examples/androidapp/src/org/appspot/apprtc/CpuMonitor.java - src.git - Git at Google

 /*
  *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */

 package org.appspot.apprtc;

 import android.annotation.TargetApi;
 import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
 import android.os.BatteryManager;
 import android.os.Build;
 import android.os.SystemClock;
 import android.util.Log;
 import java.io.BufferedReader;
 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.FileReader;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.nio.charset.Charset;
 import java.util.Arrays;
 import java.util.Scanner;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
 import javax.annotation.Nullable;

 /**
  * Simple CPU monitor.  The caller creates a CpuMonitor object which can then
  * be used via sampleCpuUtilization() to collect the percentual use of the
  * cumulative CPU capacity for all CPUs running at their nominal frequency.  3
  * values are generated: (1) getCpuCurrent() returns the use since the last
  * sampleCpuUtilization(), (2) getCpuAvg3() returns the use since 3 prior
  * calls, and (3) getCpuAvgAll() returns the use over all SAMPLE_SAVE_NUMBER
  * calls.
  *
  * <p>CPUs in Android are often "offline", and while this of course means 0 Hz
  * as current frequency, in this state we cannot even get their nominal
  * frequency.  We therefore tread carefully, and allow any CPU to be missing.
  * Missing CPUs are assumed to have the same nominal frequency as any close
  * lower-numbered CPU, but as soon as it is online, we'll get their proper
  * frequency and remember it.  (Since CPU 0 in practice always seem to be
  * online, this unidirectional frequency inheritance should be no problem in
  * practice.)
  *
  * <p>Caveats:
  *   o No provision made for zany "turbo" mode, common in the x86 world.
  *   o No provision made for ARM big.LITTLE; if CPU n can switch behind our
  *     back, we might get incorrect estimates.
  *   o This is not thread-safe.  To call asynchronously, create different
  *     CpuMonitor objects.
  *
  * <p>If we can gather enough info to generate a sensible result,
  * sampleCpuUtilization returns true.  It is designed to never throw an
  * exception.
  *
  * <p>sampleCpuUtilization should not be called too often in its present form,
  * since then deltas would be small and the percent values would fluctuate and
  * be unreadable. If it is desirable to call it more often than say once per
  * second, one would need to increase SAMPLE_SAVE_NUMBER and probably use
  * Queue<Integer> to avoid copying overhead.
  *
  * <p>Known problems:
  *   1. Nexus 7 devices running Kitkat have a kernel which often output an
  *      incorrect 'idle' field in /proc/stat.  The value is close to twice the
  *      correct value, and then returns to back to correct reading.  Both when
  *      jumping up and back down we might create faulty CPU load readings.
  */
 @TargetApi(Build.VERSION_CODES.KITKAT)
 class CpuMonitor {
   private static final String TAG = "CpuMonitor";
   private static final int MOVING_AVERAGE_SAMPLES = 5;

   private static final int CPU_STAT_SAMPLE_PERIOD_MS = 2000;
   private static final int CPU_STAT_LOG_PERIOD_MS = 6000;

   private final Context appContext;
   // User CPU usage at current frequency.
   private final MovingAverage userCpuUsage;
   // System CPU usage at current frequency.
   private final MovingAverage systemCpuUsage;
   // Total CPU usage relative to maximum frequency.
   private final MovingAverage totalCpuUsage;
   // CPU frequency in percentage from maximum.
   private final MovingAverage frequencyScale;

   @Nullable
   private ScheduledExecutorService executor;
   private long lastStatLogTimeMs;
   private long[] cpuFreqMax;
   private int cpusPresent;
   private int actualCpusPresent;
   private boolean initialized;
   private boolean cpuOveruse;
   private String[] maxPath;
   private String[] curPath;
   private double[] curFreqScales;
   @Nullable
   private ProcStat lastProcStat;

   private static class ProcStat {
     final long userTime;
     final long systemTime;
     final long idleTime;

     ProcStat(long userTime, long systemTime, long idleTime) {
       this.userTime = userTime;
       this.systemTime = systemTime;
       this.idleTime = idleTime;
     }
   }

   private static class MovingAverage {
     private final int size;
     private double sum;
     private double currentValue;
     private double[] circBuffer;
     private int circBufferIndex;

     public MovingAverage(int size) {
       if (size <= 0) {
         throw new AssertionError("Size value in MovingAverage ctor should be positive.");
       }
       this.size = size;
       circBuffer = new double[size];
     }

     public void reset() {
       Arrays.fill(circBuffer, 0);
       circBufferIndex = 0;
       sum = 0;
       currentValue = 0;
     }

     public void addValue(double value) {
       sum -= circBuffer[circBufferIndex];
       circBuffer[circBufferIndex++] = value;
       currentValue = value;
       sum += value;
       if (circBufferIndex >= size) {
         circBufferIndex = 0;
       }
     }

     public double getCurrent() {
       return currentValue;
     }

     public double getAverage() {
       return sum / (double) size;
     }
   }

   public static boolean isSupported() {
     return Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT
         && Build.VERSION.SDK_INT < Build.VERSION_CODES.N;
   }

   public CpuMonitor(Context context) {
     if (!isSupported()) {
       throw new RuntimeException("CpuMonitor is not supported on this Android version.");
     }

