主要參考的源碼爲Android2.3與8.0，從薑餅到奧瑞奧，Activity的主要邏輯並沒有根本性的改變，更多是做了一些封裝和優化，下文會在版本變化中對相關變化的代碼進行對比和說明。
Launcher發送start請求
1 Launcher.startActivitySafely
系統啓動時 PackageManagerService 解析 Androidmainfest文件， 會獲取啓動需要的laucher等信息，詳情見《安卓源碼分析與演變——PackageManager全流程》
之後根據flag走相應的啓動流程
public List<ResolveInfo> queryIntentActivities(Intent intent,
String resolvedType, int flags) {ComponentName comp = intent.getComponent();
if (comp != null) {List<ResolveInfo> list = new ArrayList<ResolveInfo>(1);
ActivityInfo ai = getActivityInfo(comp, flags);
if (ai != null) {ResolveInfo ri = new ResolveInfo();
ri.activityInfo = ai;
list.add(ri);
}
return list;
}
synchronized (mPackages) {String pkgName = intent.getPackage();
if (pkgName == null) {return (List<ResolveInfo>)mActivities.queryIntent(intent,
resolvedType, flags);
}
PackageParser.Package pkg = mPackages.get(pkgName);
if (pkg != null) {return (List<ResolveInfo>) mActivities.queryIntentForPackage(intent,
resolvedType, flags, pkg.activities);
}
return null;
}
}
void startActivitySafely(Intent intent, Object tag) {intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
try {startActivity(intent);
} catch (ActivityNotFoundException e) {Toast.makeText(this, R.string.activity_not_found, Toast.LENGTH_SHORT).show();
Log.e(TAG, "Unable to launch. tag=" + tag + " intent=" + intent, e);
} catch (SecurityException e) {Toast.makeText(this, R.string.activity_not_found, Toast.LENGTH_SHORT).show();
Log.e(TAG, "Launcher does not have the permission to launch " + intent +
". Make sure to create a MAIN intent-filter for the corresponding activity " +
"or use the exported attribute for this activity. "
+ "tag="+ tag + " intent=" + intent, e);
}
}
2 Activity.startActivity
@Override
public void startActivity(Intent intent) {startActivityForResult(intent, -1);
}
3 startActivityForResult
Instrument 監護系統和應用交互
ActivityThread 每個應用進程啓動持有，擁有ApplicationThread變量（Binder本地對象），作爲參數傳遞給ActivityManagerService，通知組件進入
paused狀態
Activity的mToken爲Ibinder（代理對象），指向ActivityManagerService的ActivityRecord
public void startActivityForResult(Intent intent, int requestCode) { if (mParent == null) {Instrumentation.ActivityResult ar =
mInstrumentation.execStartActivity(
this, mMainThread.getApplicationThread(), mToken, this,
intent, requestCode);
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;
}
} else {mParent.startActivityFromChild(this, intent, requestCode);
}
}
4 Instrument.execStartActivity
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode) {IApplicationThread whoThread = (IApplicationThread) contextThread;
if (mActivityMonitors != null) { synchronized (mSync) {final int N = mActivityMonitors.size();
for (int i=0; i<N; i++) {final ActivityMonitor am = mActivityMonitors.get(i);
if (am.match(who, null, intent)) {am.mHits++;
if (am.isBlocking()) {return requestCode >= 0 ? am.getResult() : null;
}
break;
}
}
}
}
try {int result = ActivityManagerNative.getDefault()
.startActivity(whoThread, intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
null, 0, token, target != null ? target.mEmbeddedID : null,
requestCode, false, false);
checkStartActivityResult(result, intent);
} catch (RemoteException e) {}
return null;
}
版本變化
2.3版本
ActivityManagerNative.getDefalt獲取ActivityManagerService的代理對象，封裝爲ActivityManagerProxy
static public IActivityManager getDefault()
{ if (gDefault != null) {//if (Config.LOGV) Log.v(
// "ActivityManager", "returning cur default = " + gDefault);
return gDefault;
}
IBinder b = ServiceManager.getService("activity");if (Config.LOGV) Log.v(
"ActivityManager", "default service binder = " + b);
gDefault = asInterface(b);
if (Config.LOGV) Log.v(
"ActivityManager", "default service = " + gDefault);
return gDefault;
}
8.0版本
int result = ActivityManager.getService()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
取代了之前的ActivityManagerNative和proxy類，直接獲取封裝過的單例aidl接口IActivityManager，包括startservice等大量方法
