android的Surface Flinger服务启动分析
这篇文章android启动流程讲到android的启动流程，其实中间还蕴藏了SurfaceFlinger服务的内容，但没有包括进去，目的是为尽可能简单的讲述android启动流程，从整体上把握。
好吧，现在咱们就一起学习下Surface Flinger中如何启动的。
在android4.3与android4.4版本上有所不同，下面是两个版本简单的流程图
在Andoird4.4系统出现以前，Surface Flinger服务是由system server启动的。
frameworks/base/services/java/com/android/server/SystemServer.java
public class SystemServer {
<span style="white-space:pre"> </span>...
public static void main(String[] args) {
...
System.loadLibrary("android_servers");//加载库
init1(args);//调用库函数init1()
}
<span style="white-space:pre"> </span>public static final void init2() {
Slog.i(TAG, "Entered the Android system server!");
Thread thr = new ServerThread();
thr.setName("android.server.ServerThread");
thr.start();
}
}
我们看到，首先加载了android_servers的库，然后调用库里的init1()函数完成后面的工作。
小插曲：看到init2()函数没？这个函数后面会被system_init()函数调用。
继而new了一个ServerThread线程，这是非常重要，android启动流程讲到Java系统服务，就是这里被启动的。
init1()函数在下面文件实现
frameworks/base/services/jni/com_android_server_SystemServer.cpp
extern "C" int system_init();
static void android_server_SystemServer_init1(JNIEnv* env, jobject clazz)
{
system_init();//调用这个
}
/*
* JNI registration.
*/
static JNINativeMethod gMethods[] = {
/* name, signature, funcPtr */
{ "init1", "([Ljava/lang/String;)V", (void*) android_server_SystemServer_init1 },//映射到这
};
int register_android_server_SystemServer(JNIEnv* env)
{
return jniRegisterNativeMethods(env, "com/android/server/SystemServer",
gMethods, NELEM(gMethods));
}
init1()函数实际上映射到android_server_SystemServer_init1()。然后调用另外一个函数system_init()完成后面的工作。
system_init1()函数由下面文件实现。
frameworks/base/cmds/system_server/library/system_init.cpp
extern "C" status_t system_init()
{
ALOGI("Entered system_init()");
<span style="white-space:pre"> </span>...
char propBuf[PROPERTY_VALUE_MAX];
property_get("system_init.startsurfaceflinger", propBuf, "1");
if (strcmp(propBuf, "1") == 0) {
// Start the SurfaceFlinger
SurfaceFlinger::instantiate();//启动SurfaceFlinger
}
property_get("system_init.startsensorservice", propBuf, "1");
if (strcmp(propBuf, "1") == 0) {
// Start the sensor service
SensorService::instantiate();//启动SensorService
}
...
jclass clazz = env->FindClass("com/android/server/SystemServer");
if (clazz == NULL) {
return UNKNOWN_ERROR;
}
jmethodID methodId = env->GetStaticMethodID(clazz, "init2", "()V");//仔细看，这里还调用了java类的init2()函数在上面的systemserver.java里。
if (methodId == NULL) {
return UNKNOWN_ERROR;
}
...
}
system_init()函数调用SurfaceFlinger的instantiate()函数来启动SurfaceFlinger。instantiate是实际上来自SurfaceFlinger父类BinderService
下面是函数的实现文件
frameworks/native/include/binder/BinderService.h
class BinderService
{
public:
.....
static void instantiate() { publish(); }
...
};
BinderService的静态成员函数又调用了另一个静态函数publish()来完成工作。
下面是实现
template<typename SERVICE>
class BinderService
{
public:
static status_t publish(bool allowIsolated = false) {
sp<IServiceManager> sm(defaultServiceManager());
return sm->addService(//注册到ServiceManager中去。
String16(SERVICE::getServiceName()),
new SERVICE(), allowIsolated);//new一个SurfaceFlinger实例
}
...
};
BinderService是一个类模板，当BinderService类被SurfaceFlinger类继承时，模板参数SERVICE就是SurfaceFlinger。所以这里的publish()函数实际上是new了一个SurfaceFlinger实例，并把它注册到Service Manager中去。
从sp<IServiceManager> sm(defaultServiceManager());知道sm是一个强指针。
所以addService的第二个参数SurfaceFlinger的引用是属于强指针引用，这时会调用SurfaceFlinger实例的成员函数onFristRef。关于强指针请参考Android系统的智能指针（轻量级指针、强指针和弱指针）的实现原理分析
onFristRef函数实现
frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
void SurfaceFlinger::onFirstRef()
{
mEventQueue.init(this);
run("SurfaceFlinger", PRIORITY_URGENT_DISPLAY);//调用父类Thread的成员函数run()完成后面工作
// Wait for the main thread to be done with its initialization
mReadyToRunBarrier.wait();
}
如下：
frameworks/native/libs/utils/Threads.cpp
status_t Thread::run(const char* name, int32_t priority, size_t stack)
{
...
if (mCanCallJava) {
res = createThreadEtc(_threadLoop,//创建线程__threadLoop
this, name, priority, stack, &mThread);
} else {
res = androidCreateRawThreadEtc(_threadLoop,
this, name, priority, stack, &mThread);
}
...
