Android LocationManagerService啓動（一）

Location服務是系統中很重要的一個服務，幾乎當前全部的App都會用到這個服務。

首先看代碼在Android源碼的位置

Android API

frameworks/base/location

LocationManagerService

frameworks/base/services/core/java/com/android/server/location
frameworks/base/services/core/java/com/android/server/LocationManagerService.java

SystemServer

做爲一個系統級別服務，啓動確定是在SystemServer中進行。

代碼入口：frameworks/base/services/java/com/android/server/SystemServer.java
啓動LocationManagerService的代碼在startOtherServices()函數裏面

執行流程以下

1. 建立LocationManagerService對象
2. 將建立好的的對象加入到ServiceManager裏面
3. 調用LocationManagerService的systemRunning()函數初始化相關的Provider

private void startOtherServices() {
    ////////////////////
    LocationManagerService location = null;
    traceBeginAndSlog("StartLocationManagerService");
    try {
        location = new LocationManagerService(context);
        ServiceManager.addService(Context.LOCATION_SERVICE, location);
    } catch (Throwable e) {
        reportWtf("starting Location Manager", e);
    }
    traceEnd();
    // These are needed to propagate to the runnable below.
    final LocationManagerService locationF = location;
    traceBeginAndSlog("MakeLocationServiceReady");
    try {
        if (locationF != null) locationF.systemRunning();
    } catch (Throwable e) {
        reportWtf("Notifying Location Service running", e);
    }
    traceEnd();
    ////////////////////
}

LocationManagerService

從ServiceManager啓動後，會調用systemRunning()方法，這個函數裏面會初始化全部的可用的Providers
代碼路徑：frameworks/base/services/core/java/com/android/server/LocationManagerService.java

構造函數

構造函數很簡單，除了初始化變量外，就給PackageManager設置了一個PackageProvider

public LocationManagerService(Context context) {
    super();
    mContext = context;
    mAppOps = (AppOpsManager) context.getSystemService(Context.APP_OPS_SERVICE);
    // Let the package manager query which are the default location
    // providers as they get certain permissions granted by default.
    PackageManagerInternal packageManagerInternal = LocalServices.getService(
            PackageManagerInternal.class);
    packageManagerInternal.setLocationPackagesProvider(
            new PackageManagerInternal.PackagesProvider() {
                @Override
                public String[] getPackages(int userId) {
                    return mContext.getResources().getStringArray(
                            com.android.internal.R.array.config_locationProviderPackageNames);
                }
            });
    if (D) Log.d(TAG, "Constructed");
    // most startup is deferred until systemRunning()
}

systemRunning()

做爲LocationManagerService的入口函數，主要作如下幾部分工做

1. 初始化成員變量，主要是個各類須要用的Manager
2. 初始化Provider
3. 註冊Observer，主要是包括Settings，UserChange等

public void systemRunning() {
    synchronized (mLock) {
        if (D) Log.d(TAG, "systemRunning()");
        // prepare providers
        loadProvidersLocked();
        updateProvidersLocked();
    }
    // listen for settings changes
    // ..... //
    // listen for user change
    // ..... //
}

咱們主要看第二點，包括了各類Provider的初始化

loadProvidersLocked

加載順序以下

1. PassiveProvider，必須
2. GnssLocationProvider，若是有，則加載
3. FuseProvider檢查，這裏比較重要，若是通不過，會跑出異常，不會進行下面的步驟（systemRunning會結束）
4. Bind NetworkProvider，第三方Provider
5. Bind Fused provider
6. Bind Geocoder provider
7. Bind Geofence provider

另外，針對每個Provider，建立的步驟大體都是如下幾個步驟

{
    XxxProvider xxxProvider = new XxxProvider(this);
    addProviderLocked(xxxProvider);
    mEnabledProviders.add(xxxProvider.getName());
    // or
    mRealProviders.put(LocationManager.Xxx_PROVIDER, xxxProvider);
    mXxxProvider = xxxProvider;
}

部分Provider初始化相對複雜一點，可是總體的邏輯一致。咱們這裏重點分析GnssProvider

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;

    if (GnssLocationProvider.isSupported()) {
        // 建立GnssProvider（老版本的Android上是GPS，後面整合成了GNSS，支持不一樣類型的導航系統）
        GnssLocationProvider gnssProvider = new GnssLocationProvider(mContext, this,
                mLocationHandler.getLooper());
        mGnssSystemInfoProvider = gnssProvider.getGnssSystemInfoProvider();
        mGnssBatchingProvider = gnssProvider.getGnssBatchingProvider();
        mGnssMetricsProvider = gnssProvider.getGnssMetricsProvider();
        mGnssStatusProvider = gnssProvider.getGnssStatusProvider();
        mNetInitiatedListener = gnssProvider.getNetInitiatedListener();
        addProviderLocked(gnssProvider);
        mRealProviders.put(LocationManager.GPS_PROVIDER, gnssProvider);
        mGnssMeasurementsProvider = gnssProvider.getGnssMeasurementsProvider();
        mGnssNavigationMessageProvider = gnssProvider.getGnssNavigationMessageProvider();
        mGpsGeofenceProxy = gnssProvider.getGpsGeofenceProxy();
    }

