一、概述
從應用程序的角度出發，Activity的啓動過程分爲兩種：一種是根Activity,另一種是子Activity。根Acitivity是launcher中以快捷圖標的的形式啓動，它的啓動過程代表了一個Android應用程序的啓動過程。子Activity由根Activity啓動或有其他子Activity啓動，它們可能與啓動它們的Activity運行在同一個進程中也可能運行在不同的進程中，這取決於它們的配置和啓動參數。
二、Launcher啓動MainActivity的過程
- Launcher向ActivityManagerService發送一個啓動MainActivity的進程間通信請求
- ActivityManagerService首先將要啓動的MainActivity組件的信息保存下來，然後向Launcher組件發送一個暫停狀態的進程間通信請求。
- Launcher組件進入暫停狀態之後，就會向ActivityManagerService發送一個已進入暫停狀態的進程間通信請求，以便ActivityManagerService可以繼續執行啓動MainActivity組件的操作。
- ActivityManagerService發現用來運行MainActivity組件的應用程序進程不存在，它就會啓動一個新的應用程序進程。
- 新的應用程序進程啓動完成之後，就會向ActivityManagerService發送一個啓動完成的進程間通信請求，以便ActivityManagerService可以繼續執行啓動MainActivity組件的操作。
- ActivityManagerService將2步保存下來的MainActivity組件的信息發送給4創建的應用程序進程，以便可以將MainActivity組件啓動起來。
三、源碼分析
我們點擊應用圖標時，就會調用Launcher的startActivitySafely
packages/apps/Launcher3/src/com/android/launcher3/Launcher.java
public boolean startActivitySafely(View v, Intent intent, ItemInfo item) {
...
//1、 Prepare intent
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())) {
//2、 Could be launching some bookkeeping activity
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;
}
在註釋1處設置Flag爲Intent.FLAG_ACTIVITY_NEW_TASK,這樣MainActivity就會在一個新的任務棧中啓動，在註釋2處調用父類Activity的成員函數啓動參數爲intent所描述Activity的組件。
@Override
public void startActivity(Intent intent, @Nullable Bundle options) {
if (options != null) {
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);
}
}
startActivityForResult的第二個參數爲-1,Launcher不需要知道啓動的結果，如果大於等於0就會在Activity退出時調用啓動Activity的onActivityResult()方法。
public void startActivityForResult(Intent intent, int requestCode, Bundle options) {
if (mParent == null) {
options = transferSpringboardActivityOptions(options);
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());
}
}
mInstrumentation的類型爲Instrumentation，調用Instrumentation的execStartActivity方法來執行啓動MainActivity的操作。
Activity類的成員變量mMainThread的類型爲ActivityThread,用來描述一個應用程序的進程。系統每當啓動一個應用程序進程時，都會在加載一個ActivityThread類實例，並且會將這個ActivityThread類實例保存在每一個在該進程中啓動的Activity組件的父類Activity的成員變量mMainThread中。Activity類的成員函數getApplicationThread()用來獲取它內部的一個類型爲ApplicationThread的Binder本地對象。通過execStartActivity()方法，可以將它傳遞給ActivityManagerService，這樣ActivityManagerService就可以通過它來通知Launcher組件進入Paused狀態。
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, String target,
Intent intent, int requestCode, Bundle options) {
IApplicationThread whoThread = (IApplicationThread) contextThread;
try {
intent.migrateExtraStreamToClipData();
intent.prepareToLeaveProcess(who);
int result = ActivityManager.getService()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target, requestCode, 0, null, options);
checkStartActivityResult(result, intent);
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
return null;
}
通過ActivityManager類的靜態函數getService()來獲取AMS的代理對象，接着調用startActivity方法
public static IActivityManager getService() {
return IActivityManagerSingleton.get();
}
private static final Singleton<IActivityManager> IActivityManagerSingleton =
new Singleton<IActivityManager>() {
@Override
protected IActivityManager create() {
final IBinder b = ServiceManager.getService(Context.ACTIVITY_SERVICE);
final IActivityManager am = IActivityManager.Stub.asInterface(b);
return am;
}
};
public abstract class Singleton<T> {
private T mInstance;
protected abstract T create();
public final T get() {
synchronized (this) {
if (mInstance == null) {
mInstance = create();
}
return mInstance;
}
}
}
第一次調用getService()方法時，它會通過Service Manager來獲得一個“activity”的service引用，也就是IBinder類型的AMS引用，接着將其轉化爲IActivityManager類型的對象。由於AMS實現了IActivityManager.Stub接口，因此可以與AMS間進行進程間通訊。
以上過程都是Launcher進程中進行的。
下面的過程是在AMS中執行的
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
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());
}
AMS的startActivity方法中return了startActivityAsUser方法，startActivityAsUser比startActivity多了一個UserHandle.getCallingUserId()，這個方法會獲得調用者的UserId,AMS會根據這個UserId來確定調用者的權限。
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
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) {
enforceNotIsolatedCaller("startActivity");
userId = mUserController.handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(),
userId, false, ALLOW_FULL_ONLY, "startActivity", null);
// TODO: Switch to user app stacks here.
