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Android 12(S) 图形显示系统 - SurfaceFlinger的启动和消息队列处理机制(四)

作者:互联网

1 前言

SurfaceFlinger作为Android图形显示系统处理逻辑的核心单元,我们有必要去了解其是如何启动,初始化及进行消息处理的。这篇文章我们就来简单分析SurfaceFlinger这个Binder系统服务的一些基本处理逻辑。接下来分两部分讲解:

>> SurfaceFlinger启动与初始化

>> SurfaceFlinger消息队列处理机制


Tips:

本篇涉及的代码位置:

/frameworks/native/services/surfaceflinger/


2 SurfaceFlinger的启动与初始化

SurfaceFlinger是一个Binder系统服务,Android设备开机启动时就会带起SurfaceFlinger服务进程并完成一些初始化动作。

从Android S开始,SurfaceFlinger被编译为一个可执行二进制档案:surfaceflinger(放置于设备/system/bin/下)。

 

可执行档surfaceflinger的makefile

如下这段代码中,可以看到这个可执行档与surfaceflinger.rc这个init rc档相关联,这样开机启动时,init进程就可以解析这个rc档,带起SurfaceFlinger服务进程


cc_binary {
    name: "surfaceflinger",
    defaults: ["libsurfaceflinger_binary"],
    init_rc: ["surfaceflinger.rc"],
    srcs: [
        ":surfaceflinger_binary_sources",
        // Note: SurfaceFlingerFactory is not in the filegroup so that it
        // can be easily replaced.
        "SurfaceFlingerFactory.cpp",
    ],
    shared_libs: [
        "libSurfaceFlingerProp",
    ],

     logtags: ["EventLog/EventLogTags.logtags"],
}

再来瞅瞅surfaceflinger.rc这个档案的内容,主要时设置一些SurfaceFlinger服务进程启动属性

service surfaceflinger /system/bin/surfaceflinger
    class core animation
    user system
    group graphics drmrpc readproc
    capabilities SYS_NICE
    onrestart restart zygote
    task_profiles HighPerformance
    socket pdx/system/vr/display/client     stream 0666 system graphics u:object_r:pdx_display_client_endpoint_socket:s0
    socket pdx/system/vr/display/manager    stream 0666 system graphics u:object_r:pdx_display_manager_endpoint_socket:s0
    socket pdx/system/vr/display/vsync      stream 0666 system graphics u:object_r:pdx_display_vsync_endpoint_socket:s0

这里我们就简简单单理解为:设备开机启动时,init进程解析surfaceflinger.rc,然后去执行/system/bin/surfaceflinger,从而启动了SurfaceFlinger服务进程。

如果在设备console下执行ps,你就可以看到这个进程PID了

console:/ $ ps -A | grep surfaceflinger
system          210      1  133412  38160 0                   0 S surfaceflinger

 

可执行档surfaceflinger的main函数入口

在此我们仅摘录主要的代码并注释如下:

* /frameworks/native/services/surfaceflinger/main_surfaceflinger.cpp

int main(int, char**) {
    ...
    
    // When SF is launched in its own process, limit the number of
    // binder threads to 4.
    ProcessState::self()->setThreadPoolMaxThreadCount(4);

    ...
    
    // start the thread pool
    sp<ProcessState> ps(ProcessState::self());
    ps->startThreadPool();

    ...
    
    // 创建SurfaceFlinger对象,由强指针指向。
    // SurfaceFlinger继承RefBase类,所以此处一旦new出对象赋给sp指针后,将立刻触发SurfaceFlinger类的onFirstRef方法的调用。
    // instantiate surfaceflinger
    sp<SurfaceFlinger> flinger = surfaceflinger::createSurfaceFlinger();

    ...

    // SurfaceFlinger类正式初始化
    // initialize before clients can connect
    flinger->init();

    // SurfaceFlinger向ServiceManager注册Binder服务,
    // 这样在其他进程中可以通过getService+SERVICE_NAME来获取SurfaceFlinger服务,继而可以和SurfaceFlinger类进行Binder通信。
    // publish surface flinger
    sp<IServiceManager> sm(defaultServiceManager());
    sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false,
                   IServiceManager::DUMP_FLAG_PRIORITY_CRITICAL | IServiceManager::DUMP_FLAG_PROTO);

    ...
    
