Android WifiService的啓動流程分析

最近在學習Android WiFi framework的相關知識，這裏總結以下。WiFi framework的內容大致可以分爲以下幾個模塊：

1. WiFi相關內容

2.WiFi P2P相關內容

3.Hotspot相關內容

4.WiFi Display相關內容

後面就將從這四個方面一一介紹。

WiFi service的啓動流程

Wifiservice的啓動地方在system server中，code路徑在：framwork/base/service/java/com/android/server/SystemServer.java

try{
               Slog.i(TAG,"Wi-Fi P2pService");
                wifiP2p=newWifiP2pService(context);
               ServiceManager.addService(Context.WIFI_P2P_SERVICE, wifiP2p);
           }catch(Throwable e){
                reportWtf("starting Wi-Fi P2pService", e);
           }

           try{
               Slog.i(TAG,"Wi-Fi Service");
                wifi=newWifiService(context);
               ServiceManager.addService(Context.WIFI_SERVICE, wifi);
           }catch(Throwable e){
                reportWtf("starting Wi-Fi Service", e);
           }

           try{
               Slog.i(TAG,"Connectivity Service");
                connectivity=newConnectivityService(
                        context, networkManagement, networkStats, networkPolicy);
               ServiceManager.addService(Context.CONNECTIVITY_SERVICE, connectivity);
                networkStats.bindConnectivityManager(connectivity);
                networkPolicy.bindConnectivityManager(connectivity);
                wifi.checkAndStartWifi();
                wifiP2p.connectivityServiceReady();
           }catch(Throwable e){
                reportWtf("starting Connectivity Service", e);
           }

這裏我們可以看到在system server中，先構造了WifiP2pService 和WifiService，並將它們註冊在ServiceManager當中，然後調用WifiService的checkAndStartWifi函數。那首先我們進入Wifiservice的構造函數當中，code路徑在：framwork/base/service/java/com/android/server/wifi/WifiService.java，代碼如下：

   WifiService(Context context){
        mContext= context;

        mInterfaceName=  SystemProperties.get("wifi.interface","wlan0");

        mWifiStateMachine=newWifiStateMachine(mContext, mInterfaceName);
<span style="white-space:pre">  </span>.......

       HandlerThread wifiThread=newHandlerThread("WifiService");
        wifiThread.start();
        mAsyncServiceHandler=newAsyncServiceHandler(wifiThread.getLooper());
        mWifiStateMachineHandler=newWifiStateMachineHandler(wifiThread.getLooper());
<span style="white-space:pre">  </span>mWifiController=newWifiController(mContext, this,wifiThread.getLooper());

<span style="white-space:pre">  </span>.......
   }

這裏主要創建一個WifiStateMachine的實例，然後新建一個HandlerThread來處理所有的message，並註冊一些broadcast的receive，例如WIFI_STATE_CHANGED_ACTION、NETWORK_STATE_CHANGED_ACTION等。WifiStateMachine用於控制整個wifi的開啓、關閉、連接、斷開等各個狀態切換，我們將在後面具體來介紹StateMachine。

接着回到system server中，ConnectivityService用於管控機器中所有的數據連接服務，WiFi當然也屬於其監控的對象，那我們進入到ConnectivityService構造函數中一看。code路徑在：framwork/base/service/java/com/android/server/ConnectivityService.java

publicConnectivityService(Context context,INetworkManagementService netManager,
          INetworkStatsService statsService,INetworkPolicyManager policyManager,
          NetworkFactory netFactory){
      if(DBG) log("ConnectivityService starting up");

      HandlerThread handlerThread=newHandlerThread("ConnectivityServiceThread");
       handlerThread.start();
       mHandler=newInternalHandler(handlerThread.getLooper());
       mTrackerHandler=newNetworkStateTrackerHandler(handlerThread.getLooper());

  .......