     Log.d(TAG, "CpuMonitor ctor.");
     appContext = context.getApplicationContext();
     userCpuUsage = new MovingAverage(MOVING_AVERAGE_SAMPLES);
     systemCpuUsage = new MovingAverage(MOVING_AVERAGE_SAMPLES);
     totalCpuUsage = new MovingAverage(MOVING_AVERAGE_SAMPLES);
     frequencyScale = new MovingAverage(MOVING_AVERAGE_SAMPLES);
     lastStatLogTimeMs = SystemClock.elapsedRealtime();

     scheduleCpuUtilizationTask();
   }

   public void pause() {
     if (executor != null) {
       Log.d(TAG, "pause");
       executor.shutdownNow();
       executor = null;
     }
   }

   public void resume() {
     Log.d(TAG, "resume");
     resetStat();
     scheduleCpuUtilizationTask();
   }

   // TODO(bugs.webrtc.org/8491): Remove NoSynchronizedMethodCheck suppression.
   @SuppressWarnings("NoSynchronizedMethodCheck")
   public synchronized void reset() {
     if (executor != null) {
       Log.d(TAG, "reset");
       resetStat();
       cpuOveruse = false;
     }
   }

   // TODO(bugs.webrtc.org/8491): Remove NoSynchronizedMethodCheck suppression.
   @SuppressWarnings("NoSynchronizedMethodCheck")
   public synchronized int getCpuUsageCurrent() {
     return doubleToPercent(userCpuUsage.getCurrent() + systemCpuUsage.getCurrent());
   }

   // TODO(bugs.webrtc.org/8491): Remove NoSynchronizedMethodCheck suppression.
   @SuppressWarnings("NoSynchronizedMethodCheck")
   public synchronized int getCpuUsageAverage() {
     return doubleToPercent(userCpuUsage.getAverage() + systemCpuUsage.getAverage());
   }

   // TODO(bugs.webrtc.org/8491): Remove NoSynchronizedMethodCheck suppression.
   @SuppressWarnings("NoSynchronizedMethodCheck")
   public synchronized int getFrequencyScaleAverage() {
     return doubleToPercent(frequencyScale.getAverage());
   }

   private void scheduleCpuUtilizationTask() {
     if (executor != null) {
       executor.shutdownNow();
       executor = null;
     }

     executor = Executors.newSingleThreadScheduledExecutor();
     @SuppressWarnings("unused") // Prevent downstream linter warnings.
     Future<?> possiblyIgnoredError = executor.scheduleAtFixedRate(new Runnable() {
       @Override
       public void run() {
         cpuUtilizationTask();
       }
     }, 0, CPU_STAT_SAMPLE_PERIOD_MS, TimeUnit.MILLISECONDS);
   }

   private void cpuUtilizationTask() {
     boolean cpuMonitorAvailable = sampleCpuUtilization();
     if (cpuMonitorAvailable
         && SystemClock.elapsedRealtime() - lastStatLogTimeMs >= CPU_STAT_LOG_PERIOD_MS) {
       lastStatLogTimeMs = SystemClock.elapsedRealtime();
       String statString = getStatString();
       Log.d(TAG, statString);
     }
   }

   private void init() {
     try (FileInputStream fin = new FileInputStream("/sys/devices/system/cpu/present");
          InputStreamReader streamReader = new InputStreamReader(fin, Charset.forName("UTF-8"));
          BufferedReader reader = new BufferedReader(streamReader);
          Scanner scanner = new Scanner(reader).useDelimiter("[-\n]");) {
       scanner.nextInt(); // Skip leading number 0.
       cpusPresent = 1 + scanner.nextInt();
       scanner.close();
     } catch (FileNotFoundException e) {
       Log.e(TAG, "Cannot do CPU stats since /sys/devices/system/cpu/present is missing");
     } catch (IOException e) {
       Log.e(TAG, "Error closing file");
     } catch (Exception e) {
       Log.e(TAG, "Cannot do CPU stats due to /sys/devices/system/cpu/present parsing problem");
     }

     cpuFreqMax = new long[cpusPresent];
     maxPath = new String[cpusPresent];
     curPath = new String[cpusPresent];
     curFreqScales = new double[cpusPresent];
     for (int i = 0; i < cpusPresent; i++) {
       cpuFreqMax[i] = 0; // Frequency "not yet determined".
       curFreqScales[i] = 0;
       maxPath[i] = "/sys/devices/system/cpu/cpu" + i + "/cpufreq/cpuinfo_max_freq";
       curPath[i] = "/sys/devices/system/cpu/cpu" + i + "/cpufreq/scaling_cur_freq";
     }

