我们知道系统开机时会通过ActivityManagerService把第一个Home应用Launcher3启动起来，而在Activity的启动过程中会调用ActivityThread.java中的handleResumeActivity()方法来进一步调用Activity的onResume()方法。
frameworks\base\core\java\android\app\ActivityThread.java
@Override
public void handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward,
String reason) {
// If we are getting ready to gc after going to the background, well
// we are back active so skip it.
unscheduleGcIdler();
mSomeActivitiesChanged = true;
// TODO Push resumeArgs into the activity for consideration
final ActivityClientRecord r = performResumeActivity(token, finalStateRequest, reason);
if (r == null) {
// We didn't actually resume the activity, so skipping any follow-up actions.
return;
}
...
r.nextIdle = mNewActivities;
mNewActivities = r;
if (localLOGV) Slog.v(TAG, "Scheduling idle handler for " + r);
Looper.myQueue().addIdleHandler(new Idler());
}在方法的最后调用MessageQueue的addIdleHandler(）将空闲处理器添加到了消息队列中。以便在在Launcher启动完后执行IdleHandler()的queueIdle()。
frameworks\base\core\java\android\os\MessageQueue.java
Message next() {
...
// If first time idle, then get the number of idlers to run.
// Idle handles only run if the queue is empty or if the first message
// in the queue (possibly a barrier) is due to be handled in the future.
if (pendingIdleHandlerCount < 0
&& (mMessages == null || now < mMessages.when)) {
pendingIdleHandlerCount = mIdleHandlers.size();
}
if (pendingIdleHandlerCount <= 0) {
// No idle handlers to run. Loop and wait some more.
mBlocked = true;
continue;
}
if (mPendingIdleHandlers == null) {
mPendingIdleHandlers = new IdleHandler[Math.max(pendingIdleHandlerCount, 4)];
}
mPendingIdleHandlers = mIdleHandlers.toArray(mPendingIdleHandlers);
}
// Run the idle handlers.
// We only ever reach this code block during the first iteration.
for (int i = 0; i < pendingIdleHandlerCount; i++) {
final IdleHandler idler = mPendingIdleHandlers[i];
mPendingIdleHandlers[i] = null; // release the reference to the handler
boolean keep = false;
try {
keep = idler.queueIdle();
} catch (Throwable t) {
Log.wtf(TAG, "IdleHandler threw exception", t);
}
if (!keep) {
synchronized (this) {
mIdleHandlers.remove(idler);
}
}
}
// Reset the idle handler count to 0 so we do not run them again.
pendingIdleHandlerCount = 0;
// While calling an idle handler, a new message could have been delivered
// so go back and look again for a pending message without waiting.
nextPollTimeoutMillis = 0;
}
}当应用没有其它消息处理时，空闲处理器IdlerHander会经过MessageQueue的next()函数（消息循环）得到处理。如果应用没有添加IdleHandler到MessageQueue的话，那么在消息循环处理函数里只会有一个IdleHandler，并且处理完后就进行删除。
frameworks\base\core\java\android\app\ActivityThread.java
private class Idler implements MessageQueue.IdleHandler {
@Override
public final boolean queueIdle() {
ActivityClientRecord a = mNewActivities;
boolean stopProfiling = false;
if (mBoundApplication != null && mProfiler.profileFd != null
&& mProfiler.autoStopProfiler) {
stopProfiling = true;
}
if (a != null) {
mNewActivities = null;
IActivityManager am = ActivityManager.getService();
ActivityClientRecord prev;
do {
if (localLOGV) Slog.v(
TAG, "Reporting idle of " + a +
" finished=" +
(a.activity != null && a.activity.mFinished));
if (a.activity != null && !a.activity.mFinished) {
try {
am.activityIdle(a.token, a.createdConfig, stopProfiling);
a.createdConfig = null;
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
prev = a;
a = a.nextIdle;
prev.nextIdle = null;
} while (a != null);
}
if (stopProfiling) {
mProfiler.stopProfiling();
}
ensureJitEnabled();
return false;
}
}queueIdle()里通过Binder调用ActivityManagerService的activityIdle()方法。
frameworks\base\services\core\java\com\android\server\am\ActivityManagerService.java
@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 /* fromTimeout */,
false /* processPausingActivities */, config);
if (stopProfiling) {
if ((mProfileProc == r.app) && mProfilerInfo != null) {
clearProfilerLocked();
}
}
}
}
Binder.restoreCallingIdentity(origId);
}
AMS转交给ActivityStackSupervisor进一步处理。
frameworks\base\services\core\java\com\android\server\am\ActivityStackSupervisor.java
// Checked.
@GuardedBy("mService")
final ActivityRecord activityIdleInternalLocked(final IBinder token, boolean fromTimeout,
boolean processPausingActivities, Configuration config) {
...
if (r != null) {
if (DEBUG_IDLE) Slog.d(TAG_IDLE, "activityIdleInternalLocked: Callers="
+ Debug.getCallers(4));
mHandler.removeMessages(IDLE_TIMEOUT_MSG, r);
r.finishLaunchTickingLocked();
if (fromTimeout) {
reportActivityLaunchedLocked(fromTimeout, r, -1, -1);
}
// This is a hack to semi-deal with a race condition
// in the client where it can be constructed with a
// newer configuration from when we asked it to launch.