    // SurfaceFlinger类进入主循环(此处注意SurfaceFlinger类未继承Threads类,不遵循Threads类的接口执行顺序)
    // run surface flinger in this thread
    flinger->run();

    return 0;
}

对于main函数,简简单单把握一下几点就可以了:

  1. 创建SurfaceFlinger对象,触发执行 SurfaceFlinger::onFirstRef()
  2. 调用SurfaceFlinger::init()进行初始化
  3. 注册服务到ServiceManager(名字是"SurfaceFlinger")
  4. 调用SurfaceFlinger::run()

 Tips:

在设备console上执行service list命令就可以看到注册的服务:注册的名称是SurfaceFlinger, 这个服务实现的接口是android.ui.ISurfaceComposer

console:/ $  service list | grep Surface
1       SurfaceFlinger: [android.ui.ISurfaceComposer]

 


SurfaceFlinger类定义

* /frameworks/native/services/surfaceflinger/SurfaceFlinger.h
class SurfaceFlinger : public BnSurfaceComposer,
                       public PriorityDumper,
                       private IBinder::DeathRecipient,
                       private HWC2::ComposerCallback,
                       private ISchedulerCallback {
♦ SurfaceComposer继承自BnSurfaceComposer,即为实现了ISurfaceComposer接口的Bn服务端; ♦ 实现了HWC2的ComposerCallback回调,监听Composer HAL的一些事件,比如Hotplug, Vsync ... ♦ 死亡通知DeathRecipient,当Binder服务端程序挂掉后,可以通知给绑定的Binder客户端程序; ♦ Dump信息PriorityDumper;

创建SurfaceFinger实例对象

调用surfaceflinger::createSurfaceFlinger()来创建SurfaceFlinger实例,并传递一个factory对象作为参数

* /frameworks/native/services/surfaceflinger/SurfaceFlingerFactory.cpp

sp<SurfaceFlinger> createSurfaceFlinger() {
    static DefaultFactory factory;

    return new SurfaceFlinger(factory);
}

来简单看一下Factory的定义:

* /frameworks/native/services/surfaceflinger/SurfaceFlingerFactory.h 

// The interface that SurfaceFlinger uses to create all of the implementations
// of each interface.
class Factory {
public:
    virtual std::unique_ptr<HWComposer> createHWComposer(const std::string& serviceName) = 0;
    virtual std::unique_ptr<MessageQueue> createMessageQueue() = 0;
    virtual std::unique_ptr<scheduler::VsyncConfiguration> createVsyncConfiguration(
            Fps currentRefreshRate) = 0;
    virtual std::unique_ptr<Scheduler> createScheduler(const scheduler::RefreshRateConfigs&,
                                                       ISchedulerCallback&) = 0;
    virtual sp<SurfaceInterceptor> createSurfaceInterceptor() = 0;

    virtual sp<StartPropertySetThread> createStartPropertySetThread(
            bool timestampPropertyValue) = 0;
    virtual sp<DisplayDevice> createDisplayDevice(DisplayDeviceCreationArgs&) = 0;
    virtual sp<GraphicBuffer> createGraphicBuffer(uint32_t width, uint32_t height,
                                                  PixelFormat format, uint32_t layerCount,
                                                  uint64_t usage, std::string requestorName) = 0;
    virtual void createBufferQueue(sp<IGraphicBufferProducer>* outProducer,
                                   sp<IGraphicBufferConsumer>* outConsumer,
                                   bool consumerIsSurfaceFlinger) = 0;
    virtual sp<IGraphicBufferProducer> createMonitoredProducer(const sp<IGraphicBufferProducer>&,
                                                               const sp<SurfaceFlinger>&,
                                                               const wp<Layer>&) = 0;
    virtual sp<BufferLayerConsumer> createBufferLayerConsumer(const sp<IGraphicBufferConsumer>&,
                                                              renderengine::RenderEngine&,
                                                              uint32_t tex, Layer*) = 0;

    virtual std::unique_ptr<surfaceflinger::NativeWindowSurface> createNativeWindowSurface(
            const sp<IGraphicBufferProducer>&) = 0;

    virtual std::unique_ptr<compositionengine::CompositionEngine> createCompositionEngine() = 0;

    virtual sp<BufferQueueLayer> createBufferQueueLayer(const LayerCreationArgs& args) = 0;
    virtual sp<BufferStateLayer> createBufferStateLayer(const LayerCreationArgs& args) = 0;
    virtual sp<EffectLayer> createEffectLayer(const LayerCreationArgs& args) = 0;
    virtual sp<ContainerLayer> createContainerLayer(const LayerCreationArgs& args) = 0;
    virtual std::unique_ptr<FrameTracer> createFrameTracer() = 0;
    virtual std::unique_ptr<frametimeline::FrameTimeline> createFrameTimeline(
            std::shared_ptr<TimeStats> timeStats, pid_t surfaceFlingerPid) = 0;

protected:
    ~Factory() = default;
};

