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AlarmManagerService(一)

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本篇文章主要介绍 Android 开发中的AlarmManagerService部分知识点，通过阅读本篇文章，您将收获以下内容:

1.AlarmManager的使用
2.AlarmManagerService初始化

本文转自网络地址如下：
http://www.robinheztto.com/2017/03/10/android-alarm-1/

Android系统通过AlarmManager向应用提供定时/闹钟服务，以使应用在其生命周期之外可执行基于特定时间的操作，本篇将具体分析AlarmManager的使用及AlarmManagerService服务的初始化。

AlarmManager的使用

1.获取AlarmManager:
Alarm相关的服务接口定义在AlarmManager中，与其他系统服务一样，通过Context获取AlarmManager。

Context.getSystemService(Context.ALARM_SERVICE);

Alarm的类型:

AlarmManager.RTC_WAKEUP
使用系统绝对时间(当前系统时间，System.currentTimeMillis())，系统休眠状态也将唤醒系统。
AlarmManager.RTC
使用系统绝对时间(当前系统时间，System.currentTimeMillis())，系统休眠状态下不可用。
AlarmManager.ELAPSED_REALTIME_WAKEUP
使用系统相对时间(相对系统启动时间，SystemClock.elapsedRealtime())，系统休眠状态也将唤醒系统。
AlarmManager.ELAPSED_REALTIME
使用系统相对时间(相对系统启动时间，SystemClock.elapsedRealtime())，系统休眠状态下不可用
RTC/RTC_WAKEUP和ELAPSED_REALTIME/ELAPSED_REALTIME_WAKEUP最大的差别就是RTC受time zone/locale的影响，可以通过修改手机时间触发闹钟事件，ELAPSED_REALTIME/ELAPSED_REALTIME_WAKEUP要通过真实时间的流逝，即使在休眠状态时间也会被计算。

WAKEUP类型的Alarm会唤醒系统，休眠状态下会增加系统的功耗，所以在使用中应尽量避免使用该种类型的Alarm。

Alarm的Flag:

FLAG_STANDALONE
指定stand-alone精准alarm，该alarm不会被batch，设置WINDOW_EXACT的alarm会指定此flag。
FLAG_WAKE_FROM_IDLE
指定alarm即使在idle模式也将唤醒系统，如alarm clock。
FLAG_ALLOW_WHILE_IDLE
针对Doze模式，alarm即使在系统idle状态下也会执行，但是不会使系统退出idle mode，只有特殊alarm才需要标记该Flag。
FLAG_ALLOW_WHILE_IDLE_UNRESTRICTED
针对Doze模式，alarm即使在系统idle状态下也会执行而且没有时间限制，但是不会使系统退出idle mode，只有特殊alarm才需要标记该Flag。
FLAG_IDLE_UNTIL
只有调用AlarmManager.setIdleUntil()接口才可能设置该flag，用来使系统进入idle mode直到marker alarm被执行，执行marker alarm时系统会退出idle mode(设置后进入DozeIdle状态让Alarm系统挂起，直到这个Alarm到期)。

4.Alarm的set:

非精准Alarm，其window被指定为WINDOW_HEURISTIC：


public void set(int type, long triggerAtMillis, PendingIntent operation) {}

public void set(int type, long triggerAtMillis, String tag, OnAlarmListener listener,Handler targetHandler) {}

public void setRepeating(int type, long triggerAtMillis,long intervalMillis, PendingIntent operation) {}

public void setInexactRepeating(int type, long triggerAtMillis,long intervalMillis, PendingIntent operation) {}// Doze模式下

public void setAndAllowWhileIdle(int type, long triggerAtMillis, PendingIntent operation) {}

精准Alarm，其window被标记为WINDOW_EXACT

public void setWindow(int type, long windowStartMillis, long windowLengthMillis,PendingIntent operation) {}

public void setWindow(int type, long windowStartMillis, long windowLengthMillis, String tag, OnAlarmListener listener, Handler targetHandler) {}

public void setExact(int type, long triggerAtMillis, PendingIntent operation) {}  
 
public void setExact(int type, long triggerAtMillis, String tag, OnAlarmListener listener, Handler targetHandler) {}  

public void setAlarmClock(AlarmClockInfo info, PendingIntent operation) {}// Doze模式下

public void setIdleUntil(int type, long triggerAtMillis, String tag, OnAlarmListener listener,Handler targetHandler) {}

public void setExactAndAllowWhileIdle(int type, long triggerAtMillis, PendingIntent operation) {}

