My Table
- 1. VehicleHAL启动流程
- 1.1. vehicleHal类图
- 1.1.1. types.hal/IVehicle.hal/IVehicleCallback.hal
- 1.1. vehicleHal类图
- 2. VehicleHal初始化流程
- 2.1. vehiclehal启动序列图
- 3. 车辆属性类型types.hal
- 3.1. 车辆属性VehiclePropertyType
- 3.2. 车辆区域类型VehicleArea
- 3.2.1. 车辆属性分组类型VehiclePropertyGroup
- 3.2.2. 车辆窗户区域属性VehicleAreaWindow
- 3.3. 车辆属性访问权限VehiclePropertyAccess
- 3.4. 车辆属性变化模式VehiclePropertyChangeMode
- 3.5. 车辆属性事件订阅信息SubscribeOptions
- 3.6. 车辆座椅属性VehicleAreaSeat
- 3.7. 接口调用状态值StatusCode
- 4. 回调接口函数IVehicleCallback
- 5. VehicleHal获取/设置属性流程
- 5.1. subscribe订阅属性
- 5.2. subscribe序列图
- 5.3. set设置属性请求流程
- 5.4. get获取属性请求流程
- 5.5. set和get属性流程序列图
- 6. DBus IPC通信方式
- 6.1. 应用场景
- 6.2. 通信实现原理
- 7. 参考
文档内容：1.vehicle HAL架构介绍、详细的启动流程；2.部分车辆属性类型名称说明；3.上层carservice和hal层数据subscribe/set/get流程梳理;4.dbus和vehicle hal连接交互的流程；4.从dbus回调数据返回至APP层的详细流程梳理（最终梳理方法流转调用的流程，绘制序列图）
1. VehicleHAL启动流程
- 源码位置：
hardware/interfaces/automotive/vehicle/2.0/
.rc文件android.hardware.automotive.vehicle@2.0-service.rc启动进程
该文件位于设备系统vendor/etc/init目录
//hardware/interfaces/automotive/vehicle/2.0/default/android.hardware.automotive.vehicle@2.0-service.rc
service vendor.vehicle-hal-2.0 /vendor/bin/hw/android.hardware.automotive.vehicle@2.0-service
class hal
user vehicle_network
group system inet- init进程加载启动
/vendor/etc/init目录下的脚本
static void LoadBootScripts(ActionManager& action_manager, ServiceList& service_list) {
Parser parser = CreateParser(action_manager, service_list);
std::string bootscript = GetProperty("ro.boot.init_rc", "");
if (bootscript.empty()) {
parser.ParseConfig("/init.rc");
if (!parser.ParseConfig("/system/etc/init")) {
late_import_paths.emplace_back("/system/etc/init");
}
if (!parser.ParseConfig("/product/etc/init")) {
late_import_paths.emplace_back("/product/etc/init");
}
if (!parser.ParseConfig("/odm/etc/init")) {
late_import_paths.emplace_back("/odm/etc/init");
}
if (!parser.ParseConfig("/vendor/etc/init")) {
late_import_paths.emplace_back("/vendor/etc/init");
}
} else {
parser.ParseConfig(bootscript);
}
}1.1. vehicleHal类图
1.1.1. types.hal/IVehicle.hal/IVehicleCallback.hal
均在
/hardware/interfaces/automotive/vehicle/2.0/目录下
- types.hal定义的是一些数据结构
- IVehicle.hal定义的是从CarService往HAL调用的接口
- IVehicleCallback.hal则是HAL往CarService上报回调的接口
2. VehicleHal初始化流程
初始化从执行hardware/interfaces/automotive/vehicle/2.0/default/VehicleService.cpp的main函数开始：
- 创建VehiclePropertyStore对象
- 创建EmulatedVehicleHal对象
- 创建VehicleEmulator对象
- 创建VehicleHalManager对象
int main(int /* argc */, char* /* argv */ []) {
//调用VehiclePropertyStore构造函数，构造一个对象
auto store = std::make_unique<VehiclePropertyStore>();
//调用EmulatedVehicleHal构造函数，入参VehiclePropertyStore
auto hal = std::make_unique<impl::EmulatedVehicleHal>(store.get());
//调用VehicleEmulator构造函数，入参EmulatedVehicleHal
auto emulator = std::make_unique<impl::VehicleEmulator>(hal.get());
//创建VehicleHalManager对象
auto service = std::make_unique<VehicleHalManager>(hal.get());
configureRpcThreadpool(4, true /* callerWillJoin */);//设置线程数
