Android GPS 定位流程

Android P 代码：http://androidxref.com/9.0.0_r3/

上一篇幅我们梳理了位置开关打开的一个流程，这里我们梳理下请求Gps定位的一个流程

这里我们假设一个app发起Gps定位，首先调用 LocationManager 接口，通过AIDL最终调用到 LocationManagerService 里面的  requestLocationUpdates 方法：

http://androidxref.com/9.0.0_r3/xref/frameworks/base/location/java/android/location/LocationManager.java#requestLocationUpdates

    @RequiresPermission(anyOf = {ACCESS_COARSE_LOCATION, ACCESS_FINE_LOCATION})
    public void requestLocationUpdates(String provider, long minTime, float minDistance,
            LocationListener listener) {
        checkProvider(provider);
        checkListener(listener);

        LocationRequest request = LocationRequest.createFromDeprecatedProvider(  ---> 封装成LocationRequest，作为参数传下去
                provider, minTime, minDistance, false);
        requestLocationUpdates(request, listener, null, null);
    }

http://androidxref.com/9.0.0_r3/xref/frameworks/base/services/core/java/com/android/server/LocationManagerService.java#requestLocationUpdates

    public void requestLocationUpdates(LocationRequest request, ILocationListener listener,
            PendingIntent intent, String packageName) {
        if (request == null) request = DEFAULT_LOCATION_REQUEST;
        checkPackageName(packageName);
        int allowedResolutionLevel = getCallerAllowedResolutionLevel();   ---> 这里指的就是 fine、coarse、no location data 三种
        checkResolutionLevelIsSufficientForProviderUse(allowedResolutionLevel,
                request.getProvider());
        WorkSource workSource = request.getWorkSource();
        if (workSource != null && !workSource.isEmpty()) {
            checkDeviceStatsAllowed();
        }
        boolean hideFromAppOps = request.getHideFromAppOps();
        if (hideFromAppOps) {
            checkUpdateAppOpsAllowed();
        }
        boolean callerHasLocationHardwarePermission =
                mContext.checkCallingPermission(android.Manifest.permission.LOCATION_HARDWARE)
                        == PERMISSION_GRANTED;
        LocationRequest sanitizedRequest = createSanitizedRequest(request, allowedResolutionLevel,
                callerHasLocationHardwarePermission);

        final int pid = Binder.getCallingPid();
        final int uid = Binder.getCallingUid();
        // providers may use public location API's, need to clear identity
        long identity = Binder.clearCallingIdentity();
        try {
            // We don't check for MODE_IGNORED here; we will do that when we go to deliver
            // a location.
            checkLocationAccess(pid, uid, packageName, allowedResolutionLevel);

            synchronized (mLock) {
                Receiver recevier = checkListenerOrIntentLocked(listener, intent, pid, uid,
                        packageName, workSource, hideFromAppOps);
                requestLocationUpdatesLocked(sanitizedRequest, recevier, pid, uid, packageName);  ---> 继续看下这个
            }
        } finally {
            Binder.restoreCallingIdentity(identity);
        }
    }

    private void requestLocationUpdatesLocked(LocationRequest request, Receiver receiver,
            int pid, int uid, String packageName) {
        // Figure out the provider. Either its explicitly request (legacy use cases), or
        // use the fused provider
        if (request == null) request = DEFAULT_LOCATION_REQUEST;
        String name = request.getProvider();   ---> 获取此时的provide，下面就是根据这个provide决定走GPS还是走network，所以不能为空
        if (name == null) {
            throw new IllegalArgumentException("provider name must not be null");
        }

        LocationProviderInterface provider = mProvidersByName.get(name);
        if (provider == null) {
            throw new IllegalArgumentException("provider doesn't exist: " + name);
        }

        UpdateRecord record = new UpdateRecord(name, request, receiver);
        if (D) {
            Log.d(TAG, "request " + Integer.toHexString(System.identityHashCode(receiver))
                    + " " + name + " " + request + " from " + packageName + "(" + uid + " "
                    + (record.mIsForegroundUid ? "foreground" : "background")
                    + (isThrottlingExemptLocked(receiver.mIdentity)
                    ? " [whitelisted]" : "") + ")");
        }   ---> 通过这个log就可以知道那个发起请求，请求的是gps还是network，是否是前台等