    /*
    Load package name(s) containing location provider support.
    These packages can contain services implementing location providers:
    Geocoder Provider, Network Location Provider, and
    Fused Location Provider. They will each be searched for
    service components implementing these providers.
    The location framework also has support for installation
    of new location providers at run-time. The new package does not
    have to be explicitly listed here, however it must have a signature
    that matches the signature of at least one package on this list.
    */
    Resources resources = mContext.getResources();
    ArrayList<String> providerPackageNames = new ArrayList<>();
    String[] pkgs = resources.getStringArray(
            com.android.internal.R.array.config_locationProviderPackageNames);
    if (D) {
        Log.d(TAG, "certificates for location providers pulled from: " +
                Arrays.toString(pkgs));
    }
    if (pkgs != null) providerPackageNames.addAll(Arrays.asList(pkgs));

      // 注意這裏若是沒有找到FuseProvider，會拋出異常，結束這個初始化流程
    ensureFallbackFusedProviderPresentLocked(providerPackageNames);

    // bind to network provider
    // bind to fused provider
    // bind to geocoder provider
    // bind to geofence provider
    // bind to hardware activity recognition
}

updateProvidersLocked

上一個步驟僅僅只是進行了Provider的初始化操做，這裏會調用Provider的enable方法，啓用相關的Provider，主要調用
updateProviderListenersLocked(String provider, boolean enabled)

private void updateProvidersLocked() {
    boolean changesMade = false;
    // 遍歷全部的Provider
    for (int i = mProviders.size() - 1; i >= 0; i--) {
        LocationProviderInterface p = mProviders.get(i);
        boolean isEnabled = p.isEnabled();
        String name = p.getName();
        // 經過當前用戶的Settings來判斷是否須要啓動這個Provider
        boolean shouldBeEnabled = isAllowedByCurrentUserSettingsLocked(name);
        if (isEnabled && !shouldBeEnabled) {
            // 若是已經啓動而且是不須要被啓動，就會關閉
            // 而且清除以前的記錄
            updateProviderListenersLocked(name, false);
            // If any provider has been disabled, clear all last locations for all providers.
            // This is to be on the safe side in case a provider has location derived from
            // this disabled provider.
            mLastLocation.clear();
            mLastLocationCoarseInterval.clear();
            changesMade = true;
        } else if (!isEnabled && shouldBeEnabled) {
            // 若是沒有啓動，而且須要被啓動，則啓動
            updateProviderListenersLocked(name, true);
            changesMade = true;
        }
    }
    // 若是狀態改變，就發系統廣播通知
    if (changesMade) {
        mContext.sendBroadcastAsUser(new Intent(LocationManager.PROVIDERS_CHANGED_ACTION),
                UserHandle.ALL);
        mContext.sendBroadcastAsUser(new Intent(LocationManager.MODE_CHANGED_ACTION),
                UserHandle.ALL);
    }
}

updateProviderListenersLocked

private void updateProviderListenersLocked(String provider, boolean enabled) {
    int listeners = 0;
    LocationProviderInterface p = mProvidersByName.get(provider);
    if (p == null) return;
    ArrayList<Receiver> deadReceivers = null;
    ArrayList<UpdateRecord> records = mRecordsByProvider.get(provider);
    if (records != null) {
        for (UpdateRecord record : records) {
            if (isCurrentProfile(UserHandle.getUserId(record.mReceiver.mIdentity.mUid))) {
                // Sends a notification message to the receiver
                if (!record.mReceiver.callProviderEnabledLocked(provider, enabled)) {
                    if (deadReceivers == null) {
                        deadReceivers = new ArrayList<>();
                    }
                    deadReceivers.add(record.mReceiver);
                }
                listeners++;
            }
        }
    }
    if (deadReceivers != null) {
        for (int i = deadReceivers.size() - 1; i >= 0; i--) {
            removeUpdatesLocked(deadReceivers.get(i));
        }
    }
    // 根據傳入的參數，肯定是開啓仍是關閉相關的Provider
    if (enabled) {
        p.enable();
        if (listeners > 0) {
            // 若是存在Locatoin listener，會調用下面的方法
            applyRequirementsLocked(provider);
        }
    } else {
        p.disable();
    }
}

