一、根 Activity 启动过程
可以分为三个部分：
① Launcher 请求 AMS 过程
② AMS 到 ApplicationThread 的调用过程
③ ActivityThread 启动 Activity
二、Launcher 启动 AMS 过程
在桌面点击应用图标，会调用 Launcher#startActivitySafely() 方法
public boolean startActivitySafely(View v, Intent intent, ItemInfo item) {
if (mIsSafeModeEnabled && !Utilities.isSystemApp(this, intent)) {
Toast.makeText(this, R.string.safemode_shortcut_error, Toast.LENGTH_SHORT).show();
return false;
}
// Only launch using the new animation if the shortcut has not opted out (this is a
// private contract between launcher and may be ignored in the future).
boolean useLaunchAnimation = (v != null) && !intent.hasExtra(INTENT_EXTRA_IGNORE_LAUNCH_ANIMATION);
Bundle optsBundle = useLaunchAnimation ? getActivityLaunchOptions(v) : null;
UserHandle user = item == null ? null : item.user;
// Prepare intent
// 准备 Intent，启动模式 Flag 设置成 NEW_TASK
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
if (v != null) {
intent.setSourceBounds(getViewBounds(v));
}
try {
if (Utilities.ATLEAST_MARSHMALLOW && (item instanceof ShortcutInfo) && (item.itemType == Favorites.ITEM_TYPE_SHORTCUT || item.itemType == Favorites.ITEM_TYPE_DEEP_SHORTCUT) && !((ShortcutInfo) item).isPromise()) {
// Shortcuts need some special checks due to legacy reasons.
startShortcutIntentSafely(intent, optsBundle, item);
} else if (user == null || user.equals(Process.myUserHandle())) {
// Could be launching some bookkeeping activity
// 调用此方法（在 Activity 中实现）
startActivity(intent, optsBundle);
} else {
LauncherAppsCompat.getInstance(this).startActivityForProfile(
intent.getComponent(), user, intent.getSourceBounds(), optsBundle);
}
return true;
} catch (ActivityNotFoundException|SecurityException e) {
Toast.makeText(this, R.string.activity_not_found, Toast.LENGTH_SHORT).show();
Log.e(TAG, "Unable to launch. tag=" + item + " intent=" + intent, e);
}
return false;
}
@Activity#startActivity(Intent intent, Bundle options)：
public void startActivity(Intent intent, @Nullable Bundle options) {
if (options != null) {
// 调用此方法
startActivityForResult(intent, -1, options);
} else {
// Note we want to go through this call for compatibility with
// applications that may have overridden the method.
startActivityForResult(intent, -1);
}
}
@Activity#startActivityForResult(…)：
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode, @Nullable Bundle options) {
if (mParent == null) {
options = transferSpringboardActivityOptions(options);
// 调用 Instrumentation#execStartActivity(...) 方法
Instrumentation.ActivityResult ar = mInstrumentation.execStartActivity(this, mMainThread.getApplicationThread(), mToken, this, intent, requestCode, options);
if (ar != null) {
mMainThread.sendActivityResult(mToken, mEmbeddedID, requestCode, ar.getResultCode(), ar.getResultData());
}
if (requestCode >= 0) {
// If this start is requesting a result, we can avoid making
// the activity visible until the result is received. Setting
// this code during onCreate(Bundle savedInstanceState) or onResume() will keep the
// activity hidden during this time, to avoid flickering.
// This can only be done when a result is requested because
// that guarantees we will get information back when the
// activity is finished, no matter what happens to it.
mStartedActivity = true;
}
cancelInputsAndStartExitTransition(options);
// TODO Consider clearing/flushing other event sources and events for child windows.
