一、ActivityThread的attach函数
在创立使用进程最终一步，会调用ActivityThread的main函数，调起当时使用进程的主线程。除了开始消息循环机制外，会调用ActivityThread的attach函数。
public static void main(String[] args) {
...
ActivityThread thread = new ActivityThread();
thread.attach(false, startSeq);
...
}
attach函数，首要经过Binder机制取得ActivityManger在当时进程的引证mgr，并调用其attachApplication函数，将当时的Applciation目标mAppThread作为参数,startSeq为当时进程的唯一标识序号传递给了attachApplication函数。
private void attach(boolean system, long startSeq) {
sCurrentActivityThread = this;
mSystemThread = system;
if (!system) {
...
final IActivityManager mgr = ActivityManager.getService();
try {
mgr.attachApplication(mAppThread, startSeq);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
...
} else {
...
}
}
定位到ActivityManager的attachApplication函数。
public final void attachApplication(IApplicationThread thread, long startSeq) {
if (thread == null) {
throw new SecurityException("Invalid application interface");
}
synchronized (this) {
int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid, callingUid, startSeq);
Binder.restoreCallingIdentity(origId);
}
}
attachApplicationLocked函数中咱们只关心调用了app.makeActive(thread, mProcessStats);这儿的app是ProcessRecord目标，在创立使用进程时，在ProcessList被创立并保存在AMS的mPidsSelfLocked中。在attachApplicationLocked函数中，首要经过pid从mPidsSelfLocked获取ProcessRecord目标，并调用其bindApplication函数和makeActivie函数。
ApplicationThread#bindApplication
并Application会涉及到使用Application和上下文的创立。
ProcessRecord#makeActive
public void makeActive(IApplicationThread _thread, ProcessStatsService tracker) {
if (thread == null) {
thread = _thread;
mWindowProcessController.setThread(thread);
}
这儿咱们只关心将进程ApplicationThread在AMS的使用设置给了mWindowProcessController目标的mThread变量，这个在接下来的剖析，是判别创立进程或发动Activity的重要分支点。一起，SystemServer进程经过当时进程的ApplicationThread的Binder引证来与该进程进行通信。
二、根Activity的创立
1、 startActivity
一般，咱们经过startActivity函数来发动一个Activity，此刻这个Activity可能是咱们自己使用程序的，也可能是其他使用程序的。此刻咱们假设其他使用程序，且该使用进程未发动。
public void startActivity(Intent intent) {
this.startActivity(intent, null);
}
//重载函数
public void startActivity(Intent intent, @Nullable Bundle options) {
...
if (options != null) {
startActivityForResult(intent, -1, options);
} else {
startActivityForResult(intent, -1);
}
}
//重载函数
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode) {
startActivityForResult(intent, requestCode, null);
}
2、startActivityForResult
也便是所有发动Activity的startActivity函数和startActivityForResult函数终究都会走到重载的startActivityForResult函数。
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,@Nullable Bundle options) {
//使用程序初次创立Activity，此刻是不存在父类Activity的
if (mParent == null) {
options = transferSpringboardActivityOptions(options);
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);
}
}
}
3、Instrumentation.execStartActivity
Instrumentation是用来监督使用进程和系统交互的，这儿调用其execStartActivity,该函数内部调用了ActivityTaskManager.getService().startActivity函数。ActivityTaskManager.getService()会经过AIDL机制取得ActivityTaskMangerService在使用进程的引证，调用其startActivity函数，意味调用了SystemServer进程的ATMS的startActivity函数。
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, Bundle options) {
IApplicationThread whoThread = (IApplicationThread) contextThread;
...
try {
...
int result = ActivityTaskManager.getService().startActivity(whoThread,
who.getBasePackageName(), who.getAttributionTag(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()), token,
target != null ? target.mEmbeddedID : null, requestCode, 0, null, options);
...
