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对于surfaceflinger大多数人都知道它的功能是做图形合成的#xff0c;用英语表示就是指composite。其大致框图如下:
各个Android app将自己的图形画面通过surface为载体通过AIDL接口(Binder IPC)传递到surfaceflinger进程surfaceflinger进程中的composition engine与HW…概述
对于surfaceflinger大多数人都知道它的功能是做图形合成的用英语表示就是指composite。其大致框图如下:
各个Android app将自己的图形画面通过surface为载体通过AIDL接口(Binder IPC)传递到surfaceflinger进程surfaceflinger进程中的composition engine与HWC协商哪些图层HWC可以直接显示哪些图层需要自己合成为一个图层后再送给HWC显示。surfaceflinger与HWC把合成策略协商完后再将合成后的图层和独立显示的图层分别传递给HWCHWC再操作硬件显示在屏幕上。
本系列文章会深入分析surfaceflinger的各个方面力争弄懂下列问题:
surfaceflinger做合成的动作是如何触发的进程的消息模型是什么样的 如何驱动循环做合成动作的surface是什么 surface与图形数据buffer有什么关系?surface对应在surfaceflinger进程内用什么东西表示各个app的图形数据buffer怎么传递过来的图形数据在surfaceflinger进程内部流转过程是什么样的既然涉及到跨进程传递图形buffer的生产和消费是如何同步的Fence是什么玩意Vsync是个什么意思有什么用 本篇文章先来阅读源码分析下第一个问题。
surfaceflinger进程的main函数
int main(int, char**) {signal(SIGPIPE, SIG_IGN);hardware::configureRpcThreadpool(1 /* maxThreads */,false /* callerWillJoin */);startGraphicsAllocatorService();// When SF is launched in its own process, limit the number of// binder threads to 4.ProcessState::self()-setThreadPoolMaxThreadCount(4);// start the thread poolspProcessState ps(ProcessState::self());ps-startThreadPool();// instantiate surfaceflingerspSurfaceFlinger flinger surfaceflinger::createSurfaceFlinger();setpriority(PRIO_PROCESS, 0, PRIORITY_URGENT_DISPLAY);set_sched_policy(0, SP_FOREGROUND);// Put most SurfaceFlinger threads in the system-background cpuset// Keeps us from unnecessarily using big cores// Do this after the binder thread pool initif (cpusets_enabled()) set_cpuset_policy(0, SP_SYSTEM);// initialize before clients can connectflinger-init();// publish surface flingerspIServiceManager sm(defaultServiceManager());sm-addService(String16(SurfaceFlinger::getServiceName()), flinger, false,IServiceManager::DUMP_FLAG_PRIORITY_CRITICAL | IServiceManager::DUMP_FLAG_PROTO);startDisplayService(); // dependency on SF getting registered aboveif (SurfaceFlinger::setSchedFifo(true) ! NO_ERROR) {ALOGW(Couldnt set to SCHED_FIFO: %s, strerror(errno));}// run surface flinger in this threadflinger-run();return 0;
}上面的代码大致可以缩减为三句话:
int main(int, char**) {..............................;spSurfaceFlinger flinger surfaceflinger::createSurfaceFlinger();..............................;flinger-init();..............................;flinger-run();return 0;
}下面再分别看下这三个函数分别做了什么?