調用asInterface()將服務端的Binder對象轉換爲客戶端所需要的AIDL接口類型。如果客戶端和服務端在同一個進程他返回的就是服務端Stub對象本身，否則返回封裝的Stub.proxy對象。
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;
}
};
//ServiceManager實質上是管理緩存的Ibinder對象
public static IBinder getService(String name) { try {IBinder service = sCache.get(name);
if (service != null) {return service;
} else {return Binder.allowBlocking(getIServiceManager().getService(name));
}
} catch (RemoteException e) {Log.e(TAG, "error in getService", e);
}
return null;
}
5 ActivityManagerNative.ActivityManagerProxy.startActivity
參數傳遞爲Parcel，反序列化對象
通過ActivityManagerProxy的mRemote發送START_ACTIVITY_TRANSACTION，即進程間通信請求
（Proxy類實現IActivityManager接口，而8.0將中轉的代理類去除，精簡了流程）
public int startActivity(IApplicationThread caller, Intent intent,
String resolvedType, Uri[] grantedUriPermissions, int grantedMode,
IBinder resultTo, String resultWho,
int requestCode, boolean onlyIfNeeded,
boolean debug) throws RemoteException {Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(caller != null ? caller.asBinder() : null);
intent.writeToParcel(data, 0);
data.writeString(resolvedType);
data.writeTypedArray(grantedUriPermissions, 0);
data.writeInt(grantedMode);
data.writeStrongBinder(resultTo);
data.writeString(resultWho);
data.writeInt(requestCode);
data.writeInt(onlyIfNeeded ? 1 : 0);
data.writeInt(debug ? 1 : 0);
mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0);
reply.readException();
int result = reply.readInt();
reply.recycle();
data.recycle();
return result;
}
AMS處理start請求併發送paused
6 ActivityManagerService.startActivity
成員函數ActivityStack處理IPC請求，啓動組件
public final int startActivity(IApplicationThread caller,
Intent intent, String resolvedType, Uri[] grantedUriPermissions,
int grantedMode, IBinder resultTo,
String resultWho, int requestCode, boolean onlyIfNeeded,
boolean debug) {return mMainStack.startActivityMayWait(caller, intent, resolvedType,
grantedUriPermissions, grantedMode, resultTo, resultWho,
requestCode, onlyIfNeeded, debug, null, null);
}
版本變化
8.0 使用了ActivityStarter，封裝了ActivityStack、ActivityRecord、flag，intent相關的處理
@Override
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());
}
@Override
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");
}
7 ActivityStack.startActivityMayWait
解析intent信息
final int startActivityMayWait(IApplicationThread caller,
Intent intent, String resolvedType, Uri[] grantedUriPermissions,
int grantedMode, IBinder resultTo,
String resultWho, int requestCode, boolean onlyIfNeeded,
boolean debug, WaitResult outResult, Configuration config) {ActivityInfo aInfo;
try {ResolveInfo rInfo =
AppGlobals.getPackageManager().resolveIntent(
intent, resolvedType,
PackageManager.MATCH_DEFAULT_ONLY
| ActivityManagerService.STOCK_PM_FLAGS);
aInfo = rInfo != null ? rInfo.activityInfo : null;
} catch (RemoteException e) {aInfo = null;
}
...
int res = startActivityLocked(caller, intent, resolvedType,
grantedUriPermissions, grantedMode, aInfo,
resultTo, resultWho, requestCode, callingPid, callingUid,
8 ActivityStack.startActivityLocked
ActivityManagerService獲取Caller對應的Proce***ecord對象，該對象指向Launcher所在進程，獲取pid和uid
從mHistory尋找ActivityRecord信息，保存變量sourceActivity
9 ActivityStack.startActivityUnCheckedLocked
判斷標誌位，是否新task，是否用戶操作，根據taskAffinity屬性判斷新Activity的task組歸屬
重載方法startActivityLocked，加入棧頂，保存history
final int startActivityUncheckedLocked(ActivityRecord r,
ActivityRecord sourceRecord, Uri[] grantedUriPermissions,
int grantedMode, boolean onlyIfNeeded, boolean doResume) {final Intent intent = r.intent;
final int callingUid = r.launchedFromUid;
int launchFlags = intent.getFlags();
ActivityRecord notTop = (launchFlags&Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP)
!= 0 ? r : null;
// Should this be considered a new task?
if (r.resultTo == null && !addingToTask
&& (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {// todo: should do better management of integers.