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
return null;
}
4、ATMS.startActivity
ATMS的startActivity函数startActivityAsUser,多获取了一个UserId，用于判别调用者的权限。
public final int startActivity(IApplicationThread caller, String callingPackage,
String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo,
String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo,
Bundle bOptions) {
//直接调用了startActivityAsUser
return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType,
resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions,
UserHandle.getCallingUserId());
}
startActivityAsUser函数首要检测是否包名和UserId共同，是否阻隔进程等安全权限问题。然后经过getActivityStartController().obtainStarter函数获取ActivityStarter，并经过Builder规划形式，规划相关特点，最终履行其excute函数。
public int startActivityAsUser(IApplicationThread caller, String callingPackage,
String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo,
String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo,
Bundle bOptions, int userId) {
//调用重载函数，validateIncomingUser 为true,会依据调用id和targetId，解析出用户id
return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType,
resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions, userId,
true /*validateIncomingUser*/);
}
//调用重载函数
private int startActivityAsUser(IApplicationThread caller, String callingPackage,
@Nullable String callingFeatureId, Intent intent, String resolvedType,
IBinder resultTo, String resultWho, int requestCode, int startFlags,
ProfilerInfo profilerInfo, Bundle bOptions, int userId, boolean validateIncomingUser) {
//查看包名与CallingId是否共同
assertPackageMatchesCallingUid(callingPackage);
//检测是否检测阻隔
enforceNotIsolatedCaller("startActivityAsUser");
//解析初用户ID
userId = getActivityStartController().checkTargetUser(userId, validateIncomingUser,
Binder.getCallingPid(), Binder.getCallingUid(), "startActivityAsUser");
//获取ActivityStarter，设置参数，履行其exexute函数。
return getActivityStartController().obtainStarter(intent, "startActivityAsUser")
.setCaller(caller)
.setCallingPackage(callingPackage)
.setCallingFeatureId(callingFeatureId)
.setResolvedType(resolvedType)
.setResultTo(resultTo)
.setResultWho(resultWho)
.setRequestCode(requestCode)
.setStartFlags(startFlags)
.setProfilerInfo(profilerInfo)
.setActivityOptions(bOptions)
.setUserId(userId)
.execute();
}
5、ActivityStarter.execute
execute=>executeRequest
execute和executeRequest函数，首要进行初步的查看和具有必要的权限，并把发动新的Activity的相关信息封装到ActivityRecord中，也便是说ActivityRecord描述着一个Activity。然后调用startActivityUnchecked函数。
private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, Task inTask,
boolean restrictedBgActivity, NeededUriGrants intentGrants) {
int result = START_CANCELED;
final ActivityStack startedActivityStack;
try {
mService.deferWindowLayout();
result = startActivityInner(r, sourceRecord, voiceSession, voiceInteractor,
startFlags, doResume, options, inTask, restrictedBgActivity, intentGrants);
} finally {
startedActivityStack = handleStartResult(r, result);
mService.continueWindowLayout();
}
postStartActivityProcessing(r, result, startedActivityStack);
return result;
}
依据startActivityUnchecked的注释，该函数是为了确保创立Activity反常时，该Activity能被移除。仅紧着调用startActivityInner函数。
startActivityInner函数首要设置和寻觅当时Activity适宜的栈，以及显现问题。
int startActivityInner(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, Task inTask,
boolean restrictedBgActivity, NeededUriGrants intentGrants) {
setInitialState(r, options, inTask, doResume, startFlags, sourceRecord, voiceSession,
voiceInteractor, restrictedBgActivity);
//对Activity发动形式的判别和设置
computeLaunchingTaskFlags();
computeSourceStack();
mIntent.setFlags(mLaunchFlags);
final Task reusedTask = getReusableTask();
// If requested, freeze the task list
if (mOptions != null && mOptions.freezeRecentTasksReordering()
&& mSupervisor.mRecentTasks.isCallerRecents(r.launchedFromUid)
&& !mSupervisor.mRecentTasks.isFreezeTaskListReorderingSet()) {
mFrozeTaskList = true;
mSupervisor.mRecentTasks.setFreezeTaskListReordering();
}
// Compute if there is an existing task that should be used for.
final Task targetTask = reusedTask != null ? reusedTask : computeTargetTask();
final boolean newTask = targetTask == null;
mTargetTask = targetTask;
computeLaunchParams(r, sourceRecord, targetTask);
// Check if starting activity on given task or on a new task is allowed.
int startResult = isAllowedToStart(r, newTask, targetTask);
if (startResult != START_SUCCESS) {
return startResult;
}
final ActivityRecord targetTaskTop = newTask
? null : targetTask.getTopNonFinishingActivity();
if (targetTaskTop != null) {
// Recycle the target task for this launch.