} else {
if (options != null) {
mParent.startActivityFromChild(this, intent, requestCode, options);
} else {
// Note we want to go through this method for compatibility with
// existing applications that may have overridden it.
mParent.startActivityFromChild(this, intent, requestCode);
}
}
}
@Instrumentation#execStartActivity(…)：
- Instrumentation 主要用来监控应用程序和系统的交互
- 在 ActivityThread#performLaunchActivity() 方法中被赋值，此时 Activity 还没有回调 onCreate() 方法
public ActivityResult execStartActivity(Context who, IBinder contextThread, IBinder token, Activity target, Intent intent, int requestCode, Bundle options) {
IApplicationThread whoThread = (IApplicationThread) contextThread;
Uri referrer = target != null ? target.onProvideReferrer() : null;
if (referrer != null) {
intent.putExtra(Intent.EXTRA_REFERRER, referrer);
}
if (mActivityMonitors != null) {
synchronized (mSync) {
final int N = mActivityMonitors.size();
for (int i=0; i<N; i++) {
final ActivityMonitor am = mActivityMonitors.get(i);
ActivityResult result = null;
if (am.ignoreMatchingSpecificIntents()) {
result = am.onStartActivity(intent);
}
if (result != null) {
am.mHits++;
return result;
} else if (am.match(who, null, intent)) {
am.mHits++;
if (am.isBlocking()) {
return requestCode >= 0 ? am.getResult() : null;
}
break;
}
}
}
}
try {
intent.migrateExtraStreamToClipData();
intent.prepareToLeaveProcess(who);
// 1. ActivityManager.getService()：获取 AMS 代理对象
// 2. AMS#startActivity()：调用 AMS 代理对象的 startActivity() 方法
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;
}
@ActivityManager#getService()：
public static IActivityManager getService() {
// IActivityManagerSingleton 是 Singleton 类实例
// 调用 Singleton#get()
return IActivityManagerSingleton.get(); // get() 方法会调用 Singleton#create() 方法
}
// IActivityManagerSingleton 是 Singleton 类实例，泛型传入 IActivityManager
private static final Singleton<IActivityManager> IActivityManagerSingleton = new Singleton<IActivityManager>() {
@Override
protected IActivityManager create() {
// 获取 AMS 的引用
final IBinder b = ServiceManager.getService(Context.ACTIVITY_SERVICE);
// 获取 AMS 在本地的代理
final IActivityManager am = IActivityManager.Stub.asInterface(b);
return am;
}
};
@Singleton#get()：
public abstract class Singleton<T> {
private T mInstance;
// Singleton 实现类要实现 create() 方法
protected abstract T create();
public final T get() {
synchronized (this) {
if (mInstance == null) {
// get() 方法会调用 create() 方法
mInstance = create();
}
return mInstance;
}
}
}
@ActivityManagerService#startActivity(…)：
public final int startActivity(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions, UserHandle.getCallingUserId());
}
三、AMS 到 ApplicationThread 的调用过程
@ActivityManagerService#startActivity(…)：
public final int startActivity(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
// 调用 ActivityManagerService#startActivityAsUser()
return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions, UserHandle.getCallingUserId());
}
@ActivityManagerService#startActivityAsUser(…)
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) {
// 判断调用者是否被进程隔离
// 如果被隔离，则抛 SecurityException 异常，提示 "Isolated process not allowed to call startActivity"
enforceNotIsolatedCaller("startActivity");
// 判断调用者权限，如果没权限，也会抛出 SecurityException 异常
userId = mUserController.handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId, false, ALLOW_FULL_ONLY, "startActivity", null);
// TODO: Switch to user app stacks here.
// 调用 ActivityStarter#startActivityMayWait()
return mActivityStarter.startActivityMayWait(caller, -1, callingPackage, intent, resolvedType, null, null, resultTo, resultWho, requestCode, startFlags, profilerInfo, null, null, bOptions, false, userId, null, null, "startActivityAsUser");
}
@ActivityStarter#startActivityMayWait(…)：
final int startActivityMayWait(IApplicationThread caller, int callingUid,
String callingPackage, Intent intent, String resolvedType,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode, int startFlags,
ProfilerInfo profilerInfo, WaitResult outResult,
Configuration globalConfig, Bundle bOptions, boolean ignoreTargetSecurity, int userId,
IActivityContainer iContainer, TaskRecord inTask, String reason) {
...
