源码阅读之Activity启动与App启动流程 - Android 9.0
前言
为了面试与被面试阅读了Activity的启动流程，整理了这篇文章。 以前一直好奇为何Android面试常常问Activity启动流程，由于在工做中没有相关的实践。阅读完源码之后才发现，Activity启动流程中包含了许多知识，例如Activity的启动模式如何处理、插件化的hook点等等。不过因为源码冗长，本文只分析Activity的启动流程。html
阅读建议：java
一、分析基于Android 9.0源码，整理了3张流程图。因为图文排版稀疏，建议新建一个API28的工程配合流程图阅读源码，若是发现文章有什么问题，能够联系我。android
二、源码冗长，阅读须要耐心。git
三、纸上得来终觉浅，绝知此事要躬行。github
四、若是流程图不能放大预览，请阅读原文fiftykg.comweb
Activity在应用内启动流程
话很少说，先上图，流程图1： 面试
简单介绍一下涉及的类：
工具类，包装了ActivityManagerService的调用。一些插件化方案就是经过hook该类实现的，例如didi的VirtualApkapp
Android核心服务，负责调度各应用进程，管理四大组件。实现了IActivityManager接口，应用进程能经过Binder机制调用系统服务。socket
Activity启动的工具类，处理启动activity的各类flag。ide
管理全部应用的Activity的栈，其中mFocusedStack就是当前应用的activity栈。
启动Activity的消息。收到消息后执行execute方法启动activity。
应用的主线程。
接下来开始分析流程： 流程图1，第1-3步，Activity的startActivity会调用startActivityForResult。当应用已经启动时，会先调用startActivityFromChild。可是不管应用是否启动，最后都会调用Instrumentation.execStartActivity。 正如前面所说，ActivityManagerService实现了IActivityManager.aidl接口，提供了应用进程调用系统服务的方法，而Instrumentation包装了ActivityManagerService的调用。
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode, @Nullable Bundle options) {
if (mParent == null) {
...
Instrumentation.ActivityResult ar =
mInstrumentation.execStartActivity(
this, mMainThread.getApplicationThread(), mToken, this,
intent, requestCode, options);
...
} else {
if (options != null) {
mParent.startActivityFromChild(this, intent, requestCode, options);
} else {
mParent.startActivityFromChild(this, intent, requestCode);
}
}
}
public void startActivityFromChild(@NonNull Activity child, @RequiresPermission Intent intent, int requestCode, @Nullable Bundle options) {
...
Instrumentation.ActivityResult ar =
mInstrumentation.execStartActivity(
this, mMainThread.getApplicationThread(), mToken, child,
intent, requestCode, options);
...
}
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流程图1，第4步，Instrumentation调用ActivityManagerService的startActivity
public ActivityResult execStartActivity( Context who, IBinder contextThread, IBinder token, Activity target, Intent intent, int requestCode, Bundle options) {
IApplicationThread whoThread = (IApplicationThread) contextThread;
...
try {
...
int result = ActivityManager.getService()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
checkStartActivityResult(result, intent);
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
return null;
}
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流程图1，第5-6步，ActivityManagerService建立ActivityStarter并执行。
public final int startActivityAsUser(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId, boolean validateIncomingUser) {
...
return mActivityStartController.obtainStarter(intent, "startActivityAsUser")
.setCaller(caller)
.setCallingPackage(callingPackage)
.setResolvedType(resolvedType)
.setResultTo(resultTo)
.setResultWho(resultWho)
.setRequestCode(requestCode)
.setStartFlags(startFlags)
.setProfilerInfo(profilerInfo)
.setActivityOptions(bOptions)
.setMayWait(userId)
.execute();
}
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流程图1，第7步，因为第6步setMayWait将mayWait设置为true，因此执行startActivityMayWait方法。
ActivityStarter setMayWait(int userId) {
mRequest.mayWait = true;
mRequest.userId = userId;
return this;
}
int execute() {
try {
if (mRequest.mayWait) {
return startActivityMayWait(...);
} else {
return startActivity(...);
}
} finally {
onExecutionComplete();
}
}
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流程图1，第8-11步，ActivityStarter处理启动activity的intent和flag比较繁琐，最后会调用ActivityStackSupervisor的resumeFocusedStackTopActivityLocked。
boolean resumeFocusedStackTopActivityLocked( ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
...