startResult = recycleTask(targetTask, targetTaskTop, reusedTask, intentGrants);
if (startResult != START_SUCCESS) {
return startResult;
}
} else {
mAddingToTask = true;
}
...
if (mTargetStack == null) {
mTargetStack = getLaunchStack(mStartActivity, mLaunchFlags, targetTask, mOptions);
}
if (newTask) {
final Task taskToAffiliate = (mLaunchTaskBehind && mSourceRecord != null)
? mSourceRecord.getTask() : null;
setNewTask(taskToAffiliate);
if (mService.getLockTaskController().isLockTaskModeViolation(
mStartActivity.getTask())) {
Slog.e(TAG, "Attempted Lock Task Mode violation mStartActivity=" + mStartActivity);
return START_RETURN_LOCK_TASK_MODE_VIOLATION;
}
} else if (mAddingToTask) {
addOrReparentStartingActivity(targetTask, "adding to task");
}
...
mTargetStack.mLastPausedActivity = null;
mRootWindowContainer.sendPowerHintForLaunchStartIfNeeded(
false /* forceSend */, mStartActivity);
mTargetStack.startActivityLocked(mStartActivity, topStack.getTopNonFinishingActivity(),
newTask, mKeepCurTransition, mOptions);
if (mDoResume) {
final ActivityRecord topTaskActivity =
mStartActivity.getTask().topRunningActivityLocked();
if (!mTargetStack.isTopActivityFocusable()
|| (topTaskActivity != null && topTaskActivity.isTaskOverlay()
&& mStartActivity != topTaskActivity)) {
mTargetStack.ensureActivitiesVisible(null /* starting */,
0 /* configChanges */, !PRESERVE_WINDOWS);
mTargetStack.getDisplay().mDisplayContent.executeAppTransition();
} else {
if (mTargetStack.isTopActivityFocusable()
&& !mRootWindowContainer.isTopDisplayFocusedStack(mTargetStack)) {
mTargetStack.moveToFront("startActivityInner");
}
mRootWindowContainer.resumeFocusedStacksTopActivities(
mTargetStack, mStartActivity, mOptions);
}
}
mRootWindowContainer.updateUserStack(mStartActivity.mUserId, mTargetStack);
mSupervisor.mRecentTasks.add(mStartActivity.getTask());
mSupervisor.handleNonResizableTaskIfNeeded(mStartActivity.getTask(),
mPreferredWindowingMode, mPreferredTaskDisplayArea, mTargetStack);
return START_SUCCESS;
}
6、RootWindowContainer.resumeFocusedStacksTopActivities
boolean resumeFocusedStacksTopActivities(
ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
...
boolean result = false;
if (targetStack != null && (targetStack.isTopStackInDisplayArea()
|| getTopDisplayFocusedStack() == targetStack)) {
result = targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
}
...
return result;
}
7、ActivityStack.resumeTopActivityUncheckedLocked
该函数内部又调用了resumeTopActivityInnerLocked函数。对栈顶Activity的状态进行查看。依据不同的状态做不通的处理。
private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {
...
mStackSupervisor.startSpecificActivity(next, true, true);
...
return true;
}
8、ActivityStackSupervisor.startSpecificActivity
依据第一节创立使用进程之后，调用ActivityThread的attach函数结果来看，startSpecificActivity函数中的wpc != null && wpc.hasThread()成立，走的将是realStartActivityLocked的分支来发动Activity。不然便是走创立y使用进程的流程。
void startSpecificActivity(ActivityRecord r, boolean andResume, boolean checkConfig) {
final WindowProcessController wpc =
mService.getProcessController(r.processName, r.info.applicationInfo.uid);
boolean knownToBeDead = false;
if (wpc != null && wpc.hasThread()) {
try {
realStartActivityLocked(r, wpc, andResume, checkConfig);
return;
} catch (RemoteException e) {
Slog.w(TAG, "Exception when starting activity "
+ r.intent.getComponent().flattenToShortString(), e);
}
knownToBeDead = true;
}
r.notifyUnknownVisibilityLaunchedForKeyguardTransition();
final boolean isTop = andResume && r.isTopRunningActivity();
mService.startProcessAsync(r, knownToBeDead, isTop, isTop ? "top-activity" : "activity");
}
9、ActivityStackSupervisor.realStartActivityLocked
realStartActivityLocked函数在剖析一，创立了ClientTransaction目标，并传递了使用进程的ApplicationThread引证，该引证会赋值给ClientTransaction的mClient变量。
剖析二、给ClientTransaction添加了Callback回调。参数是LaunchActivityItem目标，封装了许多信息，添加到了ClientTransaction的mActivityCallbacks列表。LaunchActivityItem承继ClientTransactionItem,具有excute函数。
剖析三、调用ATMS的ClientLifecycleManager目标履行该ClientTransaction目标。
boolean realStartActivityLocked(ActivityRecord r, WindowProcessController proc,
boolean andResume, boolean checkConfig) throws RemoteException {
...