// 调用此方法
int res = startActivityLocked(caller, intent, ephemeralIntent, resolvedType,
aInfo, rInfo, voiceSession, voiceInteractor,
resultTo, resultWho, requestCode, callingPid,
callingUid, callingPackage, realCallingPid, realCallingUid,
startFlags, options, ignoreTargetSecurity, componentSpecified,
// 倒数第二个参数 inTask，代表要启动的 Activity 所在的栈，类型为 TaskRecord
// 倒数第一个参数 reason，代表启动理由，上面传入的是 "startActivityAsUser"
outRecord, container, inTask, reason);
...
return res;
}
}
@ActivityStarter#startActivityLocked(…)：
int startActivityLocked(IApplicationThread caller, Intent intent, Intent ephemeralIntent,
String resolvedType, ActivityInfo aInfo, ResolveInfo rInfo,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode, int callingPid, int callingUid,
String callingPackage, int realCallingPid, int realCallingUid, int startFlags,
ActivityOptions options, boolean ignoreTargetSecurity, boolean componentSpecified,
ActivityRecord[] outActivity, ActivityStackSupervisor.ActivityContainer container,
TaskRecord inTask, String reason) {
// 判断启动的理由是否为空
if (TextUtils.isEmpty(reason)) {
// 启动理由为空，抛 IllegalArgumentException 异常
throw new IllegalArgumentException("Need to specify a reason.");
}
mLastStartReason = reason;
mLastStartActivityTimeMs = System.currentTimeMillis();
mLastStartActivityRecord[0] = null;
// 调用此方法
mLastStartActivityResult = startActivity(caller, intent, ephemeralIntent, resolvedType,
aInfo, rInfo, voiceSession, voiceInteractor, resultTo, resultWho, requestCode,
callingPid, callingUid, callingPackage, realCallingPid, realCallingUid, startFlags,
options, ignoreTargetSecurity, componentSpecified, mLastStartActivityRecord,
container, inTask);
if (outActivity != null) {
// mLastStartActivityRecord[0] is set in the call to startActivity above.
outActivity[0] = mLastStartActivityRecord[0];
}
return mLastStartActivityResult;
}
@ActivityStarter#startActivity(…)：
private int startActivity(IApplicationThread caller, Intent intent, Intent ephemeralIntent,
String resolvedType, ActivityInfo aInfo, ResolveInfo rInfo,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode, int callingPid, int callingUid,
String callingPackage, int realCallingPid, int realCallingUid, int startFlags,
ActivityOptions options, boolean ignoreTargetSecurity, boolean componentSpecified,
ActivityRecord[] outActivity, ActivityStackSupervisor.ActivityContainer container,
TaskRecord inTask) {
int err = ActivityManager.START_SUCCESS;
// Pull the optional Ephemeral Installer-only bundle out of the options early.
final Bundle verificationBundle = options != null ? options.popAppVerificationBundle() : null;
ProcessRecord callerApp = null;
// 判断 IApplicationThread 类型的 caller（对应 Launcher 所在的应用程序进程的 ApplicationThread 对象）是否为空
if (caller != null) {
// mService 类型是 ActivityManagerService
// 调用 AMS#getRecordForAppLocked() 得到 callerApp 对象，类型是 ProcessRecord
// ProcessRecord 用于描述一个应用程序进程
callerApp = mService.getRecordForAppLocked(caller);
if (callerApp != null) {
callingPid = callerApp.pid;
callingUid = callerApp.info.uid;
} else {
Slog.w(TAG, "Unable to find app for caller " + caller
+ " (pid=" + callingPid + ") when starting: "
+ intent.toString());
err = ActivityManager.START_PERMISSION_DENIED;
}
}
...