return mActivityStarter.startActivityMayWait(caller, -1, callingPackage, intent,
resolvedType, null, null, resultTo, resultWho, requestCode, startFlags,
profilerInfo, null, null, bOptions, false, userId, null, null,
"startActivityAsUser");
}
調用ActivityStater的startActivityMayWait方法，倒數第二個參數類型爲TaskRecord代表啓動的Activity所在的棧，最後一個參數startActivityAsUser代表啓動的理由。
frameworks/base/services/core/java/com/android/server/am/ActivityStarter.java
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) {
...
final ActivityRecord[] outRecord = new ActivityRecord[1];
int res = startActivityLocked(caller, intent, ephemeralIntent, resolvedType,
aInfo, rInfo, voiceSession, voiceInteractor,
resultTo, resultWho, requestCode, callingPid,
callingUid, callingPackage, realCallingPid, realCallingUid, startFlags,
options, ignoreTargetSecurity, componentSpecified, outRecord, container,
inTask, reason);
...
}
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) {
if (TextUtils.isEmpty(reason)) {
throw new IllegalArgumentException("Need to specify a reason.");
}
mLastStartReason = reason;
mLastStartActivityTimeMs = System.currentTimeMillis();
mLastStartActivityRecord[0] = null;
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);
return mLastStartActivityResult;
}
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;
if (caller != null) {
// 1
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;
}
}
...
//註釋2
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) {
outActivity[0] = r;
}
return startActivity(r, sourceRecord, voiceSession, voiceInteractor, startFlags, true,
options, inTask, outActivity);
}
每一個應用程序都使用一個ProcessRecord對象來描述，並且保存在ActivityManagerService內部，註釋1處通過getRecordForAppLocked來獲得與參數caller對應的一個ProcessRecord對象callerApp。註釋2處創建一個ActivityRecord對象r來描述即將啓動的Activity組件。
private int startActivity(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,//null
ActivityRecord[] outActivity) {
int result = START_CANCELED;
try {
mService.mWindowManager.deferSurfaceLayout();
result = startActivityUnchecked(r, sourceRecord, voiceSession, voiceInteractor,
startFlags, doResume, options, inTask, outActivity);
} finally {
// activity in an incomplete state can lead to issues, such as performing operations
// without a window container.
if (!ActivityManager.isStartResultSuccessful(result)
&& mStartActivity.getTask() != null) {
mStartActivity.getTask().removeActivity(mStartActivity);
}
mService.mWindowManager.continueSurfaceLayout();
}
return result;
}
private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
ActivityRecord[] outActivity) {
...
// Should this be considered a new task?
int result = START_SUCCESS;
if (mStartActivity.resultTo == null && mInTask == null && !mAddingToTask
&& (mLaunchFlags & FLAG_ACTIVITY_NEW_TASK) != 0) {
//1
newTask = true;
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)) {
// If the activity is not focusable, we can't resume it, but still would like to
// make sure it becomes visible as it starts (this will also trigger entry
// animation). An example of this are PIP activities.