if (targetStack != null && isFocusedStack(targetStack)) {
return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
}
final ActivityRecord r = mFocusedStack.topRunningActivityLocked();
if (r == null || !r.isState(RESUMED)) {
mFocusedStack.resumeTopActivityUncheckedLocked(null, null);
} else if (r.isState(RESUMED)) {
...
}
return false;
}
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流程图1，第12步，resumeTopActivityInnerLocked是一个很是冗长的方法，该方法会判断栈中是否有须要启动的Activity，判断Activity是否在栈顶等等。若是须要启动的Activity没有被建立，就会执行流程图13步ActivityStackSupervisor的startSpecificActivityLocked方法。
private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {
final ActivityRecord next = topRunningActivityLocked(true /* focusableOnly */);
if (next.app != null && next.app.thread != null) {
...
}else{
// Whoops, need to restart this activity!
...
mStackSupervisor.startSpecificActivityLocked(next, true, true);
}
}
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流程图1，第13-14步，startSpecificActivityLocked方法中先判断App是否启动，若是启动则执行realStartActivityLocked。若是未启动则调用ActivityManagerService.startProcessLocked方法启动App。 为了分析方便，咱们先看App启动的状况。在realStartActivityLocked方法中，ActivityManangerService会调用应用进程的接口，最终执行ClientTransaction的callBack，也就是LaunchActivityItem。这个调用过程将在稍后分析。
void startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig) {
// Is this activity's application already running?
ProcessRecord app = mService.getProcessRecordLocked(r.processName,
r.info.applicationInfo.uid, true);
if (app != null && app.thread != null) {
try {
...
realStartActivityLocked(r, app, andResume, checkConfig);
return;
} catch (RemoteException e) {
Slog.w(TAG, "Exception when starting activity "
+ r.intent.getComponent().flattenToShortString(), e);
}
}
mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
"activity", r.intent.getComponent(), false, false, true);
}
final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app, boolean andResume, boolean checkConfig) throws RemoteException {
...
// Create activity launch transaction.
final ClientTransaction clientTransaction = ClientTransaction.obtain(app.thread,
r.appToken);
clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),
System.identityHashCode(r), r.info,
// TODO: Have this take the merged configuration instead of separate global
// and override configs.
mergedConfiguration.getGlobalConfiguration(),
mergedConfiguration.getOverrideConfiguration(), r.compat,
r.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle,
r.persistentState, results, newIntents, mService.isNextTransitionForward(),
profilerInfo));
...
// Schedule transaction.
mService.getLifecycleManager().scheduleTransaction(clientTransaction);
...
}
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流程图1，第15步，LaunchActivityItem的execute方法执行了ClientTransactionHandler的handleLaunchActivity。而这个ClientTransactionHandler就是ActivityThread。至于为何是ActivityThread，能够看第二部分。
@Override
public void execute(ClientTransactionHandler client, IBinder token, PendingTransactionActions pendingActions) {
Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
ActivityClientRecord r = new ActivityClientRecord(token, mIntent, mIdent, mInfo,
mOverrideConfig, mCompatInfo, mReferrer, mVoiceInteractor, mState, mPersistentState,
mPendingResults, mPendingNewIntents, mIsForward,
mProfilerInfo, client);
client.handleLaunchActivity(r, pendingActions, null /* customIntent */);
Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);
}
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流程图1，第16-19，ActivityThread执行handleLaunchActivity方法，调用真正Activity启动方法performLaunchActivity。 performLaunchActivity中调用Instrumentation.newActivity方法建立Activity对象！ 建立完成后，performLaunchActivity会继续调用Instrumentation.callActivityOnCreate。这里往下走就会调用Activity.OnCreate。
// ActivityThread.java：
@Override
public Activity handleLaunchActivity(ActivityClientRecord r, PendingTransactionActions pendingActions, Intent customIntent) {
...
final Activity a = performLaunchActivity(r, customIntent);
...
return a;
}
// ActivityThread.java:
/** Core implementation of activity launch. */
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
...
