core/java/com/android/internal/os/KernelCpuThreadReader.java - platform/frameworks/base - Gitiles

 /*
  * Copyright (C) 2018 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package com.android.internal.os;

 import android.annotation.Nullable;
 import android.os.Process;
 import android.util.Slog;

 import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.util.Preconditions;

 import java.io.IOException;
 import java.nio.file.DirectoryStream;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.function.Predicate;

 /**
  * Iterates over processes, and all threads owned by those processes, and return the CPU usage for
  * each thread. The CPU usage statistics contain the amount of time spent in a frequency band. CPU
  * usage is collected using {@link ProcTimeInStateReader}.
  *
  * <p>We only collect CPU data for processes and threads that are owned by certain UIDs. These UIDs
  * are configured via {@link #setUidPredicate}.
  *
  * <p>Frequencies are bucketed together to reduce the amount of data created. This means that we
  * return less frequencies than provided by {@link ProcTimeInStateReader}. The number of frequencies
  * is configurable by {@link #setNumBuckets}. Frequencies are reported as the lowest frequency in
  * that range. Frequencies are spread as evenly as possible across the buckets. The buckets do not
  * cross over the little/big frequencies reported.
  *
  * <p>N.B.: In order to bucket across little/big frequencies correctly, we assume that the {@code
  * time_in_state} file contains every little core frequency in ascending order, followed by every
  * big core frequency in ascending order. This assumption might not hold for devices with different
  * kernel implementations of the {@code time_in_state} file generation.
  */
 public class KernelCpuThreadReader {

     private static final String TAG = "KernelCpuThreadReader";

     private static final boolean DEBUG = false;

     /**
      * The name of the file to read CPU statistics from, must be found in {@code
      * /proc/$PID/task/$TID}
      */
     private static final String CPU_STATISTICS_FILENAME = "time_in_state";

     /**
      * The name of the file to read process command line invocation from, must be found in {@code
      * /proc/$PID/}
      */
     private static final String PROCESS_NAME_FILENAME = "cmdline";

     /**
      * The name of the file to read thread name from, must be found in {@code /proc/$PID/task/$TID}
      */
     private static final String THREAD_NAME_FILENAME = "comm";

     /** Glob pattern for the process directory names under {@code proc} */
     private static final String PROCESS_DIRECTORY_FILTER = "[0-9]*";

     /** Default process name when the name can't be read */
     private static final String DEFAULT_PROCESS_NAME = "unknown_process";

     /** Default thread name when the name can't be read */
     private static final String DEFAULT_THREAD_NAME = "unknown_thread";

     /** Default mount location of the {@code proc} filesystem */
     private static final Path DEFAULT_PROC_PATH = Paths.get("/proc");

     /** The initial {@code time_in_state} file for {@link ProcTimeInStateReader} */
     private static final Path DEFAULT_INITIAL_TIME_IN_STATE_PATH =
             DEFAULT_PROC_PATH.resolve("self/time_in_state");

     /** Value returned when there was an error getting an integer ID value (e.g. PID, UID) */
     private static final int ID_ERROR = -1;

     /**
      * When checking whether to report data for a thread, we check the UID of the thread's owner
      * against this predicate
      */
     private Predicate<Integer> mUidPredicate;

     /** Where the proc filesystem is mounted */
     private final Path mProcPath;

     /**
      * Frequencies read from the {@code time_in_state} file. Read from {@link
      * #mProcTimeInStateReader#getCpuFrequenciesKhz()} and cast to {@code int[]}
      */
     private int[] mFrequenciesKhz;

     /** Used to read and parse {@code time_in_state} files */
     private final ProcTimeInStateReader mProcTimeInStateReader;

     /** Used to sort frequencies and usage times into buckets */
     private FrequencyBucketCreator mFrequencyBucketCreator;

     private final Injector mInjector;

     /**
      * Create with a path where `proc` is mounted. Used primarily for testing
      *
      * @param procPath where `proc` is mounted (to find, see {@code mount | grep ^proc})
      * @param initialTimeInStatePath where the initial {@code time_in_state} file exists to define
      *     format
      */
     @VisibleForTesting
     public KernelCpuThreadReader(
             int numBuckets,
             Predicate<Integer> uidPredicate,
             Path procPath,
             Path initialTimeInStatePath,
             Injector injector)
             throws IOException {
         mUidPredicate = uidPredicate;
         mProcPath = procPath;
         mProcTimeInStateReader = new ProcTimeInStateReader(initialTimeInStatePath);
         mInjector = injector;
         setNumBuckets(numBuckets);
     }