 Factory中定义了各种create方法,其作用如注释中说明:The interface that SurfaceFlinger uses to create all of the implementations of each interface. 

SurfaceFlinger用Factory来创建所有实现了对应接口的对象。SurfaceFlinger中默认使用的是DefaultFactory,其中定义各种createXXX()方法的实现。具体可参见:/frameworks/native/services/surfaceflinger/SurfaceFlingerDefaultFactory.cpp

SurfaceFlinger构造函数

构造函数的代码就只截取部分贴在这里了,其中主要是读取一些属性值来对一些成员变量进行初始化。其中一些属性值是debug参数。另外就是利用mFactory的createXXX方法去实例化各种对象。

比如 : 创建消息队列 mEventQueue(mFactory.createMessageQueue())

* /frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp 

SurfaceFlinger::SurfaceFlinger(Factory& factory, SkipInitializationTag)
      : mFactory(factory),
        mInterceptor(mFactory.createSurfaceInterceptor()),
        mTimeStats(std::make_shared<impl::TimeStats>()),
        mFrameTracer(mFactory.createFrameTracer()),
        mFrameTimeline(mFactory.createFrameTimeline(mTimeStats, getpid())),
        mEventQueue(mFactory.createMessageQueue()),
        mCompositionEngine(mFactory.createCompositionEngine()),
        mHwcServiceName(base::GetProperty("debug.sf.hwc_service_name"s, "default"s)),
        mTunnelModeEnabledReporter(new TunnelModeEnabledReporter()),
        mInternalDisplayDensity(getDensityFromProperty("ro.sf.lcd_density", true)),
        mEmulatedDisplayDensity(getDensityFromProperty("qemu.sf.lcd_density", false)),
        mPowerAdvisor(*this) {
    ALOGI("Using HWComposer service: %s", mHwcServiceName.c_str());

    mSetInputWindowsListener = new SetInputWindowsListener([&]() { setInputWindowsFinished(); });
}

SurfaceFlinger::SurfaceFlinger(Factory& factory) : SurfaceFlinger(factory, SkipInitialization) {
    ALOGI("SurfaceFlinger is starting");

    hasSyncFramework = running_without_sync_framework(true);

    dispSyncPresentTimeOffset = present_time_offset_from_vsync_ns(0);

    useHwcForRgbToYuv = force_hwc_copy_for_virtual_displays(false);

    maxFrameBufferAcquiredBuffers = max_frame_buffer_acquired_buffers(2);

    maxGraphicsWidth = std::max(max_graphics_width(0), 0);
    maxGraphicsHeight = std::max(max_graphics_height(0), 0);

    hasWideColorDisplay = has_wide_color_display(false);
  
  	...
    
    
  }

surfaceflinger 会去读取SurfaceFlingerProperties中的系统属性,具体可以参看源码:/frameworks/native/services/surfaceflinger/sysprop/


Tips:

关于系统属性的知识建议可以参见:

https://source.android.google.cn/devices/architecture/sysprops-apis?hl=zh-cn

https://blog.csdn.net/askfgx2010/article/details/112308665


 

SurfaceFlinger::onFirstRef

上面创建完SurfaceFlinger对象,立即就会执行到SurfaceFlinger::onFirstRef,这个方法中就做了一件事对消息队列做初始化,如下:

void SurfaceFlinger::onFirstRef() {
    mEventQueue->init(this);
}

消息队列运行的详细分析我们下节在讲,这里先不展开。

SurfaceFlinger::init

再回到可执行档surfaceflinger的main函数中,创建完SurfaceFlinger对象后,紧接着调用了SurfaceFlinger::init()方法:

* /frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

void SurfaceFlinger::init() {
    ALOGI(  "SurfaceFlinger's main thread ready to run. "
            "Initializing graphics H/W...");
    Mutex::Autolock _l(mStateLock);

