Android8.1 时间更新机制之网络更新时间和GPS更新时间_android 系统 gps自动更新时间

两种时间更新机制

NITZ

NITZ(Network Identity and Time Zone，网络标识和时区），是一种用于自动配置本地的时间和日期的机制，同时也通过无线网向移动设备提供运营商信息。NITZ是自从PHASE 2+ RELEASE 96 的GSM中的可选功能，经常被用来自动更新移动电话的系统时钟。NITZ需要运营商网络支持（通过CS网络），目前国内电信、移动都支持NITZ方式更新时间日期，而联通目前不支持

NTP

NTP：NTP(Network Time Protocol)提供准确时间，首先要有准确的时间来源，这一时间应该是国际标准时间UTC。 NTP获得UTC的时间来源可以是原子钟、天文台、卫星，也可以从Internet上获取。这样就有了准确而可靠的时间源。时间按NTP服务器的等级传播。与NITZ不同的是，NTP需要从专门的NTP服务器来获取时间，只要手机连接上网络，都可以实现时间的更新。

一、Android网络时间更新
Android网络时间更新，大体分两类。1、moderm相关更新，2、网络更新。本次主要介绍网路更新时间，主要涉及到NetworkTimeUpdateService，该类运行在SystemServer（ActivityManagerService）进程中。它有点特殊，从名字来看，其实Service，其实它和WifiService、ConnectivityManagerService等系统Service不同。
ZygoteInit.java的startSystemServer函数中启动了SyetemServer进程,代码路径如下所示：\frameworks\base\services\java\com\android\server\SystemServer.java

 /**
     * The main entry point from zygote.
     */
    public static void main(String[] args) {
        new SystemServer().run();
    }
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startOtherServices方法中，会初始化该类实例：

  if (!disableNetwork && !disableNetworkTime) {
                traceBeginAndSlog("StartNetworkTimeUpdateService");
                try {
                    networkTimeUpdater = new NetworkTimeUpdateService(context);
                    ServiceManager.addService("network_time_update_service", networkTimeUpdater);
                } catch (Throwable e) {
                    reportWtf("starting NetworkTimeUpdate service", e);
                }
                traceEnd();
 }
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网络更新的相关代码：

frameworks/base/services/core/java/com/android/server/NetworkTimeUpdateService.java
frameworks/base/core/java/android/util/NtpTrustedTime.java
frameworks/base/core/java/android/net/SntpClient.java
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NetworkTimeUpdateService构造函数初始化

  public NetworkTimeUpdateService(Context context) {
		Log.d(TAG, "NetworkTimeUpdateService()");
        mContext = context;
        mTime = NtpTrustedTime.getInstance(context);
        mAlarmManager = (AlarmManager) mContext.getSystemService(Context.ALARM_SERVICE);
        mCM = (ConnectivityManager) mContext.getSystemService(Context.CONNECTIVITY_SERVICE);
        //时间同步有可能超时，使用该PendingIntent进行（间隔再次发起）时间同步。
        Intent pollIntent = new Intent(ACTION_POLL, null);
        mPendingPollIntent = PendingIntent.getBroadcast(mContext, POLL_REQUEST, pollIntent, 0);
		//正常轮询频率 24小时
        mPollingIntervalMs = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_ntpPollingInterval);
       //再次尝试轮询间隔，以防网络请求失败 60秒
        mPollingIntervalShorterMs = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_ntpPollingIntervalShorter);
     //重试次数 3次
        mTryAgainTimesMax = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_ntpRetry);
   //如果时间差大于此阈值，则更新时间。 5秒
        mTimeErrorThresholdMs = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_ntpThreshold);

        mWakeLock = ((PowerManager) context.getSystemService(Context.POWER_SERVICE)).newWakeLock(
                PowerManager.PARTIAL_WAKE_LOCK, TAG);
		Log.d(TAG, "mPollingIntervalMs  "+mPollingIntervalMs);
		Log.d(TAG, "mPollingIntervalShorterMs  "+mPollingIntervalShorterMs);
		Log.d(TAG, "mTryAgainTimesMax  "+mTryAgainTimesMax);
		Log.d(TAG, "mTimeErrorThresholdMs  "+mTimeErrorThresholdMs);
    }
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在SystemServer.java中调用systemRunning(),初始化接收方并启动第一个NTP请求