     /**
      * Create the reader and handle exceptions during creation
      *
      * @return the reader, null if an exception was thrown during creation
      */
     @Nullable
     public static KernelCpuThreadReader create(int numBuckets, Predicate<Integer> uidPredicate) {
         try {
             return new KernelCpuThreadReader(
                     numBuckets,
                     uidPredicate,
                     DEFAULT_PROC_PATH,
                     DEFAULT_INITIAL_TIME_IN_STATE_PATH,
                     new Injector());
         } catch (IOException e) {
             Slog.e(TAG, "Failed to initialize KernelCpuThreadReader", e);
             return null;
         }
     }

     /**
      * Get the per-thread CPU usage of all processes belonging to a set of UIDs
      *
      * <p>This function will crawl through all process {@code proc} directories found by the pattern
      * {@code /proc/[0-9]*}, and then check the UID using {@code /proc/$PID/status}. This takes
      * approximately 500ms on a 2017 device. Therefore, this method can be computationally
      * expensive, and should not be called more than once an hour.
      *
      * <p>Data is only collected for UIDs passing the predicate supplied in {@link
      * #setUidPredicate}.
      */
     @Nullable
     public ArrayList<ProcessCpuUsage> getProcessCpuUsage() {
         if (DEBUG) {
             Slog.d(TAG, "Reading CPU thread usages for processes owned by UIDs");
         }

         final ArrayList<ProcessCpuUsage> processCpuUsages = new ArrayList<>();

         try (DirectoryStream<Path> processPaths =
                 Files.newDirectoryStream(mProcPath, PROCESS_DIRECTORY_FILTER)) {
             for (Path processPath : processPaths) {
                 final int processId = getProcessId(processPath);
                 final int uid = mInjector.getUidForPid(processId);
                 if (uid == ID_ERROR || processId == ID_ERROR) {
                     continue;
                 }
                 if (!mUidPredicate.test(uid)) {
                     continue;
                 }

                 final ProcessCpuUsage processCpuUsage =
                         getProcessCpuUsage(processPath, processId, uid);
                 if (processCpuUsage != null) {
                     processCpuUsages.add(processCpuUsage);
                 }
             }
         } catch (IOException e) {
             Slog.w(TAG, "Failed to iterate over process paths", e);
             return null;
         }

         if (processCpuUsages.isEmpty()) {
             Slog.w(TAG, "Didn't successfully get any process CPU information for UIDs specified");
             return null;
         }

         if (DEBUG) {
             Slog.d(TAG, "Read usage for " + processCpuUsages.size() + " processes");
         }

         return processCpuUsages;
     }

     /**
      * Get the CPU frequencies that correspond to the times reported in {@link
      * ThreadCpuUsage#usageTimesMillis}
      */
     @Nullable
     public int[] getCpuFrequenciesKhz() {
         return mFrequenciesKhz;
     }

     /** Set the number of frequency buckets to use */
     void setNumBuckets(int numBuckets) {
         if (numBuckets < 1) {
             Slog.w(TAG, "Number of buckets must be at least 1, but was " + numBuckets);
             return;
         }
         // If `numBuckets` hasn't changed since the last set, do nothing
         if (mFrequenciesKhz != null && mFrequenciesKhz.length == numBuckets) {
             return;
         }
         mFrequencyBucketCreator =
                 new FrequencyBucketCreator(mProcTimeInStateReader.getFrequenciesKhz(), numBuckets);
         mFrequenciesKhz =
                 mFrequencyBucketCreator.getBucketMinFrequencies(
                         mProcTimeInStateReader.getFrequenciesKhz());
     }

     /** Set the UID predicate for {@link #getProcessCpuUsage} */
     void setUidPredicate(Predicate<Integer> uidPredicate) {
         mUidPredicate = uidPredicate;
     }

     /**
      * Read all of the CPU usage statistics for each child thread of a process
      *
      * @param processPath the {@code /proc} path of the thread
      * @param processId the ID of the process
      * @param uid the ID of the user who owns the process
      * @return process CPU usage containing usage of all child threads. Null if the process exited
      *     and its {@code proc} directory was removed while collecting information
      */
     @Nullable
     private ProcessCpuUsage getProcessCpuUsage(Path processPath, int processId, int uid) {
         if (DEBUG) {
             Slog.d(
                     TAG,
                     "Reading CPU thread usages with directory "
                             + processPath
                             + " process ID "
                             + processId
                             + " and user ID "
                             + uid);
         }

         final Path allThreadsPath = processPath.resolve("task");
         final ArrayList<ThreadCpuUsage> threadCpuUsages = new ArrayList<>();
         try (DirectoryStream<Path> threadPaths = Files.newDirectoryStream(allThreadsPath)) {
             for (Path threadDirectory : threadPaths) {
                 ThreadCpuUsage threadCpuUsage = getThreadCpuUsage(threadDirectory);
                 if (threadCpuUsage == null) {
                     continue;
                 }
                 threadCpuUsages.add(threadCpuUsage);
             }
         } catch (IOException e) {
             // Expected when a process finishes
             return null;
         }