ALOGI("Registering as service...");
status_t status = service->registerAsService();
if (status != OK) {
ALOGE("Unable to register vehicle service (%d)", status);
return 1;
}
ALOGI("Ready");
joinRpcThreadpool();//将当前通信加入线程池进行循环
return 1;
}——> VehicleHalManager构造函数中调用init初始化：
- 重置HidlVecOfVehiclePropValuePool HIDL属性对象池大小
- 开启事件消费着队列
- VehicleHal初始化
VehicleHalManager(VehicleHal* vehicleHal)
: mHal(vehicleHal),
mSubscriptionManager(std::bind(&VehicleHalManager::onAllClientsUnsubscribed,
this, std::placeholders::_1)) {
init();
}
void VehicleHalManager::init() {
ALOGI("VehicleHalManager::init");
//1.重置HidlVecOfVehiclePropValuePool HIDL属性对象池大小为20
mHidlVecOfVehiclePropValuePool.resize(kMaxHidlVecOfVehiclPropValuePoolSize);
//2.开启事件消费着队列
mBatchingConsumer.run(&mEventQueue,
kHalEventBatchingTimeWindow,
std::bind(&VehicleHalManager::onBatchHalEvent,
this, _1));
//3.VehicleHal初始化
mHal->init(&mValueObjectPool,
std::bind(&VehicleHalManager::onHalEvent, this, _1),
std::bind(&VehicleHalManager::onHalPropertySetError, this,
_1, _2, _3));
// Initialize index with vehicle configurations received from VehicleHal.
//4.初始化从VehicleHal收到的vehicle属性的索引
auto supportedPropConfigs = mHal->listProperties();
mConfigIndex.reset(new VehiclePropConfigIndex(supportedPropConfigs));
std::vector<int32_t> supportedProperties(
supportedPropConfigs.size());
for (const auto& config : supportedPropConfigs) {
supportedProperties.push_back(config.prop);
}
}——> VehicleHal.h初始化做了以下操作： 1.初始化mValuePool 2.初始化mOnHalEvent 3.初始化mOnHalPropertySetError变量 4.调用onCreate
代码语言：javascript复制 void init(
VehiclePropValuePool* valueObjectPool,
const HalEventFunction& onHalEvent,
const HalErrorFunction& onHalError) {
mValuePool = valueObjectPool;
mOnHalEvent = onHalEvent;
mOnHalPropertySetError = onHalError;
onCreate();
}—–> 调用onCreate函数，遍历属性列表并以mPropStore，即VehiclePropertyStore保存当前值
2.1. vehiclehal启动序列图
3. 车辆属性类型types.hal
3.1. 车辆属性VehiclePropertyType
- 定义在hardware/interfaces/automotive/vehicle/2.0/types.hal（以下属性定义均在该文件内）
在上面的onCreate函数最后会调用initObd2LiveFrame和initObd2FreezeFrame —–> 调用VehicleUtils.cpp createVehiclePropValue(VehiclePropertyType::MIXED, 0)即车辆属性
std::unique_ptr<VehiclePropValue> createVehiclePropValue(
VehiclePropertyType type, size_t vecSize) {
auto val = std::unique_ptr<VehiclePropValue>(new VehiclePropValue);
switch (type) {
case VehiclePropertyType::INT32: // fall through
case VehiclePropertyType::INT32_VEC: // fall through
case VehiclePropertyType::BOOLEAN:
val->value.int32Values.resize(vecSize);
break;
case VehiclePropertyType::FLOAT: // fall through
case VehiclePropertyType::FLOAT_VEC:
val->value.floatValues.resize(vecSize);
break;
case VehiclePropertyType::INT64:
case VehiclePropertyType::INT64_VEC:
val->value.int64Values.resize(vecSize);
break;
case VehiclePropertyType::BYTES:
val->value.bytes.resize(vecSize);
break;
case VehiclePropertyType::STRING:
case VehiclePropertyType::MIXED:
break; // Valid, but nothing to do.
