继上篇文章Launcher进程的启动，我们继续分析Home界面的启动。
public final class ActivityThread {
......
public static final void main(String[] args) {
SamplingProfilerIntegration.start();
Process.setArgV0("<pre-initialized>");
Looper.prepareMainLooper();
if (sMainThreadHandler == null) {
sMainThreadHandler = new Handler();
}
ActivityThread thread = new ActivityThread();
thread.attach(false);
if (false) {
Looper.myLooper().setMessageLogging(new
LogPrinter(Log.DEBUG, "ActivityThread"));
}
Looper.loop();
if (Process.supportsProcesses()) {
throw new RuntimeException("Main thread loop unexpectedly exited");
}
thread.detach();
String name = (thread.mInitialApplication != null)
? thread.mInitialApplication.getPackageName()
: "<unknown>";
Slog.i(TAG, "Main thread of " + name + " is now exiting");
}
......
} thread.attach函数例如以下：private final void attach(boolean system) {
sThreadLocal.set(this);
mSystemThread = system;
if (!system) {
......
IActivityManager mgr = ActivityManagerNative.getDefault();
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
}
} else {
......
}
......
} static public IActivityManager getDefault()
{
if (gDefault != null) {
//if (Config.LOGV) Log.v(
// "ActivityManager", "returning cur default = " + gDefault);
return gDefault;
}
IBinder b = ServiceManager.getService("activity");
if (Config.LOGV) Log.v(
"ActivityManager", "default service binder = " + b);
gDefault = asInterface(b);
if (Config.LOGV) Log.v(
"ActivityManager", "default service = " + gDefault);
return gDefault;
} static public IActivityManager asInterface(IBinder obj)
{
if (obj == null) {
return null;
}
IActivityManager in =
(IActivityManager)obj.queryLocalInterface(descriptor);
if (in != null) {
return in;
}
return new ActivityManagerProxy(obj);
} 在ActivityThread类的成员函数attach中，调用ActivityManagerNative类的静态成员函数getDefault来获得ActivityMangerService的一个代理对象。代理对象的类型为ActivityMangerProxy。
mgr.attachApplication(mAppThread)实际上调用的是ActivityManagerProxy的attachApplication，例如以下：
class ActivityManagerProxy implements IActivityManager
{
public void attachApplication(IApplicationThread app) throws RemoteException
{
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(app.asBinder());
mRemote.transact(ATTACH_APPLICATION_TRANSACTION, data, reply, 0);
reply.readException();
data.recycle();
reply.recycle();
}
......
} 当中app为：final ApplicationThread mAppThread = new ApplicationThread();继承于ApplicationThreadNative，ApplicationThreadNative继承于Binder实现了IApplicationThread。
因为是同步传输，所以Launcher进程子线程睡眠等待，程序继续运行Looper.loop()，此时主线程的消息循环机制创立。
此时System进程Binder主线程池和子线程池都开启了，正在等待来自Launcher进程的请求。
System进程。接收到请求后，如上图的Binder进程间通信的省略步骤一样。会运行例如以下代码，是在System进程的一个子线程中运行：
public abstract class ActivityManagerNative extends Binder implements IActivityManager
{
......
public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
throws RemoteException {
switch (code) {
case ATTACH_APPLICATION_TRANSACTION: {
data.enforceInterface(IActivityManager.descriptor);
IApplicationThread app = ApplicationThreadNative.asInterface(
data.readStrongBinder());
if (app != null) {
attachApplication(app);
}
reply.writeNoException();
return true;
}
.......
}
首先生成BinderProxy对象。里面的mObject指向代理对象。向上转型为IBinder。然后生成ApplicationThreadProxy对象，里面mRemote指向BinderProxy对象。
因为ActivityManagerService类继承于ActivityManagerNative类，所以attachApplication。实际上运行的是位于ActivityManagerService中的。
public final class ActivityManagerService extends ActivityManagerNative{
public final void attachApplication(IApplicationThread thread) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid);
Binder.restoreCallingIdentity(origId);
}
}
.....
} 这里将操作转发给attachApplicationLocked函数，例如以下：public final class ActivityManagerService extends ActivityManagerNative
implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
......
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
// Find the application record that is being attached... either via
// the pid if we are running in multiple processes, or just pull the
// next app record if we are emulating process with anonymous threads.
ProcessRecord app;
if (pid != MY_PID && pid >= 0) {
synchronized (mPidsSelfLocked) {
app = mPidsSelfLocked.get(pid);//取回ProcessRecord对象。保存在app中，app就是用来描写叙述新创建的应用程序进程的
}
} else if (mStartingProcesses.size() > 0) {
......
} else {
......
}
if (app == null) {
......
return false;
}
......
