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Get Day by Day UsageStats with Android Studio [duplicate]

I'm working on an android app for tracking daily app usage. The idea is that a user can set daily time limit for any app and a notification will appear within at most 2 minutes after the limit is exceeded. (The reason for delay: I've created an alarm system using AlarmManager class that will go off every minute to run a JobIntentService which will check whether limit for any app is exceeded)
I've used queryEvents method of UsageStatsManager class to count app usage time.
Here's my code for counting app usage time (I've followed How to use queryEvents):
HashMap<String, Integer> getTimeSpent(Context context, String packageName, long beginTime, long endTime) {
UsageEvents.Event currentEvent;
List<UsageEvents.Event> allEvents = new ArrayList<>();
HashMap<String, Integer> appUsageMap = new HashMap<>();
UsageStatsManager usageStatsManager = (UsageStatsManager)context.getSystemService(Context.USAGE_STATS_SERVICE);
UsageEvents usageEvents = usageStatsManager.queryEvents(beginTime, endTime);
while (usageEvents.hasNextEvent()) {
currentEvent = new UsageEvents.Event();
usageEvents.getNextEvent(currentEvent);
if(currentEvent.getPackageName().equals(packageName) || packageName == null) {
if (currentEvent.getEventType() == UsageEvents.Event.ACTIVITY_RESUMED
|| currentEvent.getEventType() == UsageEvents.Event.ACTIVITY_PAUSED) {
allEvents.add(currentEvent);
String key = currentEvent.getPackageName();
if (appUsageMap.get(key) == null)
appUsageMap.put(key, 0);
}
}
}
for (int i = 0; i < allEvents.size() - 1; i++) {
UsageEvents.Event E0 = allEvents.get(i);
UsageEvents.Event E1 = allEvents.get(i + 1);
if (E0.getEventType() == UsageEvents.Event.ACTIVITY_RESUMED
&& E1.getEventType() == UsageEvents.Event.ACTIVITY_PAUSED
&& E0.getClassName().equals(E1.getClassName())) {
int diff = (int)(E1.getTimeStamp() - E0.getTimeStamp());
diff /= 1000;
Integer prev = appUsageMap.get(E0.getPackageName());
if(prev == null) prev = 0;
appUsageMap.put(E0.getPackageName(), prev + diff);
}
}
return appUsageMap;
}
In short the above code counts the time difference of the timestamp when an app goes foreground (UsageEvents.Event.ACTIVITY_RESUMED) and the timestamp when it goes background (UsageEvents.Event.ACTIVITY_PAUSED). Then it adds this difference to the total usage time of the app.
The problem is that the amount of time spent on foreground can't be counted unless the app goes background. So, if usage limit is exceeded, notification won't appear until the app goes background.
Is it actually possible to get foreground time while app is on foreground?
N.B. I've tried queryUsageStats along with UsageStats.getTotalTimeInForeground() but couldn't succeed since queryUsageStats had some other issues not related to this question.

I've solved the issue.
Adding difference of current time and timestamp of current running app going foreground does the trick.
I just added the following code before the return statement:
UsageEvents.Event lastEvent = allEvents.get(allEvents.size() - 1);
if(lastEvent.getEventType() == UsageEvents.Event.ACTIVITY_RESUMED) {
int diff = (int)System.currentTimeMillis() - (int)lastEvent.getTimeStamp();
diff /= 1000;
Integer prev = appUsageMap.get(lastEvent.getPackageName());
if(prev == null) prev = 0;
appUsageMap.put(lastEvent.getPackageName(), prev + diff);
}
It is pretty straightforward, I should have thought about it before posting the question.

Faster WiFi scanning alternative than WifiManager startScan()?