surfaceflinger::createSurfaceFlinger
spSurfaceFlinger createSurfaceFlinger() {static DefaultFactory factory;return new SurfaceFlinger(factory);
}surfaceflinger::init
主要是对子模块mCompositionEngineDisplays RenderEngine等模块的初始化貌似和消息传递关系不大先放着不深入分析。
void SurfaceFlinger::init() {ALOGI( SurfaceFlingers main thread ready to run. Initializing graphics H/W...);Mutex::Autolock _l(mStateLock);mCompositionEngine-setRenderEngine(renderengine::RenderEngine::create(renderengine::RenderEngineCreationArgs::Builder().setPixelFormat(static_castint32_t(defaultCompositionPixelFormat)).setImageCacheSize(maxFrameBufferAcquiredBuffers).setUseColorManagerment(useColorManagement).setEnableProtectedContext(enable_protected_contents(false)).setPrecacheToneMapperShaderOnly(false).setSupportsBackgroundBlur(mSupportsBlur).setContextPriority(useContextPriority? renderengine::RenderEngine::ContextPriority::HIGH: renderengine::RenderEngine::ContextPriority::MEDIUM).build()));mCompositionEngine-setTimeStats(mTimeStats);LOG_ALWAYS_FATAL_IF(mVrFlingerRequestsDisplay,Starting with vr flinger active is not currently supported.);mCompositionEngine-setHwComposer(getFactory().createHWComposer(getBE().mHwcServiceName));mCompositionEngine-getHwComposer().setConfiguration(this, getBE().mComposerSequenceId);// 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.);LOG_ALWAYS_FATAL_IF(!getHwComposer().isConnected(*display-getId()),Internal display is disconnected.);................................................................;// initialize our drawing statemDrawingState mCurrentState;// set initial conditions (e.g. unblank default device)initializeDisplays();char primeShaderCache[PROPERTY_VALUE_MAX];property_get(service.sf.prime_shader_cache, primeShaderCache, 1);if (atoi(primeShaderCache)) {getRenderEngine().primeCache();}// 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);if (mStartPropertySetThread-Start() ! NO_ERROR) {ALOGE(Run StartPropertySetThread failed!);}ALOGV(Done initializing);
}surfaceflinger::run
看到死循环了哈哈这应该就是本篇文章要找的死循环。看来要重点看下这个mEventQueue在wait什么Message了哪里来的Message。
void SurfaceFlinger::run() {while (true) {mEventQueue-waitMessage();}
}std::unique_ptr mEventQueue创建
SurfaceFlinger::SurfaceFlinger(Factory factory, SkipInitializationTag): mFactory(factory),mInterceptor(mFactory.createSurfaceInterceptor(this)),mTimeStats(std::make_sharedimpl::TimeStats()),mFrameTracer(std::make_uniqueFrameTracer()),mEventQueue(mFactory.createMessageQueue()),mCompositionEngine(mFactory.createCompositionEngine()),mInternalDisplayDensity(getDensityFromProperty(ro.sf.lcd_density, true)),mEmulatedDisplayDensity(getDensityFromProperty(qemu.sf.lcd_density, false)) {}std::unique_ptrMessageQueue DefaultFactory::createMessageQueue() {return std::make_uniqueandroid::impl::MessageQueue();
}MessageQueue 的定义 可以看到MessageQueue类中还定义了一个Handler类。现在还不知道这些类中的成员变量和函数的作用。那么就从waitMessage()函数入手一探究竟。
class MessageQueue final : public android::MessageQueue {class Handler : public MessageHandler {enum { eventMaskInvalidate 0x1, eventMaskRefresh 0x2, eventMaskTransaction 0x4 };MessageQueue mQueue;int32_t mEventMask;std::atomicnsecs_t mExpectedVSyncTime;public:explicit Handler(MessageQueue queue) : mQueue(queue), mEventMask(0) {}virtual void handleMessage(const Message message);void dispatchRefresh();void dispatchInvalidate(nsecs_t expectedVSyncTimestamp);};friend class Handler;spSurfaceFlinger mFlinger;spLooper mLooper;spEventThreadConnection mEvents;gui::BitTube mEventTube;spHandler mHandler;static int cb_eventReceiver(int fd, int events, void* data);int eventReceiver(int fd, int events);public:~MessageQueue() override default;void init(const spSurfaceFlinger flinger) override;void setEventConnection(const spEventThreadConnection connection) override;void waitMessage() override;void postMessage(spMessageHandler) override;// sends INVALIDATE message at next VSYNCvoid invalidate() override;// sends REFRESH message at next VSYNCvoid refresh() override;