Activity activity = null;
try {
java.lang.ClassLoader cl = appContext.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
...
} catch (Exception e) {
...
}
try {
...
if (activity != null) {
...
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.referrer, r.voiceInteractor, window, r.configCallback);
...
if (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
...
}
...
} catch (SuperNotCalledException e) {
throw e;
} catch (Exception e) {
...
}
return activity;
}
// Instrumentation.java:
public Activity newActivity(ClassLoader cl, String className, Intent intent) throws InstantiationException, IllegalAccessException, ClassNotFoundException {
String pkg = intent != null && intent.getComponent() != null
? intent.getComponent().getPackageName() : null;
return getFactory(pkg).instantiateActivity(cl, className, intent);
}
// AppComponentFactory.java:
public @NonNull Activity instantiateActivity(@NonNull ClassLoader cl, @NonNull String className, @Nullable Intent intent) throws InstantiationException, IllegalAccessException, ClassNotFoundException {
return (Activity) cl.loadClass(className).newInstance();
}
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流程图1，第20-21，Instrumentation.callActivityOnCreate中调用Activity的performCreate。performCreate调用Activity.onCreate!
// Instrumentation.java
public void callActivityOnCreate(Activity activity, Bundle icicle) {
prePerformCreate(activity);
activity.performCreate(icicle);
postPerformCreate(activity);
}
// Activity.java
final void performCreate(Bundle icicle, PersistableBundle persistentState) {
...
if (persistentState != null) {
onCreate(icicle, persistentState);
} else {
onCreate(icicle);
}
...
}
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IApplicationThread & IActivityManager
上面流程中最难理解的大概就是第15步了，clientTransaction中添加的LaunchActivityItem是如何被执行的？要理解这一步就须要先了解一下系统与应用之间的通讯。
Android进程间经过Binder机制进行通讯。AMS(ActivityManagerService)与应用进程之间的通讯，Android设计了IApplicationThread与IActivityManager两个接口。 两个通讯接口都是单向的： IApplicationThread是AMS请求应用进程的接口。 IActivityManager是应用进程请求AMS的接口。
public class ActivityManagerService extends IActivityManager.Stub // ActivityThread的内部类 private class ApplicationThread extends IApplicationThread.Stub 复制代码
再来看一下，上面流程第15步的分解流程，流程图2：
流程图2，第3步，mClient就是IApplicationThread。
private IApplicationThread mClient;
public void schedule() throws RemoteException {
mClient.scheduleTransaction(this);
}
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流程图2，第4步，ApplicationThread中scheduleTransaction方法直接调用外部类ActivityThread的scheduleTransaction，可是ActivityThread.java中没有scheduleTransaction方法，而是在父类ClientTransactionHandler。
// ApplicationThread
@Override
public void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
ActivityThread.this.scheduleTransaction(transaction);
}
//ClientTransactionHandler.java
void scheduleTransaction(ClientTransaction transaction) {
transaction.preExecute(this);
sendMessage(ActivityThread.H.EXECUTE_TRANSACTION, transaction);
}
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流程图2，第5步，ClientTransactionHandler中发了一个handler消息EXECUTE_TRANSACTION。这个Handler就是ActivityThread的子类H。在H的handleMessage中能够找到EXECUTE_TRANSACTION的处理。
case EXECUTE_TRANSACTION:
final ClientTransaction transaction = (ClientTransaction) msg.obj;
mTransactionExecutor.execute(transaction);
if (isSystem()) {
transaction.recycle();
}
break;
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最终会在TransactionExecutor中取出LaunchActivityItem，执行execute。也是Activity启动流程图中的第15步。
AMS是什么时候获取到IApplicationThread? App如何获取IActivityManager？ 答案就在ActivityThread.main方法中，main中调用了attach方法。
// ActivityThread.java
private void attach(boolean system, long startSeq) {
...
