android网络时间同步

起因:有时候android盒子起来了,半天都没有获取到时间,便查看了下这部分代码;

相关文件:

frameworks/base/services/java/com/android/server/SystemServer.java

frameworks/base/services/java/com/android/server/NetworkTimeUpdateService.java

frameworks/base/core/java/android/util/NtpTrustedTime.java

frameworks/base/core/java/android/net/SntpClient.java

frameworks/base/core/res/res/values/config.xml

一、frameworks/base/services/java/com/android/server/SystemServer.java

里边的ServerThread.run函数中会启用NetworkTimeUpdateService,在这个run函数里,先后顺序为以下代码所示:

 163         NetworkTimeUpdateService networkTimeUpdater = null;



 772             try {
 773                 Slog.i(TAG, "NetworkTimeUpdateService");
 774                 networkTimeUpdater = new NetworkTimeUpdateService(context);
 775             } catch (Throwable e) {
 776                 reportWtf("starting NetworkTimeUpdate service", e);
 777             }



 926         final NetworkTimeUpdateService networkTimeUpdaterF = networkTimeUpdater;



1034                 try {
1035                     if (networkTimeUpdaterF != null) networkTimeUpdaterF.systemReady();
1036                 } catch (Throwable e) {
1037                     reportWtf("making Network Time Service ready", e);
1038                 }

二、frameworks/base/services/java/com/android/server/NetworkTimeUpdateService.java

用一个handler处理接收三种消息来触发网络时间同步

EVENT_AUTO_TIME_CHANGED
EVENT_POLL_NETWORK_TIME
EVENT_NETWORK_CONNECTED

然后调用onPollNetworkTime去判断是否要同步网络时间,层层判断以后,会调用mTime.forceRefresh();来同步网络时间,将时间保存了mTime中,然后再调用

SystemClock.setCurrentTimeMillis(ntp);来设置系统时间,long ntp = mTime.currentTimeMillis();

其中mTime = NtpTrustedTime.getInstance(context);

三、frameworks/base/core/java/android/util/NtpTrustedTime.java

forceRefresh函数里会调用SntpClient.requestTime(mServer, (int) mTimeout)来获取时间

mServer为同步时间服务器, mTimeout为请求超时时间,在frameworks/base/core/res/res/values/config.xml中定义为

 910     <!-- Remote server that can provide NTP responses. -->
 911     <string translatable="false" name="config_ntpServer">2.android.pool.ntp.org</string>
 912     <!-- Timeout to wait for NTP server response. -->
 913     <integer name="config_ntpTimeout">20000</integer>

四、frameworks/base/core/java/android/net/SntpClient.java

跟进这个SntpClient.requestTime()函数中就能看到其使用udp协议去请求网络时间

那么到底这个网络时间同步有多不靠谱呢?将SntpClient.java拷一份出来到Eclipse上的demo工程里,在应用里用了一下,发现真的很不稳定,如果能连接到,几乎是立马能收到回应,否则就是把超时时间调得再长也没用。

只能在frameworks/base/services/java/com/android/server/NetworkTimeUpdateService.java文件中,将同步时间间隔POLLING_INTERVAL_SHORTER_MS从一分钟改成30秒,并且将最大尝试次数TRY_AGAIN_TIMES_MAX由3改成300,以此优化

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