      // Create and start trackers for hard-coded networks
      for(int targetNetworkType: mPriorityList){
          finalNetworkConfig config= mNetConfigs[targetNetworkType];
          finalNetworkStateTracker tracker;
          try{
               tracker= netFactory.createTracker(targetNetworkType, config);
               mNetTrackers[targetNetworkType]= tracker;
          }catch(IllegalArgumentException e){
              Slog.e(TAG,"Problem creating "+ getNetworkTypeName(targetNetworkType)
                      +" tracker: "+ e);
              continue;
           }

           tracker.startMonitoring(context, mTrackerHandler);
          if(config.isDefault()){
               tracker.reconnect();
          }
      }

在ConnectivityService中將根據com.android.internal.R.array.networkAttributes中配置的系統network屬性去一一的創建tracker並開始monitor其狀態，tracker.startMonitoring(context, mTrackerHandler)這行code告訴我們這些tracker可以通過mTrackerHandler發送消息給ConnectivityService，我們可以到mTrackerHandler中看看這些消息主要有哪些類型：

NetworkStateTracker.EVENT_STATE_CHANGED
NetworkStateTracker.EVENT_CONFIGURATION_CHANGED
NetworkStateTracker.EVENT_NETWORK_SUBTYPE_CHANGED

其中NetworkStateTracker.EVENT_STATE_CHANGED極爲重要，我們將在後面的內容中看到當wifi連接AP成功後，會發送這個消息給ConnectivityService來做一些其它的檢測。

回到ConnectivityService的構造函數中，剛剛說到ConnectivityService中將根據com.android.internal.R.array.networkAttributes中配置的系統network屬性去一一的創建tracker，那我們進入到netFactory.createTracker(targetNetworkType, config)去看看究竟會創建哪些tracker：

    publicNetworkStateTracker createTracker(int targetNetworkType,NetworkConfig config){
         switch(config.radio){
            case TYPE_WIFI:
                returnnewWifiStateTracker(targetNetworkType, config.name);
            case TYPE_MOBILE:
                returnnewMobileDataStateTracker(targetNetworkType, config.name);
            case TYPE_DUMMY:
                returnnewDummyDataStateTracker(targetNetworkType, config.name);
            case TYPE_BLUETOOTH:
                returnBluetoothTetheringDataTracker.getInstance();
            case TYPE_WIMAX:
                return makeWimaxStateTracker(mContext, mTrackerHandler);
            case TYPE_ETHERNET:
                returnEthernetDataTracker.getInstance();
            default:
                thrownewIllegalArgumentException(
                        "Trying to create a NetworkStateTracker for an unknown radio type: "
                        + config.radio);
        }
    }
}

這裏我們主要關係的是TYPE_WIFI，ConnectivityService將創建一個WiFiStateTracker對象，並調用其startMonitoring方法，進入到WiFiStateTracker代碼中分析：

publicWifiStateTracker(int netType,String networkName){
     mNetworkInfo=newNetworkInfo(netType,0, networkName,"");
     mLinkProperties=newLinkProperties();
     mLinkCapabilities=newLinkCapabilities();

     mNetworkInfo.setIsAvailable(false);
     setTeardownRequested(false);
}

publicvoid startMonitoring(Context context,Handler target){
     mCsHandler= target;
     mContext= context;

     mWifiManager=(WifiManager) mContext.getSystemService(Context.WIFI_SERVICE);
    IntentFilter filter=newIntentFilter();
     filter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION);
     filter.addAction(WifiManager.LINK_CONFIGURATION_CHANGED_ACTION);

     mWifiStateReceiver=newWifiStateReceiver();
     mContext.registerReceiver(mWifiStateReceiver, filter);
}

WiFiStateTracker的構造函數和startMonitoring方法都比較簡單，主要是註冊一個broadcast receiver用於接收系統的NETWORK_STATE_CHANGED_ACTION和LINK_CONFIGURATION_CHANGED_ACTION消息。

      好，到這裏我們把ConnectivityService的構造函數中與wifi相關的內容介紹完畢了，我們再回到system server當中，在把ConnectivityService加入到Service Manager後，就調用wifi.checkAndStartWifi()來檢查是否可以啓動wifi了

publicvoid checkAndStartWifi(){
     boolean wifiEnabled= mSettingStore.isWifiToggleEnabled();
    Slog.i(TAG,"WifiService starting up with Wi-Fi "+
            (wifiEnabled?"enabled":"disabled"));

    // If we are already disabled (could be due to airplane mode), avoid changing persist
    // state here
    if(wifiEnabled) setWifiEnabled(wifiEnabled);

     mWifiWatchdogStateMachine=WifiWatchdogStateMachine.
            makeWifiWatchdogStateMachine(mContext);

}

  具體的如何啓動wifi和wifi啓動流程將在下一章中分析，這裏來看一下整個Wifiservice啓動的流程圖，圖中的紅色字體部分表示新建一個thread，綠色部分表示在已有的looper當中創建一個handler，黃色部分表示註冊broadcast receiver。