String processName = app.processName;
try {
thread.asBinder().linkToDeath(new AppDeathRecipient(
app, pid, thread), 0);
} catch (RemoteException e) {
......
return false;
}
......
app.thread = thread;//thread设置为參数thread所指向的一个ApplicationThread代理对象
......
mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app);//删除ActivityMangerService所运行在的线程的消息队列中PROC_START_TIMEOUT_MSG消息
boolean normalMode = mProcessesReady || isAllowedWhileBooting(app.info);
......
thread.bindApplication(processName, app.instrumentationInfo != null
? app.instrumentationInfo : app.info, providers,
app.instrumentationClass, app.instrumentationProfileFile,
app.instrumentationArguments, app.instrumentationWatcher, testMode,
isRestrictedBackupMode || !normalMode,
mConfiguration, getCommonServicesLocked());
boolean badApp = false;
boolean didSomething = false;
// See if the top visible activity is waiting to run in this process...
ActivityRecord hr = mMainStack.topRunningActivityLocked(null);//位于栈顶的ActivityRecord是Home界面的ActivityRecord
if (hr != null && normalMode) {
if (hr.app == null && app.info.uid == hr.info.applicationInfo.uid
&& processName.equals(hr.processName)) {
try {
if (mMainStack.realStartActivityLocked(hr, app, true, true)) {//最后走这里
didSomething = true;
}
} catch (Exception e) {
......
}
} else {
......
}
}
......
return true;
}
......
} 在System进程的启动流程第二部分，最后一部分，ActivityManager以这个PID为keyword将一个ProcessRecord对象保存在了成员变量mPidsSelfLocked中。所以首先通过參数pid将这个ProcessRecord对象取回来。而且保存在app中。
然后对app初始化，当中最重要的是将它的成员变量thread设置为參数thread所指向的一个ApplicationThread代理对象。
这样，ActivityManagerService以后就能够通过这个ApplicationThread代理对象来和新创建的应用程序进程进行通信了。
还记得在System进程的启动流程第二部分，最后一部分，会向ActivityManagerService所运行的线程的消息队列发送一个类型为PROC_START_TIMEOUT_MSG的消息。而且指定这个消息在PROC_START_TIMEOUT毫秒之后处理。
Message msg = mHandler.obtainMessage(PROC_START_TIMEOUT_MSG); msg.obj = app; mHandler.sendMessageDelayed(msg, PROC_START_TIMEOUT);这里通过下面代码来删除ActivityMangerService所运行在的线程的消息队列中PROC_START_TIMEOUT_MSG消息，因为新的应用程序进程已经在规定的时间内启动起来了。
mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app)最后通过ActivityStack类的成员函数realStartActivityLocked来请求该应用程序进程启动一个Activity。
public class ActivityStack {
......
final boolean realStartActivityLocked(ActivityRecord r,
ProcessRecord app, boolean andResume, boolean checkConfig)
throws RemoteException {
......
r.app = app;//r的成员变量app的值设置为參数app，表示它描写叙述的Activity组件是在參数app所描写叙述的应用程序进程中启动的
......
int idx = app.activities.indexOf(r);
if (idx < 0) {
app.activities.add(r);//将该Activity加入到參数app所描写叙述的应用程序进程的Activity组件列表中
}
......
try {
......
List<ResultInfo> results = null;
List<Intent> newIntents = null;
if (andResume) {
results = r.results;
newIntents = r.newIntents;
}
......
app.thread.scheduleLaunchActivity(new Intent(r.intent), r,
System.identityHashCode(r),
r.info, r.icicle, results, newIntents, !andResume,
mService.isNextTransitionForward());
......
} catch (RemoteException e) {
......
}
......
return true;
}
......
}这里终于通过app.thread进入到ApplicationThreadProxy的scheduleLaunchActivity函数中，注意，这里的第二个參数r，是一个ActivityRecord类型的Binder对象。用来作来这个Activity的token值。
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Bundle state, List<ResultInfo> pendingResults,
List<Intent> pendingNewIntents, boolean notResumed, boolean isForward)
throws RemoteException {
Parcel data = Parcel.obtain();
data.writeInterfaceToken(IApplicationThread.descriptor);
intent.writeToParcel(data, 0);
data.writeStrongBinder(token);
data.writeInt(ident);
info.writeToParcel(data, 0);
data.writeBundle(state);
data.writeTypedList(pendingResults);
data.writeTypedList(pendingNewIntents);
data.writeInt(notResumed ? 1 : 0);
data.writeInt(isForward ? 1 : 0);
mRemote.transact(SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION, data, null,
IBinder.FLAG_ONEWAY);
data.recycle();
} 其Binder类图例如以下：
我们传递的数据token。是一个ActivityRecord类型的Binder对象。例如以下图：
1、运行完scheduleLaunchActivity，此时SystemServer进程向Launcher进程发送了两个Binder请求，一个是SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION，一个是ATTACH_APPLICATION_TRANSACTION的返回值。
2、因为Launcher进程在子线程中等待Binder进程间通信请求，所以分别处理这个两个请求，对于第二个请求的处理代码例如以下：
class ActivityManagerProxy implements IActivityManager
{
public void attachApplication(IApplicationThread app) throws RemoteException
{
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(app.asBinder());
mRemote.transact(ATTACH_APPLICATION_TRANSACTION, data, reply, 0);
reply.readException();
data.recycle();
reply.recycle();
}
......