// 创建 ActivityRecord，记录将要启动的 Activity 的信息
// ActivityRecord 用于描述一个 Activity，记录一个 Activity 的所有信息
ActivityRecord r = new ActivityRecord(mService, callerApp, callingPid, callingUid,
callingPackage, intent, resolvedType, aInfo, mService.getGlobalConfiguration(),
resultRecord, resultWho, requestCode, componentSpecified, voiceSession != null,
mSupervisor, container, options, sourceRecord);
if (outActivity != null) {
// 把 r（ActivityRecord 类型）赋值给 outActivity（ActivityRecord[] 类型）
outActivity[0] = r;
}
doPendingActivityLaunchesLocked(false);
// 调用此方法
return startActivity(r, sourceRecord, voiceSession, voiceInteractor, startFlags, true,
options, inTask, outActivity);
}
@ActivityStarter#startActivity(…)：
private int startActivity(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
ActivityRecord[] outActivity) {
int result = START_CANCELED;
try {
mService.mWindowManager.deferSurfaceLayout();
// 调用此方法
result = startActivityUnchecked(r, sourceRecord, voiceSession, voiceInteractor,
startFlags, doResume, options, inTask, outActivity);
}
...
return result;
}
@ActivityStarter#startActivityUnchecked(…)：
private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
ActivityRecord[] outActivity) {
...
ActivityRecord reusedActivity = getReusableIntentActivity();
...
if (reusedActivity != null) {
// When the flags NEW_TASK and CLEAR_TASK are set, then the task gets reused but
// still needs to be a lock task mode violation since the task gets cleared out and
// the device would otherwise leave the locked task.
if (mSupervisor.isLockTaskModeViolation(reusedActivity.getTask(),
(mLaunchFlags & (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK))
== (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK))) {
mSupervisor.showLockTaskToast();
Slog.e(TAG, "startActivityUnchecked: Attempt to violate Lock Task Mode");
return START_RETURN_LOCK_TASK_MODE_VIOLATION;
}
if (mStartActivity.getTask() == null) {
mStartActivity.setTask(reusedActivity.getTask());
}
if (reusedActivity.getTask().intent == null) {
// This task was started because of movement of the activity based on affinity...
// Now that we are actually launching it, we can assign the base intent.
reusedActivity.getTask().setIntent(mStartActivity);
}
// This code path leads to delivering a new intent, we want to make sure we schedule it
// as the first operation, in case the activity will be resumed as a result of later
// operations.
if ((mLaunchFlags & FLAG_ACTIVITY_CLEAR_TOP) != 0
|| isDocumentLaunchesIntoExisting(mLaunchFlags)
|| mLaunchSingleInstance || mLaunchSingleTask) {
final TaskRecord task = reusedActivity.getTask();
// In this situation we want to remove all activities from the task up to the one
// being started. In most cases this means we are resetting the task to its initial
// state.
final ActivityRecord top = task.performClearTaskForReuseLocked(mStartActivity, mLaunchFlags);
// The above code can remove {@code reusedActivity} from the task, leading to the
// the {@code ActivityRecord} removing its reference to the {@code TaskRecord}. The
// task reference is needed in the call below to
// {@link setTargetStackAndMoveToFrontIfNeeded}.
if (reusedActivity.getTask() == null) {
reusedActivity.setTask(task);
}
if (top != null) {
if (top.frontOfTask) {
// Activity aliases may mean we use different intents for the top activity,
// so make sure the task now has the identity of the new intent.
top.getTask().setIntent(mStartActivity);
}
ActivityStack.logStartActivity(AM_NEW_INTENT, mStartActivity, top.getTask());
top.deliverNewIntentLocked(mCallingUid, mStartActivity.intent, mStartActivity.launchedFromPackage);
}
}
// If the activity being launched is the same as the one currently at the top, then
// we need to check if it should only be launched once.
