android开机动画启动流程

从android的Surface Flinger服务启动分析知道，开机动画是在SurfaceFlinger实例通过调用startBootAnim()启动的。

下面我们就一起学习BootAnim是如何启动和结束的，我精读代码前都喜欢先描出框架图，以此图为基础再去研读会达到事半功倍的效果。好吧，直接上图。

技术分享

内核起来后会启动第一个进程，即init进程。

init进程会根据init.rc配置启动surfaceflinger进程。

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service surfaceflinger /system/bin/surfaceflinger
class main
user system
group graphics drmrpc
onrestart restart zygote

surfaceflinger进程便启动了，跟着就会跑进程的main()函数。

frameworks/native/services/surfaceflinger/main_surfaceflinger.cpp

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int main(int argc, char** argv) {
....
// instantiate surfaceflinger
sp<SurfaceFlinger> flinger = new SurfaceFlinger();//创建surfaceflinger服务实例
....
flinger->init();
// publish surface flinger
sp<IServiceManager> sm(defaultServiceManager());
sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false);//注册到service manager里
// run in this thread
flinger->run();//开跑
return 0;
}

首先new一个SurfaceFlinger实例，然后init，然后run

frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

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void SurfaceFlinger::init() {
ALOGI( "SurfaceFlinger's main thread ready to run. "
"Initializing graphics H/W...");
.....
// start boot animation
startBootAnim();//开始播放动画
}

初始化graphics之后，就调用startBootAnim()播放开机动画。

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void SurfaceFlinger::startBootAnim() {
// start boot animation
mBootFinished = false;
property_set("service.bootanim.exit", "0");//这个会有bootanimation进程周期检测,=1退出动画
property_set("ctl.start", "bootanim");//通过ctl.start命令启动bootanim
}

把service.bootanim.exit属性设为0，这个属性bootanimation进程里会周期检查，=1时就退出动画，这里=0表示要播放动画。

后面通过ctl.start的命令启动bootanim进程，动画就开始播放了。

下面来到bootanimation的实现

frameworks/base/cmds/bootanimation/bootanimation_main.cpp

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int main(int argc, char** argv)
{
sp<ProcessState> proc(ProcessState::self());
ProcessState::self()->startThreadPool();
// create the boot animation object
sp<BootAnimation> boot = new BootAnimation();//创建BootAnimation实例
IPCThreadState::self()->joinThreadPool();//binder线程池，与surfaceflinger通信用的。
}
return 0;
}

new一个BootAnimation实例,然后建个binder线程池，因为BootAnimation在显示动画时要与SurfaceFlinger服务进程通信，所以要启个binder线程池。

frameworks/base/cmds/bootanimation/BootAnimation.cpp

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BootAnimation::BootAnimation() : Thread(false)
{
mSession = new SurfaceComposerClient();//创建一个对象
}

创建实例时，构造函数就会被调用，new一个SurfaceComposerClient实例，他是用来与surfaceflinger通信的

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void BootAnimation::onFirstRef() {
status_t err = mSession->linkToComposerDeath(this);//注册surfaceflinger死亡消息的通知书
ALOGE_IF(err, "linkToComposerDeath failed (%s) ", strerror(-err));
if (err == NO_ERROR) {
run("BootAnimation", PRIORITY_DISPLAY);//开跑
}
}

linkTocomposerDeath的作用是当surfaceflinger死掉是，BootAnimation就会得到通知。

如下，收到通知后就退出动画了，因为surfaceflinger都挂掉了，播放不了了。

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void BootAnimation::binderDied(const wp<IBinder>& who)
{
// woah, surfaceflinger died!
ALOGD("SurfaceFlinger died, exiting...");
// calling requestExit() is not enough here because the Surface code
// might be blocked on a condition variable that will never be updated.
kill( getpid(), SIGKILL );//收到surfaceflinger死亡的消息，好吧自己也跟着去了。
requestExit();
}

另一个函数run()在BootAnimation的父类Thead里，用来创建一个线程并跑起来。

父类

system/core/libutils/Threads.cpp

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status_t Thread::run(const char* name, int32_t priority, size_t stack)
{
...
if (mCanCallJava) {
res = createThreadEtc(_threadLoop,//创建线程
this, name, priority, stack, &mThread);
} else {
res = androidCreateRawThreadEtc(_threadLoop,
this, name, priority, stack, &mThread);
}
....
}