         // If we found no threads, then the process has exited while we were reading from it
         if (threadCpuUsages.isEmpty()) {
             return null;
         }
         if (DEBUG) {
             Slog.d(TAG, "Read CPU usage of " + threadCpuUsages.size() + " threads");
         }
         return new ProcessCpuUsage(processId, getProcessName(processPath), uid, threadCpuUsages);
     }

     /**
      * Get a thread's CPU usage
      *
      * @param threadDirectory the {@code /proc} directory of the thread
      * @return thread CPU usage. Null if the thread exited and its {@code proc} directory was
      *     removed while collecting information
      */
     @Nullable
     private ThreadCpuUsage getThreadCpuUsage(Path threadDirectory) {
         // Get the thread ID from the directory name
         final int threadId;
         try {
             final String directoryName = threadDirectory.getFileName().toString();
             threadId = Integer.parseInt(directoryName);
         } catch (NumberFormatException e) {
             Slog.w(TAG, "Failed to parse thread ID when iterating over /proc/*/task", e);
             return null;
         }

         // Get the thread name from the thread directory
         final String threadName = getThreadName(threadDirectory);

         // Get the CPU statistics from the directory
         final Path threadCpuStatPath = threadDirectory.resolve(CPU_STATISTICS_FILENAME);
         final long[] cpuUsagesLong = mProcTimeInStateReader.getUsageTimesMillis(threadCpuStatPath);
         if (cpuUsagesLong == null) {
             return null;
         }
         int[] cpuUsages = mFrequencyBucketCreator.getBucketedValues(cpuUsagesLong);

         return new ThreadCpuUsage(threadId, threadName, cpuUsages);
     }

     /** Get the command used to start a process */
     private String getProcessName(Path processPath) {
         final Path processNamePath = processPath.resolve(PROCESS_NAME_FILENAME);

         final String processName = ProcStatsUtil.readSingleLineProcFile(processNamePath.toString());
         if (processName != null) {
             return processName;
         }
         return DEFAULT_PROCESS_NAME;
     }

     /** Get the name of a thread, given the {@code /proc} path of the thread */
     private String getThreadName(Path threadPath) {
         final Path threadNamePath = threadPath.resolve(THREAD_NAME_FILENAME);
         final String threadName = ProcStatsUtil.readNullSeparatedFile(threadNamePath.toString());
         if (threadName == null) {
             return DEFAULT_THREAD_NAME;
         }
         return threadName;
     }

     /**
      * Get the ID of a process from its path
      *
      * @param processPath {@code proc} path of the process
      * @return the ID, {@link #ID_ERROR} if the path could not be parsed
      */
     private int getProcessId(Path processPath) {
         String fileName = processPath.getFileName().toString();
         try {
             return Integer.parseInt(fileName);
         } catch (NumberFormatException e) {
             Slog.w(TAG, "Failed to parse " + fileName + " as process ID", e);
             return ID_ERROR;
         }
     }

     /** Puts frequencies and usage times into buckets */
     @VisibleForTesting
     public static class FrequencyBucketCreator {
         private final int mNumBuckets;
         private final int mNumFrequencies;
         private final int mBigFrequenciesStartIndex;
         private final int mLittleNumBuckets;
         private final int mBigNumBuckets;
         private final int mLittleBucketSize;
         private final int mBigBucketSize;

         /**
          * Buckets based of a list of frequencies
          *
          * @param frequencies the frequencies to base buckets off
          * @param numBuckets how many buckets to create
          */
         @VisibleForTesting
         public FrequencyBucketCreator(long[] frequencies, int numBuckets) {
             Preconditions.checkArgument(numBuckets > 0);

             mNumFrequencies = frequencies.length;
             mBigFrequenciesStartIndex = getBigFrequenciesStartIndex(frequencies);

             final int littleNumBuckets;
             final int bigNumBuckets;
             if (mBigFrequenciesStartIndex < frequencies.length) {
                 littleNumBuckets = numBuckets / 2;
                 bigNumBuckets = numBuckets - littleNumBuckets;
             } else {
                 // If we've got no big frequencies, set all buckets to little frequencies
                 littleNumBuckets = numBuckets;
                 bigNumBuckets = 0;
             }

             // Ensure that we don't have more buckets than frequencies
             mLittleNumBuckets = Math.min(littleNumBuckets, mBigFrequenciesStartIndex);
             mBigNumBuckets =
                     Math.min(bigNumBuckets, frequencies.length - mBigFrequenciesStartIndex);
             mNumBuckets = mLittleNumBuckets + mBigNumBuckets;