TL;DR version
I need to scan and get the BSSID / M.A.C address and Signal Level of the nearby Access Points several times a second. WifiManager.startScan() scans about 3.5 seconds which is a bit slow. (better than 6 seconds for others but still too slow for me).
I'm looking for a way to get results every 200ms or maybe even less.
The more detailed version.
I'm trying to build a location finding app that uses WiFi signals instead of the GPS. So far so good with the exception that i need to get a lot of data in order to have accurate and consistent results.
I need to get the BSSID and the Signal Level from every Access Point I can find and than store this data for later use.
I've tried using the WifiManager and the BroadcastReceiver to scan and get the scan results. The problem with them is that they are really slow. It takes at least 3 seconds for a single scan. In 3 seconds signal level value will change , leading to inaccurate results. I also need to have several thousand scans which will take an awful loooot of time. So far I haven't found an alternative.
My phone is currently running Android 8.0.0
Perhaps if I optimise my code the scan will perform faster?
onCreate method:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sensor);
btnMainActivity = (Button) findViewById(R.id.button_ToMainActivity);
btnGetWifiInfo = (Button) findViewById(R.id.button_GetWifiInfo);
textWifiInfo = findViewById(R.id.textView_wifiInfo);
textWifiNr = findViewById(R.id.textView_wifiNr);
mWifiManager = (WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);
mWifiReceiver = new BroadcastReceiver() {
#Override
public void onReceive(Context c, Intent intent) {
getScanResultInfo();
timeDifference = SystemClock.elapsedRealtime() - startTime;
textWifiInfo.setText("Seconds elapsed: "+Double.toString(timeDifference /1000.0));
nrOfScans++;
if (nrOfScans < 10){
mWifiManager.startScan();
}
}
};
getWifiInfo();
toMainActivity();
}
public void getScanResultInfo(){
int level;
List<ScanResult> wifiScanList = mWifiManager.getScanResults();
textWifiNr.setText("Nr of detected APs: "+ wifiScanList.size());
for (ScanResult scanResult : wifiScanList) {
level = WifiManager.calculateSignalLevel(scanResult.level, 5);
Log.d("WIFI","Level is " + level + " out of 5 " + scanResult.level + " on " + scanResult.BSSID + " ");
}
}
And when I press the button the scan starts.
public void getWifiInfo(){
btnGetWifiInfo.setOnClickListener(
new View.OnClickListener() {
#Override
public void onClick(View v) {
finePermission = false;
startTime = SystemClock.elapsedRealtime();
nrOfScans = 0;
checkPermissions();
if ( finePermission == true){
((WifiManager) getApplicationContext().getSystemService(WIFI_SERVICE)).startScan();
mWifiManager.startScan();
}
else {
Log.d("WIFI"," Missing Permissions: "+finePermission);
}
}
}
);
}
Thank you in advance for your time!

You can skip passive channel scanning by using the hidden API, startscanActive.
startScanActive is not an exposed API in android reference; so use it at your own risk. If you must use it, refer this - https://github.com/mozilla/MozStumbler/issues/40
Also, note that if the API indeed scans only active channels as the name suggests, you will not be able to get APs present on passive channels in your scan results

Bad news from official Android side
https://android.googlesource.com/platform/frameworks/base/+/478ee74428e04522d6ac0bf10c30ddaaf62028a4
and
https://android.googlesource.com/platform/frameworks/opt/net/wifi/+/4f11976612567e57eefb0b58c7aef1059f52b45c
announce (or propose?) to significantly limit scanResult requests per time from v9 Pie on.
In concrete values, your app should be limited to max 4 scanResult requests in 2 minutes.
This will be a disaster/nightmare for all existing WiFi-Tool apps.
Official reason: safe battery.
Let's unite our voices and let them know we want Android as a Swiss Army knife and not let it become another white brick.

How to generate more than 1000 events / second in java using sleep time

I have a generator which generates events for Flink CEP, code for which is given below. Basically, I am using Thread.sleep() and I have read somewhere that java can't sleep less than 1 millisecond even we use System.nanoTime(). Code for the generator is
public class RR_interval_Gen extends RichParallelSourceFunction<RRIntervalStreamEvent> {
Integer InputRate ; // events/second
Integer Sleeptime ;
Integer NumberOfEvents;
public RR_interval_Gen(Integer inputRate, Integer numberOfEvents ) {
this.InputRate = inputRate;
Sleeptime = 1000 / InputRate;
NumberOfEvents = numberOfEvents;
}
#Override
public void run(SourceContext<RRIntervalStreamEvent> sourceContext) throws Exception {
long currentTime;
Random random = new Random();
int RRInterval;
int Sensor_id;
for(int i = 1 ; i <= NumberOfEvents ; i++) {
Sensor_id = 2;
currentTime = System.currentTimeMillis();
// int randomNum = rand.nextInt((max - min) + 1) + min;
RRInterval = 10 + random.nextInt((20-10)+ 1);
RRIntervalStreamEvent stream = new RRIntervalStreamEvent(Sensor_id,currentTime,RRInterval);
synchronized (sourceContext.getCheckpointLock())
{
sourceContext.collect(stream);
}
Thread.sleep(Sleeptime);
}
}
#Override
public void cancel() {
}
}
I will specify my requirement here in simple words.
I want generator class to generate events, let's say an ECG stream at 1200 Hz. This generator will accept parameters like input rate and total time for which we have to generate the stream.
So far so good, the issue is that I need to send more than 1000 events / second. How can I do this by using generator function which is generating values U[10,20]?
Also please let me know if I am using wrong way to generate x number of events / second in the above below.
Sleeptime = 1000 / InputRate;
Thanks in advance

