时间更新NITZ和NTP详解

转载自https://www.aliyun.com/jiaocheng/20198.html

另一篇不错的文章http://blog.csdn.net/droyon/article/details/45701257 http://blog.csdn.net/jason_wzn/article/details/52893377
摘要：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:NetworkIdentityandTimeZone(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:NetworkTimeProtocol(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,NT

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_RECEIVED2、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public void systemRunning() { 
registerForTelephonyIntents(); 
registerForAlarms(); 
registerForConnectivityIntents();HandlerThread thread = new HandlerThread(TAG); 
thread.start(); 
mHandler = new MyHandler(thread.getLooper()); 
//
4000
Check the network time on the new thread 
mHandler.obtainMessage(EVENT_POLL_NETWORK_TIME).sendToTarget();mSettingsObserver = new SettingsObserver(mHandler, EVENT_AUTO_TIME_CHANGED); 
mSettingsObserver.observe(mContext); 
}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 
//frameworks/base/services/core/java/com/android/server/NetworkTimeUpdateService.java 
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; 
} 
} 
} 
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
//frameworks/base/services/core/java/com/android/server/NetworkTimeUpdateService.java
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);
}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
public NetworkTimeUpdateService(Context context) {
mContext = context;
mTime = NtpTrustedTime.getInstance(context);
...
//正常的轮询频率
mPollingIntervalMs = mContext.getResources().getInteger(
com.android.internal.R.integer.config_ntpPollingInterval);
//重试轮询间隔,以防网络请求失败
mPollingIntervalShorterMs = mContext.getResources().getInteger(
com.android.internal.R.integer.config_ntpPollingIntervalShorter);
//再次尝试次数
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。
mTimeErrorThresholdMs = mContext.getResources().getInteger(
com.android.internal.R.integer.config_ntpThreshold);
...
}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
//frameworks/base/core/res/res/values/config.xml
<!-- Normal polling frequency in milliseconds -->
<integer name="config_ntpPollingInterval">86400000</integer>
<!-- Try-again polling interval in milliseconds, in case the network request failed -->
<integer name="config_ntpPollingIntervalShorter">60000</integer>
<!-- Number of times to try again with the shorter interval, before backing
off until the normal polling interval. A value < 0 indicates infinite. -->
<integer name="config_ntpRetry">3</integer>
<!-- If the time difference is greater than this threshold in milliseconds,
then update the time. -->
<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
//frameworks/base/core/java/android/util/NtpTrustedTime.java
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();
if (client.requestTime(mServer, (int) mTimeout)) {
mHasCache = true;
mCachedNtpTime = client.getNtpTime();
mCachedNtpElapsedRealtime = client.getNtpTimeReference();
mCachedNtpCertainty = client.getRoundTripTime() / 2;
return true;
} else {
return false;
}
}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
public static synchronized NtpTrustedTime getInstance(Context context) {
if (sSingleton == null) {
final Resources res = context.getResources();
final ContentResolver resolver = context.getContentResolver();final String defaultServer = res.getString(
com.android.internal.R.string.config_ntpServer);
final long defaultTimeout = res.getInteger(
com.android.internal.R.integer.config_ntpTimeout);final String secureServer = Settings.Global.getString(
resolver, Settings.Global.NTP_SERVER);
final long timeout = Settings.Global.getLong(
resolver, Settings.Global.NTP_TIMEOUT, defaultTimeout);final String server = secureServer != null ? secureServer : defaultServer;
sSingleton = new NtpTrustedTime(server, timeout);
sContext = context;
}return sSingleton;
}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
//frameworks/base/core/res/res/values/config.xml
<!-- Remote server that can provide NTP responses. -->
<string translatable="false" name="config_ntpServer">2.android.pool.ntp.org</string>
<!-- Timeout to wait for NTP server response in milliseconds. -->
<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:
//frameworks/base/core/java/android/net/SntpClient.java
public boolean requestTime(InetAddress address, int port, int timeout) {
DatagramSocket socket = null;
try {
socket = new DatagramSocket();
socket.setSoTimeout(timeout);
byte[] buffer = new byte[NTP_PACKET_SIZE];
DatagramPacket request = new DatagramPacket(buffer, buffer.length, address, port);// set mode = 3 (client) and version = 3
// mode is in low 3 bits of first byte
// version is in bits 3-5 of first byte
buffer[0] = NTP_MODE_CLIENT | (NTP_VERSION << 3);// get current time and write it to the request packet
final long requestTime = System.currentTimeMillis();
final long requestTicks = SystemClock.elapsedRealtime();
writeTimeStamp(buffer, TRANSMIT_TIME_OFFSET, requestTime);socket.send(request);// read the response
DatagramPacket response = new DatagramPacket(buffer, buffer.length);
socket.receive(response);
final long responseTicks = SystemClock.elapsedRealtime();
final long responseTime = requestTime + (responseTicks - requestTicks);// extract the results
final byte leap = (byte) ((buffer[0] >> 6) &; 0x3);
final byte mode = (byte) (buffer[0] &; 0x7);
final int stratum = (int) (buffer[1] &; 0xff);
final long originateTime = readTimeStamp(buffer, ORIGINATE_TIME_OFFSET);
final long receiveTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET);
final long transmitTime = readTimeStamp(buffer, TRANSMIT_TIME_OFFSET);/* do sanity check according to RFC */
// TODO: validate originateTime == requestTime.
checkValidServerReply(leap, mode, stratum, transmitTime);long roundTripTime = responseTicks - requestTicks - (transmitTime - receiveTime);
// receiveTime = originateTime + transit + skew
// responseTime = transmitTime + transit - skew
// clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2
// = ((originateTime + transit + skew - originateTime) +
//(transmitTime - (transmitTime + transit - skew)))/2
// = ((transit + skew) + (transmitTime - transmitTime - transit + skew))/2
// = (transit + skew - transit + skew)/2
// = (2 * skew)/2 = skew
long clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2;
if (DBG) {
Log.d(TAG, "round trip: " + roundTripTime + "ms, " +
"clock offset: " + clockOffset + "ms");
}// save our results - use the times on this side of the network latency
// (response rather than request time)
mNtpTime = responseTime + clockOffset;
mNtpTimeReference = responseTicks;
mRoundTripTime = roundTripTime;
} catch (Exception e) {
if (DBG) Log.d(TAG, "request time failed: " + e);
return false;
} finally {
if (socket != null) {
socket.close();
}
}
return true;
}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。