AlarmManager中的set方法最终都是调用setImpl，下面是setImpl的具体实现。
frameworks/base/core/java/android/app/AlarmManager.java

 private void setImpl(@AlarmType int type, long triggerAtMillis, long windowMillis,
            long intervalMillis, int flags, PendingIntent operation, final OnAlarmListener listener,
            String listenerTag, Handler targetHandler, WorkSource workSource,
            AlarmClockInfo alarmClock) {
        if (triggerAtMillis < 0) {
            /* NOTYET
            if (mAlwaysExact) {
                // Fatal error for KLP+ apps to use negative trigger times
                throw new IllegalArgumentException("Invalid alarm trigger time "
                        + triggerAtMillis);
            }
            */
            triggerAtMillis = 0;
        }
// OnAlarmListener封装到ListenerWrapper，并添加到sWrappers管理
        ListenerWrapper recipientWrapper = null;
        if (listener != null) {
            synchronized (AlarmManager.class) {
                if (sWrappers == null) {
                    sWrappers = new ArrayMap();
                }

                recipientWrapper = sWrappers.get(listener);
                // no existing wrapper => build a new one
                if (recipientWrapper == null) {
                    recipientWrapper = new ListenerWrapper(listener);
                    sWrappers.put(listener, recipientWrapper);
                }
            }

            final Handler handler = (targetHandler != null) ? targetHandler : mMainThreadHandler;
            recipientWrapper.setHandler(handler);
        }
 // 调用AlarmManagerService
        try {
            mService.set(mPackageName, type, triggerAtMillis, windowMillis, intervalMillis, flags,
                    operation, recipientWrapper, listenerTag, workSource, alarmClock);
        } catch (RemoteException ex) {
            throw ex.rethrowFromSystemServer();
        }
    }

AlarmManagerService初始化

    public AlarmManagerService(Context context) {
        super(context);
        mConstants = new Constants(mHandler);
    }

下面先看Constants类的具体实现，主要负责Alarm相关的常量的读取及更新。

 private final class Constants extends ContentObserver {
        // Key names stored in the settings value.
        private static final String KEY_MIN_FUTURITY = "min_futurity";
        private static final String KEY_MIN_INTERVAL = "min_interval";
        private static final String KEY_ALLOW_WHILE_IDLE_SHORT_TIME = "allow_while_idle_short_time";
        private static final String KEY_ALLOW_WHILE_IDLE_LONG_TIME = "allow_while_idle_long_time";
        private static final String KEY_ALLOW_WHILE_IDLE_WHITELIST_DURATION
                = "allow_while_idle_whitelist_duration";
        private static final String KEY_LISTENER_TIMEOUT = "listener_timeout";

        private static final long DEFAULT_MIN_FUTURITY = 5 * 1000;
        private static final long DEFAULT_MIN_INTERVAL = 60 * 1000;
        private static final long DEFAULT_ALLOW_WHILE_IDLE_SHORT_TIME = DEFAULT_MIN_FUTURITY;
        private static final long DEFAULT_ALLOW_WHILE_IDLE_LONG_TIME = 9*60*1000;
        private static final long DEFAULT_ALLOW_WHILE_IDLE_WHITELIST_DURATION = 10*1000;

        private static final long DEFAULT_LISTENER_TIMEOUT = 5 * 1000;

        // Minimum futurity of a new alarm
        public long MIN_FUTURITY = DEFAULT_MIN_FUTURITY;

        // Minimum alarm recurrence interval
        public long MIN_INTERVAL = DEFAULT_MIN_INTERVAL;

        // Minimum time between ALLOW_WHILE_IDLE alarms when system is not idle.
        public long ALLOW_WHILE_IDLE_SHORT_TIME = DEFAULT_ALLOW_WHILE_IDLE_SHORT_TIME;

        // Minimum time between ALLOW_WHILE_IDLE alarms when system is idling.
        public long ALLOW_WHILE_IDLE_LONG_TIME = DEFAULT_ALLOW_WHILE_IDLE_LONG_TIME;

        // BroadcastOptions.setTemporaryAppWhitelistDuration() to use for FLAG_ALLOW_WHILE_IDLE.
        public long ALLOW_WHILE_IDLE_WHITELIST_DURATION
                = DEFAULT_ALLOW_WHILE_IDLE_WHITELIST_DURATION;