};MessageQueue
waitMessage源码分析
void MessageQueue::waitMessage() {do {IPCThreadState::self()-flushCommands();int32_t ret mLooper-pollOnce(-1);switch (ret) {case Looper::POLL_WAKE:case Looper::POLL_CALLBACK:continue;case Looper::POLL_ERROR:ALOGE(Looper::POLL_ERROR);continue;case Looper::POLL_TIMEOUT:// timeout (should not happen)continue;default:// should not happenALOGE(Looper::pollOnce() returned unknown status %d, ret);continue;}} while (true);
}看来要重点看下IPCThreadState和这个mLooper了 IPCThreadState这玩意是和Binder相关啊看着这意思是要把Binder中的消息刷出来看看各个app进程有没有通过Binder发消息过来。先放在着后面回过头再来分析。
void IPCThreadState::flushCommands()
{if (mProcess-mDriverFD 0)return;talkWithDriver(false);if (mOut.dataSize() 0) {talkWithDriver(false);}if (mOut.dataSize() 0) {ALOGW(mOut.dataSize() 0 after flushCommands());}
}再来看看这个mLooper的实现。
class Looper : public RefBase {
protected:virtual ~Looper();
publicLooper(bool allowNonCallbacks);bool getAllowNonCallbacks() const;int pollOnce(int timeoutMillis, int* outFd, int* outEvents, void** outData);inline int pollOnce(int timeoutMillis) {return pollOnce(timeoutMillis, nullptr, nullptr, nullptr);}int pollAll(int timeoutMillis, int* outFd, int* outEvents, void** outData);inline int pollAll(int timeoutMillis) {return pollAll(timeoutMillis, nullptr, nullptr, nullptr);}void wake();int addFd(int fd, int ident, int events, Looper_callbackFunc callback, void* data);int addFd(int fd, int ident, int events, const spLooperCallback callback, void* data);int removeFd(int fd);void sendMessage(const spMessageHandler handler, const Message message);void sendMessageDelayed(nsecs_t uptimeDelay, const spMessageHandler handler,const Message message);void sendMessageAtTime(nsecs_t uptime, const spMessageHandler handler,const Message message);void removeMessages(const spMessageHandler handler);void removeMessages(const spMessageHandler handler, int what);bool isPolling() const;static spLooper prepare(int opts);static void setForThread(const spLooper looper);static spLooper getForThread();
private:struct Request {int fd;int ident;int events;int seq;spLooperCallback callback;void* data;void initEventItem(struct epoll_event* eventItem) const;};struct Response {int events;Request request;};struct MessageEnvelope {MessageEnvelope() : uptime(0) { }MessageEnvelope(nsecs_t u, const spMessageHandler h,const Message m) : uptime(u), handler(h), message(m) {}nsecs_t uptime;spMessageHandler handler;Message message;};const bool mAllowNonCallbacks; // immutableandroid::base::unique_fd mWakeEventFd; // immutableMutex mLock;VectorMessageEnvelope mMessageEnvelopes; // guarded by mLockbool mSendingMessage; // guarded by mLock// Whether we are currently waiting for work. Not protected by a lock,// any use of it is racy anyway.volatile bool mPolling;android::base::unique_fd mEpollFd; // guarded by mLock but only modified on the looper threadbool mEpollRebuildRequired; // guarded by mLock// Locked list of file descriptor monitoring requests.KeyedVectorint, Request mRequests; // guarded by mLockint mNextRequestSeq;// This state is only used privately by pollOnce and does not require a lock since// it runs on a single thread.VectorResponse mResponses;size_t mResponseIndex;nsecs_t mNextMessageUptime; // set to LLONG_MAX when noneint pollInner(int timeoutMillis);int removeFd(int fd, int seq);void awoken();void pushResponse(int events, const Request request);void rebuildEpollLocked();void scheduleEpollRebuildLocked();static void initTLSKey();static void threadDestructor(void *st);static void initEpollEvent(struct epoll_event* eventItem);
