Android4.4 GPS框架分析【轉】

本文轉載自：http://blog.csdn.net/junzhang1122/article/details/46674569

GPS HAL層代碼在目錄trunk/Android/hardware/xxx/gps/skytraqskytraq_gsp.c，向下與硬件驅動通訊，向上提供接口  
GPS JNI層層代碼在目錄trunk/Android/frameworks/base/services/jni/com_android_server_location_GpsLocationProvider.cpp  C與java轉換，給java層提供接口  
GPS framework層代碼目錄Android/frameworks/base/services/java/com/android/server下，主要文件是location服務對內部的封裝並提供provider服務  
Android/frameworks/base/location/java/com/android/internal/location這個是framework對location服務內部的實現  
  
啟動GPS服務代碼流程如下  
public static void main(String[] args)  
    -->ServerThread thr = new ServerThread();  
        -->location = new LocationManagerService(context);   
        -->ServiceManager.addService(Context.LOCATION_SERVICE, location);  
        -->locationF.systemRunning()  
            -->systemRunning()  
                -->loadProvidersLocked();  
                    -->GpsLocationProvider gpsProvider = new GpsLocationProvider(mContext, this, mLocationHandler.getLooper());  
                        -->class_init_native();  
                            -->android_location_GpsLocationProvider_class_init_native(JNIEnv* env, jclass clazz)   
                                -->err = module->methods->open(module, GPS_HARDWARE_MODULE_ID, &device);  
                                    -->pen_gps(const struct hw_module_t *module, char const *name, struct hw_device_t **device)  
                                -->sGpsInterface = gps_device->get_gps_interface(gps_device);  
                                    -->const GpsInterface *gps__get_gps_interface(struct gps_device_t *dev)  
                                        -->return &skytraqGpsInterface;  
                    -->GpsLocationProvider.isSupported()  
                        -->native_is_supported()  
                            -->android_location_GpsLocationProvider_is_supported(JNIEnv* env, jclass clazz)  
                                -->return (sGpsInterface != NULL);  
                -->updateProvidersLocked  
                    -->  updateProviderListenersLocked  
                        -->  applyRequirementsLocked(provider);  
                                --> p.setRequest(providerRequest, worksource);  
                                    -->  public void setRequest(ProviderRequest request, WorkSource source)   
                                    --> sendMessage(SET_REQUEST, 0, new GpsRequest(request, source));  
                                        -->public void handleMessage(Message msg)  
                                            -->handleSetRequest(gpsRequest.request, gpsRequest.source);  
                                                -->startNavigating(singleShot);  
                                                    -->native_set_position_mode(mPositionMode, GPS_POSITION_RECURRENCE_PERIODIC,interval, 0, 0)  
                                                    -->native_start()  
  
Android系統運行的第一個進程就是init進程，在該進程中創建的第一個虛擬機就是zygote，zygote孵化的第一個虛擬機就是Dalvik,該進程就是SystemServer,  
對於的SystemServer代碼是framework\base\services\java\com\android\server\SystemServer.java  
該SystemServer對於的第一個運行函數就是main  
  
public static void main(String[] args) //SystemServer運行的第一個函數  
    ServerThread thr = new ServerThread(); //初始化一個server線程   
        class ServerThread   
        {  
             public void initAndLoop()   
             {  
                   if (!disableLocation) //開始的時候這里的 disableLocation = false  
                   {   
             try{  
                     Slog.i(TAG, "Location Manager");  
 <1>                 location = new LocationManagerService(context); //實例化一個LocationManagerService服務，該服務主要用來管理GPS地理位置的變化  
                     ServiceManager.addService(Context.LOCATION_SERVICE, location); //將這個service添加到SystemManager中  
             }   
             catch (Throwable e)   
             {  
                reportWtf("starting Location Manager", e);  
             }  
  
             try {  
                    Slog.i(TAG, "Country Detector");  
                    countryDetector = new CountryDetectorService(context);//實例化一個CountryDetectorService服務，用來探測不同國家，也就是不同地區和時區   
                    ServiceManager.addService(Context.COUNTRY_DETECTOR, countryDetector);  
             } catch (Throwable e) {  
                    reportWtf("starting Country Detector", e);  
             }  
          }  
            