default:
ALOGE("createVehiclePropValue: unknown type: %d", type);
val.reset(nullptr);
}
return val;
}此处这些值在hardware/interfaces/automotive/vehicle/2.0/types.hal中十六进制定义：
代码语言：javascript复制enum VehiclePropertyType : int32_t {
STRING = 0x00100000,
BOOLEAN = 0x00200000,
INT32 = 0x00400000,
INT32_VEC = 0x00410000,
INT64 = 0x00500000,
INT64_VEC = 0x00510000,
FLOAT = 0x00600000,
FLOAT_VEC = 0x00610000,
BYTES = 0x00700000,
//混合类型组合
MIXED = 0x00e00000,
MASK = 0x00ff0000
};3.2. 车辆区域类型VehicleArea
定义在hardware/interfaces/automotive/vehicle/2.0/types.hal
代码语言：javascript复制enum VehicleArea : int32_t {
GLOBAL = 0x01000000, //全局
/** WINDOW maps to enum VehicleAreaWindow 窗户区域*/
WINDOW = 0x03000000,
/** MIRROR maps to enum VehicleAreaMirror 反光镜区域*/
MIRROR = 0x04000000,
/** SEAT maps to enum VehicleAreaSeat 座位区域*/
SEAT = 0x05000000,
/** DOOR maps to enum VehicleAreaDoor 车门区域*/
DOOR = 0x06000000,
/** WHEEL maps to enum VehicleAreaWheel 车轮区域*/
WHEEL = 0x07000000,
MASK = 0x0f000000,
};3.2.1. 车辆属性分组类型VehiclePropertyGroup
- 定义在hardware/interfaces/automotive/vehicle/2.0/types.hal
enum VehiclePropertyGroup : int32_t {
//hardware/interfaces/automotive/vehicle/2.0/types.hal
SYSTEM = 0x10000000,
//vendor 可定制修改
VENDOR = 0x20000000,
MASK = 0xf0000000,
};3.2.2. 车辆窗户区域属性VehicleAreaWindow
代码语言：javascript复制/**
* Various windshields/windows in the car.
*/
enum VehicleAreaWindow : int32_t {
FRONT_WINDSHIELD = 0x00000001,
REAR_WINDSHIELD = 0x00000002,
ROW_1_LEFT = 0x00000010,
ROW_1_RIGHT = 0x00000040,
ROW_2_LEFT = 0x00000100,
ROW_2_RIGHT = 0x00000400,
ROW_3_LEFT = 0x00001000,
ROW_3_RIGHT = 0x00004000,
ROOF_TOP_1 = 0x00010000,
ROOF_TOP_2 = 0x00020000,
};3.3. 车辆属性访问权限VehiclePropertyAccess
- 定义在hardware/interfaces/automotive/vehicle/2.0/types.hal
enum VehiclePropertyAccess : int32_t {
NONE = 0x00,
READ = 0x01,
WRITE = 0x02,
READ_WRITE = 0x03,
};3.4. 车辆属性变化模式VehiclePropertyChangeMode
- 定义在hardware/interfaces/automotive/vehicle/2.0/types.hal
enum VehiclePropertyChangeMode : int32_t {
//静态属性，不支持subscribe订阅，只能get获取
STATIC = 0x00,
//ONCHANGE这个类型的属性当变化时必须上报
//调用get接口获取当前值;
//set接口是异步的，当属性读取（调用get接口）在属性设置(调用set接口)之后，也有可能获取到的是旧值，除非从硬件反馈属性的确发送变化
//我们大多数属性都是这个类型
ON_CHANGE = 0x01,
//CONTINUOUS类型的属性会不断的周期性的发送变化。比如速度和方向盘角度等，需要设置采样率范围