};先来看看这个pollOnce(-1)函数是在干啥 int pollOnce(int timeoutMillis, int* outFd, int* outEvents, void** outData);inline int pollOnce(int timeoutMillis) {return pollOnce(timeoutMillis, nullptr, nullptr, nullptr);}int Looper::pollOnce(int timeoutMillis, int* outFd, int* outEvents, void** outData) {int result 0;for (;;) {//因为参数outFd outEvents outData都为null所以此while循环不用太关注//如果mResponses中有事件就将mResponseIndex加一返回没有事件就执行下面的pollInner//下面重点关注mResponses里面的item在哪里push进去的while (mResponseIndex mResponses.size()) {const Response response mResponses.itemAt(mResponseIndex);int ident response.request.ident;if (ident 0) {int fd response.request.fd;int events response.events;void* data response.request.data;if (outFd ! nullptr) *outFd fd;if (outEvents ! nullptr) *outEvents events;if (outData ! nullptr) *outData data;return ident;}}if (result ! 0) {if (outFd ! nullptr) *outFd 0;if (outEvents ! nullptr) *outEvents 0;if (outData ! nullptr) *outData nullptr;return result;}//重点关注下这个实现result pollInner(timeoutMillis);}
}pollInner干了什么
int Looper::pollInner(int timeoutMillis) {//计算出timeoutMillis作为epoll_wait的timeout时长if (timeoutMillis ! 0 mNextMessageUptime ! LLONG_MAX) {nsecs_t now systemTime(SYSTEM_TIME_MONOTONIC);int messageTimeoutMillis toMillisecondTimeoutDelay(now, mNextMessageUptime);if (messageTimeoutMillis 0 (timeoutMillis 0 || messageTimeoutMillis timeoutMillis)) {timeoutMillis messageTimeoutMillis;}}// Poll.int result POLL_WAKE;mResponses.clear(); //清空mResponses我擦看来mResponses就是在这里push和clear的mResponseIndex 0;mPolling true;struct epoll_event eventItems[EPOLL_MAX_EVENTS];//epoll_wait 等待事件的到来后面再具体看下这个epoll中都有哪些被监控的文件句柄int eventCount epoll_wait(mEpollFd.get(), eventItems, EPOLL_MAX_EVENTS, timeoutMillis);mPolling false;mLock.lock();...........................;for (int i 0; i eventCount; i) {int fd eventItems[i].data.fd;uint32_t epollEvents eventItems[i].events;if (fd mWakeEventFd.get()) {............................;} else {ssize_t requestIndex mRequests.indexOfKey(fd);if (requestIndex 0) {int events 0;if (epollEvents EPOLLIN) events | EVENT_INPUT;if (epollEvents EPOLLOUT) events | EVENT_OUTPUT;if (epollEvents EPOLLERR) events | EVENT_ERROR;if (epollEvents EPOLLHUP) events | EVENT_HANGUP;//将epoll监控到的event push到mResponses中pushResponse(events, mRequests.valueAt(requestIndex));} else {ALOGW(Ignoring unexpected epoll events 0x%x on fd %d that is no longer registered., epollEvents, fd);}}}
Done: mNextMessageUptime LLONG_MAX;//处理mMessageEnvelopes中具体message这里面的message哪里来的现在还不知道while (mMessageEnvelopes.size() ! 0) {nsecs_t now systemTime(SYSTEM_TIME_MONOTONIC);const MessageEnvelope messageEnvelope mMessageEnvelopes.itemAt(0);if (messageEnvelope.uptime now) {{ // obtain handlerspMessageHandler handler messageEnvelope.handler;Message message messageEnvelope.message;mMessageEnvelopes.removeAt(0);mSendingMessage true;mLock.unlock();handler-handleMessage(message); //需要重点分析的函数} // release handlermLock.lock();mSendingMessage false;result POLL_CALLBACK;} else {// The last message left at the head of the queue determines the next wakeup time.mNextMessageUptime messageEnvelope.uptime;break;}}mLock.unlock();//处理epoll监控到的事件通过提前注册的callback来处理此event这些callback是什么时候注册的现在还不知道for (size_t i 0; i mResponses.size(); i) {Response response mResponses.editItemAt(i);if (response.request.ident POLL_CALLBACK) {int fd response.request.fd;int events response.events;void* data response.request.data;int callbackResult response.request.callback-handleEvent(fd, events, data);if (callbackResult 0) {removeFd(fd, response.request.seq);}response.request.callback.clear();result POLL_CALLBACK;}}return result;
