二、Android 数据链接的动态分析

经过前面这些过程，网络连接所需要的条件就全部准备就绪，接下来就是等待网络接入
把网络接入过程简单分为三个阶段
触发阶段
—-该阶段是由各种不同事件触发的，比如SIM载入完毕、PS域Attach成功、通话结束、APN改变等，该阶段的最终都是要调用setupDataOnConnectableApns()方法；
准备连接阶段
—-该阶段是指，在DcTracker收到建立连接的请求之后，需要进行一系列有效性检测，比如APN是否已经激活、PS是否已经就绪、用户是否打开网络开关等，然后创建/找到核实的DataConnection对象，准备发起连接请求。
发送连接命令阶段
—-该阶段是指，在DataConnection收到DcTracker的请求之后，将请求转交给RILJ的过程，RILJ通过socket将请求发送到了RILD，RILD根据请求类型再将AT指令发送到Modem层，由底层完成信令的发送和接收。简单概括就是如下步骤，此处创建的DcAsyncChannel是双向的。

1、触发条件

//漫游打开关闭（EVENT_ROAMING_ON/EVENT_ROAMING_OFF事件）static final String REASON_ROAMING_ON = "roamingOn";  static final String REASON_ROAMING_OFF = "roamingOff";  //PS attach（STATE_IN_SERVICE）static final String REASON_DATA_ATTACHED = "dataAttached";  //APN Changed（EVENT_APN_CHANGED）static final String REASON_APN_CHANGED = "apnChanged";  //通话结束  static final String REASON_VOICE_CALL_ENDED = "2GVoiceCallEnded";  //SIM载入完毕 （EVENT_RECORDS_LOADED 事件）static final String REASON_SIM_LOADED = "simLoaded";  //网络模式改变 （EVENT_DATA_RAT_CHANGED 事件）static final String REASON_NW_TYPE_CHANGED = "nwTypeChanged";  

2、有效性及状态检查

在触发条件满足后都会调用setupDataOnConnectableApns(String reason)
之后会调用trySetupData,在trySetupData里面会进行有效性检测

    private boolean trySetupData(ApnContext apnContext, ArrayList<ApnSetting> waitingApns) {        // Allow SETUP_DATA request for E-APN to be completed during emergency call and MOBILE DATA On/Off cases as well.        boolean isEmergencyApn = apnContext.getApnType().equals(PhoneConstants.APN_TYPE_EMERGENCY);        final ServiceStateTracker sst = mPhone.getServiceStateTracker();        boolean desiredPowerState = sst.getDesiredPowerState();        boolean checkUserDataEnabled = !(apnContext.getApnType().equals(PhoneConstants.APN_TYPE_IMS));        if (apnContext.isConnectable() && (isEmergencyApn ||                (isDataAllowed(apnContext) &&                getAnyDataEnabled(checkUserDataEnabled) && !isEmergency()))) {            if (apnContext.getState() == DctConstants.State.FAILED) {                apnContext.setState(DctConstants.State.IDLE);            }            int radioTech = mPhone.getServiceState().getRilDataRadioTechnology();            apnContext.setConcurrentVoiceAndDataAllowed(sst.isConcurrentVoiceAndDataAllowed());            if (apnContext.getState() == DctConstants.State.IDLE) {                 if (waitingApns == null) {                    waitingApns = buildWaitingApns(apnContext.getApnType(), radioTech);                }                if (waitingApns.isEmpty()) {                    notifyNoData(DcFailCause.MISSING_UNKNOWN_APN, apnContext);                    notifyOffApnsOfAvailability(apnContext.getReason());                    return false;                 } else {                    apnContext.setWaitingApns(waitingApns);                }             }            boolean retValue = setupData(apnContext, radioTech);            notifyOffApnsOfAvailability(apnContext.getReason());            return retValue;        }}

条件1：apnContext.isConnectable()

    public boolean isConnectable() {        return isReady() && ((mState == DctConstants.State.IDLE)                                || (mState == DctConstants.State.SCANNING)                                || (mState == DctConstants.State.RETRYING)                                || (mState == DctConstants.State.FAILED));    }   