if (!system) {
RuntimeInit.setApplicationObject(mAppThread.asBinder());
final IActivityManager mgr = ActivityManager.getService();
try {
mgr.attachApplication(mAppThread, startSeq);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
} else {
//system
}
...
}
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App进程在启动时经过ActivityManager获取单例的IActivityManager，利用IActivityManager的attachApplication接口将IApplicationThread注册到AMS。这样就实现了App与AMS的通讯。
App的启动流程
刚才提到了ActivityThread的main方法，这是应用进程的入口。在Activity启动流程中，第13步startSpecificActivityLocked，若是App未启动mService.startProcessLocked就会走到ActivityThread.main方法。
接下来看一下App的启动流程，流程图3：
流程图3，第14-15步，startSpecificActivityLocked中判断app未启动进入AMS的startProcessLocked，startProcessLocked通过屡次重载调用走到startProcess，startProcess调用Process.start启动进程。 这里注意下，Process.start的第一个参数，在其中一个startProcessLocked方法中赋值为"android.app.ActivityThread"，搜索字符串就能够找到！
// ActivityStackSupervisor.java
void startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig) {
// application is not running
mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
"activity", r.intent.getComponent(), false, false, true);
}
// ActivityManagerService.java
private ProcessStartResult startProcess(String hostingType, String entryPoint, ProcessRecord app, int uid, int[] gids, int runtimeFlags, int mountExternal, String seInfo, String requiredAbi, String instructionSet, String invokeWith, long startTime) {
try {
...
final ProcessStartResult startResult;
if (hostingType.equals("webview_service")) {
// webview process
} else {
startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, runtimeFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, invokeWith,
new String[] {PROC_START_SEQ_IDENT + app.startSeq});
}
checkTime(startTime, "startProcess: returned from zygote!");
return startResult;
} finally {
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
}
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流程图3，第16步，Process.start中出现了著名的ZygoteProcess! 传说中Android的全部进程起源于Zygote，Process类只是对Zygote的包装而已。
public static final ProcessStartResult start(final String processClass, final String niceName, int uid, int gid, int[] gids, int runtimeFlags, int mountExternal, int targetSdkVersion, String seInfo, String abi, String instructionSet, String appDataDir, String invokeWith, String[] zygoteArgs) {
return zygoteProcess.start(processClass, niceName, uid, gid, gids,
runtimeFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, invokeWith, zygoteArgs);
}
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流程图3，第17-20步，zygoteProcess.start调用zygoteProcess.startViaZygote。startViaZygote中经过socket与zygote通讯，启动app进程，zygoteSendArgsAndGetResult方法返回app进程的pid。
private Process.ProcessStartResult startViaZygote(final String processClass, final String niceName, final int uid, final int gid, final int[] gids, int runtimeFlags, int mountExternal, int targetSdkVersion, String seInfo, String abi, String instructionSet, String appDataDir, String invokeWith, boolean startChildZygote, String[] extraArgs) throws ZygoteStartFailedEx {
ArrayList<String> argsForZygote = new ArrayList<String>();
// --runtime-args, --setuid=, --setgid=,
// and --setgroups= must go first
argsForZygote.add("--runtime-args");
argsForZygote.add("--setuid=" + uid);
argsForZygote.add("--setgid=" + gid);
argsForZygote.add("--runtime-flags=" + runtimeFlags);
...
