由WifiStateMachine来理解StateMachine

来源：互联网发布：淘宝客服平台语言技巧编辑：程序博客网时间：2024/05/16 23:47

前言：前一段时间在公司分析一个由于突然关掉路由器，导致设备wifi崩溃的问题。通过一段时间的摸索和学习，了解到wifi状态机的工作原理。所谓状态机我的理解是，表示一个物体它现在所处的状态，以及所处状态对于不同指令的处理。以下是我本人所持有的开发板所带的android5.0的wifi状态机的所有状态

这里写图片描述
从图片中的代码可以看出这差不多是个树形结构（由于图片上传大小的限制，我自己画图没办法上传）。先是添加这个状态，然后进入InitialState这个初始状态，InitialState的代码如下

    class InitialState extends State {        @Override        public void enter() {            mWifiNative.unloadDriver();            if (mWifiP2pChannel == null) {                mWifiP2pChannel = new AsyncChannel();                mWifiP2pChannel.connect(mContext, getHandler(),                    mWifiP2pServiceImpl.getP2pStateMachineMessenger());            }            if (mWifiApConfigChannel == null) {                mWifiApConfigChannel = new AsyncChannel();                WifiApConfigStore wifiApConfigStore = WifiApConfigStore.makeWifiApConfigStore(                        mContext, getHandler());                wifiApConfigStore.loadApConfiguration();                mWifiApConfigChannel.connectSync(mContext, getHandler(),                        wifiApConfigStore.getMessenger());            }        }        @Override        public boolean processMessage(Message message) {            logStateAndMessage(message, getClass().getSimpleName());            switch (message.what) {                case CMD_START_SUPPLICANT:                    if (mWifiNative.loadDriver()) {                        try {                            mNwService.wifiFirmwareReload(mInterfaceName, "STA");                        } catch (Exception e) {                            loge("Failed to reload STA firmware " + e);                            // Continue                        }                        try {                            // A runtime crash can leave the interface up and                            // IP addresses configured, and this affects                            // connectivity when supplicant starts up.                            // Ensure interface is down and we have no IP                            // addresses before a supplicant start.                            mNwService.setInterfaceDown(mInterfaceName);                            mNwService.clearInterfaceAddresses(mInterfaceName);                            // Set privacy extensions                            mNwService.setInterfaceIpv6PrivacyExtensions(mInterfaceName, true);                           // IPv6 is enabled only as long as access point is connected since:                           // - IPv6 addresses and routes stick around after disconnection                           // - kernel is unaware when connected and fails to start IPv6 negotiation                           // - kernel can start autoconfiguration when 802.1x is not complete                            mNwService.disableIpv6(mInterfaceName);                        } catch (RemoteException re) {                            loge("Unable to change interface settings: " + re);                        } catch (IllegalStateException ie) {                            loge("Unable to change interface settings: " + ie);                        }                       /* Stop a running supplicant after a runtime restart                        * Avoids issues with drivers that do not handle interface down                        * on a running supplicant properly.                        */                        mWifiMonitor.killSupplicant(mP2pSupported);                        if(mWifiNative.startSupplicant(mP2pSupported)) {                            setWifiState(WIFI_STATE_ENABLING);                            if (DBG) log("Supplicant start successful");                            mWifiMonitor.startMonitoring();                            transitionTo(mSupplicantStartingState);                        } else {                            loge("Failed to start supplicant!");                        }                    } else {                        loge("Failed to load driver");                    }                    break;                case CMD_START_AP:                    if (mWifiNative.loadDriver()) {                        setWifiApState(WIFI_AP_STATE_ENABLING);                        transitionTo(mSoftApStartingState);                    } else {                        loge("Failed to load driver for softap");                    }                default:                    return NOT_HANDLED;            }            return HANDLED;        }    }

进入状态机会先执行enter(),然后ProcessMessage处理对应的CMD，transitionTo（XXXXXXState）用来切换状态机所处的状态。当一个CMD所在状态处理不了，那么会将该状态交由父状态来处理（父状态处理不了，就给爷状态来处理，依此类推）。当然，发送CMD的可以是WifiStateMachine,也可以是WifiMonitor等。状态机是个逻辑分层很清晰，好好看代码就好。

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