网站建设上市公司,简述seo和sem的区别,东平企业建站公司,医疗图片做网站图片Android NTP时间同步源码分析
Android系统设置自动时间后#xff0c;如果连接了可用的网络。会同步网络时间。这个处理是 NetworkTimeUpdateService完成的。某些定制化的系统#xff0c;需要禁止网络时间同步。比如仅仅使用GPS时间。基于Android9#xff0c;分析一下 Andro…Android NTP时间同步源码分析
Android系统设置自动时间后如果连接了可用的网络。会同步网络时间。这个处理是 NetworkTimeUpdateService完成的。某些定制化的系统需要禁止网络时间同步。比如仅仅使用GPS时间。基于Android9分析一下 Android NTP时间的同步流程。
时序图
服务启动NetworkTimeUpdateService在SystemServer的startOtherServices中启动frameworks/base/services/java/com/android/server/SystemServer.java
if (!isWatch) {traceBeginAndSlog(StartNetworkTimeUpdateService);try {networkTimeUpdater new NetworkTimeUpdateService(context);ServiceManager.addService(network_time_update_service, networkTimeUpdater);} catch (Throwable e) {reportWtf(starting NetworkTimeUpdate service, e);}traceEnd();
}
// 省略
try {if (networkTimeUpdaterF ! null) networkTimeUpdaterF.systemRunning();
} catch (Throwable e) {reportWtf(Notifying NetworkTimeService running, e);
}NetworkTimeUpdateService启动过程中会调用NTP、Conectivity服务注册监听NITZ、监听自动时间设定项(frameworks/base/services/core/java/com/android/server/NetworkTimeUpdateService.java)
public NetworkTimeUpdateService(Context context) {mContext context;mTime NtpTrustedTime.getInstance(context);mAlarmManager mContext.getSystemService(AlarmManager.class);mCM mContext.getSystemService(ConnectivityManager.class);Intent pollIntent new Intent(ACTION_POLL, null);mPendingPollIntent PendingIntent.getBroadcast(mContext, POLL_REQUEST, pollIntent, 0);mPollingIntervalMs mContext.getResources().getInteger(com.android.internal.R.integer.config_ntpPollingInterval);mPollingIntervalShorterMs mContext.getResources().getInteger(com.android.internal.R.integer.config_ntpPollingIntervalShorter);mTryAgainTimesMax mContext.getResources().getInteger(com.android.internal.R.integer.config_ntpRetry);mTimeErrorThresholdMs mContext.getResources().getInteger(com.android.internal.R.integer.config_ntpThreshold);mWakeLock context.getSystemService(PowerManager.class).newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, TAG);
}/** Initialize the receivers and initiate the first NTP request */
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);
}当自动时间设定变更、网络状态变更、更新周期达到时会触发NetworkTimeUpdateService更新系统时间。通过获取NTP时间以及进行各种判断比如近期是否更新过NITZ时间最终判断是否使用NTP时间更新参考上面的时序图
/** Handler to do the network accesses on */
private class MyHandler extends Handler {public MyHandler(Looper l) {super(l);}Overridepublic 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;}}
}private void onPollNetworkTime(int event) {// If Automatic time is not set, dont bother. Similarly, if we dont// have any default network, dont bother.if (mDefaultNetwork null) return;mWakeLock.acquire();try {onPollNetworkTimeUnderWakeLock(event);} finally {mWakeLock.release();}
}private void onPollNetworkTimeUnderWakeLock(int event) {// Force an NTP fix when outdatedif (mTime.getCacheAge() mPollingIntervalMs) {if (DBG) Log.d(TAG, Stale NTP fix; forcing refresh);mTime.forceRefresh();}if (mTime.getCacheAge() mPollingIntervalMs) {// Obtained fresh fix; schedule next normal updateresetAlarm(mPollingIntervalMs);if (isAutomaticTimeRequested()) {updateSystemClock(event);}} else {// No fresh fix; schedule retrymTryAgainCounter;if (mTryAgainTimesMax 0 || mTryAgainCounter mTryAgainTimesMax) {resetAlarm(mPollingIntervalShorterMs);} else {// Try much latermTryAgainCounter 0;resetAlarm(mPollingIntervalMs);}}
}private void updateSystemClock(int event) {final boolean forceUpdate (event EVENT_AUTO_TIME_CHANGED);if (!forceUpdate) {if (getNitzAge() mPollingIntervalMs) {if (DBG) Log.d(TAG, Ignoring NTP update due to recent NITZ);return;}final long skew Math.abs(mTime.currentTimeMillis() - System.currentTimeMillis());if (skew mTimeErrorThresholdMs) {if (DBG) Log.d(TAG, Ignoring NTP update due to low skew);return;}}SystemClock.setCurrentTimeMillis(mTime.currentTimeMillis());
}上面的代码是基于Android9的。在Android12中引入了 TimeDetect服务通过配置frameworks/base/core/res/res/values/config.xml中的 “config_autoTimeSourcesPriority”这个设定项指定优先的时间源。所以在Android12中NetworkTimeUpdateService会将时间更新请求发送给 TimeDetect服务而不是直接使用SystemClock更新时间。关于Android12的NetworkTimeUpdateService详细流程这里不进行分析。