        UpdateRecord oldRecord = receiver.mUpdateRecords.put(name, record);
        if (oldRecord != null) {
            oldRecord.disposeLocked(false);
        }

        boolean isProviderEnabled = isAllowedByUserSettingsLocked(name, uid, mCurrentUserId);
        if (isProviderEnabled) {   ---> 允许才继续执行
            applyRequirementsLocked(name);
        } else {
            // Notify the listener that updates are currently disabled
            receiver.callProviderEnabledLocked(name, false);
        }
        // Update the monitoring here just in case multiple location requests were added to the
        // same receiver (this request may be high power and the initial might not have been).
        receiver.updateMonitoring(true);
    }

    private void applyRequirementsLocked(String provider) {
        LocationProviderInterface p = mProvidersByName.get(provider);
        if (p == null) return;   ---> 再次确认

        ArrayList<UpdateRecord> records = mRecordsByProvider.get(provider);
        WorkSource worksource = new WorkSource();
        ProviderRequest providerRequest = new ProviderRequest();

        ContentResolver resolver = mContext.getContentResolver();
        long backgroundThrottleInterval = Settings.Global.getLong(  ---> 后台默认30min
                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();
                           //系统和白名单的应用不受后台刷新时间的限制
                        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);
        p.setRequest(providerRequest, worksource);  ---> 这里就是调用对应的 provide 的，因为是请求Gps_provider
    }

http://androidxref.com/9.0.0_r3/xref/frameworks/base/services/core/java/com/android/server/location/GnssLocationProvider.java#setRequest

    @Override
    public void setRequest(ProviderRequest request, WorkSource source) {
        sendMessage(SET_REQUEST, 0, new GpsRequest(request, source));
    }

handlemessage 处理这个消息： 

                case SET_REQUEST:
                    GpsRequest gpsRequest = (GpsRequest) msg.obj;
                    handleSetRequest(gpsRequest.request, gpsRequest.source);
                    break;

    private void handleSetRequest(ProviderRequest request, WorkSource source) {
        mProviderRequest = request;
        mWorkSource = source;
        updateRequirements();
    }

    // Called when the requirements for GPS may have changed
    private void updateRequirements() {
        if (mProviderRequest == null || mWorkSource == null) {
            return;
        }

        boolean singleShot = false;

        // see if the request is for a single update
        if (mProviderRequest.locationRequests != null
                && mProviderRequest.locationRequests.size() > 0) {
            // if any request has zero or more than one updates
            // requested, then this is not single-shot mode
            singleShot = true;

            for (LocationRequest lr : mProviderRequest.locationRequests) {
                if (lr.getNumUpdates() != 1) {
                    singleShot = false;
                }
            }
        }

        if (DEBUG) Log.d(TAG, "setRequest " + mProviderRequest);
        if (mProviderRequest.reportLocation && !mDisableGps && isEnabled()) {
            // update client uids
            updateClientUids(mWorkSource);

            mFixInterval = (int) mProviderRequest.interval;
            mLowPowerMode = (boolean) mProviderRequest.lowPowerMode;
            // check for overflow
            if (mFixInterval != mProviderRequest.interval) {
                Log.w(TAG, "interval overflow: " + mProviderRequest.interval);
                mFixInterval = Integer.MAX_VALUE;
            }

            // apply request to GPS engine
            if (mStarted && hasCapability(GPS_CAPABILITY_SCHEDULING)) {  ---> 这个能力表示Gps是否可以连续定位（周期性的更新位置）
                // change period and/or lowPowerMode
                if (!native_set_position_mode(mPositionMode, GPS_POSITION_RECURRENCE_PERIODIC,
                        mFixInterval, 0, 0, mLowPowerMode)) { 
                    Log.e(TAG, "set_position_mode failed in updateRequirements");
                }
            } else if (!mStarted) {  ---> 之前没有启动过，现在启动
                // start GPS
                startNavigating(singleShot);
            } else {
                // GNSS Engine is already ON, but no GPS_CAPABILITY_SCHEDULING
                mAlarmManager.cancel(mTimeoutIntent);
                if (mFixInterval >= NO_FIX_TIMEOUT) {
                    // set timer to give up if we do not receive a fix within NO_FIX_TIMEOUT
                    // and our fix interval is not short
                    mAlarmManager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP,
                            SystemClock.elapsedRealtime() + NO_FIX_TIMEOUT, mTimeoutIntent);                }
            }
        } else {
            updateClientUids(new WorkSource());