    // 对于CompositionEngine 属性进行设置, 创建 RenderEngine 对象
    // Get a RenderEngine for the given display / config (can't fail)
    // TODO(b/77156734): We need to stop casting and use HAL types when possible.
    // Sending maxFrameBufferAcquiredBuffers as the cache size is tightly tuned to single-display.
    mCompositionEngine->setRenderEngine(renderengine::RenderEngine::create(
            renderengine::RenderEngineCreationArgs::Builder()
                    .setPixelFormat(static_cast<int32_t>(defaultCompositionPixelFormat))
                    .setImageCacheSize(maxFrameBufferAcquiredBuffers)
                    .setUseColorManagerment(useColorManagement)
                    .setEnableProtectedContext(enable_protected_contents(false))
                    .setPrecacheToneMapperShaderOnly(false)
                    .setSupportsBackgroundBlur(mSupportsBlur)
                    .setContextPriority(
                            useContextPriority
                                    ? renderengine::RenderEngine::ContextPriority::REALTIME
                                    : renderengine::RenderEngine::ContextPriority::MEDIUM)
                    .build()));

    // Set SF main policy after initializing RenderEngine which has its own policy.
    if (!SetTaskProfiles(0, {"SFMainPolicy"})) {
        ALOGW("Failed to set main task profile");
    }

    // 创建HWComposer对象并传入一个name属性,再通过mCompositionEngine->setHwComposer设置对象属性。
    mCompositionEngine->setTimeStats(mTimeStats);
    mCompositionEngine->setHwComposer(getFactory().createHWComposer(mHwcServiceName));
    mCompositionEngine->getHwComposer().setCallback(this);
    ClientCache::getInstance().setRenderEngine(&getRenderEngine());

    if (base::GetBoolProperty("debug.sf.enable_hwc_vds"s, false)) {
        enableHalVirtualDisplays(true);
    }

  // processDisplayHotplugEventsLocked(); 处理 任何初始热插拔和显示更改的结果
  // 在此方法中主要有调用 initScheduler(displayId);
    // Process any initial hotplug and resulting display changes.
    processDisplayHotplugEventsLocked();
    const auto display = getDefaultDisplayDeviceLocked();
    LOG_ALWAYS_FATAL_IF(!display, "Missing internal display after registering composer callback.");
    const auto displayId = display->getPhysicalId();
    LOG_ALWAYS_FATAL_IF(!getHwComposer().isConnected(displayId),
                        "Internal display is disconnected.");

    // initialize our drawing state
    mDrawingState = mCurrentState;

    // 初始化Display信息
    // set initial conditions (e.g. unblank default device)
    initializeDisplays();

    mPowerAdvisor.init();

    char primeShaderCache[PROPERTY_VALUE_MAX];
    property_get("service.sf.prime_shader_cache", primeShaderCache, "1");
    if (atoi(primeShaderCache)) {
        if (setSchedFifo(false) != NO_ERROR) {
            ALOGW("Can't set SCHED_OTHER for primeCache");
        }

        mRenderEnginePrimeCacheFuture = getRenderEngine().primeCache();

        if (setSchedFifo(true) != NO_ERROR) {
            ALOGW("Can't set SCHED_OTHER for primeCache");
        }
    }

    getRenderEngine().onPrimaryDisplaySizeChanged(display->getSize());

    // Inform native graphics APIs whether the present timestamp is supported:

    const bool presentFenceReliable =
            !getHwComposer().hasCapability(hal::Capability::PRESENT_FENCE_IS_NOT_RELIABLE);
    mStartPropertySetThread = getFactory().createStartPropertySetThread(presentFenceReliable);
    // 开启一个设置属性的线程,在这个线程中使用property_set去设置一些属性值
    if (mStartPropertySetThread->Start() != NO_ERROR) {
        ALOGE("Run StartPropertySetThread failed!");
    }

    ALOGV("Done initializing");
}

SurfaceFlinger::init方法,完成的工作大概为:

♦ CompositionEngine的配置,创建RenderEngine对象用于Client合成模式(GPU)合成;

♦ 初始化HWComposer,注册回调接口mCompositionEngine->getHwComposer().setCallback(this),HAL会回调一些方法;

♦ 处理Display显示屏幕的热插拔和更改的事件processDisplayHotplugEventsLocked;