synchronized(mLock) {
return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi), argsForZygote);
}
}
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接下来就是须要寻找argsForZygote中的参数在哪里解析，在zygoteSendArgsAndGetResult方法中有这样一段注释：
/** * See com.android.internal.os.SystemZygoteInit.readArgumentList() * Presently the wire format to the zygote process is: * a) a count of arguments (argc, in essence) * b) a number of newline-separated argument strings equal to count * * After the zygote process reads these it will write the pid of * the child or -1 on failure, followed by boolean to * indicate whether a wrapper process was used. */
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然而找不到SystemZygoteInit这个类！ 既然argsForZygote中参数是一些hardcode的字符串，那解析的地方应该也是hardcode。因此搜了一下参数。 果真在ZygoteInit.java和ZygoteConnection.java中发现了这些参数。ZygoteInit是zygote进程启动类，main方法中建立了ZygoteServer。由ZygoteServer监听Socket请求，并执行相应的命令。ZygoteServer与客户端的通讯协议定义在ZygoteConnection.Arguments中。
流程图3，第21-22步，通过上面一波分析，咱们看到ZygoteServer的runSelectLoop方法中，接收到Socket请求后，执行了ZygoteConnection.processOneCommand。
Runnable runSelectLoop(String abiList) {
while (true) {
...
ZygoteConnection connection = peers.get(i);
final Runnable command = connection.processOneCommand(this);
...
}
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流程图3，第23-24步，processOneCommand中经过readArgumentList方法读取参数，建立Arguments对象时，在Arguments.parseArgs方法中解析参数。将解析后的参数传入Zygote.forkAndSpecialize建立子进程。
Runnable processOneCommand(ZygoteServer zygoteServer) {
String args[];
Arguments parsedArgs = null;
FileDescriptor[] descriptors;
try {
args = readArgumentList();
descriptors = mSocket.getAncillaryFileDescriptors();
} catch (IOException ex) {
throw new IllegalStateException("IOException on command socket", ex);
}
...
parsedArgs = new Arguments(args);
....
pid = Zygote.forkAndSpecialize(parsedArgs.uid, parsedArgs.gid, parsedArgs.gids,
parsedArgs.runtimeFlags, rlimits, parsedArgs.mountExternal, parsedArgs.seInfo,
parsedArgs.niceName, fdsToClose, fdsToIgnore, parsedArgs.startChildZygote,
parsedArgs.instructionSet, parsedArgs.appDataDir);
....
}
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在readArgumentList中看到了一段与zygoteSendArgsAndGetResult方法遥相呼应的注释
/** * See android.os.Process.zygoteSendArgsAndGetPid() * Presently the wire format to the zygote process is: * a) a count of arguments (argc, in essence) * b) a number of newline-separated argument strings equal to count * * After the zygote process reads these it will write the pid of * the child or -1 on failure. */
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然而在Process中也找不到zygoteSendArgsAndGetPid。感受是历史代码的注释，误导啊！
流程图3，第25步，processOneCommand执行完forkAndSpecialize后，在子进程（pid=0）中，执行handleChildProc进行子进程初始化。
Runnable processOneCommand(ZygoteServer zygoteServer) {
...
pid = Zygote.forkAndSpecialize(...);
try {
if (pid == 0) {
// in child
zygoteServer.setForkChild();
zygoteServer.closeServerSocket();
IoUtils.closeQuietly(serverPipeFd);
serverPipeFd = null;
return handleChildProc(parsedArgs, descriptors, childPipeFd,
parsedArgs.startChildZygote);
} else {
// In the parent. A pid < 0 indicates a failure and will be handled in
// handleParentProc.