//在SystemServer.java中调用systemRunning()
 traceBeginAndSlog("MakeCountryDetectionServiceReady");
            try {
                if (countryDetectorF != null) countryDetectorF.systemRunning();
            } catch (Throwable e) {
                reportWtf("Notifying CountryDetectorService running", e);
            }
 traceEnd();
 traceBeginAndSlog("MakeNetworkTimeUpdateReady");
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NetworkTimeUpdateService初始化时间同步环境开机后，会调用该类的systemRunning方法，在该方法中中实现systemRunning();

 public void systemRunning() {
        registerForTelephonyIntents();
        registerForAlarms();

        HandlerThread thread = new HandlerThread(TAG);
        thread.start();
        mHandler = new MyHandler(thread.getLooper());
        mNetworkTimeUpdateCallback = new NetworkTimeUpdateCallback();
        mCM.registerDefaultNetworkCallback(mNetworkTimeUpdateCallback, mHandler);

        mSettingsObserver = new SettingsObserver(mHandler, EVENT_AUTO_TIME_CHANGED);
        mSettingsObserver.observe(mContext);
    }
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registerForTelephonyIntents该方法，注册监听来自Telephony Ril相关的广播。此部分会在moderm相关同步时间中介绍

  private void registerForTelephonyIntents() {
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(TelephonyIntents.ACTION_NETWORK_SET_TIME);
        intentFilter.addAction(TelephonyIntents.ACTION_NETWORK_SET_TIMEZONE);
        mContext.registerReceiver(mNitzReceiver, intentFilter);
    }
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系统启动后，会收到一个Telephony的广播android.intent.action.NETWORK_SET_TIMEZONE，获取系统深度睡眠时间

//尼兹时间事件的接收者
 private BroadcastReceiver mNitzReceiver = new BroadcastReceiver() {

        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (DBG) Log.d(TAG, "Received " + action);
            if (TelephonyIntents.ACTION_NETWORK_SET_TIME.equals(action)) {
                mNitzTimeSetTime = SystemClock.elapsedRealtime();//从设备开机到现在的时间，单位毫秒，含系统深度睡眠时间
            } else if (TelephonyIntents.ACTION_NETWORK_SET_TIMEZONE.equals(action)) {
                mNitzZoneSetTime = SystemClock.elapsedRealtime();
            }
        }
    };

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当我们点击设置中的自动确定日期和时间时，然后通过观察者模式会执行如下代码，构建监听数据库的Observer，监听来自设置等发起的时间同步请求。在SettingsObserver中构建handler Message请求，发起时间同步。

源码路径：packages/apps/Settings/src/com/android/settings/DateTimeSettings.java
1

 mSettingsObserver = new SettingsObserver(mHandler, EVENT_AUTO_TIME_CHANGED);
        mSettingsObserver.observe(mContext);
  private static class SettingsObserver extends ContentObserver {

        private int mMsg;
        private Handler mHandler;

        SettingsObserver(Handler handler, int msg) {
            super(handler);
            mHandler = handler;
            mMsg = msg;
        }

        void observe(Context context) {
            ContentResolver resolver = context.getContentResolver();
            resolver.registerContentObserver(Settings.Global.getUriFor(Settings.Global.AUTO_TIME),
                    false, this);
        }

        @Override
        public void onChange(boolean selfChange) {
			Log.d(TAG, "onChange()  selfChange "+selfChange);
            mHandler.obtainMessage(mMsg).sendToTarget();
        }
    }
    
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接收的来自Telephony相关的广播，或者数据库变化，我们都会发送Message给Handler，我们的handler是如下处理这些请求的：