        ActivityManagerService.self().systemReady(new Runnable()   
        {  
            public void run()   
            {  
                try   
                {  
<2>             if (locationF != null) locationF.systemRunning();//在<1>的位置已給locationF賦值，在這里調用LocationManagerService的systemRunning()函數  
            }   
            catch(Throwable e)   
            {  
               reportWtf("Notifying Location Service running", e);  
            }  
            }  
        }  
               
            }     
        }  
  
接下來分析LocationManagerService(context)  
/**framework\base\services\java\com\android\server\LocationManagerService.java**/  
public class LocationManagerService extends ILocationManager.Stub  
{  
    public void systemRunning() //該函數有<2>處調用  
    {  
        synchronized (mLock)  
        {  
        /*GPS啟動到運行及監聽都在這兩個函數里*/  
<3>           loadProvidersLocked(); //在這里加載各種provider  
<4>           updateProvidersLocked(); //加載后更新  
        }     
    }  
}  
  
/**framework\base\services\java\com\android\server\LocationManagerService.java**/  
private void loadProvidersLocked()  
{  
 // create a passive location provider, which is always enabled  
    PassiveProvider passiveProvider = new PassiveProvider(this);  
    addProviderLocked(passiveProvider);  
    mEnabledProviders.add(passiveProvider.getName());  
    mPassiveProvider = passiveProvider;  
    // Create a gps location provider  
<5> GpsLocationProvider gpsProvider = new GpsLocationProvider(mContext, this,  
            mLocationHandler.getLooper());  
  
<6> if (GpsLocationProvider.isSupported()) //這里調用JNI的函數接口   
    {  
        mGpsStatusProvider = gpsProvider.getGpsStatusProvider(); //獲取gps狀態provider  
        mNetInitiatedListener = gpsProvider.getNetInitiatedListener(); //初始網絡監聽   
        addProviderLocked(gpsProvider); //將gpsProvider添加到mProviders中  
        mRealProviders.put(LocationManager.GPS_PROVIDER, gpsProvider);  
    }     
}  
  
/**分析  <5>  ***/  
public class GpsLocationProvider implements LocationProviderInterface   
{  
    static { class_init_native(); } //在這里調用JNI的android_location_GpsLocationProvider_class_init_native函數  
}  
  
static void android_location_GpsLocationProvider_class_init_native(JNIEnv* env, jclass clazz)   
{  
    err = module->methods->open(module, GPS_HARDWARE_MODULE_ID, &device);//打開GPS設備文件，對應trunk/Android/hardware/xxx/gps/skytraq/skytraq_gps.c  
                -->static int open_gps(const struct hw_module_t *module, char const *name, struct hw_device_t **device)  
                  
    //獲取gpsInterface接口，該函數接口在trunk/Android/hardware/xxx/gps/skytraq/skytraq_gps.c中,對應的函數是gps__get_gps_interface  
    sGpsInterface = gps_device->get_gps_interface(gps_device);  
}  
  
const GpsInterface *gps__get_gps_interface(struct gps_device_t *dev)  
{  
    return &skytraqGpsInterface;  
}  
  
/**分析 <6>  **/  
public static boolean GpsLocationProvider.isSupported()  
{  
    return native_is_supported(); //該函數對應JNI的函數如下  
}  
  
static jboolean android_location_GpsLocationProvider_is_supported(JNIEnv* env, jclass clazz)   
{  
    return (sGpsInterface != NULL);  
}  
GpsLocationProvider.isSupported()返回true，所以會走if{}里面的。在網上查閱資料，都是基於2.3的系統，2.3的系統里是直接在isSupported()函數里來獲取接口，沒有在GpsLocationProvider類中實現調用class_init_native()來獲取接口  
  