// Also, we don't want to resume activities in a task that currently has an overlay
// as the starting activity just needs to be in the visible paused state until the
// over is removed.
mTargetStack.ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
// Go ahead and tell window manager to execute app transition for this activity
// since the app transition will not be triggered through the resume channel.
mWindowManager.executeAppTransition();
} else {
// If the target stack was not previously focusable (previous top running activity
// on that stack was not visible) then any prior calls to move the stack to the
// will not update the focused stack. If starting the new activity now allows the
// task stack to be focusable, then ensure that we now update the focused stack
// accordingly.
if (mTargetStack.isFocusable() && !mSupervisor.isFocusedStack(mTargetStack)) {
mTargetStack.moveToFront("startActivityUnchecked");
}
//2
mSupervisor.resumeFocusedStackTopActivityLocked(mTargetStack, mStartActivity,
mOptions);
}
}
註釋1默認情況下目標Activity與源Activity運行在同一任務中，如果啓動組件標誌值位設置FLAG_ACTIVITY_NEW_TASK，並且源Activity不需要目標Activity的運行結果，那麼AMS就會將目標Activity運行在另一個不同的任務中。 調用註釋2 resumeFocusedStackTopActivityLocked
frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java
boolean resumeFocusedStackTopActivityLocked(
ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
if (targetStack != null && isFocusedStack(targetStack)) {
return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
}
//1
final ActivityRecord r = mFocusedStack.topRunningActivityLocked();
if (r == null || r.state != RESUMED) {
mFocusedStack.resumeTopActivityUncheckedLocked(null, null);
} else if (r.state == RESUMED) {
// Kick off any lingering app transitions form the MoveTaskToFront operation.
mFocusedStack.executeAppTransition(targetOptions);
}
return false;
}
在註釋1處topRunningActivityLocked()獲取要啓動的Activity是否在棧頂。如果r == null || r.state != RESUMED就會調用resumeTopActivityUncheckedLocked()
private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {
// If the flag RESUME_WHILE_PAUSING is set, then continue to schedule the previous activity
// to be paused, while at the same time resuming the new resume activity only if the
// previous activity can't go into Pip since we want to give Pip activities a chance to
// enter Pip before resuming the next activity.
final boolean resumeWhilePausing = (next.info.flags & FLAG_RESUME_WHILE_PAUSING) != 0
&& !lastResumedCanPip;
boolean pausing = mStackSupervisor.pauseBackStacks(userLeaving, next, false);
//1
if (mResumedActivity != null) {
pausing |= startPausingLocked(userLeaving, false, next, false);
}
if (pausing && !resumeWhilePausing) {
// At this point we want to put the upcoming activity's process
// at the top of the LRU list, since we know we will be needing it
// very soon and it would be a waste to let it get killed if it
// happens to be sitting towards the end.
if (next.app != null && next.app.thread != null) {
mService.updateLruProcessLocked(next.app, true, null);
}
return true;
}
}
由於當前resume狀態的組件爲Launcher，所以mResumedActivity != null爲true,接下來就會調用startPausingLocked
final boolean startPausingLocked(boolean userLeaving, boolean uiSleeping,
ActivityRecord resuming, boolean pauseImmediately) {
if (prev.app != null && prev.app.thread != null) {
try {
mService.updateUsageStats(prev, false);
prev.app.thread.schedulePauseActivity(prev.appToken, prev.finishing,
userLeaving, prev.configChangeFlags, pauseImmediately);
} catch (Exception e) {
// Ignore exception, if process died other code will cleanup.
Slog.w(TAG, "Exception thrown during pause", e);
mPausingActivity = null;
mLastPausedActivity = null;
mLastNoHistoryActivity = null;
}
}
}
調用ThreadActivity的內部類ApplicationThread的schedulePauseActivity方法
public final void schedulePauseActivity(IBinder token, boolean finished,
boolean userLeaving, int configChanges, boolean dontReport) {
int seq = getLifecycleSeq();
if (DEBUG_ORDER) Slog.d(TAG, "pauseActivity " + ActivityThread.this
+ " operation received seq: " + seq);
sendMessage(
finished ? H.PAUSE_ACTIVITY_FINISHING : H.PAUSE_ACTIVITY,
token,
(userLeaving ? USER_LEAVING : 0) | (dontReport ? DONT_REPORT : 0),
configChanges,
seq);
}
SomeArgs args = (SomeArgs) msg.obj;
handlePauseActivity((IBinder) args.arg1, false,
(args.argi1 & USER_LEAVING) != 0, args.argi2,
(args.argi1 & DONT_REPORT) != 0, args.argi3);
maybeSnapshot();
private void handlePauseActivity(IBinder token, boolean finished,
boolean userLeaving, int configChanges, boolean dontReport, int seq) {
ActivityClientRecord r = mActivities.get(token);
if (DEBUG_ORDER) Slog.d(TAG, "handlePauseActivity " + r + ", seq: " + seq);
if (!checkAndUpdateLifecycleSeq(seq, r, "pauseActivity")) {
return;
}
if (r != null) {
//Slog.v(TAG, "userLeaving=" + userLeaving + " handling pause of " + r);
//1
if (userLeaving) {
performUserLeavingActivity(r);
}
r.activity.mConfigChangeFlags |= configChanges;
//2
performPauseActivity(token, finished, r.isPreHoneycomb(), "handlePauseActivity");
//3 Make sure any pending writes are now committed.