applyRequirementsLocked

這裏會根據請求的Record的參數，來向具體的Provider發起位置信息請求。

private void applyRequirementsLocked(String provider) {
    LocationProviderInterface p = mProvidersByName.get(provider);
    if (p == null) return;
    ArrayList<UpdateRecord> records = mRecordsByProvider.get(provider);
    WorkSource worksource = new WorkSource();
    ProviderRequest providerRequest = new ProviderRequest();
    ContentResolver resolver = mContext.getContentResolver();
    long backgroundThrottleInterval = Settings.Global.getLong(
            resolver,
            Settings.Global.LOCATION_BACKGROUND_THROTTLE_INTERVAL_MS,
            DEFAULT_BACKGROUND_THROTTLE_INTERVAL_MS);
    // initialize the low power mode to true and set to false if any of the records requires
    providerRequest.lowPowerMode = true;
    if (records != null) {
        for (UpdateRecord record : records) {
            if (isCurrentProfile(UserHandle.getUserId(record.mReceiver.mIdentity.mUid))) {
                if (checkLocationAccess(
                        record.mReceiver.mIdentity.mPid,
                        record.mReceiver.mIdentity.mUid,
                        record.mReceiver.mIdentity.mPackageName,
                        record.mReceiver.mAllowedResolutionLevel)) {
                    LocationRequest locationRequest = record.mRealRequest;
                    long interval = locationRequest.getInterval();
                    if (!isThrottlingExemptLocked(record.mReceiver.mIdentity)) {
                        if (!record.mIsForegroundUid) {
                            interval = Math.max(interval, backgroundThrottleInterval);
                        }
                        if (interval != locationRequest.getInterval()) {
                            locationRequest = new LocationRequest(locationRequest);
                            locationRequest.setInterval(interval);
                        }
                    }
                    record.mRequest = locationRequest;
                    providerRequest.locationRequests.add(locationRequest);
                    if (!locationRequest.isLowPowerMode()) {
                        providerRequest.lowPowerMode = false;
                    }
                    if (interval < providerRequest.interval) {
                        providerRequest.reportLocation = true;
                        providerRequest.interval = interval;
                    }
                }
            }
        }
        if (providerRequest.reportLocation) {
            // calculate who to blame for power
            // This is somewhat arbitrary. We pick a threshold interval
            // that is slightly higher that the minimum interval, and
            // spread the blame across all applications with a request
            // under that threshold.
            long thresholdInterval = (providerRequest.interval + 1000) * 3 / 2;
            for (UpdateRecord record : records) {
                if (isCurrentProfile(UserHandle.getUserId(record.mReceiver.mIdentity.mUid))) {
                    LocationRequest locationRequest = record.mRequest;
                    // Don't assign battery blame for update records whose
                    // client has no permission to receive location data.
                    if (!providerRequest.locationRequests.contains(locationRequest)) {
                        continue;
                    }
                    if (locationRequest.getInterval() <= thresholdInterval) {
                        if (record.mReceiver.mWorkSource != null
                                && isValidWorkSource(record.mReceiver.mWorkSource)) {
                            worksource.add(record.mReceiver.mWorkSource);
                        } else {
                            // Assign blame to caller if there's no WorkSource associated with
                            // the request or if it's invalid.
                            worksource.add(
                                    record.mReceiver.mIdentity.mUid,
                                    record.mReceiver.mIdentity.mPackageName);
                        }
                    }
                }
            }
        }
    }
    if (D) Log.d(TAG, "provider request: " + provider + " " + providerRequest);
    // 最終調用Provider的setRequest方法，進入到Provider的內部流程
    p.setRequest(providerRequest, worksource);
}

總結

總結下LocationManagerService裏面初始化的流程

graph TD systemRunning --> loadProvidersLocked subgraph loadProvidersLockedProcess loadProvidersLocked --> loadPassiveProvider loadPassiveProvider --> loadGnssProvider loadGnssProvider --> checkFusedProvider checkFusedProvider --> bindNetworkProvider bindNetworkProvider --> bindGeocoderProvider bindGeocoderProvider --> bindGeofenceProvider bindGeofenceProvider --> bindHardwareActivityRecogneition bindHardwareActivityRecogneition --> updateProvidersLocked end subgraph updateProvidersLockedProcess updateProvidersLocked --> updateProviderListenersLocked updateProviderListenersLocked --> provider.enable provider.enable --> applyRequirementsLocked applyRequirementsLocked --> provider.setRequest end

備註： 上面代碼基於Android9 AOSP源碼