 /** Handler to do the network accesses on */
    private class MyHandler extends Handler {

        public MyHandler(Looper l) {
            super(l);
        }

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case EVENT_AUTO_TIME_CHANGED:
                case EVENT_POLL_NETWORK_TIME:
                case EVENT_NETWORK_CHANGED:
                    onPollNetworkTime(msg.what);
                    break;
            }
        }
    }
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当我们打开移动数据或者wifi打开连接网络后是就会执行如下代码

  private class NetworkTimeUpdateCallback extends NetworkCallback {
        @Override
        public void onAvailable(Network network) {
            Log.d(TAG, String.format("New default network %s; checking time.", network));
            mDefaultNetwork = network;
            // Running on mHandler so invoke directly.
            onPollNetworkTime(EVENT_NETWORK_CHANGED);
        }

        @Override
        public void onLost(Network network) {
            if (network.equals(mDefaultNetwork)) mDefaultNetwork = null;
        }
    }
    
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下面是时间同步请求处理逻辑
接收请求类型：EVENT_AUTO_TIME_CHANGED、EVENT_POLL_NETWORK_TIME、
EVENT_NETWORK_CONNECTED，这些请求逻辑，我们都会发起onPollNetworkTime来进行相关逻辑处理。也就是说，onPollNetworkTime方法就是我们时间同步的主要关注对象。

 private void onPollNetworkTime(int event) {
        // If Automatic time is not set, don't bother. Similarly, if we don't
        // have any default network, don't bother.
		Log.d(TAG, "isAutomaticTimeRequested()  "+isAutomaticTimeRequested());
		Log.d(TAG, "mDefaultNetwork()  "+mDefaultNetwork);
		//自动使用网络提供时间sAutomaticTimeRequested() 就是true
        if (!isAutomaticTimeRequested() || mDefaultNetwork == null) return;
        mWakeLock.acquire();
        try {
            onPollNetworkTimeUnderWakeLock(event);
        } finally {
            mWakeLock.release();
        }
    }
    
 private void onPollNetworkTimeUnderWakeLock(int event) {
        final long refTime = SystemClock.elapsedRealtime();
        // If NITZ time was received less than mPollingIntervalMs time ago,
        // no need to sync to NTP.
        if (mNitzTimeSetTime != NOT_SET && refTime - mNitzTimeSetTime < mPollingIntervalMs) {
            resetAlarm(mPollingIntervalMs);
            return;
        }
        final long currentTime = System.currentTimeMillis();
        if (DBG) Log.d(TAG, "System time = " + currentTime);
        // Get the NTP time
        if (mLastNtpFetchTime == NOT_SET || refTime >= mLastNtpFetchTime + mPollingIntervalMs
                || event == EVENT_AUTO_TIME_CHANGED) {
            if (DBG) Log.d(TAG, "Before Ntp fetch");

            // force refresh NTP cache when outdated
            if (mTime.getCacheAge() >= mPollingIntervalMs) {
                mTime.forceRefresh();
            }

            // only update when NTP time is fresh
            if (mTime.getCacheAge() < mPollingIntervalMs) {
                final long ntp = mTime.currentTimeMillis();
                mTryAgainCounter = 0;
                // If the clock is more than N seconds off or this is the first time it's been
                // fetched since boot, set the current time.
                if (Math.abs(ntp - currentTime) > mTimeErrorThresholdMs
                        || mLastNtpFetchTime == NOT_SET) {
                    // Set the system time
                    if (DBG && mLastNtpFetchTime == NOT_SET
                            && Math.abs(ntp - currentTime) <= mTimeErrorThresholdMs) {
                        Log.d(TAG, "For initial setup, rtc = " + currentTime);
                    }
                    if (DBG) Log.d(TAG, "Ntp time to be set = " + ntp);
                    // Make sure we don't overflow, since it's going to be converted to an int
                    if (ntp / 1000 < Integer.MAX_VALUE) {
                        SystemClock.setCurrentTimeMillis(ntp);
                    }
                } else {
                    if (DBG) Log.d(TAG, "Ntp time is close enough = " + ntp);
                }
                mLastNtpFetchTime = SystemClock.elapsedRealtime();
            } else {
                // Try again shortly
                mTryAgainCounter++;
                if (mTryAgainTimesMax < 0 || mTryAgainCounter <= mTryAgainTimesMax) {
                    resetAlarm(mPollingIntervalShorterMs);
                } else {
                    // Try much later
                    mTryAgainCounter = 0;
                    resetAlarm(mPollingIntervalMs);
                }
                return;
            }
        }
        resetAlarm(mPollingIntervalMs);
    }
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NTPServer服务器配置