     lastProcStat = new ProcStat(0, 0, 0);
     resetStat();

     initialized = true;
   }

   private synchronized void resetStat() {
     userCpuUsage.reset();
     systemCpuUsage.reset();
     totalCpuUsage.reset();
     frequencyScale.reset();
     lastStatLogTimeMs = SystemClock.elapsedRealtime();
   }

   private int getBatteryLevel() {
     // Use sticky broadcast with null receiver to read battery level once only.
     Intent intent = appContext.registerReceiver(
         null /* receiver */, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));

     int batteryLevel = 0;
     int batteryScale = intent.getIntExtra(BatteryManager.EXTRA_SCALE, 100);
     if (batteryScale > 0) {
       batteryLevel =
           (int) (100f * intent.getIntExtra(BatteryManager.EXTRA_LEVEL, 0) / batteryScale);
     }
     return batteryLevel;
   }

   /**
    * Re-measure CPU use.  Call this method at an interval of around 1/s.
    * This method returns true on success.  The fields
    * cpuCurrent, cpuAvg3, and cpuAvgAll are updated on success, and represents:
    * cpuCurrent: The CPU use since the last sampleCpuUtilization call.
    * cpuAvg3: The average CPU over the last 3 calls.
    * cpuAvgAll: The average CPU over the last SAMPLE_SAVE_NUMBER calls.
    */
   private synchronized boolean sampleCpuUtilization() {
     long lastSeenMaxFreq = 0;
     long cpuFreqCurSum = 0;
     long cpuFreqMaxSum = 0;

     if (!initialized) {
       init();
     }
     if (cpusPresent == 0) {
       return false;
     }

     actualCpusPresent = 0;
     for (int i = 0; i < cpusPresent; i++) {
       /*
        * For each CPU, attempt to first read its max frequency, then its
        * current frequency.  Once as the max frequency for a CPU is found,
        * save it in cpuFreqMax[].
        */

       curFreqScales[i] = 0;
       if (cpuFreqMax[i] == 0) {
         // We have never found this CPU's max frequency.  Attempt to read it.
         long cpufreqMax = readFreqFromFile(maxPath[i]);
         if (cpufreqMax > 0) {
           Log.d(TAG, "Core " + i + ". Max frequency: " + cpufreqMax);
           lastSeenMaxFreq = cpufreqMax;
           cpuFreqMax[i] = cpufreqMax;
           maxPath[i] = null; // Kill path to free its memory.
         }
       } else {
         lastSeenMaxFreq = cpuFreqMax[i]; // A valid, previously read value.
       }

       long cpuFreqCur = readFreqFromFile(curPath[i]);
       if (cpuFreqCur == 0 && lastSeenMaxFreq == 0) {
         // No current frequency information for this CPU core - ignore it.
         continue;
       }
       if (cpuFreqCur > 0) {
         actualCpusPresent++;
       }
       cpuFreqCurSum += cpuFreqCur;

       /* Here, lastSeenMaxFreq might come from
        * 1. cpuFreq[i], or
        * 2. a previous iteration, or
        * 3. a newly read value, or
        * 4. hypothetically from the pre-loop dummy.
        */
       cpuFreqMaxSum += lastSeenMaxFreq;
       if (lastSeenMaxFreq > 0) {
         curFreqScales[i] = (double) cpuFreqCur / lastSeenMaxFreq;
       }
     }

     if (cpuFreqCurSum == 0 || cpuFreqMaxSum == 0) {
       Log.e(TAG, "Could not read max or current frequency for any CPU");
       return false;
     }

     /*
      * Since the cycle counts are for the period between the last invocation
      * and this present one, we average the percentual CPU frequencies between
      * now and the beginning of the measurement period.  This is significantly
      * incorrect only if the frequencies have peeked or dropped in between the
      * invocations.
      */
     double currentFrequencyScale = cpuFreqCurSum / (double) cpuFreqMaxSum;
     if (frequencyScale.getCurrent() > 0) {
       currentFrequencyScale = (frequencyScale.getCurrent() + currentFrequencyScale) * 0.5;
     }

     ProcStat procStat = readProcStat();
     if (procStat == null) {
       return false;
     }

     long diffUserTime = procStat.userTime - lastProcStat.userTime;
     long diffSystemTime = procStat.systemTime - lastProcStat.systemTime;
     long diffIdleTime = procStat.idleTime - lastProcStat.idleTime;
     long allTime = diffUserTime + diffSystemTime + diffIdleTime;

     if (currentFrequencyScale == 0 || allTime == 0) {
       return false;
     }

     // Update statistics.
     frequencyScale.addValue(currentFrequencyScale);

     double currentUserCpuUsage = diffUserTime / (double) allTime;
     userCpuUsage.addValue(currentUserCpuUsage);

     double currentSystemCpuUsage = diffSystemTime / (double) allTime;
     systemCpuUsage.addValue(currentSystemCpuUsage);

     double currentTotalCpuUsage =
         (currentUserCpuUsage + currentSystemCpuUsage) * currentFrequencyScale;
     totalCpuUsage.addValue(currentTotalCpuUsage);