♦ 初始化显示设备initializeDisplays;

♦ 开启一个设置属性的线程,在这个线程中使用property_set去设置一些属性值mStartPropertySetThread->Start();

 SurfaceFlinger::run

可执行档surfaceflinger的main函数中,把SurfaceFinger这个服务注册进ServiceManger中后,后续执行了SurfaceFlinger::run这个方法,代码如下:

* /frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp 

void SurfaceFlinger::run() {
    while (true) {
        mEventQueue->waitMessage();
    }
}

这个方法也很简单,一个while(true)的无限死循环,消息队列等待消息的到来。surfaceflinger主线程中等待消息处理。


讲到这里,大概SurfaceFlinger启动的流程就完成了,当然,很多细节我们没有深入去分析。

 

3 SurfaceFlinger的消息队列处理机制

上面一节中有提到,在SurfaceFlinger的构造函数中有创建消息队列
* /frameworks/native/services/surfaceflinger/SurfaceFlinger.h

//成员变量mEventQueue的声明
std::unique_ptr<MessageQueue> mEventQueue;

========

* /frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

// SurfaceFlinger构造函数中创建消息队列
mEventQueue(mFactory.createMessageQueue()),
  创建消息队列是透过Factory完成的,这里使用的是DefaultFactory中的方法createMessageQueue,定义如下:
* /frameworks/native/services/surfaceflinger/SurfaceFlingerDefaultFactory.cpp

std::unique_ptr<MessageQueue> DefaultFactory::createMessageQueue() {
    return std::make_unique<android::impl::MessageQueue>();
}
创建消息队列时,实例化一个android::impl::MessageQueue对象,MesageQueue的定义位于:     /frameworks/native/services/surfaceflinger/Scheduler/MessageQueue.h     /frameworks/native/services/surfaceflinger/Scheduler/MessageQueue.cpp  
Tips: 在继续阅读下面的内容前,需要对Android Native Looper/Handler/Message机制有一定了解,所以我建议您阅读如下两篇文章:

Android Native -- Message/Handler/Looper机制(原理篇)

Android Native -- Message/Handler/Looper机制(应用篇)


  我们先来瞅一瞅2个非常重要的定义: ♦ MessageQueue:维护消息队列,并提供发送消息的方法等 ♦ Handler:主要是实现handleMessage方法,来处理消息  

android::impl::MessageQueue的定义

查看代码
* /frameworks/native/services/surfaceflinger/Scheduler/MessageQueue.h

namespace impl {

class MessageQueue : public android::MessageQueue {

    sp<SurfaceFlinger> mFlinger;
    sp<Looper> mLooper;
    
    sp<Handler> mHandler;
    
  ...
}
如上代码,android::impl::MessageQueue继承自android::MessageQueue,实现了这个虚基类中定义的方法:
* /frameworks/native/services/surfaceflinger/Scheduler/MessageQueue.h

    void init(const sp<SurfaceFlinger>& flinger) override;
    void initVsync(scheduler::VSyncDispatch&, frametimeline::TokenManager&,
                   std::chrono::nanoseconds workDuration) override;
    void setDuration(std::chrono::nanoseconds workDuration) override;
    void setInjector(sp<EventThreadConnection>) override;
    void waitMessage() override;
    void postMessage(sp<MessageHandler>&&) override;

    // sends INVALIDATE message at next VSYNC
    void invalidate() override;

    // sends REFRESH message at next VSYNC
    void refresh() override;
  android::impl::MessageQueue中含有成员: ♦ mFlinger == 指向SurfaceFlinger的引用,我们前面有提到在SurfaceFlinger::onFirstRef中调用mEventQueue->init(this)来设置的; ♦ mLooper == 其中维护了一个消息队列和待监测的fd队列,当用户调用pollOnce或pollAll时,就会去判断是否有消息或fd事件要处理; ♦ mHandler == 消息处理类对象通过实现handleMessage来实现特定Message的处理逻辑;    
重要: android::impl::MessageQueue这个类,从名字看就知晓这是一个“消息队列”,但从其类定义中却没有看到有成员是“队列”这个属性。 其实,消息队列是由mLooper内部来维护的,在Looper这个类中有一个成员   Vector<MessageEnvelope> mMessageEnvelopes,这是一个Vector可变数组。 这个数组中存储着有哪些待处理的Message及对应的Handler   如果不理解还是再去看看前面提到的参考文章。
 