             // Set the size of each little and big bucket. If they have no buckets, the size is zero
             mLittleBucketSize =
                     mLittleNumBuckets == 0 ? 0 : mBigFrequenciesStartIndex / mLittleNumBuckets;
             mBigBucketSize =
                     mBigNumBuckets == 0
                             ? 0
                             : (frequencies.length - mBigFrequenciesStartIndex) / mBigNumBuckets;
         }

         /** Find the index where frequencies change from little core to big core */
         @VisibleForTesting
         public static int getBigFrequenciesStartIndex(long[] frequenciesKhz) {
             for (int i = 0; i < frequenciesKhz.length - 1; i++) {
                 if (frequenciesKhz[i] > frequenciesKhz[i + 1]) {
                     return i + 1;
                 }
             }

             return frequenciesKhz.length;
         }

         /** Get the minimum frequency in each bucket */
         @VisibleForTesting
         public int[] getBucketMinFrequencies(long[] frequenciesKhz) {
             Preconditions.checkArgument(frequenciesKhz.length == mNumFrequencies);
             // If there's only one bucket, we bucket everything together so the first bucket is the
             // min frequency
             if (mNumBuckets == 1) {
                 return new int[] {(int) frequenciesKhz[0]};
             }

             final int[] bucketMinFrequencies = new int[mNumBuckets];
             // Initialize little buckets min frequencies
             for (int i = 0; i < mLittleNumBuckets; i++) {
                 bucketMinFrequencies[i] = (int) frequenciesKhz[i * mLittleBucketSize];
             }
             // Initialize big buckets min frequencies
             for (int i = 0; i < mBigNumBuckets; i++) {
                 final int frequencyIndex = mBigFrequenciesStartIndex + i * mBigBucketSize;
                 bucketMinFrequencies[mLittleNumBuckets + i] = (int) frequenciesKhz[frequencyIndex];
             }
             return bucketMinFrequencies;
         }

         /**
          * Put an array of values into buckets. This takes a {@code long[]} and returns {@code
          * int[]} as everywhere this method is used will have to do the conversion anyway, so we
          * save time by doing it here instead
          *
          * @param values the values to bucket
          * @return the bucketed usage times
          */
         @VisibleForTesting
         @SuppressWarnings("ForLoopReplaceableByForEach")
         public int[] getBucketedValues(long[] values) {
             Preconditions.checkArgument(values.length == mNumFrequencies);
             final int[] bucketed = new int[mNumBuckets];

             // If there's only one bucket, add all frequencies in
             if (mNumBuckets == 1) {
                 for (int i = 0; i < values.length; i++) {
                     bucketed[0] += values[i];
                 }
                 return bucketed;
             }

             // Initialize the little buckets
             for (int i = 0; i < mBigFrequenciesStartIndex; i++) {
                 final int bucketIndex = Math.min(i / mLittleBucketSize, mLittleNumBuckets - 1);
                 bucketed[bucketIndex] += values[i];
             }
             // Initialize the big buckets
             for (int i = mBigFrequenciesStartIndex; i < values.length; i++) {
                 final int bucketIndex =
                         Math.min(
                                 mLittleNumBuckets
                                         + (i - mBigFrequenciesStartIndex) / mBigBucketSize,
                                 mNumBuckets - 1);
                 bucketed[bucketIndex] += values[i];
             }
             return bucketed;
         }
     }

     /** CPU usage of a process */
     public static class ProcessCpuUsage {
         public final int processId;
         public final String processName;
         public final int uid;
         public ArrayList<ThreadCpuUsage> threadCpuUsages;

         @VisibleForTesting
         public ProcessCpuUsage(
                 int processId,
                 String processName,
                 int uid,
                 ArrayList<ThreadCpuUsage> threadCpuUsages) {
             this.processId = processId;
             this.processName = processName;
             this.uid = uid;
             this.threadCpuUsages = threadCpuUsages;
         }
     }

     /** CPU usage of a thread */
     public static class ThreadCpuUsage {
         public final int threadId;
         public final String threadName;
         public int[] usageTimesMillis;

         @VisibleForTesting
         public ThreadCpuUsage(int threadId, String threadName, int[] usageTimesMillis) {
             this.threadId = threadId;
             this.threadName = threadName;
             this.usageTimesMillis = usageTimesMillis;
         }
     }