     // Save new measurements for next round's deltas.
     lastProcStat = procStat;

     return true;
   }

   private int doubleToPercent(double d) {
     return (int) (d * 100 + 0.5);
   }

   private synchronized String getStatString() {
     StringBuilder stat = new StringBuilder();
     stat.append("CPU User: ")
         .append(doubleToPercent(userCpuUsage.getCurrent()))
         .append("/")
         .append(doubleToPercent(userCpuUsage.getAverage()))
         .append(". System: ")
         .append(doubleToPercent(systemCpuUsage.getCurrent()))
         .append("/")
         .append(doubleToPercent(systemCpuUsage.getAverage()))
         .append(". Freq: ")
         .append(doubleToPercent(frequencyScale.getCurrent()))
         .append("/")
         .append(doubleToPercent(frequencyScale.getAverage()))
         .append(". Total usage: ")
         .append(doubleToPercent(totalCpuUsage.getCurrent()))
         .append("/")
         .append(doubleToPercent(totalCpuUsage.getAverage()))
         .append(". Cores: ")
         .append(actualCpusPresent);
     stat.append("( ");
     for (int i = 0; i < cpusPresent; i++) {
       stat.append(doubleToPercent(curFreqScales[i])).append(" ");
     }
     stat.append("). Battery: ").append(getBatteryLevel());
     if (cpuOveruse) {
       stat.append(". Overuse.");
     }
     return stat.toString();
   }

   /**
    * Read a single integer value from the named file.  Return the read value
    * or if an error occurs return 0.
    */
   private long readFreqFromFile(String fileName) {
     long number = 0;
     try (FileInputStream stream = new FileInputStream(fileName);
          InputStreamReader streamReader = new InputStreamReader(stream, Charset.forName("UTF-8"));
          BufferedReader reader = new BufferedReader(streamReader)) {
       String line = reader.readLine();
       number = parseLong(line);
     } catch (FileNotFoundException e) {
       // CPU core is off, so file with its scaling frequency .../cpufreq/scaling_cur_freq
       // is not present. This is not an error.
     } catch (IOException e) {
       // CPU core is off, so file with its scaling frequency .../cpufreq/scaling_cur_freq
       // is empty. This is not an error.
     }
     return number;
   }

   private static long parseLong(String value) {
     long number = 0;
     try {
       number = Long.parseLong(value);
     } catch (NumberFormatException e) {
       Log.e(TAG, "parseLong error.", e);
     }
     return number;
   }

   /*
    * Read the current utilization of all CPUs using the cumulative first line
    * of /proc/stat.
    */
   @SuppressWarnings("StringSplitter")
   private @Nullable ProcStat readProcStat() {
     long userTime = 0;
     long systemTime = 0;
     long idleTime = 0;
     try (FileInputStream stream = new FileInputStream("/proc/stat");
          InputStreamReader streamReader = new InputStreamReader(stream, Charset.forName("UTF-8"));
          BufferedReader reader = new BufferedReader(streamReader)) {
       // line should contain something like this:
       // cpu  5093818 271838 3512830 165934119 101374 447076 272086 0 0 0
       //       user    nice  system     idle   iowait  irq   softirq
       String line = reader.readLine();
       String[] lines = line.split("\\s+");
       int length = lines.length;
       if (length >= 5) {
         userTime = parseLong(lines[1]); // user
         userTime += parseLong(lines[2]); // nice
         systemTime = parseLong(lines[3]); // system
         idleTime = parseLong(lines[4]); // idle
       }
       if (length >= 8) {
         userTime += parseLong(lines[5]); // iowait
         systemTime += parseLong(lines[6]); // irq
         systemTime += parseLong(lines[7]); // softirq
       }
     } catch (FileNotFoundException e) {
       Log.e(TAG, "Cannot open /proc/stat for reading", e);
       return null;
     } catch (Exception e) {
       Log.e(TAG, "Problems parsing /proc/stat", e);
       return null;
     }
     return new ProcStat(userTime, systemTime, idleTime);
   }
 }
	/*
	* Copyright 2015 The WebRTC Project Authors. All rights reserved.
	*
	* Use of this source code is governed by a BSD-style license
	* that can be found in the LICENSE file in the root of the source
	* tree. An additional intellectual property rights grant can be found
	* in the file PATENTS. All contributing project authors may
	* be found in the AUTHORS file in the root of the source tree.
	*/