CONTINUOUS = 0x02,
};3.5. 车辆属性事件订阅信息SubscribeOptions
代码语言：javascript复制struct SubscribeOptions {
/** Property to subscribe */
//订阅的属性的Id
int32_t propId;
//以Hz为单位的采样率
//必须为具有VehiclePropertyChangeMode::CONTINUOUS的属性提供
//值必须包含在VehiclePropConfig#minSamplingRate .. VehiclePropConfig#maxSamplingRate给定的范围内
//该值标志每秒客户端想要接受多少更新
float sampleRate;
/** 指定监听哪个事件的标志 */
SubscribeFlags flags;
};
enum SubscribeFlags : int32_t {
UNDEFINED = 0x0,
//订阅来自vehicle hal的属性，极有可能来自于车辆本身
EVENTS_FROM_CAR = 0x1,
//当被vehicle hal的client客户端（即car service）调用set时使用该标志订阅事件
EVENTS_FROM_ANDROID = 0x2,
};3.6. 车辆座椅属性VehicleAreaSeat
代码语言：javascript复制/**
* Various Seats in the car.
*/
enum VehicleAreaSeat : int32_t {
ROW_1_LEFT = 0x0001,
ROW_1_CENTER = 0x0002,
ROW_1_RIGHT = 0x0004,
ROW_2_LEFT = 0x0010,
ROW_2_CENTER = 0x0020,
ROW_2_RIGHT = 0x0040,
ROW_3_LEFT = 0x0100,
ROW_3_CENTER = 0x0200,
ROW_3_RIGHT = 0x0400
};3.7. 接口调用状态值StatusCode
代码语言：javascript复制enum StatusCode : int32_t {
OK = 0,
/** Try again. */
TRY_AGAIN = 1,
/** Invalid argument provided. */
INVALID_ARG = 2,
/**
* This code must be returned when device that associated with the vehicle
* property is not available. For example, when client tries to set HVAC
* temperature when the whole HVAC unit is turned OFF.
*/
NOT_AVAILABLE = 3,
/** Access denied */
ACCESS_DENIED = 4,
/** Something unexpected has happened in Vehicle HAL */
//vehicle hal内部错误
INTERNAL_ERROR = 5,
};4. 回调接口函数IVehicleCallback
- 定义于：hardware/interfaces/automotive/vehicle/2.0/IVehicleCallback.hal
interface IVehicleCallback {
/**
* @param values that has been updated.入参时已经更新的value值
*/
//每当一个API使用者已经订阅的变量需要去report报告的时候，事件回调就会发生
//这可能基于阙值和频率（一个规律性的订阅，看订阅调用的参数）或者set函数被调用并且实际的变化需要report报告
//这个回调和属性的零界值或更新频率有关
oneway onPropertyEvent(vec<VehiclePropValue> propValues);
/**
* @param value Value that was set by a client.被上层客户端设置的value的值
*/
//如果客户端已经订阅了一个SubscribeFlags::EVENTS_FROM_ANDROID标志的属性，并且调用了set方法，该函数会被触发回调
//这些事件必须没有任何batching批处理，就立刻传递给订阅者
//当客户端订阅属性时使用SubscribeFlags::SET_CALL标志，并且当IVehicle的set接口被调用时就会回调这个接口
oneway onPropertySet(VehiclePropValue propValue);
/**
* @param errorCode - any value from StatusCode enum.来自状态码枚举中的任何值
* @param property - a property where error has happened.