IoUtils.closeQuietly(childPipeFd);
childPipeFd = null;
handleParentProc(pid, descriptors, serverPipeFd);
return null;
}
} finally {
IoUtils.closeQuietly(childPipeFd);
IoUtils.closeQuietly(serverPipeFd);
}
}
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流程图3，第26步，handleChildProc中，invokeWith是socket参数"--invoke-with"，在ActivityManagerService的startProcessLocked中赋值，只有在debug的状况下才!null。 isZygote是参数"--start-child-zygote"，在ZygoteProcess.start方法中为false。 因此handleChildProc会走到ZygoteInit.zygoteInit。 这里比较奇怪，为何不是走childZygoteInit，但愿有想法的朋友告知一下=。=
private Runnable handleChildProc(Arguments parsedArgs, FileDescriptor[] descriptors, FileDescriptor pipeFd, boolean isZygote) {
...
if (parsedArgs.invokeWith != null) {
WrapperInit.execApplication(parsedArgs.invokeWith,
parsedArgs.niceName, parsedArgs.targetSdkVersion,
VMRuntime.getCurrentInstructionSet(),
pipeFd, parsedArgs.remainingArgs);
// Should not get here.
throw new IllegalStateException("WrapperInit.execApplication unexpectedly returned");
} else {
if (!isZygote) {
return ZygoteInit.zygoteInit(parsedArgs.targetSdkVersion, parsedArgs.remainingArgs,
null /* classLoader */);
} else {
return ZygoteInit.childZygoteInit(parsedArgs.targetSdkVersion,
parsedArgs.remainingArgs, null /* classLoader */);
}
}
}
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流程图3，第27-28步，zygoteInit中执行RuntimeInit.applicationInit，applicationInit调用findStaticMain，反射ActivityThread.main方法！
public static final Runnable zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader) {
if (RuntimeInit.DEBUG) {
Slog.d(RuntimeInit.TAG, "RuntimeInit: Starting application from zygote");
}
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ZygoteInit");
RuntimeInit.redirectLogStreams();
RuntimeInit.commonInit();
ZygoteInit.nativeZygoteInit();
return RuntimeInit.applicationInit(targetSdkVersion, argv, classLoader);
}
protected static Runnable applicationInit(int targetSdkVersion, String[] argv, ClassLoader classLoader) {
...
final Arguments args = new Arguments(argv);
...
return findStaticMain(args.startClass, args.startArgs, classLoader);
}
protected static Runnable findStaticMain(String className, String[] argv, ClassLoader classLoader) {
Class<?> cl;
try {
cl = Class.forName(className, true, classLoader);
} catch (ClassNotFoundException ex) {
throw new RuntimeException(
"Missing class when invoking static main " + className,
ex);
}
Method m;
try {
m = cl.getMethod("main", new Class[] { String[].class });
} catch (NoSuchMethodException ex) {
throw new RuntimeException(
"Missing static main on " + className, ex);
} catch (SecurityException ex) {
throw new RuntimeException(
"Problem getting static main on " + className, ex);
}
...
return new MethodAndArgsCaller(m, argv);
}
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流程图3，第29-33步，回到ActivityThread.main方法中，走到attach中，向AMS注册IApplicationThread，通过屡次attachApplicationLocked走到Activity的启动流程，ActivityStackSupervisor的realStartActivityLocked，也就是流程图1的第14步。
// ActivityManagerService.java
public final void attachApplication(IApplicationThread thread, long startSeq) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid, callingUid, startSeq);
Binder.restoreCallingIdentity(origId);
}
}
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巨人的肩膀
老罗：Android应用程序内部启动Activity过程（startActivity）的源代码分析
Android四大组件之Activity--应用进程与系统进程的通讯
ps: 源码阅读过程当中，遇得了许多疑惑的地方。一方面是能力有限，须要多参考前辈的文章，另外一方面源码也并不是完美，代码中也有许多todo存在，也许还能发现一些bug。对于ZygoteProcess.zygoteSendArgsAndGetResult()与ZygoteConnection.readArgumentList中出现的误导注释，给google提了一个issue，就当阅读源码的记念了。
以上。
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- 1. Android源码阅读分析：从Activity开始（一）——启动流程
- 2. 源码阅读---AMS与Activity启动流程
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