	package org.appspot.apprtc;

	import android.annotation.TargetApi;
	import android.content.Context;
	import android.content.Intent;
	import android.content.IntentFilter;
	import android.os.BatteryManager;
	import android.os.Build;
	import android.os.SystemClock;
	import android.util.Log;
	import java.io.BufferedReader;
	import java.io.FileInputStream;
	import java.io.FileNotFoundException;
	import java.io.FileReader;
	import java.io.IOException;
	import java.io.InputStreamReader;
	import java.nio.charset.Charset;
	import java.util.Arrays;
	import java.util.Scanner;
	import java.util.concurrent.Executors;
	import java.util.concurrent.Future;
	import java.util.concurrent.ScheduledExecutorService;
	import java.util.concurrent.TimeUnit;
	import javax.annotation.Nullable;

	/**
	* Simple CPU monitor. The caller creates a CpuMonitor object which can then
	* be used via sampleCpuUtilization() to collect the percentual use of the
	* cumulative CPU capacity for all CPUs running at their nominal frequency. 3
	* values are generated: (1) getCpuCurrent() returns the use since the last
	* sampleCpuUtilization(), (2) getCpuAvg3() returns the use since 3 prior
	* calls, and (3) getCpuAvgAll() returns the use over all SAMPLE_SAVE_NUMBER
	* calls.
	*
	* <p>CPUs in Android are often "offline", and while this of course means 0 Hz
	* as current frequency, in this state we cannot even get their nominal
	* frequency. We therefore tread carefully, and allow any CPU to be missing.
	* Missing CPUs are assumed to have the same nominal frequency as any close
	* lower-numbered CPU, but as soon as it is online, we'll get their proper
	* frequency and remember it. (Since CPU 0 in practice always seem to be
	* online, this unidirectional frequency inheritance should be no problem in
	* practice.)
	*
	* <p>Caveats:
	* o No provision made for zany "turbo" mode, common in the x86 world.
	* o No provision made for ARM big.LITTLE; if CPU n can switch behind our
	* back, we might get incorrect estimates.
	* o This is not thread-safe. To call asynchronously, create different
	* CpuMonitor objects.
	*
	* <p>If we can gather enough info to generate a sensible result,
	* sampleCpuUtilization returns true. It is designed to never throw an
	* exception.
	*
	* <p>sampleCpuUtilization should not be called too often in its present form,
	* since then deltas would be small and the percent values would fluctuate and
	* be unreadable. If it is desirable to call it more often than say once per
	* second, one would need to increase SAMPLE_SAVE_NUMBER and probably use
	* Queue<Integer> to avoid copying overhead.
	*
	* <p>Known problems:
	* 1. Nexus 7 devices running Kitkat have a kernel which often output an
	* incorrect 'idle' field in /proc/stat. The value is close to twice the
	* correct value, and then returns to back to correct reading. Both when
	* jumping up and back down we might create faulty CPU load readings.
	*/
	@TargetApi(Build.VERSION_CODES.KITKAT)
	class CpuMonitor {
	private static final String TAG = "CpuMonitor";
	private static final int MOVING_AVERAGE_SAMPLES = 5;

	private static final int CPU_STAT_SAMPLE_PERIOD_MS = 2000;
	private static final int CPU_STAT_LOG_PERIOD_MS = 6000;

	private final Context appContext;
	// User CPU usage at current frequency.
	private final MovingAverage userCpuUsage;
	// System CPU usage at current frequency.
	private final MovingAverage systemCpuUsage;
	// Total CPU usage relative to maximum frequency.
	private final MovingAverage totalCpuUsage;
	// CPU frequency in percentage from maximum.
	private final MovingAverage frequencyScale;

	@Nullable
	private ScheduledExecutorService executor;
	private long lastStatLogTimeMs;
	private long[] cpuFreqMax;
	private int cpusPresent;
	private int actualCpusPresent;
	private boolean initialized;
	private boolean cpuOveruse;
	private String[] maxPath;
	private String[] curPath;
	private double[] curFreqScales;
	@Nullable
	private ProcStat lastProcStat;

	private static class ProcStat {
	final long userTime;
	final long systemTime;
	final long idleTime;