final ActivityStack topStack = mSupervisor.mFocusedStack;
final ActivityRecord topFocused = topStack.topActivity();
final ActivityRecord top = topStack.topRunningNonDelayedActivityLocked(mNotTop);
final boolean dontStart = top != null && mStartActivity.resultTo == null
&& top.realActivity.equals(mStartActivity.realActivity)
&& top.userId == mStartActivity.userId
&& top.app != null && top.app.thread != null
&& ((mLaunchFlags & FLAG_ACTIVITY_SINGLE_TOP) != 0
|| mLaunchSingleTop || mLaunchSingleTask);
if (dontStart) {
ActivityStack.logStartActivity(AM_NEW_INTENT, top, top.getTask());
// For paranoia, make sure we have correctly resumed the top activity.
topStack.mLastPausedActivity = null;
if (mDoResume) {
mSupervisor.resumeFocusedStackTopActivityLocked();
}
ActivityOptions.abort(mOptions);
if ((mStartFlags & START_FLAG_ONLY_IF_NEEDED) != 0) {
// We don't need to start a new activity, and the client said not to do
// anything if that is the case, so this is it!
return START_RETURN_INTENT_TO_CALLER;
}
top.deliverNewIntentLocked(mCallingUid, mStartActivity.intent, mStartActivity.launchedFromPackage);
// Don't use mStartActivity.task to show the toast. We're not starting a new activity
// but reusing 'top'. Fields in mStartActivity may not be fully initialized.
mSupervisor.handleNonResizableTaskIfNeeded(top.getTask(), preferredLaunchStackId,
preferredLaunchDisplayId, topStack.mStackId);
return START_DELIVERED_TO_TOP;
}
boolean newTask = false;
final TaskRecord taskToAffiliate = (mLaunchTaskBehind && mSourceRecord != null) ? mSourceRecord.getTask() : null;
// Should this be considered a new task?
int result = START_SUCCESS;
if (mStartActivity.resultTo == null && mInTask == null && !mAddingToTask
// 根 Activity 的 Intent 的 Flag 为 FLAG_ACTIVITY_NEW_TASK
// 此判断条件满足
&& (mLaunchFlags & FLAG_ACTIVITY_NEW_TASK) != 0) {
newTask = true;
// 创建新的 TaskRecord，用来描述一个 Activity 任务栈
result = setTaskFromReuseOrCreateNewTask(taskToAffiliate, preferredLaunchStackId, topStack);
} else if (mSourceRecord != null) {
result = setTaskFromSourceRecord();
} else if (mInTask != null) {
result = setTaskFromInTask();
} else {
// This not being started from an existing activity, and not part of a new task...
// just put it in the top task, though these days this case should never happen.
setTaskToCurrentTopOrCreateNewTask();
}
if (result != START_SUCCESS) {
return result;
}
...
if (mDoResume) {
final ActivityRecord topTaskActivity =
mStartActivity.getTask().topRunningActivityLocked();
if (!mTargetStack.isFocusable()
|| (topTaskActivity != null && topTaskActivity.mTaskOverlay
&& mStartActivity != topTaskActivity)) {
...
} else {
if (mTargetStack.isFocusable() && !mSupervisor.isFocusedStack(mTargetStack)) {
mTargetStack.moveToFront("startActivityUnchecked");
}
// 调用此方法
mSupervisor.resumeFocusedStackTopActivityLocked(mTargetStack, mStartActivity, mOptions);
}
} else {
mTargetStack.addRecentActivityLocked(mStartActivity);
}
...