* @param areaId - bitmask that specifies in which areas the problem has
* occurred, must be 0 for global properties
*/
//set属性通常是异步操作
//因此即使客户端从set接口函数接收到StatusCode::OK的状态码，这并不能保证value被成功传递到车载网络
//如果发生这种小概率事件，该函数会被调用
oneway onPropertySetError(StatusCode errorCode,
int32_t propId,
int32_t areaId);
};5. VehicleHal获取/设置属性流程
5.1. subscribe订阅属性
CarService在onCreate中创建ICarImpl时，构造函数中new VehicleHal对象，然后又在CarImpl的init函数中调用VehicleHal对象的init函数
packages/services/Car/service/src/com/android/car/hal/VehicleHal.java - 构造函数new各个HalService（继承于PropertyHalServiceBase->基类HalServiceBase），并且new HalClient客户端对象
—-> init函数执行mHalClient.getAllPropConfigs()从Vehicle HAL(IVehicle.hal)获取所有的属性，调用到VehicleHalManager.cpp的该函数
—-> 遍历HALService执行service.takeSupportedProperties获取CarService支持的属性
—–> 在该遍历代码块最后执行service.init()初始化各个HALService
—–> 例如PowerHalService.java - PowerHalService执行init，调用mHal.subscribeProperty
—–> 调用VehicleHal.java的subscribeProperty，然后调用mHalClient.subscribe(opts)
—–> 调用HalClient.java的subscribe，调用mVehicle.subscribe(...)
——> 调用hardware/interfaces/automotive/vehicle/2.0/IVehicle.hal的subscribe
——> 调用hardware/interfaces/automotive/vehicle/2.0/default/common/src/VehicleHalManager.cpp的subscribe
(1) ——-> SubscriptionManager.cpp - addOrUpdateSubscription (2) ——> subscribe，返回statusCode结果状态码
—–> isContinuousProperty 改变VehiclePropConfig的changemode为CONTINUOUS（即不断的周期性的发送变化）
代码语言：javascript复制//hardware/interfaces/automotive/vehicle/2.0/default/impl/vhal_v2_0/VehicleEmulator.h
class EmulatedVehicleHalIface : public VehicleHal{.....}
//hardware/interfaces/automotive/vehicle/2.0/default/impl/vhal_v2_0/EmulatedVehicleHal.h
class EmulatedVehicleHal : public EmulatedVehicleHalIface{....}
//hardware/interfaces/automotive/vehicle/2.0/default/impl/vhal_v2_0/EmulatedVehicleHal.cpp
....此时所有属性都subscribe，CarService就可以所有接收到Vehicle HAL发上来的所有属性变化
同理，unsubscribe注销订阅
5.2. subscribe序列图
5.3. set设置属性请求流程
例如空调APP的设置开关状态：packages/apps/Car/Hvac/src/com/android/car/hvac/HvacController.java - setHvacPowerState
—–> packages/services/Car/car-lib/src/android/car/hardware/hvac/CarHvacManager.java - setBooleanProperty
—–> packages/services/Car/car-lib/src/android/car/hardware/property/CarPropertyManager.java(大部分会使用该manager) - setBooleanProperty
——> setProperty(将propId,area,value三个参数组成CarPropertyValue参数并设置到CarPropertyServiceBase端)
——> packages/services/Car/car-lib/src/android/car/hardware/property/ICarProperty.aidl - setProperty[AIDL通信]
—–> packages/services/Car/service/src/com/android/car/CarPropertyService.java - setProperty
代码语言：javascript复制public class CarPropertyService extends ICarProperty.Stub
implements CarServiceBase, PropertyHalServiceBase.PropertyHalListener {
......