if (r.isPreHoneycomb()) {
QueuedWork.waitToFinish();
}
// 4 Tell the activity manager we have paused.
if (!dontReport) {
try {
ActivityManager.getService().activityPaused(token);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
mSomeActivitiesChanged = true;
}
}
註釋1處調用成員函數performUserLeavingActivity向Launcher發送一個用戶離開事件通知。註釋2調用performPauseActivity使Launcher發送一個進入pause狀態的通知即調用成員函數onPause。註釋3處調用QueuedWork類的靜態成員函數waitToFinish等待前面的一些數據寫入操作。註釋4dontReport爲false,因此會調用AMS的activityPaused方法通知AMS Launcher已經進入Paused狀態
@Override
public final void activityPaused(IBinder token) {
final long origId = Binder.clearCallingIdentity();
synchronized(this) {
ActivityStack stack = ActivityRecord.getStackLocked(token);
if (stack != null) {
stack.activityPausedLocked(token, false);
}
}
Binder.restoreCallingIdentity(origId);
}
final void activityPausedLocked(IBinder token, boolean timeout) {
final ActivityRecord r = isInStackLocked(token);
if (r != null) {
mHandler.removeMessages(PAUSE_TIMEOUT_MSG, r);
if (mPausingActivity == r) {
if (DEBUG_STATES) Slog.v(TAG_STATES, "Moving to PAUSED: " + r
+ (timeout ? " (due to timeout)" : " (pause complete)"));
mService.mWindowManager.deferSurfaceLayout();
try {
completePauseLocked(true /* resumeNext */, null /* resumingActivity */);
} finally {
mService.mWindowManager.continueSurfaceLayout();
}
return;
}
}
private void completePauseLocked(boolean resumeNext, ActivityRecord resuming) {
if (resumeNext) {
final ActivityStack topStack = mStackSupervisor.getFocusedStack();
//1
if (!mService.isSleepingOrShuttingDownLocked()) {
mStackSupervisor.resumeFocusedStackTopActivityLocked(topStack, prev, null);
} else {
mStackSupervisor.checkReadyForSleepLocked();
ActivityRecord top = topStack.topRunningActivityLocked();
if (top == null || (prev != null && top != prev)) {
// If there are no more activities available to run, do resume anyway to start
// something. Also if the top activity on the stack is not the just paused
// activity, we need to go ahead and resume it to ensure we complete an
// in-flight app switch.
mStackSupervisor.resumeFocusedStackTopActivityLocked();
}
}
}
}
註釋1處檢查系統是不是正在進入睡眠或者關閉狀態，如果不是就會調用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.state != RESUMED) {
mFocusedStack.resumeTopActivityUncheckedLocked(null, null);
} else if (r.state == RESUMED) {
// Kick off any lingering app transitions form the MoveTaskToFront operation.
mFocusedStack.executeAppTransition(targetOptions);
}
return false;
}
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!
if (!next.hasBeenLaunched) {
next.hasBeenLaunched = true;
} else {
if (SHOW_APP_STARTING_PREVIEW) {
next.showStartingWindow(null /* prev */, false /* newTask */,
false /* taskSwich */);
}
if (DEBUG_SWITCH) Slog.v(TAG_SWITCH, "Restarting: " + next);
}
if (DEBUG_STATES) Slog.d(TAG_STATES, "resumeTopActivityLocked: Restarting " + next);
mStackSupervisor.startSpecificActivityLocked(next, true, true);
}
}
由於 topRunningActivityLocked獲取的是位於Activity堆棧頂端的，即將啓動的activity的一個ActivityRecord對象。由於對應Activity還沒有啓動，因此app爲null
void startSpecificActivityLocked(ActivityRecord r,
boolean andResume, boolean checkConfig) {
// 1 Is this activity's application already running?