}通过上面的代码分析pollInner主要逻辑如下:
通过epoll_wait监控获取event将获取到的event封装成response结构push到mResponses中。处理mMessageEnvelopes中的message: sp handler messageEnvelope.handler; Message message messageEnvelope.message; handler-handleMessage(message);处理mResponses中每一个response response.request.callback-handleEvent(fd, events, data)
现在新疑问来了
mMessageEnvelopes中message哪里来的?epoll中被监控的fd是什么后添加到epoll中的
void MessageQueue::setEventConnection(const spEventThreadConnection connection) {if (mEventTube.getFd() 0) {mLooper-removeFd(mEventTube.getFd());}mEvents connection;mEvents-stealReceiveChannel(mEventTube);//往epoll中添加mEventTube的fd其中MessageQueue::cb_eventReceiver是epoll监控到事件后执行的callbackmLooper-addFd(mEventTube.getFd(), 0, Looper::EVENT_INPUT, MessageQueue::cb_eventReceiver,this);
}
//找到答案了: epoll中被监控的fd是什么后添加到epoll中的
int Looper::addFd(int fd, int ident, int events, const spLooperCallback callback, void* data) {....................;{ // acquire lockAutoMutex _l(mLock);Request request;request.fd fd;request.ident ident;request.events events;request.seq mNextRequestSeq;request.callback callback;request.data data;struct epoll_event eventItem;request.initEventItem(eventItem);ssize_t requestIndex mRequests.indexOfKey(fd);if (requestIndex 0) {int epollResult epoll_ctl(mEpollFd.get(), EPOLL_CTL_ADD, fd, eventItem);mRequests.add(fd, request);} else {........................;}} // release lockreturn 1;
}int MessageQueue::cb_eventReceiver(int fd, int events, void* data) {MessageQueue* queue reinterpret_castMessageQueue*(data);//执行MessageQueue中的eventReceiver函数return queue-eventReceiver(fd, events);
}int MessageQueue::eventReceiver(int /*fd*/, int /*events*/) {ssize_t n;DisplayEventReceiver::Event buffer[8];//监控到mEventTube中有事件后从mEventTube中读取事件处理事件while ((n DisplayEventReceiver::getEvents(mEventTube, buffer, 8)) 0) {for (int i 0; i n; i) {if (buffer[i].header.type DisplayEventReceiver::DISPLAY_EVENT_VSYNC) {mHandler-dispatchInvalidate(buffer[i].vsync.expectedVSyncTimestamp);break;}}}return 1;
}void MessageQueue::Handler::dispatchInvalidate(nsecs_t expectedVSyncTimestamp) {if ((android_atomic_or(eventMaskInvalidate, mEventMask) eventMaskInvalidate) 0) {mExpectedVSyncTime expectedVSyncTimestamp;//从mEventTube读取VSYNC事件后先Looper中发一个MessageQueue::INVALIDATE类型的消息mQueue.mLooper-sendMessage(this, Message(MessageQueue::INVALIDATE));}
}void Looper::sendMessage(const spMessageHandler handler, const Message message) {nsecs_t now systemTime(SYSTEM_TIME_MONOTONIC);sendMessageAtTime(now, handler, message);
}void Looper::sendMessageDelayed(nsecs_t uptimeDelay, const spMessageHandler handler,const Message message) {nsecs_t now systemTime(SYSTEM_TIME_MONOTONIC);sendMessageAtTime(now uptimeDelay, handler, message);
}void Looper::sendMessageAtTime(nsecs_t uptime, const spMessageHandler handler,const Message message) {{ // acquire lockAutoMutex _l(mLock);size_t messageCount mMessageEnvelopes.size();while (i messageCount uptime mMessageEnvelopes.itemAt(i).uptime) {i 1;}MessageEnvelope messageEnvelope(uptime, handler, message);//找到答案了: mMessageEnvelopes中message哪里来的?mMessageEnvelopes.insertAt(messageEnvelope, i, 1);if (mSendingMessage) {return;}} // release lockif (i 0) {wake();}
}上面的问题解答后又来两个新疑问:
MessageQueue::setEventConnection(…) 什么时候有谁调用的 mEventTube是个什么玩意
下一篇文章继续深入分析然后画图…