return START_SUCCESS;
}
@ActivityStackSupervisor#resumeFocusedStackTopActivityLocked(…)：
/** The stack currently receiving input or launching the next activity.*/
// 接收输入事件或启动下一个 Activity 的栈
ActivityStack mFocusedStack;
boolean resumeFocusedStackTopActivityLocked(ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
if (targetStack != null && isFocusedStack(targetStack)) {
return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
}
// 获取要启动的 Activity 所在栈中位于栈顶，且不是停止状态的 ActivityRecord
final ActivityRecord r = mFocusedStack.topRunningActivityLocked();
// 获取的 ActivityRecord 为 null，或 Activity 的状态不是 RESUMED 状态
// 对应即将要启动的 Activity，此处判断条件满足
if (r == null || r.state != RESUMED) {
// 调用此方法
mFocusedStack.resumeTopActivityUncheckedLocked(null, null);
} else if (r.state == RESUMED) {
mFocusedStack.executeAppTransition(targetOptions);
}
return false;
}
@ActivityStack#resumeTopActivityUncheckedLocked(…)：
/** Run all ActivityStacks through this */
// 通过 mStackSupervisor 对象运行所有 ActivityStack
protected final ActivityStackSupervisor mStackSupervisor;
boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
if (mStackSupervisor.inResumeTopActivity) {
// Don't even start recursing.
return false;
}
boolean result = false;
try {
// Protect against recursion.
mStackSupervisor.inResumeTopActivity = true;
// 调用此方法
result = resumeTopActivityInnerLocked(prev, options);
} finally {
mStackSupervisor.inResumeTopActivity = false;
}
mStackSupervisor.checkReadyForSleepLocked();
return result;
}
@ActivityStack#resumeTopActivityInnerLocked(…)：
private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {
...
boolean pausing = mStackSupervisor.pauseBackStacks(userLeaving, next, false);
final boolean resumeWhilePausing = (next.info.flags & FLAG_RESUME_WHILE_PAUSING) != 0
&& !lastResumedCanPip;
boolean pausing = mStackSupervisor.pauseBackStacks(userLeaving, next, false);
if (mResumedActivity != null) {
pausing |= startPausingLocked(userLeaving, false, next, false);
}
...
if (next.app != null && next.app.thread != null) {
...
try {
...
next.app.thread.scheduleResumeActivity(next.appToken, next.app.repProcState,
mService.isNextTransitionForward(), resumeAnimOptions);
} catch (Exception e) {
...
mStackSupervisor.startSpecificActivityLocked(next, true, false);
...
}
...
} else {
...
// 调用此方法
mStackSupervisor.startSpecificActivityLocked(next, true, true);
}
if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
return true;
}
@ActivityStackSupervisor#startSpecificActivityLocked(…)：
void startSpecificActivityLocked(ActivityRecord r,
boolean andResume, boolean checkConfig) {
// Is this activity's application already running?
// 获取即将启动的 Activity 所在的应用程序进程
ProcessRecord app = mService.getProcessRecordLocked(r.processName,
r.info.applicationInfo.uid, true);
r.getStack().setLaunchTime(r);
// 若要启动的 Activity 所在的应用程序进程不为 null，且进程对应的 thread（IApplicationThread 类型）不为 null
if (app != null && app.thread != null) {
try {
if ((r.info.flags&ActivityInfo.FLAG_MULTIPROCESS) == 0
|| !"android".equals(r.info.packageName)) {
// Don't add this if it is a platform component that is marked
// to run in multiple processes, because this is actually
// part of the framework so doesn't make sense to track as a
// separate apk in the process.
app.addPackage(r.info.packageName, r.info.applicationInfo.versionCode,
mService.mProcessStats);
}
// 情况一：调用此方法，启动 Activity
// 第二个参数传入要启动的 Activity 所在的应用程序进程
realStartActivityLocked(r, app, andResume, checkConfig);
return;
} catch (RemoteException e) {
Slog.w(TAG, "Exception when starting activity "
+ r.intent.getComponent().flattenToShortString(), e);
}
// If a dead object exception was thrown -- fall through to
// restart the application.