}
__threadLoop线程实现
int Thread::_threadLoop(void* user)
{
....
do {
bool result;
if (first) {
first = false;
self->mStatus = self->readyToRun();//readyToRun函数，在SurfaceFlinger实例里实现
...
result = self->threadLoop();
}
} else {
result = self->threadLoop();//threadLoop函数，在SurfaceFlinger实例里实现
}
....
}
...
} while(strong != 0);
return 0;
}
从上面看出，__threadLoop线程分别调用了readyToRun函数，然后就循环执行threadLoop()函数。
这两个函数都在SurfaceFlinger实例里重写了。
如下：
frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
status_t SurfaceFlinger::readyToRun()
{
ALOGI( "SurfaceFlinger's main thread ready to run. "
"Initializing graphics H/W...");
.....
for (size_t i=0 ; i<DisplayDevice::NUM_DISPLAY_TYPES ; i++) {
DisplayDevice::DisplayType type((DisplayDevice::DisplayType)i);
// set-up the displays that are already connected
if (mHwc->isConnected(i) || type==DisplayDevice::DISPLAY_PRIMARY) {
// All non-virtual displays are currently considered secure.
bool isSecure = true;
createBuiltinDisplayLocked(type);
wp<IBinder> token = mBuiltinDisplays[i];
sp<DisplayDevice> hw = new DisplayDevice(this,
type, allocateHwcDisplayId(type), isSecure, token,
new FramebufferSurface(*mHwc, i),
mEGLConfig);
if (i > DisplayDevice::DISPLAY_PRIMARY) {
// FIXME: currently we don't get blank/unblank requests
// for displays other than the main display, so we always
// assume a connected display is unblanked.
ALOGD("marking display %d as acquired/unblanked", i);
hw->acquireScreen();
}
mDisplays.add(token, hw);
}
}
...
// initialize OpenGL ES
DisplayDevice::makeCurrent(mEGLDisplay, hw, mEGLContext);
initializeGL(mEGLDisplay);
// start the EventThread
mEventThread = new EventThread(this);
mEventQueue.setEventThread(mEventThread);
....
如上ReadyToRun开始初步化display devices,然后创建消息线程，然后就调用startBootAnim();
好吧，可以看见开机动画了。
--------------------------------------------------------------------------------------------------------------------------------------------------
上面是android4.3的流程，下面分析一下android4.4流程，有点不太一样哦
android4.3是systemserver进程调用init1()函数来完成surfaceFlinger启动的。
android4.4则不同，由init直接创建。
init.rc
service surfaceflinger /system/bin/surfaceflinger
class main
user system
group graphics drmrpc
onrestart restart zygote
init进程直接根据init.rc配置启动了surfaceflinger进程。
frameworks/native/services/surfaceflinger/main_surfaceflinger.cpp
int main(int argc, char** argv) {
....
// instantiate surfaceflinger
sp<SurfaceFlinger> flinger = new SurfaceFlinger();//新实例
...
// initialize before clients can connect
flinger->init();//调用surfaceflinger的初始化函数
// publish surface flinger
sp<IServiceManager> sm(defaultServiceManager());
sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false);//向service manager注册服务
// run in this thread
flinger->run();//开跑
return 0;
}
来到surfaceflinger进程的main函数，new一个SurfaceFlinger实例，跟着调用SurfaceFlinger类的init()函数完成后面工作，然后向service manager注册服务
然后thread开跑。
frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
void SurfaceFlinger::init() {
ALOGI( "SurfaceFlinger's main thread ready to run. "
"Initializing graphics H/W...");
.....
// initialize our non-virtual displays
for (size_t i=0 ; i<DisplayDevice::NUM_BUILTIN_DISPLAY_TYPES ; i++) {
DisplayDevice::DisplayType type((DisplayDevice::DisplayType)i);
// set-up the displays that are already connected
if (mHwc->isConnected(i) || type==DisplayDevice::DISPLAY_PRIMARY) {
// All non-virtual displays are currently considered secure.
bool isSecure = true;
createBuiltinDisplayLocked(type);
wp<IBinder> token = mBuiltinDisplays[i];
sp<BufferQueue> bq = new BufferQueue(new GraphicBufferAlloc());
sp<FramebufferSurface> fbs = new FramebufferSurface(*mHwc, i, bq);
sp<DisplayDevice> hw = new DisplayDevice(this,
type, allocateHwcDisplayId(type), isSecure, token,
fbs, bq,
mEGLConfig);
if (i > DisplayDevice::DISPLAY_PRIMARY) {
// FIXME: currently we don't get blank/unblank requests
// for displays other than the main display, so we always
// assume a connected display is unblanked.
ALOGD("marking display %d as acquired/unblanked", i);
hw->acquireScreen();
}
mDisplays.add(token, hw);
}
}
...
// start the EventThread
...
mSFEventThread = new EventThread(sfVsyncSrc);
mEventQueue.setEventThread(mSFEventThread);
mEventControlThread = new EventControlThread(this);
mEventControlThread->run("EventControl", PRIORITY_URGENT_DISPLAY);
...
// set initial conditions (e.g. unblank default device)
initializeDisplays();
// start boot animation
startBootAnim();
}
这个init()函数与4.3系统的ReadyToRun()函数的功能是一样的，内容上有些不同，但大体也分成三个部分，第一硬件初始化，第二建立消息线程，第三启动开机动画。
void SurfaceFlinger::run() {
do {
waitForEvent();
} while (true);
}
最后调用run()函数开跑，看见没有，一直在等待消息呢。
后续我还会分析android L的代码，看看有什么不同。