/**分析 <4> **/  
/**framework\base\services\java\com\android\server\LocationManagerService.java**/  
private void updateProvidersLocked()   
{  
    for (int i = mProviders.size() - 1; i >= 0; i--)  
    {  
        boolean isEnabled = p.isEnabled(); //開始的時候返回false  
        boolean shouldBeEnabled = isAllowedByCurrentUserSettingsLocked(name); //在loadProvidersLocked()函數就說了，一直是enabled  
        所以會走else  
        else if (!isEnabled && shouldBeEnabled)  
         {  
<7>      updateProviderListenersLocked(name, true, mCurrentUserId);  
         changesMade = true;  
     }  
    }  
    /*發送廣播，app和framework都可以接受該廣播*/  
    if (changesMade) {  
            mContext.sendBroadcastAsUser(new Intent(LocationManager.PROVIDERS_CHANGED_ACTION),  
                    UserHandle.ALL);  
            mContext.sendBroadcastAsUser(new Intent(LocationManager.MODE_CHANGED_ACTION),  
                    UserHandle.ALL);  
  }  
}  
  
/**分析 <7>   framework\base\services\java\com\android\server\locationManagerService.java **/  
private void updateProviderListenersLocked(String provider, boolean enabled, int userId)   
{  
    if (records != null)  
    {  
        //這里主要是從UserHandle里解析UserId 是否等於 mCurrentUserId，如果是則發送notification給receiver    
    }   
    if (enabled) //這里的 enabled == true  
    {  
<8>  p.enable();  
     if (listeners > 0)   
     {  
<9>       applyRequirementsLocked(provider);  
     }  
  }  
     else   
     {  
     p.disable();  
   }  
     
}  
  
/**分析 <8>   framework\base\services\java\com\android\server\location\gpsLocationProvider.java**/  
public void enable()   
{  
    synchronized (mLock)   
    {  
    if (mEnabled) return;//開始的時候這里是false  
    mEnabled = true;       
    }  
<10>  sendMessage(ENABLE, 1, null);//發送消息  
}  
/**分析  <10>     base\services\java\com\android\server\location\gpsLocationProvider.java**/  
private void sendMessage(int message, int arg, Object obj)   
{  
        // hold a wake lock until this message is delivered  
        // note that this assumes the message will not be removed from the queue before  
        // it is handled (otherwise the wake lock would be leaked).  
        mWakeLock.acquire();  
<11>    mHandler.obtainMessage(message, arg, 1, obj).sendToTarget(); //通過handler機制來發送消息  
}  
  
/**分析  <11>     base\services\java\com\android\server\location\gpsLocationProvider.java**/  
private final class ProviderHandler extends Handler   
{  
    public void handleMessage(Message msg)   
    {  
        switch (message)   
        {  
        case ENABLE:  //有<10>可知，message == ENABLE ， msg.arg1 == 1  
        if (msg.arg1 == 1) {     
<12>        handleEnable(); //所以會調用這個函數  
        } else {  
            handleDisable();  
        }  
        break;  
    .....  
    }  
    }  
}  
  
/**分析  <12>     framework\base\services\java\com\android\server\location\gpsLocationProvider.java**/  
private void handleEnable()   
{  
<13>  boolean enabled = native_init(); //調用JNI中的 static jboolean android_location_GpsLocationProvider_init(JNIEnv* env, jobject obj)  
  if (enabled)   
  {  
      mSupportsXtra = native_supports_xtra(); //native_supports_xtra()直接返回true，在class_init_native()已經賦值  
  
      if (mSuplServerHost != null)   
      {  
        /*這里沒做任何事，因為sAGpsInterface為空，代碼流程如下*/  
          native_set_agps_server(AGPS_TYPE_SUPL, mSuplServerHost, mSuplServerPort);  
            -->static void android_location_GpsLocationProvider_set_agps_server(JNIEnv* env, jobject obj, jint type, jstring hostname, jint port)  
                -->if (!sAGpsInterface) return;  
            -->sAGpsInterface = (const AGpsInterface*)sGpsInterface->get_extension(AGPS_INTERFACE);  
                -->static const void *skytraq_gps_get_extension(const char* name)  
                                {  
                                ALOGD("%s: called", __FUNCTION__);  
                                return NULL;  
                                }  
                  
      }  
      if (mC2KServerHost != null) { //同理這里也直接返回了  
          native_set_agps_server(AGPS_TYPE_C2K, mC2KServerHost, mC2KServerPort);  
      }  
  }else{  
      synchronized (mLock) {  
          mEnabled = false;  
      }  
      Log.w(TAG, "Failed to enable location provider");  
  }  
      