MessageQueue::init方法

我们前面有提到在SurfaceFlinger::onFirstRef中调用mEventQueue->init(this),init方法中会去创建Looper和Handler对象
* /frameworks/native/services/surfaceflinger/Scheduler/MessageQueue.cpp

void MessageQueue::init(const sp<SurfaceFlinger>& flinger) {
    mFlinger = flinger;
    mLooper = new Looper(true);
    mHandler = new Handler(*this);
}
 

MessageQueue::postMessage方法

postMessage用于发送消息到队列中中,并指定处理该消息的handler
void MessageQueue::postMessage(sp<MessageHandler>&& handler) {
    mLooper->sendMessage(handler, Message());
}
 

MessageQueue::waitMessage方法

waitMessage方法中不断去调用mLooper->pollOnce(-1),检查Looper中是否有消息需要处理,如果有,则调用该消息对应的MessageHandler去处理。

void MessageQueue::waitMessage() {
    do {
        IPCThreadState::self()->flushCommands();
        int32_t ret = mLooper->pollOnce(-1);
        ...
    } while (true);
}
  前面也有讲到了SurfaceFlinger::run这个方法在一个while(true)循环中不断呼叫waitMessage  

Handler的定义

Handler继承自MessageHandler并实现了handleMessage方法,在这个方法中对消息进行处理

Handler中还有一个成员mQueue指向MessageQueue对象引用

    class Handler : public MessageHandler {
        enum : uint32_t {
            eventMaskInvalidate = 0x1,
            eventMaskRefresh = 0x2,
            eventMaskTransaction = 0x4
        };
        MessageQueue& mQueue;
        std::atomic<uint32_t> mEventMask;
        std::atomic<int64_t> mVsyncId;
        std::atomic<nsecs_t> mExpectedVSyncTime;

    public:
        explicit Handler(MessageQueue& queue) : mQueue(queue), mEventMask(0) {}
        void handleMessage(const Message& message) override;
        virtual void dispatchRefresh();
        virtual void dispatchInvalidate(int64_t vsyncId, nsecs_t expectedVSyncTimestamp);
        virtual bool invalidatePending();
    };

 




 

前面讲到的都是一些定义啊,方法呀,他们之间的联系,如何运作似乎还是云里雾里,没有讲到。

其实SurfaceFlinger消息队列主要处理2个重要事件:Refresh Invalidate

我们就分析下Refresh的处理流程

某些操作下需要进行refresh动作时,会调用到SurfaceFlinger::signalRefresh()

void SurfaceFlinger::signalRefresh() {
    mRefreshPending = true;
    mEventQueue->refresh();
}

SurfaceFlinger::signalRefresh()方法中会继续调用mEventQueue->refresh()

void MessageQueue::refresh() {
    mHandler->dispatchRefresh();
}

继而调用到mHandler->dispatchRefresh()

void MessageQueue::Handler::dispatchRefresh() {
    if ((mEventMask.fetch_or(eventMaskRefresh) & eventMaskRefresh) == 0) {
        mQueue.mLooper->sendMessage(this, Message(MessageQueue::REFRESH));
    }
}

Handler::dispatchRefresh()方法中就要准备消息并指定Handler来处理这个消息,然后seedMessage到Looper的消息队列中去,等待后续处理。

对于refresh消息,其what字段为MessageQueue::REFRESH, 处理它就是在MessageQueue::Handler::handleMessage方法中,如下:

void MessageQueue::Handler::handleMessage(const Message& message) {
    switch (message.what) {
        case INVALIDATE:
            mEventMask.fetch_and(~eventMaskInvalidate);
            mQueue.mFlinger->onMessageReceived(message.what, mVsyncId, mExpectedVSyncTime);
            break;
        case REFRESH:
            mEventMask.fetch_and(~eventMaskRefresh);
            mQueue.mFlinger->onMessageReceived(message.what, mVsyncId, mExpectedVSyncTime);
            break;
    }
}

看到这里是不是稍微清晰一点了,当waitMessage --> Looper::pollOnce 检测到这个refresh消息要处理时,就会回调到MessageQueue::Handler::handleMessage方法,进而执行到SurfaceFlinger::onMessageReceived

void SurfaceFlinger::onMessageReceived(int32_t what, int64_t vsyncId, nsecs_t expectedVSyncTime) {
    switch (what) {
        case MessageQueue::INVALIDATE: {
            onMessageInvalidate(vsyncId, expectedVSyncTime);
            break;
        }
        case MessageQueue::REFRESH: {
            onMessageRefresh();
            break;
        }
    }
}

之后就是具体refresh要完成的具体工作了,此处省略一万字....

