Android 7.1.1时间更新NITZ和NTP详解
1、NTP和NITZ简介
最近在项目中遇到手机首次插上移动卡时不能自动更新时间的问题,就特意跟了下Android系统中手机时间更新有两种方式NTP和NITZ,下面先来看看NTP和NITZ的简介
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,需要运营商支持,可从运营商获取时间和时区具体信息。
NTP:Network Time Protocol(网络时间协议),用来同步网络中各个计算机的时间的协议。在手机中,NTP更新时间的方式是通过GPRS或wifi向特定服务器获取时间信息(不包含时区信息)。
接着我们来看看两种方式具体更新流程
2、NITZ更新时间流程
NITZ更新时间依赖运营商,当运营商基站发出更新时间的消息,基站附近的手机接收到对应消息后,会通过RIL层上报UNSOL_NITZ_TIME_RECEIVED事件,此时ServiceStateTracker便会处理相关时间更新流程,
相关时序图如下:
由于NITZ主要依赖于运营商,但在国内移动和联通貌似不怎么好用,在这里就不在详细说了,简单总结下如下:
1、在ServiceStateTracker构造方法里调用setOnNITZTime注册RIL事件RIL_UNSOL_NITZ_TIME_RECEIVED
2、RIL层上报RIL_UNSOL_NITZ_TIME_RECEIVED,在ServiceStateTracker的handleMessage里处理
3、调用ServiceStateTracker的setTimeFromNITZString设置时间和时区,在setAndBroadcastNetworkSetTime里调用setCurrentTimeMillis设置系统时间,并发送广播通知NetworkTimeUpdateService
3、NTP时间更新流程
NTP时间更新主要依赖于GPRS和wifi,即通过网络的方式去获取时间,在NetworkTimeUpdateService中调用onPollNetworkTime访问NtpServer获取网络时间,我们先来看看整体流程
当SystemServer启动,会调用networkTimeUpdaterF.systemRunning()初始化各种NTP request监听
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public void systemRunning() {
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registerForTelephonyIntents();
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registerForAlarms();
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registerForConnectivityIntents();
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HandlerThread thread = new HandlerThread(TAG);
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thread.start();
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mHandler = new MyHandler(thread.getLooper());
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// Check the network time on the new thread
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mHandler.obtainMessage(EVENT_POLL_NETWORK_TIME).sendToTarget();
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mSettingsObserver = new SettingsObserver(mHandler, EVENT_AUTO_TIME_CHANGED);
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mSettingsObserver.observe(mContext);
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}
在registerForTelephonyIntents中主要是监听ACTION_NETWORK_SET_TIME和ACTION_NETWORK_SET_TIMEZONE的广播,registerForAlarms中监听"com.android.server.NetworkTimeUpdateService.action.POLL"广播,registerForConnectivityIntents监听网络状态改变的广播,SettingsObserver里监听Settings.Global.AUTO_TIME值的改变
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//frameworks/base/services/core/java/com/android/server/NetworkTimeUpdateService.java
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private class MyHandler extends Handler {
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public MyHandler(Looper l) {
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super(l);
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}
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@Override
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public void handleMessage(Message msg) {
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switch (msg.what) {
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case EVENT_AUTO_TIME_CHANGED:
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case EVENT_POLL_NETWORK_TIME:
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case EVENT_NETWORK_CHANGED:
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onPollNetworkTime(msg.what);
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break;
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}
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}
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}
在这个MyHandler中可以看到,当上面某种监听触发时都会调用onPollNetworkTime,而这个方法里主要调用了onPollNetworkTimeUnderWakeLock,接下来看看这个方法
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//frameworks/base/services/core/java/com/android/server/NetworkTimeUpdateService.java
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private void onPollNetworkTimeUnderWakeLock(int event) {
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final long refTime = SystemClock.elapsedRealtime();
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// If NITZ time was received less than mPollingIntervalMs time ago,
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// no need to sync to NTP.
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if (mNitzTimeSetTime != NOT_SET && refTime - mNitzTimeSetTime < mPollingIntervalMs) {
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resetAlarm(mPollingIntervalMs);
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return;
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}
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final long currentTime = System.currentTimeMillis();
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if (DBG) Log.d(TAG, "System time = " + currentTime);
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// Get the NTP time
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if (mLastNtpFetchTime == NOT_SET || refTime >= mLastNtpFetchTime + mPollingIntervalMs
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|| event == EVENT_AUTO_TIME_CHANGED) {
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if (DBG) Log.d(TAG, "Before Ntp fetch");
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// force refresh NTP cache when outdated
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if (mTime.getCacheAge() >= mPollingIntervalMs) {
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mTime.forceRefresh();
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}
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// only update when NTP time is fresh
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if (mTime.getCacheAge() < mPollingIntervalMs) {
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final long ntp = mTime.currentTimeMillis();
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mTryAgainCounter = 0;
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// If the clock is more than N seconds off or this is the first time it's been
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// fetched since boot, set the current time.