}  
  
/**分析  <13>  framework\base\services\jni\com_android_server_location_GpsLocationProvider.cpp **/  
static jboolean android_location_GpsLocationProvider_init(JNIEnv* env, jobject obj)  
{  
<14>  if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0)//sGpsInterface不為null，在一開始的就已賦值，所以會調用init函數  
            return false;  
            .....  
}  
  
/**分析  <14>   hardware\xxx\gps\skytraq\Skytraq_gps.c **/  
static int skytraq_gps_init(GpsCallbacks* callbacks) //callbacks回調函數時有JNI傳下來的，在JNI中實現的  
{  
    GpsState*  s = &_gps_state; //該結構圖數組初始化的時候都為0  
    if (!s->init)  
<15>      gps_state_init(s, callbacks);  
}  
  
/**分析  <15>   hardware\xxx\gps\skytraq\Skytraq_gps.c **/  
static void gps_state_init( GpsState*  state, GpsCallbacks* callbacks )  
{  
    state->fd = gps_channel_open(GPS_CHANNEL_NAME);  
            --> fd = open("/dev/skytraq_gps_ipc", O_RDWR |  O_SYNC); //打開串口  
    int ret = ioctl(state->fd, GPS_IPC_SET, &gps_connect_info); //調用驅動函數ioctl設置gps  
    state->thread = callbacks->create_thread_cb( "gps_state_thread", gps_state_thread, state );//創建線程，用來監聽發送的命令和監聽數據上報，  
}  
  
  
/**分析<9> frwmework\base\services\java\com\android\server\LocationManagerService.java 
private void applyRequirementsLocked(String provider) 
{ 
    //設置worksource和providerRequest 
    ..... 
<16>  p.setRequest(providerRequest, worksource); //location provider 發送請求 
} 
  
 
/**分析<16> frwmework\base\services\java\com\android\server\location\GpsLocationProvider.java**/  
public void setRequest(ProviderRequest request, WorkSource source)   
{  
<17>   sendMessage(SET_REQUEST, 0, new GpsRequest(request, source)); //發送消息，SET_REQUEST == 3  
}  
  
/**分析<17> frwmework\base\services\java\com\android\server\location\GpsLocationProvider.java**/  
public void handleMessage(Message msg)  
{  
    ...  
    case SET_REQUEST:  
       GpsRequest gpsRequest = (GpsRequest) msg.obj;  
<18>   handleSetRequest(gpsRequest.request, gpsRequest.source);  
       break;  
}  
  
/**分析<18> frwmework\base\services\java\com\android\server\location\GpsLocationProvider.java**/  
private void handleSetRequest(ProviderRequest request, WorkSource source)   
{  
    ...  
<19>  startNavigating(singleShot);//開始導航  
}  
  
/**分析<19> frwmework\base\services\java\com\android\server\location\GpsLocationProvider.java**/  
private void startNavigating(boolean singleShot)  
{  
<20>  native_set_position_mode(mPositionMode, GPS_POSITION_RECURRENCE_PERIODIC, interval, 0, 0)//該函數在HAL層直接返回了，沒做任何事  
<21>  native_start()  
}   
  
/**分析<20> framework\base\services\jni\com_android_server_location_GpsLocationProvider.cpp**/  
static jboolean android_location_GpsLocationProvider_set_position_mode(JNIEnv* env, jobject obj,  
        jint mode, jint recurrence, jint min_interval, jint preferred_accuracy, jint preferred_time)  
{  
    if (sGpsInterface)  
<22>        return (sGpsInterface->set_position_mode(mode, recurrence, min_interval, preferred_accuracy,   
                preferred_time) == 0); //調用HAL層接口  
}  
  
/**分析<22> xxx\gps\skytraq\skytraq.gps.c**/  
static int skytraq_gps_set_position_mode(GpsPositionMode mode,  
                                      GpsPositionRecurrence recurrence,  
                                      uint32_t min_interval,  
                                      uint32_t preferred_accuracy,  
                                      uint32_t preferred_time)  
{  
    ALOGD("%s: called", __FUNCTION__);  
    return 0;  
}  
/**分析<21> framework\base\services\jni\com_android_server_location_GpsLocationProvider.cpp**/  
static jboolean android_location_GpsLocationProvider_start(JNIEnv* env, jobject obj)  
{  
    if (sGpsInterface)  
<23>      return (sGpsInterface->start() == 0); //調用HAL 層的static int skytraq_gps_start()  
}  
  