//剖析一
final ClientTransaction clientTransaction = ClientTransaction.obtain(
proc.getThread(), r.appToken);
final DisplayContent dc = r.getDisplay().mDisplayContent;
//剖析二
clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),System.identityHashCode(r), r.info,mergedConfiguration.getGlobalConfiguration(),
mergedConfiguration.getOverrideConfiguration(), r.compat,
r.launchedFromPackage, task.voiceInteractor, proc.getReportedProcState(),
r.getSavedState(), r.getPersistentSavedState(), results, newIntents,
dc.isNextTransitionForward(), proc.createProfilerInfoIfNeeded(),
r.assistToken, r.createFixedRotationAdjustmentsIfNeeded()));
...
// 剖析3
mService.getLifecycleManager().scheduleTransaction(clientTransaction);
...
return true;
}
10、ClientLifecycleManager.scheduleTransaction
void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
...
transaction.schedule();
...
}
11、ClientTransaction.schedule
public void schedule() throws RemoteException {
mClient.scheduleTransaction(this);
}
依据第9步的剖析，mClient是使用进程的ApplicationThread在SystemServer进程的使用，这儿经过IPC调用了使用进程的ApplicationThrad的scheduleTransaction函数。
12、ApplicationThread.scheduleTransaction
ApplicationThread是ActivityThread的内部类，是ATMS经过AIDL调用使用进程的相关功能的完成类。
public void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
ActivityThread.this.scheduleTransaction(transaction);
}
13、ActivityThread.scheduleTransaction
ActivityThread的scheduleTransaction函数定义在它的父类继ClientTransactionHandler。
14、ClientTransactionHandler.scheduleTransaction
给Handler目标H,发送了EXECUTE_TRANSACTION状态码。
void scheduleTransaction(ClientTransaction transaction) {
transaction.preExecute(this);
sendMessage(ActivityThread.H.EXECUTE_TRANSACTION, transaction);
}
15、ActivityThread.mH.EXECUTE_TRANSACTION
调用业务履行器履行了一路从ATMS传递过来的ClientTransaction目标。
case EXECUTE_TRANSACTION:
final ClientTransaction transaction = (ClientTransaction) msg.obj;
mTransactionExecutor.execute(transaction);
if (isSystem()) {
transaction.recycle();
}
16、TransactionExecutor.execute
public void execute(ClientTransaction transaction) {
...
executeCallbacks(transaction);
...
}
17、TransactionExecutor.executeCallbacks
经过遍历ClientTransaction目标的mActivityCallbacks列表，并调用每个元素ClientTransactionItem的execute函数。在第9步的时候，给mActivityCallbacks添加了LaunchActivityItem实例。
public void executeCallbacks(ClientTransaction transaction) {
final List<ClientTransactionItem> callbacks = transaction.getCallbacks();
...
final IBinder token = transaction.getActivityToken();
ActivityClientRecord r = mTransactionHandler.getActivityClient(token);
...
final int size = callbacks.size();
for (int i = 0; i < size; ++i) {
final ClientTransactionItem item = callbacks.get(i);
item.execute(mTransactionHandler, token, mPendingActions);
item.postExecute(mTransactionHandler, token, mPendingActions);
...
