5.4 WifiWatchdogStateMachine介绍

**1、WifiWatchdogStateMachine介绍** WifiWatchdogStateMachine用于监控无线网络的信号质量，它在WifiService的checkAndStartWifi函数中被创建，其创建函数是makeWifiWatchdogStateMachine，代码如下所示： **WifiWatchdogStateMachine.java::makeWifiWatchdogStateMachine** ~~~ public static WifiWatchdogStateMachine makeWifiWatchdogStateMachine(Context context) { ContentResolver contentResolver = context.getContentResolver(); ConnectivityManager cm = (ConnectivityManager) context.getSystemService( Context.CONNECTIVITY_SERVICE); //判断手机是否只支持Wifi。很显然，对于大部分手机来说，sWifiOnly为false sWifiOnly = (cm.isNetworkSupported(ConnectivityManager.TYPE_MOBILE) == false); //WIFI_WATCHDOG_ON功能默认是打开的 putSettingsGlobalBoolean(contentResolver, Settings.Global.WIFI_WATCHDOG_ON, true); //创建一个WifiWatchdogStateMachine对象，它也是一个HSM WifiWatchdogStateMachine wwsm = new WifiWatchdogStateMachine(context); wwsm.start();//启动HSM return wwsm; } ~~~ 先来看WifiWatchdogStateMachine的初始化流程。 **①、WifiWatchdogStateMachine构造函数分析** **WifiWatchdogStateMachine.java::WifiWatchdogStateMachine** ~~~ private WifiWatchdogStateMachine(Context context) { super(TAG); mContext = context; mContentResolver = context.getContentResolver(); mWifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE); //mWsmChannel用于和WifiStateMachine交互 mWsmChannel.connectSync(mContext, getHandler(), mWifiManager.getWifiStateMachineMessenger()); //关键函数：setupNetworkReceiver将创建一个广播接收对象，用于接收NETWORK_STATE_CHANGED_ACTION、 // WIFI_STATE_CHANGED_ACTION、RSSI_CHANGED_ACTION、SUPPLICANT_STATE_CHANGED_ACTION等广播 setupNetworkReceiver(); //监控Wifi Watchdog设置的变化情况 registerForSettingsChanges(); registerForWatchdogToggle(); addState(mDefaultState); ......//添加状态，一共有9个状态。如图5-7所示 //Wifi Watchdog默认是开启的，故状态机转入NotConnectedState状态 if (isWatchdogEnabled()) setInitialState(mNotConnectedState); else setInitialState(mWatchdogDisabledState); updateSettings(); } ~~~ 上面代码中，WifiWatchdogStateMachine的初始状态是NotConnectedState。不过这个状态仅实现了enter函数，而且该函数中仅实现了一句打印输出的代码。所以NotConnectedState是一个象征意义远大于实际作用的类。 图5-7所示为WifiWatchdogStateMachine中的各个状态及层级关系： :-:  图5-7 WifiWatchdogStateMachine状态及层级关系 WifiWatchdogStateMachine完全靠广播事件来驱动。相关代码在setupNetworkReceiver函数中。 **WifiWatchdogStateMachine.java::setupNetworkReceiver** ~~~ private void setupNetworkReceiver() { mBroadcastReceiver = new BroadcastReceiver() { public void onReceive(Context context, Intent intent) { String action = intent.getAction(); if (action.equals(WifiManager.RSSI_CHANGED_ACTION)) { obtainMessage(EVENT_RSSI_CHANGE, intent.getIntExtra(WifiManager.EXTRA_NEW_RSSI, -200), 0).sendToTarget(); } else if (action.equals(WifiManager.SUPPLICANT_STATE_CHANGED_ACTION)) { sendMessage(EVENT_SUPPLICANT_STATE_CHANGE, intent); } else if (action.equals(WifiManager.NETWORK_STATE_CHANGED_ACTION)) { sendMessage(EVENT_NETWORK_STATE_CHANGE, intent); } ...... else if (action.equals(WifiManager.WIFI_STATE_CHANGED_ACTION)) sendMessage(EVENT_WIFI_RADIO_STATE_CHANGE,intent.getIntExtra( WifiManager.EXTRA_WIFI_STATE, WifiManager.WIFI_STATE_UNKNOWN)); } }; mIntentFilter = new IntentFilter(); mIntentFilter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION); ......//添加感兴趣的广播事件类型 mContext.registerReceiver(mBroadcastReceiver, mIntentFilter); } ~~~ 在前面介绍的WifiService工作流程中，SUPPLICANT_STATE_CHANGED_ACTION和NETWORK_STATE_CHANGED_ACTION广播发送的次数非常频繁。所以，WifiWatchdogStateMachine也不会太清闲。 下面，我们直接从WifiStateMachine在VerifyingLinkState的enter函数中发送的NETWORK_STATE_CHANGED_ACTION广播开始分析WifiWatchdogStateMachine的处理流程。 **②、EVENT_NETWORK_STATE_CHANGE处理流程分析** 该消息被NotConnectedState的父状态WatchdogEnabledState处理，相关代码如下所示： **WifiWatchdogStateMachine.java::WatchdogEnabledState:processMessage** ~~~ public boolean processMessage(Message msg) { Intent intent; switch (msg.what) { ...... case EVENT_NETWORK_STATE_CHANGE: intent = (Intent) msg.obj; NetworkInfo networkInfo = (NetworkInfo) intent.getParcelableExtra( WifiManager.EXTRA_NETWORK_INFO); mWifiInfo = (WifiInfo) intent.getParcelableExtra(WifiManager.EXTRA_WIFI_INFO); //更新bssid信息 updateCurrentBssid(mWifiInfo != null ? mWifiInfo.getBSSID() : null); switch (networkInfo.getDetailedState()) { case VERIFYING_POOR_LINK://WifiStateMachine在VerifyingLinkState中设置的状态 mLinkProperties = (LinkProperties) intent.getParcelableExtra( WifiManager.EXTRA_LINK_PROPERTIES); //mPoorNetworkDetectionEnabled用于判断是否需要监控AP的信号质量 if (mPoorNetworkDetectionEnabled) { if (mWifiInfo == null || mCurrentBssid == null) { //下面这个函数将通过mWsmChannel向WifiStateMachine发送 //GOOD_LINK_DETECTED消息 sendLinkStatusNotification(true); } else transitionTo(mVerifyingLinkState);//进入VerifyingLinkState } else sendLinkStatusNotification(true); break; case CONNECTED://WifiStateMachine在ConnectedState中设置的状态，请读者自行分析 //OnlineWatchState的处理流程 transitionTo(mOnlineWatchState); } ....... } return HANDLED; } ~~~ 如果WifiWatchdogStateMachine开启了无线网络信号质量监控的话，它将转入VerifyingLinkState，其enter函数如下所示： **WifiWatchdogStateMachine.java::VerifyingLinkState:enter** ~~~ public void enter() { mSampleCount = 0; mCurrentBssid.newLinkDetected(); //向自己发送CMD_RSSI_FETCH消息 sendMessage(obtainMessage(CMD_RSSI_FETCH, ++mRssiFetchToken, 0)); } ~~~ 来看CMD_RSSI_FETCH消息的处理。 **③、CMD_RSSI_FETCH处理流程分析** **WifiWatchdogStateMachine.java::VerifyingLinkState:processMessage** ~~~ public boolean processMessage(Message msg) { switch (msg.what) { ...... case CMD_RSSI_FETCH: if (msg.arg1 == mRssiFetchToken) { /* 向WifiStateMachine发送RSSI_PKTCNT_FETCH消息，WifiStateMachine的处理过程 就是调用WifiNative的signalPoll和pktcntPoll以获取RSSI、LinkSpeed、发送 Packet的总个数、发送失败的Packet总个数。注意，4.2中的WPAS才支持pktcntPoll。 WifiStateMachine处理完RSSI_PKTCNT_FETCH后将回复RSSI_PKTCNT_FETCH_SUCCEEDED 消息给WifiWatchdogStateMachine */ mWsmChannel.sendMessage(WifiManager.RSSI_PKTCNT_FETCH); //LINK_SAMPLING_INTERVAL_MS值为1000ms sendMessageDelayed(obtainMessage(CMD_RSSI_FETCH, ++mRssiFetchToken, 0), LINK_SAMPLING_INTERVAL_MS); } break; case WifiManager.RSSI_PKTCNT_FETCH_SUCCEEDED: //WifiStateMachine回复的消息中携带一个RssiPacketCountInfo对象 RssiPacketCountInfo info = (RssiPacketCountInfo) msg.obj; int rssi = info.rssi; /* WifiWatchdog用了一个名为指数加权移动平均算法（Volume-weighted Exponential Moving Average）的方法来辨别网络信号质量的好坏。本书不拟对它进行讨论，感兴趣的读者不妨 自行研究 */ long time = mCurrentBssid.mBssidAvoidTimeMax - SystemClock.elapsedRealtime(); //假设网络质量很好，则调用sendLinkStateNotification以发送GOOD_LINK_DETECT消息给 //WifiStateMachine if (time <= 0) sendLinkStatusNotification(true); else { //此时的rssi好于某个阈值。mGoodLinkTargetRssi由算法计算得来 if (rssi >= mCurrentBssid.mGoodLinkTargetRssi) { //当采样次数大于一定值时，才认为网络状态变好。mGoodLinkTargetCount也是通过 //相关方法计算得来 if (++mSampleCount >= mCurrentBssid.mGoodLinkTargetCount) { mCurrentBssid.mBssidAvoidTimeMax = 0; sendLinkStatusNotification(true); } } else mSampleCount = 0; } break; ...... } return HANDLED; } ~~~ 当WifiWatchdogStateMachine检测到Pool link时，它将发送POOL_LINK_DETECT消息给WifiStateMachine去处理。相关流程请感兴趣的读者自行研究。 WifiWatchdogStateMachine是一个比较有趣的模块。其目的很简单，就是监测无线网络的信号质量，然后做相应动作。另外，WifiWatchdogStateMachine还使用了一些比较高级的算法来判断网络信号质量的好坏，感兴趣的读者不妨进行一番深入研究。