	ProcStat(long userTime, long systemTime, long idleTime) {
	this.userTime = userTime;
	this.systemTime = systemTime;
	this.idleTime = idleTime;
	}
	}

	private static class MovingAverage {
	private final int size;
	private double sum;
	private double currentValue;
	private double[] circBuffer;
	private int circBufferIndex;

	public MovingAverage(int size) {
	if (size <= 0) {
	throw new AssertionError("Size value in MovingAverage ctor should be positive.");
	}
	this.size = size;
	circBuffer = new double[size];
	}

	public void reset() {
	Arrays.fill(circBuffer, 0);
	circBufferIndex = 0;
	sum = 0;
	currentValue = 0;
	}

	public void addValue(double value) {
	sum -= circBuffer[circBufferIndex];
	circBuffer[circBufferIndex++] = value;
	currentValue = value;
	sum += value;
	if (circBufferIndex >= size) {
	circBufferIndex = 0;
	}
	}

	public double getCurrent() {
	return currentValue;
	}

	public double getAverage() {
	return sum / (double) size;
	}
	}

	public static boolean isSupported() {
	return Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT
	&& Build.VERSION.SDK_INT < Build.VERSION_CODES.N;
	}

	public CpuMonitor(Context context) {
	if (!isSupported()) {
	throw new RuntimeException("CpuMonitor is not supported on this Android version.");
	}

	Log.d(TAG, "CpuMonitor ctor.");
	appContext = context.getApplicationContext();
	userCpuUsage = new MovingAverage(MOVING_AVERAGE_SAMPLES);
	systemCpuUsage = new MovingAverage(MOVING_AVERAGE_SAMPLES);
	totalCpuUsage = new MovingAverage(MOVING_AVERAGE_SAMPLES);
	frequencyScale = new MovingAverage(MOVING_AVERAGE_SAMPLES);
	lastStatLogTimeMs = SystemClock.elapsedRealtime();

	scheduleCpuUtilizationTask();
	}

	public void pause() {
	if (executor != null) {
	Log.d(TAG, "pause");
	executor.shutdownNow();
	executor = null;
	}
	}

	public void resume() {
	Log.d(TAG, "resume");
	resetStat();
	scheduleCpuUtilizationTask();
	}

	// TODO(bugs.webrtc.org/8491): Remove NoSynchronizedMethodCheck suppression.
	@SuppressWarnings("NoSynchronizedMethodCheck")
	public synchronized void reset() {
	if (executor != null) {
	Log.d(TAG, "reset");
	resetStat();
	cpuOveruse = false;
	}
	}

	// TODO(bugs.webrtc.org/8491): Remove NoSynchronizedMethodCheck suppression.
	@SuppressWarnings("NoSynchronizedMethodCheck")
	public synchronized int getCpuUsageCurrent() {
	return doubleToPercent(userCpuUsage.getCurrent() + systemCpuUsage.getCurrent());
	}

	// TODO(bugs.webrtc.org/8491): Remove NoSynchronizedMethodCheck suppression.
	@SuppressWarnings("NoSynchronizedMethodCheck")
	public synchronized int getCpuUsageAverage() {
	return doubleToPercent(userCpuUsage.getAverage() + systemCpuUsage.getAverage());
	}

	// TODO(bugs.webrtc.org/8491): Remove NoSynchronizedMethodCheck suppression.
	@SuppressWarnings("NoSynchronizedMethodCheck")
	public synchronized int getFrequencyScaleAverage() {
	return doubleToPercent(frequencyScale.getAverage());
	}

	private void scheduleCpuUtilizationTask() {
	if (executor != null) {
	executor.shutdownNow();
	executor = null;
	}

	executor = Executors.newSingleThreadScheduledExecutor();
	@SuppressWarnings("unused") // Prevent downstream linter warnings.
	Future<?> possiblyIgnoredError = executor.scheduleAtFixedRate(new Runnable() {
	@Override
	public void run() {
	cpuUtilizationTask();
	}
	}, 0, CPU_STAT_SAMPLE_PERIOD_MS, TimeUnit.MILLISECONDS);
	}

	private void cpuUtilizationTask() {
	boolean cpuMonitorAvailable = sampleCpuUtilization();
	if (cpuMonitorAvailable
	&& SystemClock.elapsedRealtime() - lastStatLogTimeMs >= CPU_STAT_LOG_PERIOD_MS) {
	lastStatLogTimeMs = SystemClock.elapsedRealtime();
	String statString = getStatString();
	Log.d(TAG, statString);
	}
	}

	private void init() {
	try (FileInputStream fin = new FileInputStream("/sys/devices/system/cpu/present");
	InputStreamReader streamReader = new InputStreamReader(fin, Charset.forName("UTF-8"));
	BufferedReader reader = new BufferedReader(streamReader);
	Scanner scanner = new Scanner(reader).useDelimiter("[-\n]");) {
	scanner.nextInt(); // Skip leading number 0.
	cpusPresent = 1 + scanner.nextInt();
	scanner.close();
	} catch (FileNotFoundException e) {
	Log.e(TAG, "Cannot do CPU stats since /sys/devices/system/cpu/present is missing");
	} catch (IOException e) {
	Log.e(TAG, "Error closing file");
	} catch (Exception e) {
	Log.e(TAG, "Cannot do CPU stats due to /sys/devices/system/cpu/present parsing problem");
	}