}
// 情况二：此时代表要启动的 Activity 所在的应用程序进程不存在
// 调用 ActivityManagerService#startProcessLocked() 方法
mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
"activity", r.intent.getComponent(), false, false, true);
}
情况一：要启动的 Activity 所在的应用程序进程存在
@ActivityStackSupervisor#realStartActivityLocked(…)：
final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
boolean andResume, boolean checkConfig) throws RemoteException {
// app：要启动的 Activity 所在的应用程序进程（ProcessRecord 类型）
// app.thread：IApplicationThread（对应实现是 ActivityThread 内部类 ApplicationThread）
app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
System.identityHashCode(r), r.info,
mergedConfiguration.getGlobalConfiguration(),
mergedConfiguration.getOverrideConfiguration(), r.compat,
r.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle,
r.persistentState, results, newIntents, !andResume,
mService.isNextTransitionForward(), profilerInfo);
...
return true;
}
至此，app.thread.scheduleLaunchActivity(...) 代码逻辑运行在 ActivityManagerService 所在的进程（SystemServer），app 对应应用程序进程，app.thread 对应 ActivityThread 内部类 ApplicationThread，ApplicationThread 是 ActivityManagerService 所在进程（SystemServer）和应用程序进程通信的桥梁
情况二：要启动的 Activity 所在的应用程序进程不存在
@ActivityManagerService#startProcessLocked(…)：
final ProcessRecord startProcessLocked(String processName,
ApplicationInfo info, boolean knownToBeDead, int intentFlags,
String hostingType, ComponentName hostingName, boolean allowWhileBooting,
boolean isolated, boolean keepIfLarge) {
return startProcessLocked(processName, info, knownToBeDead, intentFlags, hostingType,
hostingName, allowWhileBooting, isolated, 0 /* isolatedUid */, keepIfLarge,
null /* ABI override */, null /* entryPoint */, null /* entryPointArgs */,
null /* crashHandler */);
}
final ProcessRecord startProcessLocked(String processName, ApplicationInfo info,
boolean knownToBeDead, int intentFlags, String hostingType, ComponentName hostingName,
boolean allowWhileBooting, boolean isolated, int isolatedUid, boolean keepIfLarge,
String abiOverride, String entryPoint, String[] entryPointArgs, Runnable crashHandler) {
...
startProcessLocked(app, hostingType, hostingNameStr, abiOverride, entryPoint, entryPointArgs);
...
}
@ActivityManagerService#startProcessLocked(…)：
private final void startProcessLocked(ProcessRecord app, String hostingType,
String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs) {
...
// 启动 Activity 所属的应用进程流程：调用 Zygote，通过 socket 通信的方式让 Zygote 进程 fork 出一个新进程，并根据字符串 "android.app.ActivityThread" 反射出 ActivityThread 实例，接着调用其 main() 方法。至此，应用进程已经启动，只不过还没执行相应的初始化操作
startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, debugFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, invokeWith, entryPointArgs);
...
}
@ActivityThread：
ActivityThread#main() ->
thread.attach(false) ->
mgr.attachApplication(mAppThread); ->
@ActivityManagerService：
attachApplication(mAppThread); ->
attachApplicationLocked(thread, callingPid); ->
mStackSupervisor.attachApplicationLocked(app)
最终调用了
@ActivityStackSupervisor#attachApplicationLocked(…)：
boolean attachApplicationLocked(ProcessRecord app) throws RemoteException {
final String processName = app.processName;
boolean didSomething = false;
for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {
final ActivityStack stack = stacks.get(stackNdx);
if (!isFocusedStack(stack)) {
continue;
}
ActivityRecord hr = stack.topRunningActivityLocked();
if (hr != null) {
if (hr.app == null && app.uid == hr.info.applicationInfo.uid
&& processName.equals(hr.processName)) {
try {
// 调用此方法
// 之后和情况一要启动的 Activity 所在的应用程序进程存在的逻辑相同
if (realStartActivityLocked(hr, app, true, true)) {
didSomething = true;
}
} catch (RemoteException e) {
Slog.w(TAG, "Exception in new application when starting activity "
+ hr.intent.getComponent().flattenToShortString(), e);
throw e;
}
}
}
}
}
if (!didSomething) {
ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
}
return didSomething;
}
以上为 AMS 到 ApplicationThread 的调用过程