ProcessRecord app = mService.getProcessRecordLocked(r.processName,
r.info.applicationInfo.uid, true);
r.getStack().setLaunchTime(r);
// 2
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);
}
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.
}
mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
"activity", r.intent.getComponent(), false, false, true);
}
在AMS中每個Activity組件都有一個用戶ID和一個進程名稱；其中用戶ID是在安裝該Activity時有PMS分配的，而進程名稱則是由該Activity的android:process屬性決定。AMS在啓動一個Activity時，首先會用它的用戶ID和進程名稱來檢查系統中是否存在一個對應的應用程序進程。如果存在，就會直接通知這個應用程序將該Activity啓動起來，否則，就會先以這個用戶ID和進程名稱創建一個應用程序進程，然後再通知這個應用程序進程將該Activity啓動起來。
註釋1就是獲取應用程序進程是否已經存在，如果存在就會直接調用realStartActivityLocked來啓動該Activity，否則就會調用startProcessLocked爲該Activity創建一個應用程序進程，然後將它啓動起來。由於是第一次啓動應用程序，這時候不可能存在所需的應用程序進程，因此會調用startProcessLocked來創建一個應用程序進程。
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) {
if (hostingType.equals("webview_service")) {
startResult = startWebView(entryPoint,
app.processName, uid, uid, gids, debugFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, null, entryPointArgs);
} else {
startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, debugFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, invokeWith, entryPointArgs);
}
}
在函數中調用了Process類的靜態成員函數start來啓動一個新的應用程序進程，該函數指定該進程的入口函數爲android.app.ActivityThread類的靜態成員函數main,接下來就開始一個新的應用程序進程啓動。
frameworks/base/core/java/android/app/ActivityThread.java
public static void main(String[] args) {
// Make sure TrustedCertificateStore looks in the right place for CA certificates
final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());
TrustedCertificateStore.setDefaultUserDirectory(configDir);
Process.setArgV0("<pre-initialized>");
Looper.prepareMainLooper();
ActivityThread thread = new ActivityThread();
thread.attach(false);
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
Looper.loop();
}
該函數主要做了兩件事情：
- 在進程中創建一個ActivityThread對象，並調用它的成員函數attach向AMS發送一個啓動完成通知。
- 調用Looper.prepareMainLooper()創建一個消息循環，並且在向AMS發送啓動完成通知後，使得當前進程進入消息循環中。
private void attach(boolean system) {
sCurrentActivityThread = this;
mSystemThread = system;
if (!system) {
ViewRootImpl.addFirstDrawHandler(new Runnable() {
@Override
public void run() {
ensureJitEnabled();
}
});
android.ddm.DdmHandleAppName.setAppName("<pre-initialized>",
UserHandle.myUserId());
RuntimeInit.setApplicationObject(mAppThread.asBinder());
final IActivityManager mgr = ActivityManager.getService();
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
}
在該函數中獲取AMS對象，然後調用它的成員函數attachApplication將創建的ApplicationThread對象傳遞給AMS
frameworks/base/services/java/com/android/server/am/ActivityManagerService.java
@Override
public final void attachApplication(IApplicationThread thread) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid);
Binder.restoreCallingIdentity(origId);
}
}
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
ProcessRecord app;
// 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.
//1
long startTime = SystemClock.uptimeMillis();
if (pid != MY_PID && pid >= 0) {
synchronized (mPidsSelfLocked) {
app = mPidsSelfLocked.get(pid);
}
} else {
app = null;
}
...
app.makeActive(thread, mProcessStats);
app.curAdj = app.setAdj = app.verifiedAdj = ProcessList.INVALID_ADJ;
app.curSchedGroup = app.setSchedGroup = ProcessList.SCHED_GROUP_DEFAULT;
app.forcingToImportant = null;
updateProcessForegroundLocked(app, false, false);
app.hasShownUi = false;
app.debugging = false;
app.cached = false;
app.killedByAm = false;
app.killed = false;
app.unlocked = StorageManager.isUserKeyUnlocked(app.userId);
mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app);
boolean normalMode = mProcessesReady ||isAllowedWhileBooting(app.info);
...