 

讲到这里不知您明白了没,没有图形化的注解确实不太系统,不过只要你理解Android Native Looper/Handler/Message机制应该很容易看懂。

 


 简简单单的理解:

  1. SurfaceFlinger主线程中不断去调用waitMessage --> Looper::pollOnce 检测是否有消息要处理;
  2. 如果有消息要处理,则Looper就会取出这个消息并回调与之对应的MessageHandler::handleMessage方法,处理消息事件;
  3. 外部可以通过MessageQueue::postMessage,Looper::sendMessage等方法向消息队列中发送待处理的Message;

 


实用技巧

武林中有两招绝学,一阳指和狮吼功,我用了整整三十年的时间,将两招绝学并成了一整招。你过来啊!

Android 11之前的一阳指和狮吼功:

* /frameworks/native/services/surfaceflinger/SurfaceFlinger.h

// post an asynchronous message to the main thread
status_t postMessageAsync(const sp<MessageBase>& msg, nsecs_t reltime = 0, uint32_t flags = 0);

// post a synchronous message to the main thread
status_t postMessageSync(const sp<MessageBase>& msg, nsecs_t reltime = 0, uint32_t flags = 0);

Android 11之后两招绝学并成了一整招

* /frameworks/native/services/surfaceflinger/SurfaceFlinger.h

// Schedule an asynchronous or synchronous task on the main thread.
template <typename F, typename T = std::invoke_result_t<F>>
[[nodiscard]] std::future<T> schedule(F&&);

这些方法的作用就是把指定的任务放到main thread中去执行。

看一下schedule的定义:

template <typename F, typename T>
inline std::future<T> SurfaceFlinger::schedule(F&& f) {
    auto [task, future] = makeTask(std::move(f));
    mEventQueue->postMessage(std::move(task));
    return std::move(future);
}

再看makeTask和Task的定义:

*  /frameworks/native/services/surfaceflinger/Scheduler/MessageQueue.h

template <typename F>
class Task : public MessageHandler {
    template <typename G>
    friend auto makeTask(G&&);

    explicit Task(F&& f) : mTask(std::move(f)) {}

    void handleMessage(const Message&) override { mTask(); }

    using T = std::invoke_result_t<F>;
    std::packaged_task<T()> mTask;
};

template <typename F>
inline auto makeTask(F&& f) {
    sp<Task<F>> task = new Task<F>(std::move(f));
    return std::make_pair(task, task->mTask.get_future());
}

MessageQueue::postMessage

*  /frameworks/native/services/surfaceflinger/Scheduler/MessageQueue.cpp

void MessageQueue::postMessage(sp<MessageHandler>&& handler) {
    mLooper->sendMessage(handler, Message());
}

看到这里是不是基本就清楚了,熟悉的字眼:postMessage,MessageHandler,handleMessage本质还是main thread上消息队列处理。

其实换汤不换药,只是利用C++的新特型做了抽象与封装,本质还是向主线程发送一个Message并指定其MessageHandler,主线程收到消息时调用MessageHandler::handleMessage,进而呼叫到我们指定的函数实体代码。

 

我们已一个例子来说明:

    static_cast<void>(schedule([=]()  {
        ALOGD("我在主线程被打印");
    }));

我们传递给schedule的函数实体将在主线程执行。

这在我们修改某些逻辑且要保证主线程执行时可能是个不错的技巧。


 

4 小结

写到这里 SurfaceFlinger启动与初始化流程和SurfaceFlinger消息队列处理机制就完了,很多内容自己也没有完全吃透,本篇的目的还是着重讲解流程而忽视具体细节,搞懂流程再去按工作需要分析细节,这样感觉会更实用主义。

 


必读:

Android 12(S) 图形显示系统 - 开篇


 

 

 


最后分享一份好心情

 

 

 

 

标签:std,12,MessageQueue,void,sp,surfaceflinger,SurfaceFlinger,Android
来源: https://www.cnblogs.com/roger-yu/p/15761646.html