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1 概述

最近正好在做关机充电这个，就详细看看吧。还是本着保密的原则，项目里的代码也不能直接用，这里就用的Github的。https://github.com/aosp-mirror

具体位置是：https://github.com/aosp-mirror/platform_system_core/tree/main/healthd

核心代码压缩包只有3M，比起AOSP整包的极度臃肿真是对比强烈。 

2 代码框架

首先还是看BP，编译的产物是charger，但是在新版AOSP中服务却不是这个名字。新的是android.hardware.health-service.qti，此外后面带一个--charger的参数。

cc_binary {name: "charger",defaults: ["charger_defaults"],recovery_available: true,srcs: ["charger.cpp","charger_utils.cpp",],shared_libs: ["android.hardware.health@2.0","android.hardware.health@2.1",],target: {recovery: {// No UI and libsuspend for recovery charger.cflags: ["-DCHARGER_FORCE_NO_UI=1",],exclude_shared_libs: ["libpng",],exclude_static_libs: ["libhealthd_draw","libhealthd_charger","libhealthd_charger_ui","libminui","libsuspend",],}}
}

 模块里面有个测试程序，可以看看整个模块的用法。

int main(int /*argc*/, char** /*argv*/) {const char* dumpFile = "/data/local/tmp/dump.txt";auto config = std::make_unique<healthd_config>();InitHealthdConfig(config.get());healthd_board_init(config.get());sp<IHealth> passthrough = new TestHealth(std::move(config));std::thread bgThread([=] {android::ChargerHidl charger(passthrough);charger.StartLoop();});// wait for healthd_init to finishif (!getUpdateNotifier().waitFor(1000 /* wait ms */, true /* updated */)) {LOG_THIS("Time out.");exit(1);}passthrough->debug(createHidlHandle(dumpFile), {} /* options */);std::string content = openToString(dumpFile);int status = expectContains(content, {"status: 4","health: 6","present: 1","level: 47","voltage: 45","temp: 987","current now: 99000","current avg: 98000","charge counter: 600","current now: 99","cycle count: 77","Full charge: 3515547"});if (status == 0) {LOG_THIS("Test success.");} else {LOG_THIS("Actual dump:\n%s", content.c_str());}exit(status);  // force bgThread to exit
}

可以看到，就是

android::ChargerHidl charger(passthrough);

charger.StartLoop();

在Android的HIDL（HAL Interface Definition Language）框架中，StartLoop是一个用于启动HIDL服务端线程循环的方法。它允许HIDL服务端在一个独立的线程中运行，以便可以接收和处理来自客户端的请求。具体来说，StartLoop方法会创建一个线程池，并在这个线程池中运行，使得服务端可以异步处理多个客户端请求

3 重点流程

整个其实是一个提供Hidl接口的服务。提供的接口如下：

AIDL implementation	HIDL implementation
Health::getChargeCounterUah	Health::getChargeCounter
Health::getCurrentNowMicroamps	Health::getCurrentNow
Health::getCurrentAverageMicroamps	Health::getCurrentAverage
Health::getCapacity	Health::getCapacity
Health::getChargeStatus	Health::getChargeStatus
Health::getEnergyCounterNwh	Health::getEnergyCounter
Health::getDiskStats	Health::getDiskStats
Health::getStorageInfo	Health::getStorageInfo
Health::BinderEvent	BinderHealth::BinderEvent
Health::dump	Health::debug
Health::ShouldKeepScreenOn	Health::shouldKeepScreenOn
Health::UpdateHealthInfo	Health::UpdateHealthInfo

类的定义如下：

namespace android {// An implementation of Charger backed by HIDL implementation. Uses HIDL health
// HAL's HalHealthLoop.
class ChargerHidl : public ::android::ChargerConfigurationInterface,public ::android::hardware::health::V2_1::implementation::HalHealthLoop {using HalHealthLoop = ::android::hardware::health::V2_1::implementation::HalHealthLoop;using HealthInfo_2_1 = android::hardware::health::V2_1::HealthInfo;public:explicit ChargerHidl(const sp<android::hardware::health::V2_1::IHealth>& service);std::optional<bool> ChargerShouldKeepScreenOn() override;bool ChargerIsOnline() override { return HalHealthLoop::charger_online(); }void ChargerInitConfig(healthd_config* config) override { return HalHealthLoop::Init(config); }int ChargerRegisterEvent(int fd, BoundFunction func, EventWakeup wakeup) override {return HalHealthLoop::RegisterEvent(fd, func, wakeup);}bool ChargerEnableSuspend() override;// HealthLoop overridesvoid Heartbeat() override { charger_->OnHeartbeat(); }int PrepareToWait() override { return charger_->OnPrepareToWait(); }void Init(struct healthd_config* config) override { charger_->OnInit(config); }// HalHealthLoop overridesvoid OnHealthInfoChanged(const HealthInfo_2_1& health_info) override;private:sp<android::hardware::health::V2_1::IHealth> service_;std::unique_ptr<Charger> charger_;
};

这里面有个私有变量是std::unique_ptr<Charger> charger_;，在init的时候会同时初始化charger类。ChargerHidl类很多实现还是直接调用的Charger类方法。主要的定义还是在Charger类中。

这部分主要的功能也是在Charger::OnInit里面启动的。这里有一个epoll。之前写过这部分，可以参考：小试epoll-CSDN博客

不过charger好像不是epoll，里面有一个Charger::OnHeartbeat()，在每次的心跳中处理状态和事件。包括插拔充电器和按下电源键。

大概就是这些吧，只是粗略的过了一遍，看的也不是太仔细。。。

4 题外话

对了， 从代码中可以看出，对于C++的高级应用还是很熟的。这点挺厉害的。

template <typename T>
class Atomic {public:Atomic(T&& init) : mValue(std::move(init)) {}void set(T&& newVal) {{std::lock_guard<std::mutex> lock(mMutex);mValue = std::move(newVal);}mChanged.notify_all();}bool waitFor(long ms, const T& expectVal) {std::unique_lock<std::mutex> lock(mMutex);return mChanged.wait_for(lock, std::chrono::milliseconds(ms),[this, &expectVal] { return mValue == expectVal; });}private:std::mutex mMutex;std::condition_variable mChanged;T mValue;
};Atomic<bool>& getUpdateNotifier() {static Atomic<bool> val(false);return val;
}

5 参考

https://source.android.com/docs/core/perf/health?hl=zh-cn