/**分析<23> xxx\gps\skytraq\skytraq.gps.c**/  
static int skytraq_gps_start()  
{  
    gps_state_start(s);  
        -->s->status = CMD_START;   
  /*在<15>線程函數gps_state_thread()中while(1)中等該命令，進入獲取數據*/  
}  
此時GPS就已運行  

 

GPS HAL層代碼在目錄trunk/Android/hardware/xxx/gps/skytraqskytraq_gsp.c，向下與硬件驅動通訊，向上提供接口
GPS JNI層層代碼在目錄trunk/Android/frameworks/base/services/jni/com_android_server_location_GpsLocationProvider.cpp  C與java轉換，給java層提供接口
GPS framework層代碼目錄Android/frameworks/base/services/java/com/android/server下，主要文件是location服務對內部的封裝並提供provider服務
Android/frameworks/base/location/java/com/android/internal/location這個是framework對location服務內部的實現

啟動GPS服務代碼流程如下
public static void main(String[] args)
    -->ServerThread thr = new ServerThread();
        -->location = new LocationManagerService(context);
        -->ServiceManager.addService(Context.LOCATION_SERVICE, location);
        -->locationF.systemRunning()
            -->systemRunning()
                -->loadProvidersLocked();
                    -->GpsLocationProvider gpsProvider = new GpsLocationProvider(mContext, this, mLocationHandler.getLooper());
                        -->class_init_native();
                            -->android_location_GpsLocationProvider_class_init_native(JNIEnv* env, jclass clazz)
                                -->err = module->methods->open(module, GPS_HARDWARE_MODULE_ID, &device);
                                    -->pen_gps(const struct hw_module_t *module, char const *name, struct hw_device_t **device)
                                -->sGpsInterface = gps_device->get_gps_interface(gps_device);
                                    -->const GpsInterface *gps__get_gps_interface(struct gps_device_t *dev)
                                        -->return &skytraqGpsInterface;
                    -->GpsLocationProvider.isSupported()
                        -->native_is_supported()
                            -->android_location_GpsLocationProvider_is_supported(JNIEnv* env, jclass clazz)
                                -->return (sGpsInterface != NULL);
                -->updateProvidersLocked
                    -->  updateProviderListenersLocked
                        -->  applyRequirementsLocked(provider);
                                --> p.setRequest(providerRequest, worksource);
                                    -->  public void setRequest(ProviderRequest request, WorkSource source)
                                    --> sendMessage(SET_REQUEST, 0, new GpsRequest(request, source));
                                        -->public void handleMessage(Message msg)
                                            -->handleSetRequest(gpsRequest.request, gpsRequest.source);
                                                -->startNavigating(singleShot);
                                                    -->native_set_position_mode(mPositionMode, GPS_POSITION_RECURRENCE_PERIODIC,interval, 0, 0)
                                                    -->native_start()

Android系統運行的第一個進程就是init進程，在該進程中創建的第一個虛擬機就是zygote，zygote孵化的第一個虛擬機就是Dalvik,該進程就是SystemServer,
對於的SystemServer代碼是framework\base\services\java\com\android\server\SystemServer.java
該SystemServer對於的第一個運行函數就是main

public static void main(String[] args) //SystemServer運行的第一個函數
    ServerThread thr = new ServerThread(); //初始化一個server線程
        class ServerThread
        {
             public void initAndLoop()
             {
                   if (!disableLocation) //開始的時候這里的 disableLocation = false
                   {
             try{
                     Slog.i(TAG, "Location Manager");
 <1>                 location = new LocationManagerService(context); //實例化一個LocationManagerService服務，該服務主要用來管理GPS地理位置的變化
                     ServiceManager.addService(Context.LOCATION_SERVICE, location); //將這個service添加到SystemManager中
             }
             catch (Throwable e)
             {
                reportWtf("starting Location Manager", e);
             }

             try {
                    Slog.i(TAG, "Country Detector");
                    countryDetector = new CountryDetectorService(context);//實例化一個CountryDetectorService服務，用來探測不同國家，也就是不同地區和時區
                    ServiceManager.addService(Context.COUNTRY_DETECTOR, countryDetector);
             } catch (Throwable e) {
                    reportWtf("starting Country Detector", e);
             }
          }