     /** Used to inject static methods from {@link Process} */
     @VisibleForTesting
     public static class Injector {
         /** Get the UID for the process with ID {@code pid} */
         public int getUidForPid(int pid) {
             return Process.getUidForPid(pid);
         }
     }
 }
	/*
	* Copyright (C) 2018 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	package com.android.internal.os;

	import android.annotation.Nullable;
	import android.os.Process;
	import android.util.Slog;

	import com.android.internal.annotations.VisibleForTesting;
	import com.android.internal.util.Preconditions;

	import java.io.IOException;
	import java.nio.file.DirectoryStream;
	import java.nio.file.Files;
	import java.nio.file.Path;
	import java.nio.file.Paths;
	import java.util.ArrayList;
	import java.util.function.Predicate;

	/**
	* Iterates over processes, and all threads owned by those processes, and return the CPU usage for
	* each thread. The CPU usage statistics contain the amount of time spent in a frequency band. CPU
	* usage is collected using {@link ProcTimeInStateReader}.
	*
	* <p>We only collect CPU data for processes and threads that are owned by certain UIDs. These UIDs
	* are configured via {@link #setUidPredicate}.
	*
	* <p>Frequencies are bucketed together to reduce the amount of data created. This means that we
	* return less frequencies than provided by {@link ProcTimeInStateReader}. The number of frequencies
	* is configurable by {@link #setNumBuckets}. Frequencies are reported as the lowest frequency in
	* that range. Frequencies are spread as evenly as possible across the buckets. The buckets do not
	* cross over the little/big frequencies reported.
	*
	* <p>N.B.: In order to bucket across little/big frequencies correctly, we assume that the {@code
	* time_in_state} file contains every little core frequency in ascending order, followed by every
	* big core frequency in ascending order. This assumption might not hold for devices with different
	* kernel implementations of the {@code time_in_state} file generation.
	*/
	public class KernelCpuThreadReader {

	private static final String TAG = "KernelCpuThreadReader";

	private static final boolean DEBUG = false;

	/**
	* The name of the file to read CPU statistics from, must be found in {@code
	* /proc/$PID/task/$TID}
	*/
	private static final String CPU_STATISTICS_FILENAME = "time_in_state";

	/**
	* The name of the file to read process command line invocation from, must be found in {@code
	* /proc/$PID/}
	*/
	private static final String PROCESS_NAME_FILENAME = "cmdline";

	/**
	* The name of the file to read thread name from, must be found in {@code /proc/$PID/task/$TID}
	*/
	private static final String THREAD_NAME_FILENAME = "comm";

	/** Glob pattern for the process directory names under {@code proc} */
	private static final String PROCESS_DIRECTORY_FILTER = "[0-9]*";

	/** Default process name when the name can't be read */
	private static final String DEFAULT_PROCESS_NAME = "unknown_process";

	/** Default thread name when the name can't be read */
	private static final String DEFAULT_THREAD_NAME = "unknown_thread";

	/** Default mount location of the {@code proc} filesystem */
	private static final Path DEFAULT_PROC_PATH = Paths.get("/proc");

	/** The initial {@code time_in_state} file for {@link ProcTimeInStateReader} */
	private static final Path DEFAULT_INITIAL_TIME_IN_STATE_PATH =
	DEFAULT_PROC_PATH.resolve("self/time_in_state");

	/** Value returned when there was an error getting an integer ID value (e.g. PID, UID) */
	private static final int ID_ERROR = -1;

	/**
	* When checking whether to report data for a thread, we check the UID of the thread's owner
	* against this predicate
	*/
	private Predicate<Integer> mUidPredicate;

	/** Where the proc filesystem is mounted */
	private final Path mProcPath;

	/**
	* Frequencies read from the {@code time_in_state} file. Read from {@link
	* #mProcTimeInStateReader#getCpuFrequenciesKhz()} and cast to {@code int[]}
	*/
	private int[] mFrequenciesKhz;

	/** Used to read and parse {@code time_in_state} files */
	private final ProcTimeInStateReader mProcTimeInStateReader;

	/** Used to sort frequencies and usage times into buckets */
	private FrequencyBucketCreator mFrequencyBucketCreator;

	private final Injector mInjector;

	/**
	* Create with a path where `proc` is mounted. Used primarily for testing
	*
	* @param procPath where `proc` is mounted (to find, see {@code mount \| grep ^proc})
	* @param initialTimeInStatePath where the initial {@code time_in_state} file exists to define
	* format
	*/
	@VisibleForTesting
	public KernelCpuThreadReader(
	int numBuckets,
	Predicate<Integer> uidPredicate,
	Path procPath,
	Path initialTimeInStatePath,
	Injector injector)
	throws IOException {
	mUidPredicate = uidPredicate;
	mProcPath = procPath;
	mProcTimeInStateReader = new ProcTimeInStateReader(initialTimeInStatePath);
	mInjector = injector;
	setNumBuckets(numBuckets);
	}