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if (Math.abs(ntp - currentTime) > mTimeErrorThresholdMs
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|| mLastNtpFetchTime == NOT_SET) {
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// Set the system time
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if (DBG && mLastNtpFetchTime == NOT_SET
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&& Math.abs(ntp - currentTime) <= mTimeErrorThresholdMs) {
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Log.d(TAG, "For initial setup, rtc = " + currentTime);
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}
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if (DBG) Log.d(TAG, "Ntp time to be set = " + ntp);
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// Make sure we don't overflow, since it's going to be converted to an int
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if (ntp / 1000 < Integer.MAX_VALUE) {
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SystemClock.setCurrentTimeMillis(ntp);
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}
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} else {
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if (DBG) Log.d(TAG, "Ntp time is close enough = " + ntp);
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}
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mLastNtpFetchTime = SystemClock.elapsedRealtime();
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} else {
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// Try again shortly
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mTryAgainCounter++;
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if (mTryAgainTimesMax < 0 || mTryAgainCounter <= mTryAgainTimesMax) {
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resetAlarm(mPollingIntervalShorterMs);
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} else {
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// Try much later
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mTryAgainCounter = 0;
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resetAlarm(mPollingIntervalMs);
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}
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return;
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}
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}
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resetAlarm(mPollingIntervalMs);
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}
这个方法中主要调用了TrustedTime实例的forceRefresh方法去获取时间,获取之后通过mTime.currentTimeMillis获得获取成功之后的时间ntp,最后调用 SystemClock.setCurrentTimeMillis(ntp)设置系统时间有几个参数需要特别说下
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public NetworkTimeUpdateService(Context context) {
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mContext = context;
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mTime = NtpTrustedTime.getInstance(context);
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...
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//正常的轮询频率
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mPollingIntervalMs = mContext.getResources().getInteger(
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com.android.internal.R.integer.config_ntpPollingInterval);
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//重试轮询间隔,以防网络请求失败
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mPollingIntervalShorterMs = mContext.getResources().getInteger(
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com.android.internal.R.integer.config_ntpPollingIntervalShorter);
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//再次尝试次数
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mTryAgainTimesMax = mContext.getResources().getInteger(
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com.android.internal.R.integer.config_ntpRetry);
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//如果时间差大于此阈值,则更新时间。
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mTimeErrorThresholdMs = mContext.getResources().getInteger(
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com.android.internal.R.integer.config_ntpThreshold);
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...
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}
对应参数的配置如下,可能存在overlay替换,此处是framework里默认配置的值
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//frameworks/base/core/res/res/values/config.xml
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<!-- Normal polling frequency in milliseconds -->
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<integer name="config_ntpPollingInterval">86400000</integer>
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<!-- Try-again polling interval in milliseconds, in case the network request failed -->
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<integer name="config_ntpPollingIntervalShorter">60000</integer>
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<!-- Number of times to try again with the shorter interval, before backing
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off until the normal polling interval. A value < 0 indicates infinite. -->
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<integer name="config_ntpRetry">3</integer>
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<!-- If the time difference is greater than this threshold in milliseconds,
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then update the time. -->
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<integer name="config_ntpThreshold">5000</integer>
上面讲到主要通过TrustedTime实例的forceRefresh获取时间,下面就来跟下这个方法
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//frameworks/base/core/java/android/util/NtpTrustedTime.java
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public boolean forceRefresh() {
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if (TextUtils.isEmpty(mServer)) {
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// missing server, so no trusted time available
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return false;
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}
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// We can't do this at initialization time: ConnectivityService might not be running yet.
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synchronized (this) {
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if (mCM == null) {
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mCM = (ConnectivityManager) sContext.getSystemService(Context.CONNECTIVITY_SERVICE);
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}
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}
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final NetworkInfo ni = mCM == null ? null : mCM.getActiveNetworkInfo();
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if (ni == null || !ni.isConnected()) {
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if (LOGD) Log.d(TAG, "forceRefresh: no connectivity");
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return false;
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}
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if (LOGD) Log.d(TAG, "forceRefresh() from cache miss");
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final SntpClient client = new SntpClient();
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if (client.requestTime(mServer, (int) mTimeout)) {
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mHasCache = true;
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mCachedNtpTime = client.getNtpTime();
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mCachedNtpElapsedRealtime = client.getNtpTimeReference();
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mCachedNtpCertainty = client.getRoundTripTime() / 2;
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return true;
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} else {
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return false;
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}
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}
上面方法中主要是通过SntpClient的requestTime根据传入的mServer获取时间,mServer是在调用NtpTrustedTime的getInstance中初始化的,具体如下
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public static synchronized NtpTrustedTime getInstance(Context context) {
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if (sSingleton == null) {
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final Resources res = context.getResources();
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final ContentResolver resolver = context.getContentResolver();