创建_threadLoop线程

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int Thread::_threadLoop(void* user)
{
....
do {
bool result;
if (first) {
first = false;
self->mStatus = self->readyToRun();//这个函数被bootanimation重写了
result = (self->mStatus == NO_ERROR);
if (result && !self->exitPending()) {
...
result = self->threadLoop();//这个函数被bootanimation重写了
}
} else {
result = self->threadLoop();
}
...
return 0;
}

readyToRun函数实现

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status_t BootAnimation::readyToRun() {
mAssets.addDefaultAssets();
sp<IBinder> dtoken(SurfaceComposerClient::getBuiltInDisplay(
ISurfaceComposer::eDisplayIdMain));
DisplayInfo dinfo;
status_t status = SurfaceComposerClient::getDisplayInfo(dtoken, &dinfo);
if (status)
return -1;
char value[PROPERTY_VALUE_MAX];
property_get("persist.panel.orientation", value, "0");
int orient = atoi(value) / 90;
if(orient == eOrientation90 || orient == eOrientation270) {
int temp = dinfo.h;
dinfo.h = dinfo.w;
dinfo.w = temp;
}
Rect destRect(dinfo.w, dinfo.h);
mSession->setDisplayProjection(dtoken, orient, destRect, destRect);
// create the native surface
sp<SurfaceControl> control = session()->createSurface(String8("BootAnimation"),
dinfo.w, dinfo.h, PIXEL_FORMAT_RGB_565);
SurfaceComposerClient::openGlobalTransaction();
control->setLayer(0x40000000);
SurfaceComposerClient::closeGlobalTransaction();
sp<Surface> s = control->getSurface();
// initialize opengl and egl
const EGLint attribs[] = {
EGL_RED_SIZE, 8,
EGL_GREEN_SIZE, 8,
EGL_BLUE_SIZE, 8,
EGL_DEPTH_SIZE, 0,
EGL_NONE
};
EGLint w, h, dummy;
EGLint numConfigs;
EGLConfig config;
EGLSurface surface;
EGLContext context;
EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
eglInitialize(display, 0, 0);
eglChooseConfig(display, attribs, &config, 1, &numConfigs);
surface = eglCreateWindowSurface(display, config, s.get(), NULL);
context = eglCreateContext(display, config, NULL, NULL);
eglQuerySurface(display, surface, EGL_WIDTH, &w);
eglQuerySurface(display, surface, EGL_HEIGHT, &h);
if (eglMakeCurrent(display, surface, surface, context) == EGL_FALSE)
return NO_INIT;
mDisplay = display;
mContext = context;
mSurface = surface;
mWidth = w;
mHeight = h;
mFlingerSurfaceControl = control;
mFlingerSurface = s;
mAndroidAnimation = true;
// If the device has encryption turned on or is in process
// of being encrypted we show the encrypted boot animation.
char decrypt[PROPERTY_VALUE_MAX];
property_get("vold.decrypt", decrypt, "");
bool encryptedAnimation = atoi(decrypt) != 0 || !strcmp("trigger_restart_min_framework", decrypt);
if ((encryptedAnimation &&
(access(SYSTEM_ENCRYPTED_BOOTANIMATION_FILE, R_OK) == 0) &&
(mZip.open(SYSTEM_ENCRYPTED_BOOTANIMATION_FILE) == NO_ERROR)) ||
((access(USER_BOOTANIMATION_FILE, R_OK) == 0) &&
(mZip.open(USER_BOOTANIMATION_FILE) == NO_ERROR)) ||
((access(SYSTEM_BOOTANIMATION_FILE, R_OK) == 0) &&
(mZip.open(SYSTEM_BOOTANIMATION_FILE) == NO_ERROR))) {
mAndroidAnimation = false;
}
return NO_ERROR;
}

threadloop实现

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bool BootAnimation::threadLoop()
{
bool r;
if (mAndroidAnimation) {
r = android();//显示android默认动画
} else {
r = movie();//显示自定义的动画
}
// No need to force exit anymore
property_set(EXIT_PROP_NAME, "0");
eglMakeCurrent(mDisplay, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
eglDestroyContext(mDisplay, mContext);
eglDestroySurface(mDisplay, mSurface);
mFlingerSurface.clear();
mFlingerSurfaceControl.clear();
eglTerminate(mDisplay);
IPCThreadState::self()->stopProcess();
return r;
}