其中isReady()就是检查APN type有没有使能，所以在数据链接之前一定要调用ApnContext的setEnabled()将要打开的数据类型对应的APN使能；然后就是检查APN的状态，这个状态会在DataConnection状态机随着联网状态的变迁而改变。
条件2：isEmergencyApn 是否是紧急APN
条件3：isDataAllowed(apnContext)

  private boolean isDataAllowed(ApnContext apnContext) {        return apnContext.isReady() && isDataAllowed();     }    protected boolean isDataAllowed() {        final boolean internalDataEnabled;        synchronized (mDataEnabledLock) {            internalDataEnabled = mInternalDataEnabled;        }        boolean attachedState = mAttached.get();        boolean desiredPowerState = mPhone.getServiceStateTracker().getDesiredPowerState();        IccRecords r = mIccRecords.get();        boolean recordsLoaded = false;        if (r != null) {            recordsLoaded = r.getRecordsLoaded();        }        //FIXME always attach        boolean psRestricted = mIsPsRestricted;        int phoneNum = TelephonyManager.getDefault().getPhoneCount();        if (phoneNum > 1) {            attachedState = true;            psRestricted = false;        }        int dataSub = SubscriptionManager.getDefaultDataSubId();        boolean defaultDataSelected = SubscriptionManager.isValidSubscriptionId(dataSub);        PhoneConstants.State state = PhoneConstants.State.IDLE;        if (mPhone.getCallTracker() != null) {            state = mPhone.getCallTracker().getState();         }                    boolean allowed =                    (attachedState || mAutoAttachOnCreation) &&                    recordsLoaded &&                    (state == PhoneConstants.State.IDLE ||                     mPhone.getServiceStateTracker().isConcurrentVoiceAndDataAllowed()) &&                    internalDataEnabled &&                    defaultDataSelected &&                    (!mPhone.getServiceState().getDataRoaming() || getDataOnRoamingEnabled()) &&                    //!mIsPsRestricted &&                    !psRestricted &&                    desiredPowerState;

—-判断是否已经ATTACH成功，SIM是否初始化完毕，当前手机服务是否支持，漫游下是否允许上网等
条件4：getAnyDataEnabled(checkUserDataEnabled)
—-该条件主要判断用户是否打开了数据开关
这部分代码很混乱，如果出现问题得一一排查

3、找到可用的APN

其中waitingApns = buildWaitingApns(apnContext.getApnType(), radioTech)便是找到可用的APN
buildWaitingApns中主要的逻辑有两个：
1、如果用户是否设置了Preferred，该值通过以下代码读取的：

        usePreferred = ! mPhone.getContext().getResources().getBoolean(com.android.                internal.R.bool.config_dontPreferApn);

如果用户设置了Preferred APN，并且mPreferredApn不为空（mPreferredApn来自于数据业务APN参数的创建createAllApnList中保存的，例如用户手动选择了APN TYPE那么这个APN就会被保留下来）因此此时waitingApns就会等于mPreferredApn
2、如果用户没有设置Preferred APN，那么就会在mAllApnSettings（来自于createAllApnList）中去寻找可用的APN，并将所有的可用的APN放在waitingApns中
最终联网采用的是waitingApns0

4、找到/创建DataConnection状态机

    private boolean setupData(ApnContext apnContext, int radioTech) {        if (dcac == null) {            dcac = findFreeDataConnection();            if (dcac == null) {                dcac = createDataConnection();            }        }        apnContext.setDataConnectionAc(dcac);        apnContext.setApnSetting(apnSetting);        apnContext.setState(DctConstants.State.CONNECTING);        mPhone.notifyDataConnection(apnContext.getReason(), apnContext.getApnType());        Message msg = obtainMessage();        msg.what = DctConstants.EVENT_DATA_SETUP_COMPLETE;        msg.obj = apnContext;        dcac.bringUp(apnContext, getInitialMaxRetry(), profileId, radioTech, mAutoAttachOnCreation,msg);        return true;

