idle procs:1 seq(0,0,0)}
we have to continue down the rabbit hole: requireForeground gets assigned to fgRequired parameter and the message is here. The condition to allow this depends on the start mode returned by ActivityManagerService.getAppStartModeLocked(packageTargetSdk = 26 or greater, disabledOnly = false, forcedStandby = false).
There are 4 start modes:
APP_START_MODE_NORMAL (needs to be different than this, i.e. !=)
APP_START_MODE_DELAYED (this is ok, i.e. return null)
APP_START_MODE_DELAYED_RIGID
APP_START_MODE_DISABLED
Ephemeral apps will immediately return APP_START_MODE_DISABLED, but assuming this is a normal app, we end up in appServicesRestrictedInBackgroundLocked.
Note: this is where some of the whitelist mentioned in https://stackoverflow.com/a/46445436/253468 is decided.
Since all branches but last return APP_START_MODE_NORMAL, this redirects to appRestrictedInBackgroundLocked where we find our most likely suspect:
int appRestrictedInBackgroundLocked(int uid, String packageName, int packageTargetSdk) {
// Apps that target O+ are always subject to background check
if (packageTargetSdk >= Build.VERSION_CODES.O) {
return ActivityManager.APP_START_MODE_DELAYED_RIGID;
}
So the reason for denial is simply targeting O. I think the final answer to your question of how the OS decides if your app is foreground or background is this condition in getAppStartModeLocked
UidRecord uidRec = mActiveUids.get(uid);
if (uidRec == null || alwaysRestrict || uidRec.idle) {
My guess is that a missing record means it's not running (but then how is it starting a service?!), and idle means it's backgrounded. Notice that in my exception message the UidRecord is saying that it's idle and has been backgrounded for 3m52s.
I peeked into your getAppTasks and it's based on TaskRecord.effectiveUid, so I'm guessing that's quite close to listing UidRecords for your app.
Not sure if this helps, but I'll post it anyway, so if anyone wants to investigate more, they have more info.

Read logs from Logcat without killing the tablet

I have to read the logs from Logcat and send them to a server through UDP.
For this task I have used this code: https://github.com/chemik/logcatudp
The main problem of that code is that the async Thread that is launched enters a while(true) loop that drains the tablet's battery on the long run.
Is there a way to get the logs in real time but without using a busy wait like that? Hopefully without adding some sleep(some_milliseconds) to reduce the problem?
It would be great to use some sort of event listener but I haven't found one. I have searched in every similar library but without any success.
The code is the following:
while (true) {
String sendingLine = "";
// assume that log writes whole lines
if (bufferedReader.ready()) {
logLine = bufferedReader.readLine();
sendingLine += logLine + System.getProperty("line.separator");
DatagramPacket packet = new DatagramPacket(sendingLine.getBytes(), sendingLine.length(),
InetAddress.getByName(mConfig.mDestServer), mConfig.mDestPort);
try {
mSocket.send(packet);
...
Any idea? Thanks.

Finally the answer was to put a Thread.sleep(10) in the while(true) loop.
It may seem really strange, but also with only 10ms of sleep it reduces the battery usage from almost 40% to 1%.

Android. NDK. How to log calling destructor of global variable?

As we all know android doesn't unload *.so after close application. I had found the solve by adding "exit(0)" at the end, that is solved problem, but I wanna know exactly that all are OK.
The code is work fine as expected after solving the problem:
static int value = 0;
// In android_main
LOGI("value = %d", value); // always print 0, but not 1 after second run of
// application as it was without "exit(0)" at the end
value = 1;
I wanna to test that on class like:
class A {
A() {
LOGI("Constructor");
}
~A() {
LOGI("Destructor");
}
statis A a;
In such way prints only "Constructor".
Maybe because of destructor is calling after when LOGI isn't working more for application that will be closed ?
Question: why LOGI in destructor isn't working? According to first example on top destructor is calling really.

This is not only pointless, but quite possibly counterproductive. If android wants the memory utilized by your process, it will terminate the process to reclaim it; if it doesn't, it won't.
To specifically address your question, killing or exiting a process does not invoke destructors, it merely terminates execution and the kernel bulk-releases all memory and (conventional) resources.
Do not try to second guess the system, as that can frequently result in killing a process only to have android immediately restart it. Further, it can allegedly cause problems with a few Android IPC resources (like the camera) which may not be freed up when the process of a utilizing application unexpectedly dies.

Keep Logcat from deleting entries

In Eclipse, I notice that Logcat only retains a few dozen entries and deletes the older ones as soon as a new one come in. Is there a way to prevent this? I need my app to run for a long time and not lose any entries because my app eventually hangs or crashes after a few days, and I want to see if something in Logcat has been recorded.