}3、对于第一个Binder请求处理例如以下，如Binder类图所看到的，開始运行例如以下代码：
public abstract class ApplicationThreadNative extends Binder
implements IApplicationThread {
........
public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
throws RemoteException {
switch (code) {
case SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION:
{
data.enforceInterface(IApplicationThread.descriptor);
Intent intent = Intent.CREATOR.createFromParcel(data);
IBinder b = data.readStrongBinder();
int ident = data.readInt();
ActivityInfo info = ActivityInfo.CREATOR.createFromParcel(data);
Bundle state = data.readBundle();
List<ResultInfo> ri = data.createTypedArrayList(ResultInfo.CREATOR);
List<Intent> pi = data.createTypedArrayList(Intent.CREATOR);
boolean notResumed = data.readInt() != 0;
boolean isForward = data.readInt() != 0;
scheduleLaunchActivity(intent, b, ident, info, state, ri, pi,
notResumed, isForward);
return true;
}
.....
} 当中b为一个BinderProxy的Binder代理对象。指向了ActivityManagerService中与Launcher进程相应的一个AcitivityRecord对象，如上图所看到的。因为ApplicationThread继承于ApplicationThreadNative，所以真正运行的是ApplicationThread里面的scheduleLaunchActivity方法。
public final class ActivityThread {
......
private final class ApplicationThread extends ApplicationThreadNative {
......
// we use token to identify this activity without having to send the
// activity itself back to the activity manager. (matters more with ipc)
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Bundle state, List<ResultInfo> pendingResults,
List<Intent> pendingNewIntents, boolean notResumed, boolean isForward) {
ActivityClientRecord r = new ActivityClientRecord();
r.token = token;
r.ident = ident;
r.intent = intent;
r.activityInfo = info;
r.state = state;
r.pendingResults = pendingResults;
r.pendingIntents = pendingNewIntents;
r.startsNotResumed = notResumed;
r.isForward = isForward;
queueOrSendMessage(H.LAUNCH_ACTIVITY, r);
}
......
}
......
} 函数首先创建一个ActivityClientRecord实例，而且初始化它的成员变量，然后调用ActivityThread类的queueOrSendMessage函数进一步处理。public final class ActivityThread {
......
private final class ApplicationThread extends ApplicationThreadNative {
......
// if the thread hasn't started yet, we don't have the handler, so just
// save the messages until we're ready.
private final void queueOrSendMessage(int what, Object obj) {
queueOrSendMessage(what, obj, 0, 0);
}
......
private final void queueOrSendMessage(int what, Object obj, int arg1, int arg2) {
synchronized (this) {
......
Message msg = Message.obtain();
msg.what = what;
msg.obj = obj;
msg.arg1 = arg1;
msg.arg2 = arg2;
mH.sendMessage(msg);
}
}
......
}
......
} 因为眼下是在Binder子线程池中处理的请求。所以queueOrSendMessage眼下处于子线程，大家知道mH是主线程中Handler，刚刚完毕了Loop.loop()进入了消息循环。public final class ActivityThread {
......
private final class H extends Handler {
......
public void handleMessage(Message msg) {
......
switch (msg.what) {
case LAUNCH_ACTIVITY: {
ActivityClientRecord r = (ActivityClientRecord)msg.obj;
r.packageInfo = getPackageInfoNoCheck(
r.activityInfo.applicationInfo);
handleLaunchActivity(r, null);
} break;
......
}
......
}
......
} 这里最后调用ActivityThread类的handleLaunchActivity函数进一步处理。public final class ActivityThread {
......
private final void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
......
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
r.createdConfig = new Configuration(mConfiguration);
Bundle oldState = r.state;
handleResumeActivity(r.token, false, r.isForward);
......
} else {
......
}
}
......
} 这里首先调用performLaunchActivity函数来载入这个Activity类，即Home界面Activity，然后调用它的onCreate函数，最后回到handleLaunchActivity函数时，再调用handleResumeActivity函数来使这个Activity进入Resumed状态，即会调用这个Activity的onResume函数，这是遵循Activity的生命周期的。public final class ActivityThread {
......
private final Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
......
ComponentName component = r.intent.getComponent();
......
Activity activity = null;
try {
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
......
} catch (Exception e) {
......
}
try {
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
......
if (activity != null) {
ContextImpl appContext = new ContextImpl();
appContext.init(r.packageInfo, r.token, this);
appContext.setOuterContext(activity);
CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
Configuration config = new Configuration(mConfiguration);
......
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstance,
r.lastNonConfigurationChildInstances, config);
.......
mInstrumentation.callActivityOnCreate(activity, r.state);
......
}
......
mActivities.put(r.token, r);
} catch (SuperNotCalledException e) {
......
} catch (Exception e) {
......
}
return activity;
}
......
} 这样。就開始运行Home界面的onCreate。1、至此，Launcher进程Binder子线程池在给主线程发送消息后，又进入睡眠等待状态。onCreate是通过消息机制。在主线程中运行的。
2、System进程又在线程池(主线程和子线程)继续等待了。
消息机制在子线程中循环。
3、Zygote进程等待连接请求，创建新的应用程序进程。