// 2 See if the top visible activity is waiting to run in this process...
if (normalMode) {
try {
if (mStackSupervisor.attachApplicationLocked(app)) {
didSomething = true;
}
} catch (Exception e) {
Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);
badApp = true;
}
}
...
}
參數pid指向了前面創建的應用程序進程PID,AMS以這個PID爲關鍵字將ProcessRecord對象保存在成員變量mPidsSelfLocked中。註釋1處通過pid將這個ProcessRecord對象取回來，並保存在變量app中。 由於normalMode未true註釋2處調用attachApplicationLocked
frameworks/base/services/java/com/android/server/am/ActivityStackSupervisor.java
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 {
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;
}
由於目標Activity還沒有和應用進程綁定hr.app爲null,因此會調用realStartActivityLocked方法
final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
boolean andResume, boolean checkConfig){
...
r.app = app;
app.waitingToKill = null;
r.launchCount++;
r.lastLaunchTime = SystemClock.uptimeMillis();
//1
app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
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, !andResume,
mService.isNextTransitionForward(), profilerInfo);
...
}
註釋1處會調用app.thread.scheduleLaunchActivity來通知前面創建的的應用程序進程參數r所描述的一個Activity。
/frameworks/base/core/java/android/app/ActivityThread.java
@Override
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Configuration curConfig, Configuration overrideConfig,
CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor,
int procState, Bundle state, PersistableBundle persistentState,
List<ResultInfo> pendingResults, List<ReferrerIntent> pendingNewIntents,
boolean notResumed, boolean isForward, ProfilerInfo profilerInfo) {
updateProcessState(procState, false);
ActivityClientRecord r = new ActivityClientRecord();
r.token = token;
r.ident = ident;
r.intent = intent;
r.referrer = referrer;
r.voiceInteractor = voiceInteractor;
r.activityInfo = info;
r.compatInfo = compatInfo;
r.state = state;
r.persistentState = persistentState;
r.pendingResults = pendingResults;
r.pendingIntents = pendingNewIntents;
r.startsNotResumed = notResumed;
r.isForward = isForward;
r.profilerInfo = profilerInfo;
r.overrideConfig = overrideConfig;
updatePendingConfiguration(curConfig);
sendMessage(H.LAUNCH_ACTIVITY, r);
}
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) {
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
r.createdConfig = new Configuration(mConfiguration);
reportSizeConfigurations(r);
Bundle oldState = r.state;
handleResumeActivity(r.token, false, r.isForward,
!r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);
if (!r.activity.mFinished && r.startsNotResumed) {
// The activity manager actually wants this one to start out paused, because it
// needs to be visible but isn't in the foreground. We accomplish this by going
// through the normal startup (because activities expect to go through onResume()
// the first time they run, before their window is displayed), and then pausing it.
// However, in this case we do -not- need to do the full pause cycle (of freezing
// and such) because the activity manager assumes it can just retain the current
// state it has.
performPauseActivityIfNeeded(r, reason);
// We need to keep around the original state, in case we need to be created again.
// But we only do this for pre-Honeycomb apps, which always save their state when
// pausing, so we can not have them save their state when restarting from a paused
// state. For HC and later, we want to (and can) let the state be saved as the
// normal part of stopping the activity.
if (r.isPreHoneycomb()) {
r.state = oldState;
}
}
}
}
在該方法中會調用performLaunchActivity和handleResumeActivity方法。
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
ContextImpl appContext = createBaseContextForActivity(r);
Activity activity = null;
try {
java.lang.ClassLoader cl = appContext.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
StrictMode.incrementExpectedActivityCount(activity.getClass());
r.intent.setExtrasClassLoader(cl);
r.intent.prepareToEnterProcess();
if (r.state != null) {
r.state.setClassLoader(cl);
}
} catch (Exception e) {
if (!mInstrumentation.onException(activity, e)) {
throw new RuntimeException(
"Unable to instantiate activity " + component
+ ": " + e.toString(), e);
}
}
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
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);
}
if (!r.activity.mFinished) {
activity.performStart();
r.stopped = false;
}
}
方法中會調用Actvity的onCreate和onStart方法，Activity正是啓動了。
參考資料
《Android系統源碼情景分析》羅昇陽