// We'll update with whatever configuration it now says
// it used to launch.
if (config != null) {
r.setLastReportedGlobalConfiguration(config);
}
// We are now idle. If someone is waiting for a thumbnail from
// us, we can now deliver.
r.idle = true;
//Slog.i(TAG, "IDLE: mBooted=" + mBooted + ", fromTimeout=" + fromTimeout);
if (isFocusedStack(r.getStack()) || fromTimeout) {
booting = checkFinishBootingLocked();
}
}
...
// Stop any activities that are scheduled to do so but have been
// waiting for the next one to start.
for (int i = 0; i < NS; i++) {
r = stops.get(i);
final ActivityStack stack = r.getStack();
if (stack != null) {
if (r.finishing) {
stack.finishCurrentActivityLocked(r, ActivityStack.FINISH_IMMEDIATELY, false,
"activityIdleInternalLocked");
} else {
stack.stopActivityLocked(r);
}
}
}
...
return r;
}activityIdleInternalLocked会调用checkFinishBootingLocked()来关闭开机动画的显示，而且还会调用finishCurrentActivityLocked()来触发Activity的onPause()调用。
frameworks\base\services\core\java\com\android\server\am\ActivityStackSupervisor.java
/**
* Called when the frontmost task is idle.
* @return the state of mService.mBooting before this was called.
*/
@GuardedBy("mService")
private boolean checkFinishBootingLocked() {
final boolean booting = mService.mBooting;
boolean enableScreen = false;
mService.mBooting = false;
if (!mService.mBooted) {
mService.mBooted = true;
enableScreen = true;
}
if (booting || enableScreen) {
mService.postFinishBooting(booting, enableScreen);
}
return booting;
}
通过log打印我们可以知道booting和enableScreen的值都是true.从而FINISH_BOOTING_MSG消息处理的finishBooting()和enableScreenAfterBoot()方法都会执行。
frameworks\base\services\core\java\com\android\server\am\ActivityManagerService.java
void postFinishBooting(boolean finishBooting, boolean enableScreen) {
mHandler.sendMessage(mHandler.obtainMessage(FINISH_BOOTING_MSG,
finishBooting ? 1 : 0, enableScreen ? 1 : 0));
}case FINISH_BOOTING_MSG: {
if (msg.arg1 != 0) {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "FinishBooting");
finishBooting();
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
if (msg.arg2 != 0) {
enableScreenAfterBoot();
}
break;
}enableScreenAfterBoot()经过多次调用就会执行WMS的performEnableScreen()方法，在此方法中我们就可以看到surfaceflinger的身影了，通过transact调用发送BOOT_FINISHED的消息给surfaceflinger。
frameworks\base\services\core\java\com\android\server\wm\WindowManagerService.java
private void performEnableScreen() {
...
try {
IBinder surfaceFlinger = ServiceManager.getService("SurfaceFlinger");
if (surfaceFlinger != null) {
Slog.i(TAG_WM, "******* TELLING SURFACE FLINGER WE ARE BOOTED!");
Parcel data = Parcel.obtain();
data.writeInterfaceToken("android.ui.ISurfaceComposer");
surfaceFlinger.transact(IBinder.FIRST_CALL_TRANSACTION, // BOOT_FINISHED
data, null, 0);
data.recycle();
}
} catch (RemoteException ex) {
Slog.e(TAG_WM, "Boot completed: SurfaceFlinger is dead!");
}
...
}WMS最终通过binder调用，经过ISurfaceComposer处理，最终通知SurfaceFlinger关闭开机动画。
frameworks\native\services\surfaceflinger\SurfaceFlinger.cpp
void SurfaceFlinger::bootFinished()
{
if (mStartPropertySetThread->join() != NO_ERROR) {
ALOGE("Join StartPropertySetThread failed!");
}
const nsecs_t now = systemTime();
const nsecs_t duration = now - mBootTime;
ALOGI("Boot is finished (%ld ms)", long(ns2ms(duration)) );
// wait patiently for the window manager death
const String16 name("window");
sp<IBinder> window(defaultServiceManager()->getService(name));
if (window != 0) {
window->linkToDeath(static_cast<IBinder::DeathRecipient*>(this));
}
if (mVrFlinger) {
mVrFlinger->OnBootFinished();
}
// stop boot animation
// formerly we would just kill the process, but we now ask it to exit so it
// can choose where to stop the animation.
property_set("service.bootanim.exit", "1");
const int LOGTAG_SF_STOP_BOOTANIM = 60110;
LOG_EVENT_LONG(LOGTAG_SF_STOP_BOOTANIM,
ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));
sp<LambdaMessage> readProperties = new LambdaMessage([&]() {
readPersistentProperties();
});
postMessageAsync(readProperties);
}在高通的平台上实验证明，只要设置了service.bootanim.exit=1，开机动画就会立马关闭。