The least sleep time in Windows systems is ~ 10 ms and in Linux and Macintosh is 1 millisecond as mentioned here.
The granularity of sleep is generally bound by the thread scheduler's
interrupt period. In Linux, this interrupt period is generally 1ms in
recent kernels. In Windows, the scheduler's interrupt period is
normally around 10 or 15 milliseconds
Through my research, I learned that using the nano time sleep in java will not help as the issue in at OS level. If you want to send data at arrival rate > 1000 in a controlled way, then it can be done using Real-Time Operating Systems (RTOS), as they can sleep for less then a millisecond. Now, I have come up with another way of doing it, but in this solution, the interarrival times will not be constantly distributed.
Let's say you want arrival rate of 3000 events/ second, then you can create a for loop which iterates 3 times to send data in each iteration and then sleep for 1ms. So for the 3 tuples, the interarrival time will be close to one another, but the issue will be solved. This may be a stupid solution but it works.
Please let me know if there is some better solution to this.

Java calculations that takes X amount of time

This is just a hypothetical question, but could be a way to get around an issue I have been having.
Imagine you want to be able to time a calculation function based not on the answer, but on the time it takes to calculating. So instead of finding out what a + b is, you wish to continue perform some calculation while time < x seconds.
Look at this pseudo code:
public static void performCalculationsForTime(int seconds)
{
// Get start time
int millisStart = System.currentTimeMillis();
// Perform calculation to find the 1000th digit of PI
// Check if the given amount of seconds have passed since millisStart
// If number of seconds have not passed, redo the 1000th PI digit calculation
// At this point the time has passed, return the function.
}
Now I know that I am horrible, despicable person for using precious CPU cycles to simple get time to pass, but what I am wondering is:
A) Is this possible and would JVM start complaining about non-responsiveness?
B) If it is possible, what calculations would be best to try to perform?
Update - Answer:
Based on the answers and comments, the answer seems to be that "Yes, this is possible. But only if it is not done in Android main UI thread, because the user's GUI will be become unresponsive and will throw an ANR after 5 seconds."

A) Is this possible and would JVM start complaining about non-responsiveness?
It is possible, and if you run it in the background, neither JVM nor Dalvik will complain.
B) If it is possible, what calculations would be best to try to perform?
If the objective is to just run any calculation for x seconds, just keep adding 1 to a sum until the required time has reached. Off the top of my head, something like:
public static void performCalculationsForTime(int seconds)
{
// Get start time
int secondsStart = System.currentTimeMillis()/1000;
int requiredEndTime = millisStart + seconds;
float sum = 0;
while(secondsStart != requiredEndTime) {
sum = sum + 0.1;
secondsStart = System.currentTimeMillis()/1000;
}
}

You can and JVM won't complain if your code is not part of some complex system that actually tracks thread execution time.
long startTime = System.currentTimeMillis();
while(System.currentTimeMillis() - startTime < 100000) {
// do something
}
Or even a for loop that checks time only every 1000 cycles.
for (int i = 0; ;i++) {
if (i % 1000 == 0 && System.currentTimeMillis() - startTime < 100000)
break;
// do something
}
As for your second question, the answer is probably calculating some value that can always be improved upon, like your PI digits example.

Attempting to create a stable game engine loop

I'm writing a fairly simple 2D multiplayer-over-network game. Right now, I find it nearly impossible for myself to create a stable loop. By stable I mean such kind of loop inside which certain calculations are done and which is repeated over strict periods of time (let's say, every 25 ms, that's what I'm fighting for right now). I haven't faced many severe hindrances this far except for this one.
In this game, several threads are running, both in server and client applications, assigned to various tasks. Let's take for example engine thread in my server application. In this thread, I try to create game loop using Thread.sleep, trying to take in account time taken by game calculations. Here's my loop, placed within run() method. Tick() function is payload of the loop. It simply contains ordered calls to other methods doing constant game updating.
long engFPS = 40;
long frameDur = 1000 / engFPS;
long lastFrameTime;
long nextFrame;
<...>
while(true)
{
lastFrameTime = System.currentTimeMillis();
nextFrame = lastFrameTime + frameDur;
Tick();
if(nextFrame - System.currentTimeMillis() > 0)
{
try
{
Thread.sleep(nextFrame - System.currentTimeMillis());
}
catch(Exception e)
{
System.err.println("TSEngine :: run :: " + e);
}
}
}
The major problem is that Thread.sleep just loves to betray your expectations about how much it will sleep. It can easily put thread to rest for much longer or much shorter time, especially on some machines with Windows XP (I've tested it myself, WinXP gives really nasty results compared to Win7 and other OS). I've poked around internets quite a lot, and result was disappointing. It seems to be fault of the thread scheduler of the OS we're running on, and its so-called granularity. As far as I understood, this scheduler constantly, over certain amount of time, checks demands of every thread in system, in particular, puts/awakes them from sleep. When re-checking time is low, like 1ms, things may seem smooth. Although, it is said that WinXP has granularity as high as 10 or 15 ms. I've also read that not only Java programmers, but those using other languages face this problem as well.
Knowing this, it seems almost impossible to make a stable, sturdy, reliable game engine. Nevertheless, they're everywhere.
I'm highly wondering by which means this problem can be fought or circumvented. Could someone more experienced give me a hint on this?