	cpuFreqMax = new long[cpusPresent];
	maxPath = new String[cpusPresent];
	curPath = new String[cpusPresent];
	curFreqScales = new double[cpusPresent];
	for (int i = 0; i < cpusPresent; i++) {
	cpuFreqMax[i] = 0; // Frequency "not yet determined".
	curFreqScales[i] = 0;
	maxPath[i] = "/sys/devices/system/cpu/cpu" + i + "/cpufreq/cpuinfo_max_freq";
	curPath[i] = "/sys/devices/system/cpu/cpu" + i + "/cpufreq/scaling_cur_freq";
	}

	lastProcStat = new ProcStat(0, 0, 0);
	resetStat();

	initialized = true;
	}

	private synchronized void resetStat() {
	userCpuUsage.reset();
	systemCpuUsage.reset();
	totalCpuUsage.reset();
	frequencyScale.reset();
	lastStatLogTimeMs = SystemClock.elapsedRealtime();
	}

	private int getBatteryLevel() {
	// Use sticky broadcast with null receiver to read battery level once only.
	Intent intent = appContext.registerReceiver(
	null /* receiver */, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));

	int batteryLevel = 0;
	int batteryScale = intent.getIntExtra(BatteryManager.EXTRA_SCALE, 100);
	if (batteryScale > 0) {
	batteryLevel =
	(int) (100f * intent.getIntExtra(BatteryManager.EXTRA_LEVEL, 0) / batteryScale);
	}
	return batteryLevel;
	}

	/**
	* Re-measure CPU use. Call this method at an interval of around 1/s.
	* This method returns true on success. The fields
	* cpuCurrent, cpuAvg3, and cpuAvgAll are updated on success, and represents:
	* cpuCurrent: The CPU use since the last sampleCpuUtilization call.
	* cpuAvg3: The average CPU over the last 3 calls.
	* cpuAvgAll: The average CPU over the last SAMPLE_SAVE_NUMBER calls.
	*/
	private synchronized boolean sampleCpuUtilization() {
	long lastSeenMaxFreq = 0;
	long cpuFreqCurSum = 0;
	long cpuFreqMaxSum = 0;

	if (!initialized) {
	init();
	}
	if (cpusPresent == 0) {
	return false;
	}

	actualCpusPresent = 0;
	for (int i = 0; i < cpusPresent; i++) {
	/*
	* For each CPU, attempt to first read its max frequency, then its
	* current frequency. Once as the max frequency for a CPU is found,
	* save it in cpuFreqMax[].
	*/

	curFreqScales[i] = 0;
	if (cpuFreqMax[i] == 0) {
	// We have never found this CPU's max frequency. Attempt to read it.
	long cpufreqMax = readFreqFromFile(maxPath[i]);
	if (cpufreqMax > 0) {
	Log.d(TAG, "Core " + i + ". Max frequency: " + cpufreqMax);
	lastSeenMaxFreq = cpufreqMax;
	cpuFreqMax[i] = cpufreqMax;
	maxPath[i] = null; // Kill path to free its memory.
	}
	} else {
	lastSeenMaxFreq = cpuFreqMax[i]; // A valid, previously read value.
	}

	long cpuFreqCur = readFreqFromFile(curPath[i]);
	if (cpuFreqCur == 0 && lastSeenMaxFreq == 0) {
	// No current frequency information for this CPU core - ignore it.
	continue;
	}
	if (cpuFreqCur > 0) {
	actualCpusPresent++;
	}
	cpuFreqCurSum += cpuFreqCur;

	/* Here, lastSeenMaxFreq might come from
	* 1. cpuFreq[i], or
	* 2. a previous iteration, or
	* 3. a newly read value, or
	* 4. hypothetically from the pre-loop dummy.
	*/
	cpuFreqMaxSum += lastSeenMaxFreq;
	if (lastSeenMaxFreq > 0) {
	curFreqScales[i] = (double) cpuFreqCur / lastSeenMaxFreq;
	}
	}

	if (cpuFreqCurSum == 0 \|\| cpuFreqMaxSum == 0) {
	Log.e(TAG, "Could not read max or current frequency for any CPU");
	return false;
	}

	/*
	* Since the cycle counts are for the period between the last invocation
	* and this present one, we average the percentual CPU frequencies between
	* now and the beginning of the measurement period. This is significantly
	* incorrect only if the frequencies have peeked or dropped in between the
	* invocations.
	*/
	double currentFrequencyScale = cpuFreqCurSum / (double) cpuFreqMaxSum;
	if (frequencyScale.getCurrent() > 0) {
	currentFrequencyScale = (frequencyScale.getCurrent() + currentFrequencyScale) * 0.5;
	}