        ActivityManagerService.self().systemReady(new Runnable()
        {
            public void run()
            {
                try
                {
<2>             if (locationF != null) locationF.systemRunning();//在<1>的位置已給locationF賦值，在這里調用LocationManagerService的systemRunning()函數
            }
            catch(Throwable e)
            {
               reportWtf("Notifying Location Service running", e);
            }
            }
        }

            }
        }

接下來分析LocationManagerService(context)
/**framework\base\services\java\com\android\server\LocationManagerService.java**/
public class LocationManagerService extends ILocationManager.Stub
{
    public void systemRunning() //該函數有<2>處調用
    {
        synchronized (mLock)
        {
        /*GPS啟動到運行及監聽都在這兩個函數里*/
<3>           loadProvidersLocked(); //在這里加載各種provider
<4>           updateProvidersLocked(); //加載后更新
        }
    }
}

/**framework\base\services\java\com\android\server\LocationManagerService.java**/
private void loadProvidersLocked()
{
 // create a passive location provider, which is always enabled
    PassiveProvider passiveProvider = new PassiveProvider(this);
    addProviderLocked(passiveProvider);
    mEnabledProviders.add(passiveProvider.getName());
    mPassiveProvider = passiveProvider;
    // Create a gps location provider
<5> GpsLocationProvider gpsProvider = new GpsLocationProvider(mContext, this,
            mLocationHandler.getLooper());

<6> if (GpsLocationProvider.isSupported()) //這里調用JNI的函數接口
    {
        mGpsStatusProvider = gpsProvider.getGpsStatusProvider(); //獲取gps狀態provider
        mNetInitiatedListener = gpsProvider.getNetInitiatedListener(); //初始網絡監聽
        addProviderLocked(gpsProvider); //將gpsProvider添加到mProviders中
        mRealProviders.put(LocationManager.GPS_PROVIDER, gpsProvider);
    }
}

/**分析  <5>  ***/
public class GpsLocationProvider implements LocationProviderInterface
{
    static { class_init_native(); } //在這里調用JNI的android_location_GpsLocationProvider_class_init_native函數
}

static void android_location_GpsLocationProvider_class_init_native(JNIEnv* env, jclass clazz)
{
    err = module->methods->open(module, GPS_HARDWARE_MODULE_ID, &device);//打開GPS設備文件，對應trunk/Android/hardware/xxx/gps/skytraq/skytraq_gps.c
                -->static int open_gps(const struct hw_module_t *module, char const *name, struct hw_device_t **device)

    //獲取gpsInterface接口，該函數接口在trunk/Android/hardware/xxx/gps/skytraq/skytraq_gps.c中,對應的函數是gps__get_gps_interface
    sGpsInterface = gps_device->get_gps_interface(gps_device);
}

const GpsInterface *gps__get_gps_interface(struct gps_device_t *dev)
{
    return &skytraqGpsInterface;
}

/**分析 <6>  **/
public static boolean GpsLocationProvider.isSupported()
{
    return native_is_supported(); //該函數對應JNI的函數如下
}

static jboolean android_location_GpsLocationProvider_is_supported(JNIEnv* env, jclass clazz)
{
    return (sGpsInterface != NULL);
}
GpsLocationProvider.isSupported()返回true，所以會走if{}里面的。在網上查閱資料，都是基於2.3的系統，2.3的系統里是直接在isSupported()函數里來獲取接口，沒有在GpsLocationProvider類中實現調用class_init_native()來獲取接口