        // Direct alarm listener callback timeout
        public long LISTENER_TIMEOUT = DEFAULT_LISTENER_TIMEOUT;

        private ContentResolver mResolver;
        private final KeyValueListParser mParser = new KeyValueListParser(',');
        private long mLastAllowWhileIdleWhitelistDuration = -1;

        public Constants(Handler handler) {
            super(handler);
            updateAllowWhileIdleMinTimeLocked();
            updateAllowWhileIdleWhitelistDurationLocked();
        }

        public void start(ContentResolver resolver) {
            mResolver = resolver;
            mResolver.registerContentObserver(Settings.Global.getUriFor(
                    Settings.Global.ALARM_MANAGER_CONSTANTS), false, this);
            updateConstants();
        }

        public void updateAllowWhileIdleMinTimeLocked() {
            mAllowWhileIdleMinTime = mPendingIdleUntil != null
                    ? ALLOW_WHILE_IDLE_LONG_TIME : ALLOW_WHILE_IDLE_SHORT_TIME;
        }

        public void updateAllowWhileIdleWhitelistDurationLocked() {
            if (mLastAllowWhileIdleWhitelistDuration != ALLOW_WHILE_IDLE_WHITELIST_DURATION) {
                mLastAllowWhileIdleWhitelistDuration = ALLOW_WHILE_IDLE_WHITELIST_DURATION;
                BroadcastOptions opts = BroadcastOptions.makeBasic();
                opts.setTemporaryAppWhitelistDuration(ALLOW_WHILE_IDLE_WHITELIST_DURATION);
                mIdleOptions = opts.toBundle();
            }
        }

        @Override
        public void onChange(boolean selfChange, Uri uri) {
            updateConstants();
        }

        private void updateConstants() {
            synchronized (mLock) {
                try {
                    mParser.setString(Settings.Global.getString(mResolver,
                            Settings.Global.ALARM_MANAGER_CONSTANTS));
                } catch (IllegalArgumentException e) {
                    // Failed to parse the settings string, log this and move on
                    // with defaults.
                    Slog.e(TAG, "Bad alarm manager settings", e);
                }

                MIN_FUTURITY = mParser.getLong(KEY_MIN_FUTURITY, DEFAULT_MIN_FUTURITY);
                MIN_INTERVAL = mParser.getLong(KEY_MIN_INTERVAL, DEFAULT_MIN_INTERVAL);
                ALLOW_WHILE_IDLE_SHORT_TIME = mParser.getLong(KEY_ALLOW_WHILE_IDLE_SHORT_TIME,
                        DEFAULT_ALLOW_WHILE_IDLE_SHORT_TIME);
                ALLOW_WHILE_IDLE_LONG_TIME = mParser.getLong(KEY_ALLOW_WHILE_IDLE_LONG_TIME,
                        DEFAULT_ALLOW_WHILE_IDLE_LONG_TIME);
                ALLOW_WHILE_IDLE_WHITELIST_DURATION = mParser.getLong(
                        KEY_ALLOW_WHILE_IDLE_WHITELIST_DURATION,
                        DEFAULT_ALLOW_WHILE_IDLE_WHITELIST_DURATION);
                LISTENER_TIMEOUT = mParser.getLong(KEY_LISTENER_TIMEOUT,
                        DEFAULT_LISTENER_TIMEOUT);

                updateAllowWhileIdleMinTimeLocked();
                updateAllowWhileIdleWhitelistDurationLocked();
            }
        }

        void dump(PrintWriter pw) {
            pw.println("  Settings:");

            pw.print("    "); pw.print(KEY_MIN_FUTURITY); pw.print("=");
            TimeUtils.formatDuration(MIN_FUTURITY, pw);
            pw.println();

            pw.print("    "); pw.print(KEY_MIN_INTERVAL); pw.print("=");
            TimeUtils.formatDuration(MIN_INTERVAL, pw);
            pw.println();

            pw.print("    "); pw.print(KEY_LISTENER_TIMEOUT); pw.print("=");
            TimeUtils.formatDuration(LISTENER_TIMEOUT, pw);
            pw.println();

            pw.print("    "); pw.print(KEY_ALLOW_WHILE_IDLE_SHORT_TIME); pw.print("=");
            TimeUtils.formatDuration(ALLOW_WHILE_IDLE_SHORT_TIME, pw);
            pw.println();

            pw.print("    "); pw.print(KEY_ALLOW_WHILE_IDLE_LONG_TIME); pw.print("=");
            TimeUtils.formatDuration(ALLOW_WHILE_IDLE_LONG_TIME, pw);
            pw.println();

            pw.print("    "); pw.print(KEY_ALLOW_WHILE_IDLE_WHITELIST_DURATION); pw.print("=");
            TimeUtils.formatDuration(ALLOW_WHILE_IDLE_WHITELIST_DURATION, pw);
            pw.println();
        }
    }