private final PropertyHalServiceBase mHal;
@Override
public void setProperty(CarPropertyValue prop) {
ICarImpl.assertPermission(mContext, mPermission);
mHal.setProperty(prop);
}—–> ./hal/PropertyHalServiceBase.java - setProperty
代码语言：javascript复制 public void setProperty(CarPropertyValue prop) {
//获取到halPropId，这个halPropId是Vehiclehal定义生成的
int halPropId = managerToHalPropId(prop.getPropertyId());
//将CarPropertyValue参数转换成VehiclePropValue
VehiclePropValue halProp = toVehiclePropValue(prop, halPropId);
try {
mVehicleHal.set(halProp);
} catch (PropertyTimeoutException e) {
Log.e(CarLog.TAG_PROPERTY, "set, property not ready 0x" toHexString(halPropId), e);
throw new RuntimeException(e);
}
}——> ./hal/VehicleHal.java - set()
——> ./hal/HalClient.java - setValued调用mVehicle.set(propValue)
——> hardware/interfaces/automotive/vehicle/2.0/IVehicle.hal - set(VehiclePropValue propValue)…
——> hardware/interfaces/automotive/vehicle/2.0/default/common/src/VehicleHalManager.cpp - set设置属性
(1) 回调流程： —-> handlePropertySetEvent调用SubscriptionManager.cpp的getSubscribedClients返回订阅的HalClient对象list列表 —-> handlePropertySetEvent最后会遍历HALClient列表，然后回调client->getCallback()->onPropertySet(value); —-> HalClient.java - class VehicleCallback extends IVehicleCallback.Stub从而调用onPropertySet的sendMessage，然后handlemessage处理消息
(2) —-> EmulatedVehicleHal.cpp - set函数(和get相同)，此处会返回statusCode设置结果的状态码
—–> SendMsgtoVehicle(msg)
5.4. get获取属性请求流程
packages/services/Car/car-lib/src/android/car/hardware/CarVendorExtensionManager.java - getProperty
—–> CarPropertyManagerBase.java - getProperty
—–> ICarProperty.aidl - getProperty[AIDL通信]
—–> packages/services/Car/service/src/com/android/car/CarPropertyServiceBase.java - getProperty
代码语言：javascript复制public class CarPropertyServiceBase extends ICarProperty.Stub
implements CarServiceBase, PropertyHalServiceBase.PropertyHalListener {
......
private final PropertyHalServiceBase mHal;
@Override
public CarPropertyValue getProperty(int prop, int zone) {
ICarImpl.assertPermission(mContext, mPermission);
return mHal.getProperty(prop, zone);
}—–> ./hal/PropertyHalServiceBase.java - setProperty
代码语言：javascript复制 public CarPropertyValue getProperty(int mgrPropId, int areaId) {
int halPropId = managerToHalPropId(mgrPropId);
VehiclePropValue value = null;
try {
value = mVehicleHal.get(halPropId, areaId);
} catch (PropertyTimeoutException e) {
Log.e(CarLog.TAG_PROPERTY, "get, property not ready 0x" toHexString(halPropId), e);
}
return value == null ? null : toCarPropertyValue(value, mgrPropId);
}——> ./hal/VehicleHal.java - get()设置VehiclePropValue对象，并初始化参数
代码语言：javascript复制 public VehiclePropValue get(int propertyId, int areaId) throws PropertyTimeoutException {
VehiclePropValue propValue = new VehiclePropValue();
propValue.prop = propertyId;
propValue.areaId = areaId;
return mHalClient.getValue(propValue);
}——> ./hal/HalClient.java - getValue调用mVehicle.get...