/**分析 <4> **/
/**framework\base\services\java\com\android\server\LocationManagerService.java**/
private void updateProvidersLocked()
{
    for (int i = mProviders.size() - 1; i >= 0; i--)
    {
        boolean isEnabled = p.isEnabled(); //開始的時候返回false
        boolean shouldBeEnabled = isAllowedByCurrentUserSettingsLocked(name); //在loadProvidersLocked()函數就說了，一直是enabled
        所以會走else
        else if (!isEnabled && shouldBeEnabled)
         {
<7>      updateProviderListenersLocked(name, true, mCurrentUserId);
         changesMade = true;
     }
    }
    /*發送廣播，app和framework都可以接受該廣播*/
    if (changesMade) {
            mContext.sendBroadcastAsUser(new Intent(LocationManager.PROVIDERS_CHANGED_ACTION),
                    UserHandle.ALL);
            mContext.sendBroadcastAsUser(new Intent(LocationManager.MODE_CHANGED_ACTION),
                    UserHandle.ALL);
  }
}

/**分析 <7>   framework\base\services\java\com\android\server\locationManagerService.java **/
private void updateProviderListenersLocked(String provider, boolean enabled, int userId)
{
    if (records != null)
    {
        //這里主要是從UserHandle里解析UserId 是否等於 mCurrentUserId，如果是則發送notification給receiver
    }
    if (enabled) //這里的 enabled == true
    {
<8>  p.enable();
     if (listeners > 0)
     {
<9>       applyRequirementsLocked(provider);
     }
  }
     else
     {
     p.disable();
   }

}

/**分析 <8>   framework\base\services\java\com\android\server\location\gpsLocationProvider.java**/
public void enable()
{
    synchronized (mLock)
    {
    if (mEnabled) return;//開始的時候這里是false
    mEnabled = true;
    }
<10>  sendMessage(ENABLE, 1, null);//發送消息
}
/**分析  <10>     base\services\java\com\android\server\location\gpsLocationProvider.java**/
private void sendMessage(int message, int arg, Object obj)
{
        // hold a wake lock until this message is delivered
        // note that this assumes the message will not be removed from the queue before
        // it is handled (otherwise the wake lock would be leaked).
        mWakeLock.acquire();
<11>    mHandler.obtainMessage(message, arg, 1, obj).sendToTarget(); //通過handler機制來發送消息
}

/**分析  <11>     base\services\java\com\android\server\location\gpsLocationProvider.java**/
private final class ProviderHandler extends Handler
{
    public void handleMessage(Message msg)
    {
        switch (message)
        {
        case ENABLE:  //有<10>可知，message == ENABLE ， msg.arg1 == 1
        if (msg.arg1 == 1) {
<12>        handleEnable(); //所以會調用這個函數
        } else {
            handleDisable();
        }
        break;
    .....
    }
    }
}

/**分析  <12>     framework\base\services\java\com\android\server\location\gpsLocationProvider.java**/
private void handleEnable()
{
<13>  boolean enabled = native_init(); //調用JNI中的 static jboolean android_location_GpsLocationProvider_init(JNIEnv* env, jobject obj)
  if (enabled)
  {
      mSupportsXtra = native_supports_xtra(); //native_supports_xtra()直接返回true，在class_init_native()已經賦值

      if (mSuplServerHost != null)
      {
        /*這里沒做任何事，因為sAGpsInterface為空，代碼流程如下*/
          native_set_agps_server(AGPS_TYPE_SUPL, mSuplServerHost, mSuplServerPort);
            -->static void android_location_GpsLocationProvider_set_agps_server(JNIEnv* env, jobject obj, jint type, jstring hostname, jint port)
                -->if (!sAGpsInterface) return;
            -->sAGpsInterface = (const AGpsInterface*)sGpsInterface->get_extension(AGPS_INTERFACE);
                -->static const void *skytraq_gps_get_extension(const char* name)
                                {
                                ALOGD("%s: called", __FUNCTION__);
                                return NULL;
                                }

      }
      if (mC2KServerHost != null) { //同理這里也直接返回了
          native_set_agps_server(AGPS_TYPE_C2K, mC2KServerHost, mC2KServerPort);
      }
  }else{
      synchronized (mLock) {
          mEnabled = false;
      }
      Log.w(TAG, "Failed to enable location provider");
  }

}

/**分析  <13>  framework\base\services\jni\com_android_server_location_GpsLocationProvider.cpp **/
static jboolean android_location_GpsLocationProvider_init(JNIEnv* env, jobject obj)
{
<14>  if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0)//sGpsInterface不為null，在一開始的就已賦值，所以會調用init函數
            return false;
            .....
}