	/**
	* Create the reader and handle exceptions during creation
	*
	* @return the reader, null if an exception was thrown during creation
	*/
	@Nullable
	public static KernelCpuThreadReader create(int numBuckets, Predicate<Integer> uidPredicate) {
	try {
	return new KernelCpuThreadReader(
	numBuckets,
	uidPredicate,
	DEFAULT_PROC_PATH,
	DEFAULT_INITIAL_TIME_IN_STATE_PATH,
	new Injector());
	} catch (IOException e) {
	Slog.e(TAG, "Failed to initialize KernelCpuThreadReader", e);
	return null;
	}
	}

	/**
	* Get the per-thread CPU usage of all processes belonging to a set of UIDs
	*
	* <p>This function will crawl through all process {@code proc} directories found by the pattern
	* {@code /proc/[0-9]*}, and then check the UID using {@code /proc/$PID/status}. This takes
	* approximately 500ms on a 2017 device. Therefore, this method can be computationally
	* expensive, and should not be called more than once an hour.
	*
	* <p>Data is only collected for UIDs passing the predicate supplied in {@link
	* #setUidPredicate}.
	*/
	@Nullable
	public ArrayList<ProcessCpuUsage> getProcessCpuUsage() {
	if (DEBUG) {
	Slog.d(TAG, "Reading CPU thread usages for processes owned by UIDs");
	}

	final ArrayList<ProcessCpuUsage> processCpuUsages = new ArrayList<>();

	try (DirectoryStream<Path> processPaths =
	Files.newDirectoryStream(mProcPath, PROCESS_DIRECTORY_FILTER)) {
	for (Path processPath : processPaths) {
	final int processId = getProcessId(processPath);
	final int uid = mInjector.getUidForPid(processId);
	if (uid == ID_ERROR \|\| processId == ID_ERROR) {
	continue;
	}
	if (!mUidPredicate.test(uid)) {
	continue;
	}

	final ProcessCpuUsage processCpuUsage =
	getProcessCpuUsage(processPath, processId, uid);
	if (processCpuUsage != null) {
	processCpuUsages.add(processCpuUsage);
	}
	}
	} catch (IOException e) {
	Slog.w(TAG, "Failed to iterate over process paths", e);
	return null;
	}

	if (processCpuUsages.isEmpty()) {
	Slog.w(TAG, "Didn't successfully get any process CPU information for UIDs specified");
	return null;
	}

	if (DEBUG) {
	Slog.d(TAG, "Read usage for " + processCpuUsages.size() + " processes");
	}

	return processCpuUsages;
	}

	/**
	* Get the CPU frequencies that correspond to the times reported in {@link
	* ThreadCpuUsage#usageTimesMillis}
	*/
	@Nullable
	public int[] getCpuFrequenciesKhz() {
	return mFrequenciesKhz;
	}

	/** Set the number of frequency buckets to use */
	void setNumBuckets(int numBuckets) {
	if (numBuckets < 1) {
	Slog.w(TAG, "Number of buckets must be at least 1, but was " + numBuckets);
	return;
	}
	// If `numBuckets` hasn't changed since the last set, do nothing
	if (mFrequenciesKhz != null && mFrequenciesKhz.length == numBuckets) {
	return;
	}
	mFrequencyBucketCreator =
	new FrequencyBucketCreator(mProcTimeInStateReader.getFrequenciesKhz(), numBuckets);
	mFrequenciesKhz =
	mFrequencyBucketCreator.getBucketMinFrequencies(
	mProcTimeInStateReader.getFrequenciesKhz());
	}

	/** Set the UID predicate for {@link #getProcessCpuUsage} */
	void setUidPredicate(Predicate<Integer> uidPredicate) {
	mUidPredicate = uidPredicate;
	}

	/**
	* Read all of the CPU usage statistics for each child thread of a process
	*
	* @param processPath the {@code /proc} path of the thread
	* @param processId the ID of the process
	* @param uid the ID of the user who owns the process
	* @return process CPU usage containing usage of all child threads. Null if the process exited
	* and its {@code proc} directory was removed while collecting information
	*/
	@Nullable
	private ProcessCpuUsage getProcessCpuUsage(Path processPath, int processId, int uid) {
	if (DEBUG) {
	Slog.d(
	TAG,
	"Reading CPU thread usages with directory "
	+ processPath
	+ " process ID "
	+ processId
	+ " and user ID "
	+ uid);
	}

	final Path allThreadsPath = processPath.resolve("task");
	final ArrayList<ThreadCpuUsage> threadCpuUsages = new ArrayList<>();
	try (DirectoryStream<Path> threadPaths = Files.newDirectoryStream(allThreadsPath)) {
	for (Path threadDirectory : threadPaths) {
	ThreadCpuUsage threadCpuUsage = getThreadCpuUsage(threadDirectory);
	if (threadCpuUsage == null) {
	continue;
	}
	threadCpuUsages.add(threadCpuUsage);
	}
	} catch (IOException e) {
	// Expected when a process finishes
	return null;
	}