这个方法内部主要完成了两个任务：
1、更新当前APN参数的状态并把状态发送到系统中(还是通过notifyDataConnection()来完成)
2、通过DcAsyncChannel的bringUp()方法发起连接请求
这里显示通过findFreeDataConnection()方法搜索可用的DcAsyncChannel，找不到的话就通过createDataConnection()创建，如果没有找到，就需要创建新的DcAsyncChannel
/* Return the DC AsyncChannel for the new data connection /
private DcAsyncChannel createDataConnection() {

    int id = mUniqueIdGenerator.getAndIncrement();    DataConnection conn = DataConnection.makeDataConnection(mPhone, id,this, mDcTesterFailBringUpAll, mDcc);    mDataConnections.put(id, conn);    DcAsyncChannel dcac = new DcAsyncChannel(conn, LOG_TAG);    int status = dcac.fullyConnectSync(mPhone.getContext(), this, conn.getHandler());    if (status == AsyncChannel.STATUS_SUCCESSFUL) {        mDataConnectionAcHashMap.put(dcac.getDataConnectionIdSync(), dcac); //将创建好的DcAsyncChannel保存起来，以便下一次链接的时候可以找到可用的DcAsyncChannel    }    return dcac;}

创建DcAsyncChannel通道，是链接DcTracker和DataConnection的通道，但是他们不在同一个线程中，在DcTrackerBase的构造中new了一个新的HandlerThread，并将looper给了DcController和DataConnection。
为什么要闯将DcAsyncChannel通道，而不直接将DcTracker消息传到DataConnection中去呢？
因为在DcTracker中有需要同步获取DataConnection中的情况，比如在findFreeDataConnection中调用了

dcac.isInactiveSync()    private DcAsyncChannel findFreeDataConnection() {        for (DcAsyncChannel dcac : mDataConnectionAcHashMap.values()) {            if (dcac.isInactiveSync() && dataConnectionNotInUse(dcac)) {                return dcac;            }           }        return null;    }    public boolean isInactiveSync() {        boolean value;        if (isCallerOnDifferentThread()) {            Message response = sendMessageSynchronously(REQ_IS_INACTIVE);            if ((response != null) && (response.what == RSP_IS_INACTIVE)) {                value = rspIsInactive(response);            } else {                value = false;            }        } else {            value = mDc.getIsInactive();        }           return value;    }  

其中的sendMessageSynchronously(REQ_IS_INACTIVE);即需要获取DataConnection中的是否处于INACTIVE状态，这不能是异步的。

5、通过DcAsyncChannel将消息传入状态机

将apnContext通过dcac传入DataConnection状态机进行数据连接

dcac.bringUp(apnContext, getInitialMaxRetry(), profileId, radioTech, mAutoAttachOnCreation,msg);

6、状态机状态轮转

DataConnection默认状态是DcInactiveState,首先会在DcInactiveState调用onConnect去调用setupDataCall

private void onConnect(ConnectionParams cp) {    // msg.obj will be returned in AsyncResult.userObj;    Message msg = obtainMessage(EVENT_SETUP_DATA_CONNECTION_DONE, cp);    msg.obj = cp;     int authType = mApnSetting.authType;    if (authType == -1) {        authType = TextUtils.isEmpty(mApnSetting.user) ? RILConstants.SETUP_DATA_AUTH_NONE                : RILConstants.SETUP_DATA_AUTH_PAP_CHAP;    }    String protocol;    if (mPhone.getServiceState().getDataRoaming()) {        protocol = mApnSetting.roamingProtocol;    } else {            protocol = mApnSetting.protocol;    }    mPhone.mCi.setupDataCall(            Integer.toString(cp.mRilRat + 2),            Integer.toString(cp.mProfileId),            mApnSetting.apn, mApnSetting.user, mApnSetting.password,            Integer.toString(authType),            protocol, msg);}

在onConnect会包装一个EVENT_SETUP_DATA_CONNECTION_DONE消息在msg中，这个消息会一并发往RILJ->RILD，当RILD返回响应时会携带这消息并发出来，DataConnection状态机的DcActivatingState会扑捉到此消息进行状态机轮状，然后这里面全是状态机轮状来维护网络的链接状态：

至此数据连接的发起过程完毕，但是理上网还有很远，后续工作还要更新路由表等等