movie()的实现

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bool BootAnimation::movie()
{
//读取bootanimation.zip文件并解释
// clear screen
//下面是循环显示
for (int i=0 ; i<pcount ; i++) {
const Animation::Part& part(animation.parts[i]);
const size_t fcount = part.frames.size();
glBindTexture(GL_TEXTURE_2D, 0);
for (int r=0 ; !part.count || r<part.count ; r++) {
// Exit any non playuntil complete parts immediately
if(exitPending() && !part.playUntilComplete)
break;
for (int j=0 ; j<fcount && (!exitPending() || part.playUntilComplete) ; j++) {
const Animation::Frame& frame(part.frames[j]);
nsecs_t lastFrame = systemTime();
if (r > 0) {
glBindTexture(GL_TEXTURE_2D, frame.tid);
} else {
if (part.count != 1) {
glGenTextures(1, &frame.tid);
glBindTexture(GL_TEXTURE_2D, frame.tid);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
}
initTexture(
frame.map->getDataPtr(),
frame.map->getDataLength());
}
if (!clearReg.isEmpty()) {
Region::const_iterator head(clearReg.begin());
Region::const_iterator tail(clearReg.end());
glEnable(GL_SCISSOR_TEST);
while (head != tail) {
const Rect& r(*head++);
glScissor(r.left, mHeight - r.bottom,
r.width(), r.height());
glClear(GL_COLOR_BUFFER_BIT);
}
glDisable(GL_SCISSOR_TEST);
}
glDrawTexiOES(xc, yc, 0, animation.width, animation.height);
eglSwapBuffers(mDisplay, mSurface);
nsecs_t now = systemTime();
nsecs_t delay = frameDuration - (now - lastFrame);
//ALOGD("%lld, %lld", ns2ms(now - lastFrame), ns2ms(delay));
lastFrame = now;
if (delay > 0) {
struct timespec spec;
spec.tv_sec = (now + delay) / 1000000000;
spec.tv_nsec = (now + delay) % 1000000000;
int err;
do {
err = clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &spec, NULL);
} while (err<0 && errno == EINTR);
}
checkExit();//检测是否退出动画
}
usleep(part.pause * ns2us(frameDuration));
// For infinite parts, we've now played them at least once, so perhaps exit
if(exitPending() && !part.count)
break;
}
// free the textures for this part
if (part.count != 1) {
for (int j=0 ; j<fcount ; j++) {
const Animation::Frame& frame(part.frames[j]);
glDeleteTextures(1, &frame.tid);
}
}
}
return false;
}

那么到movie为止，动画是在播放了，而且还在循环检测是否退出，即checkExit()

checkExit()的实现

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void BootAnimation::checkExit() {
// Allow surface flinger to gracefully request shutdown
char value[PROPERTY_VALUE_MAX];
property_get(EXIT_PROP_NAME, value, "0");//属性为1，说明要退出了
int exitnow = atoi(value);
if (exitnow) {
requestExit();
}
}

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property_get(EXIT_PROP_NAME, value, "0");检测这个属性，=1就退出动画

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#define EXIT_PROP_NAME "service.bootanim.exit"

这个属性就是上面讲到的，等到launcher跑起来后就会置1

那动画是什么时候退出的？

当launcher应用程序主线程跑起来后，如果主线程处于空闲，就会向ActivityManagerService发送一个activityIdle的消息。

应用程序主线程是ActivityThread.java来描述的，activityIdle是这个类来实现的

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private class Idler implements MessageQueue.IdleHandler {
...
IActivityManager am = ActivityManagerNative.getDefault();
...
try {
am.activityIdle(a.token, a.createdConfig, stopProfiling);
a.createdConfig = null;
} catch (RemoteException ex) {
// Ignore
}
....
}

上面的ActivityManagerNavtive.getDefault()得到am

来到frameworks/base/core/java/android/app/ActivityManagerNative.java

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static public IActivityManager getDefault() {
return gDefault.get();//getDefault的实现
}

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private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() {
protected IActivityManager create() {
IBinder b = ServiceManager.getService("activity");
if (false) {
Log.v("ActivityManager", "default service binder = " + b);
}
IActivityManager am = asInterface(b);
if (false) {
Log.v("ActivityManager", "default service = " + am);
}
return am;
}
};

gDefault实际上是IActivityManager,往下看

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class ActivityManagerProxy implements IActivityManager
{

ActivityManagerProxy实现了IActivityManager

那么am.activityIdle()就是ActivityManagerProxy里的函数，如下

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public void activityIdle(IBinder token, Configuration config, boolean stopProfiling)
throws RemoteException
{
...
mRemote.transact(ACTIVITY_IDLE_TRANSACTION, data, reply, IBinder.FLAG_ONEWAY);//发送ACTIVITY_IDLE_TRANSACTION
....
}