	// If we found no threads, then the process has exited while we were reading from it
	if (threadCpuUsages.isEmpty()) {
	return null;
	}
	if (DEBUG) {
	Slog.d(TAG, "Read CPU usage of " + threadCpuUsages.size() + " threads");
	}
	return new ProcessCpuUsage(processId, getProcessName(processPath), uid, threadCpuUsages);
	}

	/**
	* Get a thread's CPU usage
	*
	* @param threadDirectory the {@code /proc} directory of the thread
	* @return thread CPU usage. Null if the thread exited and its {@code proc} directory was
	* removed while collecting information
	*/
	@Nullable
	private ThreadCpuUsage getThreadCpuUsage(Path threadDirectory) {
	// Get the thread ID from the directory name
	final int threadId;
	try {
	final String directoryName = threadDirectory.getFileName().toString();
	threadId = Integer.parseInt(directoryName);
	} catch (NumberFormatException e) {
	Slog.w(TAG, "Failed to parse thread ID when iterating over /proc/*/task", e);
	return null;
	}

	// Get the thread name from the thread directory
	final String threadName = getThreadName(threadDirectory);

	// Get the CPU statistics from the directory
	final Path threadCpuStatPath = threadDirectory.resolve(CPU_STATISTICS_FILENAME);
	final long[] cpuUsagesLong = mProcTimeInStateReader.getUsageTimesMillis(threadCpuStatPath);
	if (cpuUsagesLong == null) {
	return null;
	}
	int[] cpuUsages = mFrequencyBucketCreator.getBucketedValues(cpuUsagesLong);

	return new ThreadCpuUsage(threadId, threadName, cpuUsages);
	}

	/** Get the command used to start a process */
	private String getProcessName(Path processPath) {
	final Path processNamePath = processPath.resolve(PROCESS_NAME_FILENAME);

	final String processName = ProcStatsUtil.readSingleLineProcFile(processNamePath.toString());
	if (processName != null) {
	return processName;
	}
	return DEFAULT_PROCESS_NAME;
	}

	/** Get the name of a thread, given the {@code /proc} path of the thread */
	private String getThreadName(Path threadPath) {
	final Path threadNamePath = threadPath.resolve(THREAD_NAME_FILENAME);
	final String threadName = ProcStatsUtil.readNullSeparatedFile(threadNamePath.toString());
	if (threadName == null) {
	return DEFAULT_THREAD_NAME;
	}
	return threadName;
	}

	/**
	* Get the ID of a process from its path
	*
	* @param processPath {@code proc} path of the process
	* @return the ID, {@link #ID_ERROR} if the path could not be parsed
	*/
	private int getProcessId(Path processPath) {
	String fileName = processPath.getFileName().toString();
	try {
	return Integer.parseInt(fileName);
	} catch (NumberFormatException e) {
	Slog.w(TAG, "Failed to parse " + fileName + " as process ID", e);
	return ID_ERROR;
	}
	}

	/** Puts frequencies and usage times into buckets */
	@VisibleForTesting
	public static class FrequencyBucketCreator {
	private final int mNumBuckets;
	private final int mNumFrequencies;
	private final int mBigFrequenciesStartIndex;
	private final int mLittleNumBuckets;
	private final int mBigNumBuckets;
	private final int mLittleBucketSize;
	private final int mBigBucketSize;

	/**
	* Buckets based of a list of frequencies
	*
	* @param frequencies the frequencies to base buckets off
	* @param numBuckets how many buckets to create
	*/
	@VisibleForTesting
	public FrequencyBucketCreator(long[] frequencies, int numBuckets) {
	Preconditions.checkArgument(numBuckets > 0);

	mNumFrequencies = frequencies.length;
	mBigFrequenciesStartIndex = getBigFrequenciesStartIndex(frequencies);

	final int littleNumBuckets;
	final int bigNumBuckets;
	if (mBigFrequenciesStartIndex < frequencies.length) {
	littleNumBuckets = numBuckets / 2;
	bigNumBuckets = numBuckets - littleNumBuckets;
	} else {
	// If we've got no big frequencies, set all buckets to little frequencies
	littleNumBuckets = numBuckets;
	bigNumBuckets = 0;
	}

