android 9.x 开机自动同步时间较慢（2~3分钟）_java.time.datetimeexception: missing ntp fix-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_15347925/article/details/114635847

问题描述

不插sim卡，连接wifi启动，系统时间在2~3分钟之后才会同步到最新时间。

NITZ和NTP机制

在解决这个问题之前，让我们来学习一下NITZ和NTP的相关知识
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。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：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)。

关于NITZ和NTP更新时间流程，建议参考博客：https://blog.youkuaiyun.com/yin1031468524/article/details/65447849
大佬的流程写的非常详细，建议大家去学习学习。

解决问题

遇事不决先抓Log，先来看看过滤ntp字段后的日志

	Line 3819: 03-10 12:42:15.954   908  1079 W BestClock: java.time.DateTimeException: Missing NTP fix
	Line 3827: 03-10 12:42:15.958   908  1079 W BestClock: java.time.DateTimeException: Missing NTP fix
	Line 3829: 03-10 12:42:15.960   908  1073 W BestClock: java.time.DateTimeException: Missing NTP fix
	Line 3831: 03-10 12:42:15.967   908  1073 W BestClock: java.time.DateTimeException: Missing NTP fix
	Line 4857: 03-10 12:42:20.994   908  1224 D SntpClient: request time failed: java.net.SocketTimeoutException: Poll timed out
	Line 4858: 03-10 12:42:20.995   908  1224 D NtpTrustedTime: setServer:[time.android.com]
	Line 5510: 03-10 12:42:25.708   908  1072 W BestClock: java.time.DateTimeException: Missing NTP fix
	Line 5526: 03-10 12:42:25.729   908  1072 W BestClock: java.time.DateTimeException: Missing NTP fix
	Line 5527: 03-10 12:42:25.731   908  1073 W BestClock: java.time.DateTimeException: Missing NTP fix
	Line 7007: 03-10 12:43:21.408   908  1224 D NetworkTimeUpdateService: Stale NTP fix; forcing refresh
	Line 7008: 03-10 12:43:21.408   908  1224 D NetworkTimeUpdateService: mTryAgainCounter = 1;mNtpServers.size() = 2;index = 1;mNtpServers = asia.pool.ntp.org
	Line 7009: 03-10 12:43:21.408   908  1224 D NtpTrustedTime: setServer:[asia.pool.ntp.org]
	Line 7152: 03-10 12:43:21.636   908  1224 D SntpClient: round trip: 209ms, clock offset: 7919964ms

先来看看java.time.DateTimeException: Missing NTP fix这个异常，定位到代码位置
/frameworks/base/services/core/java/com/android/server/AlarmManagerService.java

        @Override
        public long currentNetworkTimeMillis() {
            final NtpTrustedTime time = NtpTrustedTime.getInstance(getContext());
            if (time.hasCache()) {
                return time.currentTimeMillis();
            } else {
                throw new ParcelableException(new DateTimeException("Missing NTP fix"));
            }
        }

接着看time.hasCache()方法
/frameworks/base/core/java/android/util/NtpTrustedTime.java

    @Override
    public boolean hasCache() {
        return mHasCache;
    }

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

只有client.requestTime()获取时间成功，才会把mHasCache置为true，说明这些异常发生时，获取时间一直是失败的。

继续看日志：

NtpTrustedTime: setServer:[time.android.com]，

设置ntp server为time.android.com之后，还是会出现Missing NTP fix的异常，获取时间失败。

再往下看日志：

NetworkTimeUpdateService: mTryAgainCounter = 1;mNtpServers.size() = 2;index = 1;mNtpServers = asia.pool.ntp.org
NtpTrustedTime: setServer:[asia.pool.ntp.org]
SntpClient: round trip: 209ms, clock offset: 7919964ms

对应到代码，在这个位置：
/frameworks/base/services/core/java/com/android/server/NetworkTimeUpdateService.java

    private void onPollNetworkTimeUnderWakeLock(int event) {
        // Force an NTP fix when outdated
        if (mTime.getCacheAge() >= mPollingIntervalMs) {
            if (DBG) Log.d(TAG, "Stale NTP fix; forcing refresh");
            //M: For multiple NTP server retry
            //mTime.forceRefresh();
            int index = mTryAgainCounter % mNtpServers.size();
            if (DBG) Log.d(TAG, "mTryAgainCounter = " + mTryAgainCounter
                + ";mNtpServers.size() = " + mNtpServers.size()
                + ";index = " + index + ";mNtpServers = " + mNtpServers.get(index));
            //轮询ntp server
            if (mTime instanceof NtpTrustedTime){
                ((NtpTrustedTime) mTime).setServer(mNtpServers.get(index));
                mTime.forceRefresh();
                ((NtpTrustedTime) mTime).setServer(mDefaultServer);
            }
            else{
                mTime.forceRefresh();
            }
        }
        if (mTime.getCacheAge() < mPollingIntervalMs) {
            // Obtained fresh fix; schedule next normal update
            resetAlarm(mPollingIntervalMs);
            if (isAutomaticTimeRequested()) {
                updateSystemClock(event);
            }
        } else {
            // No fresh fix; schedule retry
            mTryAgainCounter++;
            if (mTryAgainTimesMax < 0 || mTryAgainCounter <= mTryAgainTimesMax) {
                resetAlarm(mPollingIntervalShorterMs);
            } else {
                // Try much later
                mTryAgainCounter = 0;
                resetAlarm(mPollingIntervalMs);
            }
        }
    }

onPollNetworkTimeUnderWakeLock()方法里面轮询访问ntp server获取时间。
adb shell进去设备，分别ping服务器time.android.com和asia.pool.ntp.org，前者Ping不同，后者可以ping通。

继续看代码resetAlarm()方法，发现轮训的时间间隔是60秒，和这个问题的现象对上了。


    private void resetAlarm(long interval) {
        mAlarmManager.cancel(mPendingPollIntent);
        long now = SystemClock.elapsedRealtime();
        long next = now + interval;
        mAlarmManager.set(AlarmManager.ELAPSED_REALTIME, next, mPendingPollIntent);
    }
        ...........
        mPollingIntervalShorterMs = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_ntpPollingIntervalShorter);


     <!-- Remote server that can provide NTP responses. -->
    <string translatable="false" name="config_ntpServer">time.android.com</string>
    <!-- Try-again polling interval in milliseconds, in case the network request failed -->
    <integer name="config_ntpPollingIntervalShorter">60000</integer>