发送了ACTIVITY_IDLE_TRANSACTION的进程间通信，这个消息被ActivityManagerNative接收处理了。

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case ACTIVITY_IDLE_TRANSACTION: {//收到消息
data.enforceInterface(IActivityManager.descriptor);
IBinder token = data.readStrongBinder();
Configuration config = null;
if (data.readInt() != 0) {
config = Configuration.CREATOR.createFromParcel(data);
}
boolean stopProfiling = data.readInt() != 0;
if (token != null) {
activityIdle(token, config, stopProfiling);//这个函数在ActivityManagerService被重写
}
reply.writeNoException();
return true;
}

收到消息后就调用了activityIdle函数，这个函数被ActivityManagerService重写了，如下

frameworks/base/services/java/com/android/server/am/ActivityManagerService.java

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@Override
public final void activityIdle(IBinder token, Configuration config, boolean stopProfiling) {
final long origId = Binder.clearCallingIdentity();
synchronized (this) {
ActivityStack stack = ActivityRecord.getStackLocked(token);
if (stack != null) {
ActivityRecord r =
mStackSupervisor.activityIdleInternalLocked(token, false, config);
if (stopProfiling) {
if ((mProfileProc == r.app) && (mProfileFd != null)) {
try {
mProfileFd.close();
} catch (IOException e) {
}
clearProfilerLocked();
}
}
}
}
Binder.restoreCallingIdentity(origId);
}

调用activityIdleInternalLocked函数，在下面实现

frameworks/base/services/java/com/android/server/am/ActivityStackSupervisor.java

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final ActivityRecord activityIdleInternalLocked(final IBinder token, boolean fromTimeout,
Configuration config) {
....
if (enableScreen) {
mService.enableScreenAfterBoot();//调ActivityManagerService类的enableScreenAfterBoot()函数
}
....
if (activityRemoved) {
resumeTopActivitiesLocked();
}
return r;
}

来到frameworks/base/services/java/com/android/server/am/ActivityManagerService.java

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void enableScreenAfterBoot() {
EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_ENABLE_SCREEN,
SystemClock.uptimeMillis());
mWindowManager.enableScreenAfterBoot();//调WindowManagerService类里的enableScreenAfterBoot()函数
synchronized (this) {
updateEventDispatchingLocked();
}
}

来到frameworks/base/services/java/com/android/server/wm/WindowManagerService.java

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public void enableScreenAfterBoot() {
....
performEnableScreen();
}

performEnableScreen()实现

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public void performEnableScreen() {
..
surfaceFlinger.transact(IBinder.FIRST_CALL_TRANSACTION, // BOOT_FINISHED
data, null, 0);
....
}

发送了FIRST_CALL_TRANSACTION的请求

因为从下面知道FIRST_CALL_TRANSACTION = BOOT_FINISHED

所以BnSurfaceComposer收到消息

frameworks/native/include/gui/ISurfaceComposer.h

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class BnSurfaceComposer: public BnInterface<ISurfaceComposer> {
public:
enum {
// Note: BOOT_FINISHED must remain this value, it is called from
// Java by ActivityManagerService.
BOOT_FINISHED = IBinder::FIRST_CALL_TRANSACTION,
...
};
virtual status_t onTransact(uint32_t code, const Parcel& data,
Parcel* reply, uint32_t flags = 0);
};

[cpp] view plain copy

</pre>frameworks/native/libs/gui/ISurfaceComposer.cpp<pre name="code" class="cpp">status_t BnSurfaceComposer::onTransact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
switch(code) {
....
case BOOT_FINISHED: {
CHECK_INTERFACE(ISurfaceComposer, data, reply);
bootFinished();//调用 bootFinished()
return NO_ERROR;
}
....
}
// should be unreachable
return NO_ERROR;
}

bootFinished()函数BpSurfaceComposer里实现，但发现没有，他又发了一个BOOT_FINISHED，死循环了，其实没有。bootFinished()被SurfaceFlinger类重写了

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class BpSurfaceComposer : public BpInterface<ISurfaceComposer>
{
virtual void bootFinished()
{
Parcel data, reply;
data.writeInterfaceToken(ISurfaceComposer::getInterfaceDescriptor());
remote()->transact(BnSurfaceComposer::BOOT_FINISHED, data, &reply);
}

重写

frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

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void SurfaceFlinger::bootFinished()
{
...
property_set("service.bootanim.exit", "1");
}

把service.bootanim.exit写成1，然后bootanimation进程的checkExit()检测到就退出进程，停止播放。

来源：oschina

链接：https://my.oschina.net/u/920274/blog/3009691

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