	// Ensure that we don't have more buckets than frequencies
	mLittleNumBuckets = Math.min(littleNumBuckets, mBigFrequenciesStartIndex);
	mBigNumBuckets =
	Math.min(bigNumBuckets, frequencies.length - mBigFrequenciesStartIndex);
	mNumBuckets = mLittleNumBuckets + mBigNumBuckets;

	// Set the size of each little and big bucket. If they have no buckets, the size is zero
	mLittleBucketSize =
	mLittleNumBuckets == 0 ? 0 : mBigFrequenciesStartIndex / mLittleNumBuckets;
	mBigBucketSize =
	mBigNumBuckets == 0
	? 0
	: (frequencies.length - mBigFrequenciesStartIndex) / mBigNumBuckets;
	}

	/** Find the index where frequencies change from little core to big core */
	@VisibleForTesting
	public static int getBigFrequenciesStartIndex(long[] frequenciesKhz) {
	for (int i = 0; i < frequenciesKhz.length - 1; i++) {
	if (frequenciesKhz[i] > frequenciesKhz[i + 1]) {
	return i + 1;
	}
	}

	return frequenciesKhz.length;
	}

	/** Get the minimum frequency in each bucket */
	@VisibleForTesting
	public int[] getBucketMinFrequencies(long[] frequenciesKhz) {
	Preconditions.checkArgument(frequenciesKhz.length == mNumFrequencies);
	// If there's only one bucket, we bucket everything together so the first bucket is the
	// min frequency
	if (mNumBuckets == 1) {
	return new int[] {(int) frequenciesKhz[0]};
	}

	final int[] bucketMinFrequencies = new int[mNumBuckets];
	// Initialize little buckets min frequencies
	for (int i = 0; i < mLittleNumBuckets; i++) {
	bucketMinFrequencies[i] = (int) frequenciesKhz[i * mLittleBucketSize];
	}
	// Initialize big buckets min frequencies
	for (int i = 0; i < mBigNumBuckets; i++) {
	final int frequencyIndex = mBigFrequenciesStartIndex + i * mBigBucketSize;
	bucketMinFrequencies[mLittleNumBuckets + i] = (int) frequenciesKhz[frequencyIndex];
	}
	return bucketMinFrequencies;
	}

	/**
	* Put an array of values into buckets. This takes a {@code long[]} and returns {@code
	* int[]} as everywhere this method is used will have to do the conversion anyway, so we
	* save time by doing it here instead
	*
	* @param values the values to bucket
	* @return the bucketed usage times
	*/
	@VisibleForTesting
	@SuppressWarnings("ForLoopReplaceableByForEach")
	public int[] getBucketedValues(long[] values) {
	Preconditions.checkArgument(values.length == mNumFrequencies);
	final int[] bucketed = new int[mNumBuckets];

	// If there's only one bucket, add all frequencies in
	if (mNumBuckets == 1) {
	for (int i = 0; i < values.length; i++) {
	bucketed[0] += values[i];
	}
	return bucketed;
	}

	// Initialize the little buckets
	for (int i = 0; i < mBigFrequenciesStartIndex; i++) {
	final int bucketIndex = Math.min(i / mLittleBucketSize, mLittleNumBuckets - 1);
	bucketed[bucketIndex] += values[i];
	}
	// Initialize the big buckets
	for (int i = mBigFrequenciesStartIndex; i < values.length; i++) {
	final int bucketIndex =
	Math.min(
	mLittleNumBuckets
	+ (i - mBigFrequenciesStartIndex) / mBigBucketSize,
	mNumBuckets - 1);
	bucketed[bucketIndex] += values[i];
	}
	return bucketed;
	}
	}

	/** CPU usage of a process */
	public static class ProcessCpuUsage {
	public final int processId;
	public final String processName;
	public final int uid;
	public ArrayList<ThreadCpuUsage> threadCpuUsages;

	@VisibleForTesting
	public ProcessCpuUsage(
	int processId,
	String processName,
	int uid,
	ArrayList<ThreadCpuUsage> threadCpuUsages) {
	this.processId = processId;
	this.processName = processName;
	this.uid = uid;
	this.threadCpuUsages = threadCpuUsages;
	}
	}

	/** CPU usage of a thread */
	public static class ThreadCpuUsage {
	public final int threadId;
	public final String threadName;
	public int[] usageTimesMillis;

	@VisibleForTesting
	public ThreadCpuUsage(int threadId, String threadName, int[] usageTimesMillis) {
	this.threadId = threadId;
	this.threadName = threadName;
	this.usageTimesMillis = usageTimesMillis;
	}
	}

	/** Used to inject static methods from {@link Process} */
	@VisibleForTesting
	public static class Injector {
	/** Get the UID for the process with ID {@code pid} */
	public int getUidForPid(int pid) {
	return Process.getUidForPid(pid);
	}
	}
	}