Don't rely on the OS or any timer mechanism to wake your thread or invoke some callback at a precise point in time or after a precise delay. It's just not going to happen.
The way to deal with this is instead of setting a sleep/callback/poll interval and then assuming that the interval is kept with a high degree of precision, keep track of the amount of time that has elapsed since the previous iteration and use that to determine what the current state should be. Pass this amount through to anything that updates state based upon the current "frame" (really you should design your engine in a way that the internal components don't know or care about anything as concrete as a frame; so that instead there is just state that moves fluidly through time, and when a new frame needs to be sent for rendering a snapshot of this state is used).
So for example, you might do:
long maxWorkingTimePerFrame = 1000 / FRAMES_PER_SECOND; //this is optional
lastStartTime = System.currentTimeMillis();
while(true)
{
long elapsedTime = System.currentTimeMillis() - lastStartTime;
lastStartTime = System.currentTimeMillis();
Tick(elapsedTime);
//enforcing a maximum framerate here is optional...you don't need to sleep the thread
long processingTimeForCurrentFrame = System.currentTimeMillis() - lastStartTime;
if(processingTimeForCurrentFrame < maxWorkingTimePerFrame)
{
try
{
Thread.sleep(maxWorkingTimePerFrame - processingTimeForCurrentFrame);
}
catch(Exception e)
{
System.err.println("TSEngine :: run :: " + e);
}
}
}
Also note that you can get greater timer granularity by using System.nanoTime() in place of System.currentTimeMillis().

You may getter better results with
LockSupport.parkNanos(long nanos)
altho it complicates the code a bit compared to sleep()

maybe this helps you.
its from david brackeen's bock developing games in java
and calculates average granularity to fake a more fluent framerate:
link
public class TimeSmoothie {
/**
How often to recalc the frame rate
*/
protected static final long FRAME_RATE_RECALC_PERIOD = 500;
/**
Don't allow the elapsed time between frames to be more than 100 ms
*/
protected static final long MAX_ELAPSED_TIME = 100;
/**
Take the average of the last few samples during the last 100ms
*/
protected static final long AVERAGE_PERIOD = 100;
protected static final int NUM_SAMPLES_BITS = 6; // 64 samples
protected static final int NUM_SAMPLES = 1 << NUM_SAMPLES_BITS;
protected static final int NUM_SAMPLES_MASK = NUM_SAMPLES - 1;
protected long[] samples;
protected int numSamples = 0;
protected int firstIndex = 0;
// for calculating frame rate
protected int numFrames = 0;
protected long startTime;
protected float frameRate;
public TimeSmoothie() {
samples = new long[NUM_SAMPLES];
}
/**
Adds the specified time sample and returns the average
of all the recorded time samples.
*/
public long getTime(long elapsedTime) {
addSample(elapsedTime);
return getAverage();
}
/**
Adds a time sample.
*/
public void addSample(long elapsedTime) {
numFrames++;
// cap the time
elapsedTime = Math.min(elapsedTime, MAX_ELAPSED_TIME);
// add the sample to the list
samples[(firstIndex + numSamples) & NUM_SAMPLES_MASK] =
elapsedTime;
if (numSamples == samples.length) {
firstIndex = (firstIndex + 1) & NUM_SAMPLES_MASK;
}
else {
numSamples++;
}
}
/**
Gets the average of the recorded time samples.
*/
public long getAverage() {
long sum = 0;
for (int i=numSamples-1; i>=0; i--) {
sum+=samples[(firstIndex + i) & NUM_SAMPLES_MASK];
// if the average period is already reached, go ahead and return
// the average.
if (sum >= AVERAGE_PERIOD) {
Math.round((double)sum / (numSamples-i));
}
}
return Math.round((double)sum / numSamples);
}
/**
Gets the frame rate (number of calls to getTime() or
addSample() in real time). The frame rate is recalculated
every 500ms.
*/
public float getFrameRate() {
long currTime = System.currentTimeMillis();
// calculate the frame rate every 500 milliseconds
if (currTime > startTime + FRAME_RATE_RECALC_PERIOD) {
frameRate = (float)numFrames * 1000 /
(currTime - startTime);
startTime = currTime;
numFrames = 0;
}
return frameRate;
}
}