            stopNavigating();
            mAlarmManager.cancel(mWakeupIntent);
            mAlarmManager.cancel(mTimeoutIntent);
        }
    }

    private void startNavigating(boolean singleShot) {
        if (!mStarted) {
            if (DEBUG) Log.d(TAG, "startNavigating, singleShot is " + singleShot);
            mTimeToFirstFix = 0;
            mLastFixTime = 0;
            mStarted = true;
            mSingleShot = singleShot;
            mPositionMode = GPS_POSITION_MODE_STANDALONE;
            // Notify about suppressed output, if speed limit was previously exceeded.
            // Elsewhere, we check again with every speed output reported.
            if (mItarSpeedLimitExceeded) {
                Log.i(TAG, "startNavigating with ITAR limit in place. Output limited  " +
                        "until slow enough speed reported.");
            }

            boolean agpsEnabled =
                    (Settings.Global.getInt(mContext.getContentResolver(),
                            Settings.Global.ASSISTED_GPS_ENABLED, 1) != 0);
            mPositionMode = getSuplMode(mProperties, agpsEnabled, singleShot);

            if (DEBUG) {
                String mode;

                switch (mPositionMode) {   ---> GPS 几种工作模式
                    case GPS_POSITION_MODE_STANDALONE:
                        mode = "standalone";
                        break;
                    case GPS_POSITION_MODE_MS_ASSISTED:
                        mode = "MS_ASSISTED";
                        break;
                    case GPS_POSITION_MODE_MS_BASED:
                        mode = "MS_BASED";
                        break;
                    default:
                        mode = "unknown";
                        break;
                }
                Log.d(TAG, "setting position_mode to " + mode);
            }
            //这里最短时间一般就是1s上报GPS位置，如果低于1s，底层会去判断
            int interval = (hasCapability(GPS_CAPABILITY_SCHEDULING) ? mFixInterval : 1000);
            mLowPowerMode = (boolean) mProviderRequest.lowPowerMode;
            if (!native_set_position_mode(mPositionMode, GPS_POSITION_RECURRENCE_PERIODIC,
                    interval, 0, 0, mLowPowerMode)) {
                mStarted = false;
                Log.e(TAG, "set_position_mode failed in startNavigating()");
                return;
            }
            if (!native_start()) {  ---> 通过JNI往底层
                mStarted = false;
                Log.e(TAG, "native_start failed in startNavigating()");
                return;
            }

            // reset SV count to zero
            updateStatus(LocationProvider.TEMPORARILY_UNAVAILABLE);
            mLocationExtras.reset();
            mFixRequestTime = SystemClock.elapsedRealtime();
            if (!hasCapability(GPS_CAPABILITY_SCHEDULING)) {
                // set timer to give up if we do not receive a fix within NO_FIX_TIMEOUT
                // and our fix interval is not short
http://androidxref.com/9.0.0_r3/xref/frameworks/base/services/core/jni/com_android_server_location_GnssLocationProvider.cpp#native_start1546                if (mFixInterval >= NO_FIX_TIMEOUT) {
                    mAlarmManager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP,
                            SystemClock.elapsedRealtime() + NO_FIX_TIMEOUT, mTimeoutIntent);
                }
            }
        }
    }

http://androidxref.com/9.0.0_r3/xref/frameworks/base/services/core/jni/com_android_server_location_GnssLocationProvider.cpp#native_start

static jboolean android_location_GnssLocationProvider_start(JNIEnv* /* env */, jobject /* obj */) {
    if (gnssHal != nullptr) {
        auto result = gnssHal->start(); ---> 因为涉及到各平台，代码无法展示，大家可以跟着流程看下Vendor仓库
        if (!result.isOk()) {
            return JNI_FALSE;
        } else {
            return result;
        }
    } else {
        return JNI_FALSE;
    }
}

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