平台

RK3288 + Android 7.1

问题

在测试Thread.sleep过程中发现, 当App进入后台后, 服务中的Thread.sleep会有不同程度的精确度丢失.
测试sleep 2ms, 当置于后台时, 实际延迟达到 [10 - 40] ms

相关测试代码:

|-- AndroidManifest.xml

    <applicationandroid:allowBackup="true"android:icon="@mipmap/ic_factory_test"android:label="@string/app_name"android:supportsRtl="true"android:theme="@style/AppTheme"android:directBootAware="true"><activity android:name="MainActivity"><intent-filter><action android:name="android.intent.action.MAIN" /><category android:name="android.intent.category.LAUNCHER" /><category android:name="android.intent.category.DEFAULT"/></intent-filter></activity><service android:name="NormalService"/></application>

|-- layout/main_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:orientation="vertical" android:layout_width="match_parent"android:layout_height="match_parent"><Button android:id="@+id/btStart"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="@string/start"/>
</LinearLayout>

|-- MainActivity.java

public class MainActivity extends Activity implements View.OnClickListener {boolean serviceStarted = false;Button btStart;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.service_test);btStart = (Button)findViewById(R.id.btStart);btStart.setOnClickListener(this);}@Overridepublic void onClick(View view) {if(view.getId() == R.id.btStart){if(serviceStarted){btStart.setText(R.string.start);stopService(new Intent(this, NormalService.class));serviceStarted = false;}else{btStart.setText(R.string.stop);startService(new Intent(this, NormalService.class));serviceStarted = true;}}}
}

|-- NormalService.java

public class NormalService extends Service {final String TAG = "NormalService";@Overridepublic IBinder onBind(Intent intent) {return null;}@Overridepublic int onStartCommand(Intent intent, int flags, int startId) {testSleep();return super.onStartCommand(intent, flags, startId);}void testSleep(){new Thread(TAG){@Overridepublic void run() {try{sleep(5000);for(int i = 0; i < 30; i ++){sleep(2);Global.d(TAG, "testSleep");}}catch(Exception e){}}}.start();}
}

测试过程

正常

  1. 打开Activity
  2. 点击按键启动服务.
  3. 等待线程执行并打印结果.
2019-05-09 13:55:42.295  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.298  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.301  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.305  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.308  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.312  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.315  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.318  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.322  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.325  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.328  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.332  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.336  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.339  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.342  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.346  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.349  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.352  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.356  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.359  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.362  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.366  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.369  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.371  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.374  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.377  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.381  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.383  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.386  D/NormalService: ALog > testSleep
2019-05-09 13:55:42.389  D/NormalService: ALog > testSleep

延迟

  1. 打开Activity
  2. 点击按键启动服务.
  3. 点击HOME 键退出到桌面.
  4. 等待线程执行并打印结果.
2019-05-09 13:53:49.313  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.354  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.396  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.440  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.459  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.501  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.544  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.560  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.572  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.583  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.596  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.606  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.618  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.629  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.641  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.653  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.664  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.676  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.723  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.746  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.758  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.769  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.781  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.793  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.805  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.816  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.828  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.839  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.851  D/NormalService: ALog > testSleep
2019-05-09 13:53:49.862  D/NormalService: ALog > testSleep

解决方法

以上问题是后台进程的CPU调度优先级降低导致.

关于CPU调度请参考:
随笔之Android平台上的进程调度探讨-https://blog.csdn.net/innost/article/details/6940136
[RK3288][Android6.0] CPU频率调度策略小结-https://blog.csdn.net/kris_fei/article/details/78016996

解决方法可参考:
Android Foreground Service (前台服务)-http://www.cnblogs.com/renhui/p/8575299.html

关键代码:

// 参数一：唯一的通知标识；参数二：通知消息。
startForeground(110, notification);// 开始前台服务

附源码相关
|-- frameworks/base/core/java/android/app/Service.java

    public final void startForeground(int id, Notification notification) {try {mActivityManager.setServiceForeground(new ComponentName(this, mClassName), mToken, id,notification, 0);} catch (RemoteException ex) {}}

|-- frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

    @Overridepublic void setServiceForeground(ComponentName className, IBinder token,int id, Notification notification, int flags) {synchronized(this) {mServices.setServiceForegroundLocked(className, token, id, notification, flags);}}

|-- frameworks/base/services/core/java/com/android/server/am/ActiveServices.java

    public void setServiceForegroundLocked(ComponentName className, IBinder token,int id, Notification notification, int flags) {final int userId = UserHandle.getCallingUserId();final long origId = Binder.clearCallingIdentity();try {ServiceRecord r = findServiceLocked(className, token, userId);if (r != null) {if (id != 0) {if (notification == null) {throw new IllegalArgumentException("null notification");}if (r.foregroundId != id) {cancelForegroudNotificationLocked(r);r.foregroundId = id;}notification.flags |= Notification.FLAG_FOREGROUND_SERVICE;r.foregroundNoti = notification;r.isForeground = true;r.postNotification();if (r.app != null) {updateServiceForegroundLocked(r.app, true);}getServiceMap(r.userId).ensureNotStartingBackground(r);mAm.notifyPackageUse(r.serviceInfo.packageName,PackageManager.NOTIFY_PACKAGE_USE_FOREGROUND_SERVICE);} else {if (r.isForeground) {r.isForeground = false;if (r.app != null) {mAm.updateLruProcessLocked(r.app, false, null);updateServiceForegroundLocked(r.app, true);}}if ((flags & Service.STOP_FOREGROUND_REMOVE) != 0) {cancelForegroudNotificationLocked(r);r.foregroundId = 0;r.foregroundNoti = null;} else if (r.appInfo.targetSdkVersion >= Build.VERSION_CODES.LOLLIPOP) {r.stripForegroundServiceFlagFromNotification();if ((flags & Service.STOP_FOREGROUND_DETACH) != 0) {r.foregroundId = 0;r.foregroundNoti = null;}}}}} finally {Binder.restoreCallingIdentity(origId);}}private void updateServiceForegroundLocked(ProcessRecord proc, boolean oomAdj) {boolean anyForeground = false;for (int i=proc.services.size()-1; i>=0; i--) {ServiceRecord sr = proc.services.valueAt(i);if (sr.isForeground) {anyForeground = true;break;}}mAm.updateProcessForegroundLocked(proc, anyForeground, oomAdj);}

|-- frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

    final void updateProcessForegroundLocked(ProcessRecord proc, boolean isForeground,boolean oomAdj) {if (isForeground != proc.foregroundServices) {proc.foregroundServices = isForeground;ArrayList<ProcessRecord> curProcs = mForegroundPackages.get(proc.info.packageName,proc.info.uid);if (isForeground) {if (curProcs == null) {curProcs = new ArrayList<ProcessRecord>();mForegroundPackages.put(proc.info.packageName, proc.info.uid, curProcs);}if (!curProcs.contains(proc)) {curProcs.add(proc);mBatteryStatsService.noteEvent(BatteryStats.HistoryItem.EVENT_FOREGROUND_START,proc.info.packageName, proc.info.uid);}} else {if (curProcs != null) {if (curProcs.remove(proc)) {mBatteryStatsService.noteEvent(BatteryStats.HistoryItem.EVENT_FOREGROUND_FINISH,proc.info.packageName, proc.info.uid);if (curProcs.size() <= 0) {mForegroundPackages.remove(proc.info.packageName, proc.info.uid);}}}}if (oomAdj) {updateOomAdjLocked();}}}

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