}
}
18、LaunchActivityItem.execute
创立了ActivityClientRecord目标，描述要创立的Activity的特点。并调用ActivityThread的handleLaunchActivity函数。
public void execute(ClientTransactionHandler client, IBinder token,
PendingTransactionActions pendingActions) {
ActivityClientRecord r = new ActivityClientRecord(token, mIntent, mIdent, mInfo,
mOverrideConfig, mCompatInfo, mReferrer, mVoiceInteractor, mState, mPersistentState,
mPendingResults, mPendingNewIntents, mIsForward,
mProfilerInfo, client, mAssistToken, mFixedRotationAdjustments);
client.handleLaunchActivity(r, pendingActions, null /* customIntent */);
}
19、ActivityThread.handleLaunchActivity
public Activity handleLaunchActivity(ActivityClientRecord r,
PendingTransactionActions pendingActions, Intent customIntent) {
...
final Activity a = performLaunchActivity(r, customIntent);
...
return a;
}
20、ActivityThread.performLaunchActivity
函数经过 mInstrumentation.newActivity函数反射创立了Activity,并经过mInstrumentation.callActivityOnCreate调用Activity的onCreate函数。
这儿创立了许多要害目标，例如Activity的上下文，Application目标和上下文。以及绑定联系。
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
ActivityInfo aInfo = r.activityInfo;
if (r.packageInfo == null) {
r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo,
Context.CONTEXT_INCLUDE_CODE);
}
ComponentName component = r.intent.getComponent();
if (component == null) {
component = r.intent.resolveActivity(
mInitialApplication.getPackageManager());
r.intent.setComponent(component);
}
if (r.activityInfo.targetActivity != null) {
component = new ComponentName(r.activityInfo.packageName,
r.activityInfo.targetActivity);
}
//Activity的上下文
ContextImpl appContext = createBaseContextForActivity(r);
Activity activity = null;
try {
//经过反射办法方法创立Activity
java.lang.ClassLoader cl = appContext.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
...
} catch (Exception e) {
...
}
try {
//Application及上下文的创立
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
if (activity != null) {
...
//Activity与上下文彼此绑定
appContext.setOuterContext(activity);
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,
r.assistToken);
...
if (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
...
r.activity = activity;
mLastReportedWindowingMode.put(activity.getActivityToken(),
config.windowConfiguration.getWindowingMode());
}
...
} catch (SuperNotCalledException e) {
...
}
return activity;
}
21、Instrumentation.callActivityOnCreate
public void callActivityOnCreate(Activity activity, Bundle icicle) {
prePerformCreate(activity);
activity.performCreate(icicle);
postPerformCreate(activity);
}
22、Activity.performCreate
final void performCreate(Bundle icicle, PersistableBundle persistentState) {
dispatchActivityPreCreated(icicle);
mCanEnterPictureInPicture = true;
// initialize mIsInMultiWindowMode and mIsInPictureInPictureMode before onCreate
final int windowingMode = getResources().getConfiguration().windowConfiguration
.getWindowingMode();
mIsInMultiWindowMode = inMultiWindowMode(windowingMode);
mIsInPictureInPictureMode = windowingMode == WINDOWING_MODE_PINNED;
restoreHasCurrentPermissionRequest(icicle);
if (persistentState != null) {
onCreate(icicle, persistentState);
} else {
onCreate(icicle);
}
EventLogTags.writeWmOnCreateCalled(mIdent, getComponentName().getClassName(),
"performCreate");
mActivityTransitionState.readState(icicle);
mVisibleFromClient = !mWindow.getWindowStyle().getBoolean(
com.android.internal.R.styleable.Window_windowNoDisplay, false);
mFragments.dispatchActivityCreated();
mActivityTransitionState.setEnterActivityOptions(this, getActivityOptions());
dispatchActivityPostCreated(icicle);
}
至此，Activity的onCreate函数现已被调用。到了Activity的生命周期第一步。
三、总结
流程看是看懂了，也关联到平常经常开发的知识点，将平常零星的知识点串联起来。例如Activity的Context创立时机，它两的彼此绑定。为啥Activity的创立要经过ClientTransaction最终回调到Handler或者Executor进行创立Activity实例。切到AMS中去走Activity的发动流程，是为了完成一些权限查看、资源管控、业务需求（例如使命栈的切换）、资源和数据的加载。而切换到使用的主线程来创立Activity，是为了与使用进程的生命周期、资源绑定、Activity的归属。但我总感觉少了点什么？看来还是得持续努力。
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