I am not sure if this is the most elegant solution to the problem, but you can always increase the LogCat message size in Eclipse.
Window -> Preferences -> Android -> LogCat -> Maximum number of LogCat messages to buffer
The default is 5000, I believe. You can set it to be very high if you are planning to run your application for a long time.

i think you need to increase this show image

Here's a better solution:
Set the Default Uncaught Exception Handler. Whenever the app crashes, this will be called with the exception. Simply write a log entry saying it crashed then dump the logcat to a file. Finally, make sure you re-throw the exception to make sure the app crashes and funky things don't happen. Note: This is per thread, keep that in mind.
Thread.setDefaultUncaughtExceptionHandler(new UncaughtExceptionHandler() {
#Override
public void uncaughtException(Thread thread, Throwable ex) {
Log.e("TAG", "---My app crashed just now---", ex);
//TODO: Dump logcat to file
throw new RuntimeException(ex);
}
});

if you want to keep your app running for days.. its better you capture your logs from adb shell.
the common shell command would be :
logcat -c \\ to clear previous logs
logcat -v time>yourLogs.txt & \\ to capture fresh logs

Measure Android app startup time

What is the most precise way to measure startup time of an Android app?
By startup time I mean the difference between 2. and 3. :
The app process is not running
User clicks on app icon in the launcher
Main Activity is fully initialized
So I basically need to somehow get time elapsed since JVM started and log it.

I understand I am too late to answer, nonetheless, this precisely answers the question.
This information gets logged on Logcat by default for API version 19 or higher.
From Android 4.4 (API level 19), logcat includes an output line containing a value called Displayed. This value represents the amount of time elapsed between launching the process and finishing drawing the corresponding activity on the screen.
ActivityManager: Displayed com.android.myexample/.StartupTiming: +3s534ms
The key is looking for it in the right place -
If you’re tracking logcat output from the command line, or in a terminal, finding the elapsed time is straightforward. To find elapsed time in Android Studio, you must disable filters in your logcat view. Disabling the filters is necessary because the system server, not the app itself, serves this log.
The extracts are from the documentation.

I'm going to interpret your question as 'Is my app startup time fast enough. How can I check I have done everything I can do?'
The startup time is largely a false metric as it will vary across devices and ROMs. I guess what you're most likely to be interested in is how much of your code is taking a long time to execute and what is potentially blocking the main thread.
I've found the most effective way of doing this is to use Traceview on the app start and then reviewing how long it takes the method to execute and if there are any gaps on the main thread.
Start tracing:
public class MyApplication extends Application {
#Override
public void onCreate() {
super.onCreate();
Debug.startMethodTracing("startup");
}
}
Stop tracing:
#Override
public void onViewCreated(final View view, final Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
Debug.stopMethodTracing();
}
Once the trace has been collected, you should be able to see anything that is having a major impact on startup time. In my case, seen below, there was a big gap on the UI thread where is was being blocked.
It transpired that both Crashlytics and Coremetrics were requiring a call to randomUUID() which was then being synchronized across threads and blocking the main thread. The solution was just to spin up a new thread to initialise the Coremetrics code.
This is something I would not have otherwise picked up with just measuring the startup time, but it actually sped up the app 'startup time' by a few hundred milliseconds.
Here's another snapshot after spinning off a separate thread for Coremetrics initialisation:

Check in adb shell in below manner.
adb shell
adb logcat -b events | grep am_activity_launch_time
[Output]
01-01 12:32:53.469 1236 1262 I am_activity_launch_time:
[0,205360373,com.sec.android.app.clockpackage/.ClockPackage,378,**378**,0]
Remarks:
Launch time for Clock is 378ms.

Wrap the entire onCreate() method in a TimingLogger. Just put this at the beginning:
TimingLogger timings = new TimingLogger(TAG, "methodA");
and this at the end:
timings.dumpToLog();
If you want to drop times at some intermediate step, you can do timings.addSplit("name"); to get the time it took to get to that step.

A simple way to display startup time in android.
Sometimes the Displayed line in the logcat output contains an additional field for total time. For example:
ActivityManager: Displayed com.android.myexample/.StartupTiming: +3s534ms (total +1m22s643ms)
In this case, the first time measurement is only for the activity that was first drawn
Source: Time to initial display

It is possible to implement time tracking using the next code:
Override your Application:
public class CustomApplication extends Application {
public final static long APP_START_TIME = System.currentTimeMillis();
/**
* Do all other application stuff
*/
}
And add few rows to your main Activity:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final View contentView = findViewById(android.R.id.content);
contentView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
#Override
public void onGlobalLayout() {
if (Build.VERSION.SDK_INT >= 16) {
contentView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
} else {
contentView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
}
long launchTime = System.currentTimeMillis() - CustomApplication.APP_START_TIME;
Log.e("TEST", "App launch time = " + launchTime);
}
});
}
}
And don't forget to define your custom application in Manifest:
<application
android:label="#string/app_name"
android:name=".CustomApplication" >
</application>
Important: You have to kill your application before launch, because Application stores static variable which tracks initial time.

Use SysTrace
Also the Trace class can be used to measure sections using
Trace.beginSection("name");
Trace.endSection();
This YouTube video is a quick primer as well.

I think this has been built into Firebase Console, under performance now

One possibility would be is to save the time at the beginning of the onCreate() method and at the end of the onCreate() method and then subtract those times from each other to get the time taken to initialize the app.