修改配置位置：frameworks\base\core\res\res\values\config.xml
 <string translatable="false" name="config_ntpServer">2.android.pool.ntp.org</string>
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NTP从服务器获取时间分析
首先定义一个接口类TrustedTime，里面有如下方法：

public interface TrustedTime {
    /**
     * Force update with an external trusted time source, returning {@code true}
     * when successful.
     */
    public boolean forceRefresh();

    /**
     * Check if this instance has cached a response from a trusted time source.
     */
    public boolean hasCache();

    /**
     * Return time since last trusted time source contact, or
     * {@link Long#MAX_VALUE} if never contacted.
     */
    public long getCacheAge();

    /**
     * Return certainty of cached trusted time in milliseconds, or
     * {@link Long#MAX_VALUE} if never contacted. Smaller values are more
     * precise.
     */
    public long getCacheCertainty();

    /**
     * Return current time similar to {@link System#currentTimeMillis()},
     * possibly using a cached authoritative time source.
     */
    public long currentTimeMillis();
}

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NtpTrustedTime类实现TrustedTime的方法，在forceRefresh（）中获取服务器的时间。

 @Override
    public boolean forceRefresh() {
        if (TextUtils.isEmpty(mServer)) {
            // missing server, so no trusted time available
            return false;
        }

        // We can't do this at initialization time: ConnectivityService might not be running yet.
        synchronized (this) {
            if (mCM == null) {
                mCM = (ConnectivityManager) sContext.getSystemService(Context.CONNECTIVITY_SERVICE);
            }
        }

        final NetworkInfo ni = mCM == null ? null : mCM.getActiveNetworkInfo();
        if (ni == null || !ni.isConnected()) {
            if (LOGD) Log.d(TAG, "forceRefresh: no connectivity");
            return false;
        }


        if (LOGD) Log.d(TAG, "forceRefresh() from cache miss");
        //final SntpClient client = new SntpClient();
        final SprdSntpClient client = new SprdSntpClient();
        if (client.requestTime(mServer, (int) mTimeout)) {
            mHasCache = true;
            mCachedNtpTime = client.getNtpTime();
            mCachedNtpElapsedRealtime = client.getNtpTimeReference();
            mCachedNtpCertainty = client.getRoundTripTime() / 2;
            return true;
        } else {
            return false;
        }
    }
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日志流程

05-29 11:14:38.284   901   901 D NetworkTimeUpdateService: NetworkTimeUpdateService()
05-29 11:14:38.285   901   901 D NetworkTimeUpdateService: mPollingIntervalMs  86400000
05-29 11:14:38.285   901   901 D NetworkTimeUpdateService: mPollingIntervalShorterMs  60000
05-29 11:14:38.285   901   901 D NetworkTimeUpdateService: mTryAgainTimesMax  3
05-29 11:14:38.285   901   901 D NetworkTimeUpdateService: mTimeErrorThresholdMs  5000
05-29 11:14:44.805   901   901 D NetworkTimeUpdateService: Received android.intent.action.NETWORK_SET_TIMEZONE
05-29 11:20:12.155   901  1303 D NetworkTimeUpdateService: New default network 100; checking time.
05-29 11:20:12.158   901  1303 D NetworkTimeUpdateService: System time = 1590722412158
05-29 11:20:12.158   901  1303 D NetworkTimeUpdateService: Before Ntp fetch
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