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final String defaultServer = res.getString(
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com.android.internal.R.string.config_ntpServer);
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final long defaultTimeout = res.getInteger(
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com.android.internal.R.integer.config_ntpTimeout);
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final String secureServer = Settings.Global.getString(
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resolver, Settings.Global.NTP_SERVER);
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final long timeout = Settings.Global.getLong(
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resolver, Settings.Global.NTP_TIMEOUT, defaultTimeout);
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final String server = secureServer != null ? secureServer : defaultServer;
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sSingleton = new NtpTrustedTime(server, timeout);
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sContext = context;
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}
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return sSingleton;
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}
config_ntpServer和config_ntpTimeout也是在framework下res中配置的,Settings.Global.NTP_SERVER和Settings.Global.NTP_TIMEOUT是配置在SettingProvider中的,就不在具体说明了。从上面代码可看出server是由secureServer和defaultServer决定的
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//frameworks/base/core/res/res/values/config.xml
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<!-- Remote server that can provide NTP responses. -->
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<string translatable="false" name="config_ntpServer">2.android.pool.ntp.org</string>
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<!-- Timeout to wait for NTP server response in milliseconds. -->
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<integer name="config_ntpTimeout">5000</integer>
其中SntpClient主要是提供访问Ntp server的一个类,在requestTime中主要通过DatagramSocket访问传入的server,来获取时间,具体实现如下:
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//frameworks/base/core/java/android/net/SntpClient.java
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public boolean requestTime(InetAddress address, int port, int timeout) {
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DatagramSocket socket = null;
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try {
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socket = new DatagramSocket();
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socket.setSoTimeout(timeout);
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byte[] buffer = new byte[NTP_PACKET_SIZE];
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DatagramPacket request = new DatagramPacket(buffer, buffer.length, address, port);
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// set mode = 3 (client) and version = 3
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// mode is in low 3 bits of first byte
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// version is in bits 3-5 of first byte
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buffer[0] = NTP_MODE_CLIENT | (NTP_VERSION << 3);
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// get current time and write it to the request packet
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final long requestTime = System.currentTimeMillis();
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final long requestTicks = SystemClock.elapsedRealtime();
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writeTimeStamp(buffer, TRANSMIT_TIME_OFFSET, requestTime);
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socket.send(request);
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// read the response
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DatagramPacket response = new DatagramPacket(buffer, buffer.length);
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socket.receive(response);
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final long responseTicks = SystemClock.elapsedRealtime();
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final long responseTime = requestTime + (responseTicks - requestTicks);
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// extract the results
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final byte leap = (byte) ((buffer[0] >> 6) & 0x3);
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final byte mode = (byte) (buffer[0] & 0x7);
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final int stratum = (int) (buffer[1] & 0xff);
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final long originateTime = readTimeStamp(buffer, ORIGINATE_TIME_OFFSET);
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final long receiveTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET);
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final long transmitTime = readTimeStamp(buffer, TRANSMIT_TIME_OFFSET);
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/* do sanity check according to RFC */
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// TODO: validate originateTime == requestTime.
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checkValidServerReply(leap, mode, stratum, transmitTime);
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long roundTripTime = responseTicks - requestTicks - (transmitTime - receiveTime);
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// receiveTime = originateTime + transit + skew
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// responseTime = transmitTime + transit - skew
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// clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2
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// = ((originateTime + transit + skew - originateTime) +
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// (transmitTime - (transmitTime + transit - skew)))/2
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// = ((transit + skew) + (transmitTime - transmitTime - transit + skew))/2
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// = (transit + skew - transit + skew)/2
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// = (2 * skew)/2 = skew
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long clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2;
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if (DBG) {
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Log.d(TAG, "round trip: " + roundTripTime + "ms, " +
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"clock offset: " + clockOffset + "ms");
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}
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// save our results - use the times on this side of the network latency
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// (response rather than request time)
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mNtpTime = responseTime + clockOffset;
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mNtpTimeReference = responseTicks;
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mRoundTripTime = roundTripTime;
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} catch (Exception e) {
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if (DBG) Log.d(TAG, "request time failed: " + e);
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return false;
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} finally {
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if (socket != null) {
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socket.close();
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}
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}
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return true;
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}
其实Ntp说的明白点,就是通过网络去获取时间然后更新系统时间,具体流程上面也简单说了下,当遇到手机不能更新时间时,先要看看网络是否可用,网络可用的情况下,就得看看对应的NtpServer是否能够访问。曾经就遇到过移动的数据业务不能访问NtpServer,导致手机不能更新时间。一般可以通过ntp等关键字在log中搜索,一般是SocketException或unknown host的错误。也可以直接adb shell命令进去手机,然后利用ping NtpServer 查看当前服务器是否可访问。在这里需要说的一点是,NtpServer一般都是对应的网址,访问网络时会根据当前的运营商网络,找到对应的IP地址,再去访问,有可能存在同一个NtpServer联通网络可以访问而移动网络不行的情况。
4、NITZ和NTP的总结
①NITZ的优先级要高于NTP的优先级,当NITZ更新系统时间后,NTP即使触发更新条件,也会检查NITZ更新时间距今是否超过864000000毫秒(10天,config_ntpPollingInterval),若不满10天,则重设Alarm并取消此次NTP更新请求。
②NITZ主要依赖于运营商上报,NTP则主要依赖于网络环境,NITZ通过被动接收获取时间,NTP通过访问NtpServer获取网络时间,最后都是通过调用SystemClock.setCurrentTimeMillis更新手机时间。