AlarmManagerService实例化后即调用onStart()方法。

  @Override
    public void onStart() {
       // native层初始化
        mNativeData = init();
        mNextWakeup = mNextNonWakeup = 0;

        // We have to set current TimeZone info to kernel
        // because kernel doesn't keep this after reboot
        setTimeZoneImpl(SystemProperties.get(TIMEZONE_PROPERTY));
        /// M:add for PPL feature ,@{
        initPpl();
        ///@}
        /// M: For handling non-wakeup alarms while WFD is connected
        registerWFDStatusChangeReciever();
        ///@}
        /// M: added for BG powerSaving feature @{
        initAlarmGrouping();
        ///@}
        // Also sure that we're booting with a halfway sensible current time
        if (mNativeData != 0) {
            final long systemBuildTime = Environment.getRootDirectory().lastModified();
            if (System.currentTimeMillis() < systemBuildTime) {
                Slog.i(TAG, "Current time only " + System.currentTimeMillis()
                        + ", advancing to build time " + systemBuildTime);
                setKernelTime(mNativeData, systemBuildTime);
            }
        }

        // Determine SysUI's uid
        final PackageManager packMan = getContext().getPackageManager();
        try {
            PermissionInfo sysUiPerm = packMan.getPermissionInfo(SYSTEM_UI_SELF_PERMISSION, 0);
            ApplicationInfo sysUi = packMan.getApplicationInfo(sysUiPerm.packageName, 0);
            if ((sysUi.privateFlags&ApplicationInfo.PRIVATE_FLAG_PRIVILEGED) != 0) {
                mSystemUiUid = sysUi.uid;
            } else {
                Slog.e(TAG, "SysUI permission " + SYSTEM_UI_SELF_PERMISSION
                        + " defined by non-privileged app " + sysUi.packageName
                        + " - ignoring");
            }
        } catch (NameNotFoundException e) {
        }

        if (mSystemUiUid <= 0) {
            Slog.wtf(TAG, "SysUI package not found!");
        }

        PowerManager pm = (PowerManager) getContext().getSystemService(Context.POWER_SERVICE);
        mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "*alarm*");

        mTimeTickSender = PendingIntent.getBroadcastAsUser(getContext(), 0,
                new Intent(Intent.ACTION_TIME_TICK).addFlags(
                        Intent.FLAG_RECEIVER_REGISTERED_ONLY
                        | Intent.FLAG_RECEIVER_FOREGROUND
                        | Intent.FLAG_RECEIVER_VISIBLE_TO_INSTANT_APPS), 0,
                        UserHandle.ALL);
        Intent intent = new Intent(Intent.ACTION_DATE_CHANGED);
        intent.addFlags(Intent.FLAG_RECEIVER_REPLACE_PENDING
                | Intent.FLAG_RECEIVER_VISIBLE_TO_INSTANT_APPS);
        mDateChangeSender = PendingIntent.getBroadcastAsUser(getContext(), 0, intent,
                Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT, UserHandle.ALL);
        
        // now that we have initied the driver schedule the alarm
        mClockReceiver = new ClockReceiver();
        mClockReceiver.scheduleTimeTickEvent();
        mClockReceiver.scheduleDateChangedEvent();
        mInteractiveStateReceiver = new InteractiveStateReceiver();
        mUninstallReceiver = new UninstallReceiver();
        
        if (mNativeData != 0) {
            AlarmThread waitThread = new AlarmThread();
            waitThread.start();
        } else {
            Slog.w(TAG, "Failed to open alarm driver. Falling back to a handler.");
        }

        try {
            ActivityManager.getService().registerUidObserver(new UidObserver(),
                    ActivityManager.UID_OBSERVER_IDLE, ActivityManager.PROCESS_STATE_UNKNOWN, null);
        } catch (RemoteException e) {
            // ignored; both services live in system_server
        }

        publishBinderService(Context.ALARM_SERVICE, mService);
        publishLocalService(LocalService.class, new LocalService());
    }

在onStart()后，SYSTEM_SERVICES_READY时onBootPhase()将被回调。

    @Override
    public void onBootPhase(int phase) {
        if (phase == PHASE_SYSTEM_SERVICES_READY) {
            mConstants.start(getContext().getContentResolver());
            mAppOps = (AppOpsManager) getContext().getSystemService(Context.APP_OPS_SERVICE);
            mLocalDeviceIdleController
                    = LocalServices.getService(DeviceIdleController.LocalService.class);
        }
    }

回到onStart()，分析native层init的调用，下面看native init()的实现。

frameworks/base/services/core/java/com/android/server/AlarmManagerService.java

private native long init();