/**分析  <14>   hardware\xxx\gps\skytraq\Skytraq_gps.c **/
static int skytraq_gps_init(GpsCallbacks* callbacks) //callbacks回調函數時有JNI傳下來的，在JNI中實現的
{
    GpsState*  s = &_gps_state; //該結構圖數組初始化的時候都為0
    if (!s->init)
<15>      gps_state_init(s, callbacks);
}

/**分析  <15>   hardware\xxx\gps\skytraq\Skytraq_gps.c **/
static void gps_state_init( GpsState*  state, GpsCallbacks* callbacks )
{
    state->fd = gps_channel_open(GPS_CHANNEL_NAME);
            --> fd = open("/dev/skytraq_gps_ipc", O_RDWR |  O_SYNC); //打開串口
    int ret = ioctl(state->fd, GPS_IPC_SET, &gps_connect_info); //調用驅動函數ioctl設置gps
    state->thread = callbacks->create_thread_cb( "gps_state_thread", gps_state_thread, state );//創建線程，用來監聽發送的命令和監聽數據上報，
}


/**分析<9> frwmework\base\services\java\com\android\server\LocationManagerService.java
private void applyRequirementsLocked(String provider)
{
    //設置worksource和providerRequest
    .....
<16>  p.setRequest(providerRequest, worksource); //location provider 發送請求
}


/**分析<16> frwmework\base\services\java\com\android\server\location\GpsLocationProvider.java**/
public void setRequest(ProviderRequest request, WorkSource source)
{
<17>   sendMessage(SET_REQUEST, 0, new GpsRequest(request, source)); //發送消息，SET_REQUEST == 3
}

/**分析<17> frwmework\base\services\java\com\android\server\location\GpsLocationProvider.java**/
public void handleMessage(Message msg)
{
    ...
    case SET_REQUEST:
       GpsRequest gpsRequest = (GpsRequest) msg.obj;
<18>   handleSetRequest(gpsRequest.request, gpsRequest.source);
       break;
}

/**分析<18> frwmework\base\services\java\com\android\server\location\GpsLocationProvider.java**/
private void handleSetRequest(ProviderRequest request, WorkSource source)
{
    ...
<19>  startNavigating(singleShot);//開始導航
}

/**分析<19> frwmework\base\services\java\com\android\server\location\GpsLocationProvider.java**/
private void startNavigating(boolean singleShot)
{
<20>  native_set_position_mode(mPositionMode, GPS_POSITION_RECURRENCE_PERIODIC, interval, 0, 0)//該函數在HAL層直接返回了，沒做任何事
<21>  native_start()
}

/**分析<20> framework\base\services\jni\com_android_server_location_GpsLocationProvider.cpp**/
static jboolean android_location_GpsLocationProvider_set_position_mode(JNIEnv* env, jobject obj,
        jint mode, jint recurrence, jint min_interval, jint preferred_accuracy, jint preferred_time)
{
    if (sGpsInterface)
<22>        return (sGpsInterface->set_position_mode(mode, recurrence, min_interval, preferred_accuracy,
                preferred_time) == 0); //調用HAL層接口
}

/**分析<22> xxx\gps\skytraq\skytraq.gps.c**/
static int skytraq_gps_set_position_mode(GpsPositionMode mode,
                                      GpsPositionRecurrence recurrence,
                                      uint32_t min_interval,
                                      uint32_t preferred_accuracy,
                                      uint32_t preferred_time)
{
    ALOGD("%s: called", __FUNCTION__);
    return 0;
}
/**分析<21> framework\base\services\jni\com_android_server_location_GpsLocationProvider.cpp**/
static jboolean android_location_GpsLocationProvider_start(JNIEnv* env, jobject obj)
{
    if (sGpsInterface)
<23>      return (sGpsInterface->start() == 0); //調用HAL 層的static int skytraq_gps_start()
}

/**分析<23> xxx\gps\skytraq\skytraq.gps.c**/
static int skytraq_gps_start()
{
    gps_state_start(s);
        -->s->status = CMD_START;
  /*在<15>線程函數gps_state_thread()中while(1)中等該命令，進入獲取數據*/
}
此時GPS就已運行