——> hardware/interfaces/automotive/vehicle/2.0/IVehicle.hal - get(VehiclePropValue requestedPropValue)…
——> hardware/interfaces/automotive/vehicle/2.0/default/common/src/VehicleHalManager.cpp - get属性
——-> hardware/interfaces/automotive/vehicle/2.0/default/impl/vhal_v2_0/EmulatedVehicleHal.cpp - get函数
代码语言：javascript复制//hardware/interfaces/automotive/vehicle/2.0/default/impl/vhal_v2_0/VehicleEmulator.h
class EmulatedVehicleHalIface : public VehicleHal{.....}
//hardware/interfaces/automotive/vehicle/2.0/default/impl/vhal_v2_0/EmulatedVehicleHal.h
class EmulatedVehicleHal : public EmulatedVehicleHalIface{....}
//hardware/interfaces/automotive/vehicle/2.0/default/impl/vhal_v2_0/EmulatedVehicleHal.cpp
VehicleHal::VehiclePropValuePtr EmulatedVehicleHal::get(
const VehiclePropValue& requestedPropValue, StatusCode* outStatus) {
auto propId = requestedPropValue.prop;
auto& pool = *getValuePool();
VehiclePropValuePtr v = nullptr;
switch (propId) {
case OBD2_FREEZE_FRAME:
v = pool.obtainComplex();
*outStatus = fillObd2FreezeFrame(requestedPropValue, v.get());
break;
case OBD2_FREEZE_FRAME_INFO:
v = pool.obtainComplex();
*outStatus = fillObd2DtcInfo(v.get());
break;
default:
auto internalPropValue = mPropStore->readValueOrNull(requestedPropValue);
if (internalPropValue != nullptr) {
v = getValuePool()->obtain(*internalPropValue);
}
*outStatus = v != nullptr ? StatusCode::OK : StatusCode::INVALID_ARG;
break;
}
return v;
}—–> VehiclePropertyStore.cpp - readValueOrNull
—–> getRecordIdLocked 根据入参VehiclePropValue获取RecordId，关于VehiclePropValue对象可查看上层VehicleHal.java的get函数的流程
——> 调用getValueOrNullLocked，根据RecordId从VehiclePropertyStore中读取
代码语言：javascript复制//VehiclePropertyStore.cpp
VehiclePropertyStore::RecordId VehiclePropertyStore::getRecordIdLocked(
const VehiclePropValue& valuePrototype) const {
RecordId recId = {
.prop = valuePrototype.prop,
.area = isGlobalProp(valuePrototype.prop) ? 0 : valuePrototype.areaId,
.token = 0
};
auto it = mConfigs.find(recId.prop);
if (it == mConfigs.end()) return {};
if (it->second.tokenFunction != nullptr) {
recId.token = it->second.tokenFunction(valuePrototype);
}
return recId;
}
const VehiclePropValue* VehiclePropertyStore::getValueOrNullLocked(
const VehiclePropertyStore::RecordId& recId) const {
auto it = mPropertyValues.find(recId);
return it == mPropertyValues.end() ? nullptr : &it->second;
}
//VehiclePropertyStore.h
class VehiclePropertyStore {
...
struct RecordId {
int32_t prop;
int32_t area;
int64_t token;
bool operator==(const RecordId& other) const;
bool operator<(const RecordId& other) const;
};
using PropertyMap = std::map<RecordId, VehiclePropValue>;
.....
PropertyMap mPropertyValues;
}5.5. set和get属性流程序列图
6. DBus IPC通信方式
- DBus是一种低延迟、低开销、高可用性的IPC（interprocess communication ）机制总线系统，用于进程间的通信（会话总线）或进程与内核的通信（系统总线）
6.1. 应用场景
根据DBUS消息类型可知，DBUS提供一种高效的进程间通信机制，主要用于进程间函数调用以及进程间信号广播。
- 函数调用：DBUS可以实现进程间函数调用，进程A发送函数调用的请求（Methodcall消息），经过总线转发至进程B。进程B将应答函数返回值（Method return消息）或者错误消息（Error消息）
- 消息广播：进程间消息广播（Signal消息）不需要响应，接收方需要向总线注册感兴趣的消息类型，当总线接收到“Signal消息”类型的消息时，会将消息转发至希望接收的进程
6.2. 通信实现原理
在DBUS通信过程中，存在一个后台进程（BUS Daemon Process）。后台进程和普通进程间信息交互是通过域套接字进行通信
7. 参考
- Item 21: 比起直接使用new优先使用std::make_unique和std::make_shared