	ProcStat procStat = readProcStat();
	if (procStat == null) {
	return false;
	}

	long diffUserTime = procStat.userTime - lastProcStat.userTime;
	long diffSystemTime = procStat.systemTime - lastProcStat.systemTime;
	long diffIdleTime = procStat.idleTime - lastProcStat.idleTime;
	long allTime = diffUserTime + diffSystemTime + diffIdleTime;

	if (currentFrequencyScale == 0 \|\| allTime == 0) {
	return false;
	}

	// Update statistics.
	frequencyScale.addValue(currentFrequencyScale);

	double currentUserCpuUsage = diffUserTime / (double) allTime;
	userCpuUsage.addValue(currentUserCpuUsage);

	double currentSystemCpuUsage = diffSystemTime / (double) allTime;
	systemCpuUsage.addValue(currentSystemCpuUsage);

	double currentTotalCpuUsage =
	(currentUserCpuUsage + currentSystemCpuUsage) * currentFrequencyScale;
	totalCpuUsage.addValue(currentTotalCpuUsage);

	// Save new measurements for next round's deltas.
	lastProcStat = procStat;

	return true;
	}

	private int doubleToPercent(double d) {
	return (int) (d * 100 + 0.5);
	}

	private synchronized String getStatString() {
	StringBuilder stat = new StringBuilder();
	stat.append("CPU User: ")
	.append(doubleToPercent(userCpuUsage.getCurrent()))
	.append("/")
	.append(doubleToPercent(userCpuUsage.getAverage()))
	.append(". System: ")
	.append(doubleToPercent(systemCpuUsage.getCurrent()))
	.append("/")
	.append(doubleToPercent(systemCpuUsage.getAverage()))
	.append(". Freq: ")
	.append(doubleToPercent(frequencyScale.getCurrent()))
	.append("/")
	.append(doubleToPercent(frequencyScale.getAverage()))
	.append(". Total usage: ")
	.append(doubleToPercent(totalCpuUsage.getCurrent()))
	.append("/")
	.append(doubleToPercent(totalCpuUsage.getAverage()))
	.append(". Cores: ")
	.append(actualCpusPresent);
	stat.append("( ");
	for (int i = 0; i < cpusPresent; i++) {
	stat.append(doubleToPercent(curFreqScales[i])).append(" ");
	}
	stat.append("). Battery: ").append(getBatteryLevel());
	if (cpuOveruse) {
	stat.append(". Overuse.");
	}
	return stat.toString();
	}

	/**
	* Read a single integer value from the named file. Return the read value
	* or if an error occurs return 0.
	*/
	private long readFreqFromFile(String fileName) {
	long number = 0;
	try (FileInputStream stream = new FileInputStream(fileName);
	InputStreamReader streamReader = new InputStreamReader(stream, Charset.forName("UTF-8"));
	BufferedReader reader = new BufferedReader(streamReader)) {
	String line = reader.readLine();
	number = parseLong(line);
	} catch (FileNotFoundException e) {
	// CPU core is off, so file with its scaling frequency .../cpufreq/scaling_cur_freq
	// is not present. This is not an error.
	} catch (IOException e) {
	// CPU core is off, so file with its scaling frequency .../cpufreq/scaling_cur_freq
	// is empty. This is not an error.
	}
	return number;
	}

	private static long parseLong(String value) {
	long number = 0;
	try {
	number = Long.parseLong(value);
	} catch (NumberFormatException e) {
	Log.e(TAG, "parseLong error.", e);
	}
	return number;
	}

	/*
	* Read the current utilization of all CPUs using the cumulative first line
	* of /proc/stat.
	*/
	@SuppressWarnings("StringSplitter")
	private @Nullable ProcStat readProcStat() {
	long userTime = 0;
	long systemTime = 0;
	long idleTime = 0;
	try (FileInputStream stream = new FileInputStream("/proc/stat");
	InputStreamReader streamReader = new InputStreamReader(stream, Charset.forName("UTF-8"));
	BufferedReader reader = new BufferedReader(streamReader)) {
	// line should contain something like this:
	// cpu 5093818 271838 3512830 165934119 101374 447076 272086 0 0 0
	// user nice system idle iowait irq softirq
	String line = reader.readLine();
	String[] lines = line.split("\\s+");
	int length = lines.length;
	if (length >= 5) {
	userTime = parseLong(lines[1]); // user
	userTime += parseLong(lines[2]); // nice
	systemTime = parseLong(lines[3]); // system
	idleTime = parseLong(lines[4]); // idle
	}
	if (length >= 8) {
	userTime += parseLong(lines[5]); // iowait
	systemTime += parseLong(lines[6]); // irq
	systemTime += parseLong(lines[7]); // softirq
	}
	} catch (FileNotFoundException e) {
	Log.e(TAG, "Cannot open /proc/stat for reading", e);
	return null;
	} catch (Exception e) {
	Log.e(TAG, "Problems parsing /proc/stat", e);
	return null;
	}
	return new ProcStat(userTime, systemTime, idleTime);
	}
	}