mService.mCurTask++;
if (mService.mCurTask <= 0) {mService.mCurTask = 1;
}
r.task = new TaskRecord(mService.mCurTask, r.info, intent,
(r.info.flags&ActivityInfo.FLAG_CLEAR_TASK_ON_LAUNCH) != 0);
if (DEBUG_TASKS) Slog.v(TAG, "Starting new activity " + r
+ " in new task " + r.task);
newTask = true;
if (mMainStack) {mService.addRecentTaskLocked(r.task);
}
} else if (sourceRecord != null) {if (!addingToTask &&
(launchFlags&Intent.FLAG_ACTIVITY_CLEAR_TOP) != 0) {10 ActivityStack.resumeTopActivityLocked
如果將要啓動的Activity已經resume或者pause直接返回，否則通知進入pause狀態準備啓動
final boolean resumeTopActivityLocked(ActivityRecord prev) {// Find the first activity that is not finishing.
ActivityRecord next = topRunningActivityLocked(null);
...
// If the top activity is the resumed one, nothing to do.
if (mResumedActivity == next && next.state == ActivityState.RESUMED) {// Make sure we have executed any pending transitions, since there
// should be nothing left to do at this point.
mService.mWindowManager.executeAppTransition();
mNoAnimActivities.clear();
return false;
}
// If we are sleeping, and there is no resumed activity, and the top
// activity is paused, well that is the state we want.
if ((mService.mSleeping || mService.mShuttingDown)
&& mLastPausedActivity == next && next.state == ActivityState.PAUSED) {// Make sure we have executed any pending transitions, since there
// should be nothing left to do at this point.
mService.mWindowManager.executeAppTransition();
mNoAnimActivities.clear();
return false;
}
// The activity may be waiting for stop, but that is no longer
// appropriate for it.
mStoppingActivities.remove(next);
mWaitingVisibleActivities.remove(next);
// We need to start pausing the current activity so the top one
// can be resumed...
if (mResumedActivity != null) {if (DEBUG_SWITCH) Slog.v(TAG, "Skip resume: need to start pausing");
startPausingLocked(userLeaving, false);
return true;
}
...
}
版本變化
8.0
ActivityStackSupervisor封裝了ActivityStack有關的方法
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;
}
11 startPausingLocked
調用AMP通知主Activity，進入pause狀態。延時發送handler超時消息
private final void startPausingLocked(boolean userLeaving, boolean uiSleeping) {ActivityRecord prev = mResumedActivity;
...
if (prev.app != null && prev.app.thread != null) {if (DEBUG_PAUSE) Slog.v(TAG, "Enqueueing pending pause: " + prev);
try {EventLog.writeEvent(EventLogTags.AM_PAUSE_ACTIVITY,
System.identityHashCode(prev),
prev.shortComponentName);
prev.app.thread.schedulePauseActivity(prev, prev.finishing, userLeaving,
prev.configChangeFlags);
if (mMainStack) {mService.updateUsageStats(prev, false);
}
} catch (Exception e) {// Ignore exception, if process died other code will cleanup.
Slog.w(TAG, "Exception thrown during pause", e);
mPausingActivity = null;
mLastPausedActivity = null;
}
} else {mPausingActivity = null;
mLastPausedActivity = null;
}
...
if (mPausingActivity != null) {// Schedule a pause timeout in case the app doesn't respond.
// We don't give it much time because this directly impacts the
// responsiveness seen by the user.
Message msg = mHandler.obtainMessage(PAUSE_TIMEOUT_MSG);
msg.obj = prev;
mHandler.sendMessageDelayed(msg, PAUSE_TIMEOUT);
if (DEBUG_PAUSE) Slog.v(TAG, "Waiting for pause to complete...");
} else {// This activity failed to schedule the
// pause, so just treat it as being paused now.
if (DEBUG_PAUSE) Slog.v(TAG, "Activity not running, resuming next.");
resumeTopActivityLocked(null);
}
}
case PAUSE_TIMEOUT_MSG: {IBinder token = (IBinder)msg.obj;
// We don't at this point know if the activity is fullscreen,
// so we need to be conservative and assume it isn't.
Slog.w(TAG, "Activity pause timeout for " + token);
activityPaused(token, null, true);
}
12 APN.ApplicationThreadProxy.scheduePauseActivity
Ibinder發往Laucher組件（異步請求）
public final void schedulePauseActivity(IBinder token, boolean finished,
boolean userLeaving, int configChanges) throws RemoteException {Parcel data = Parcel.obtain();
data.writeInterfaceToken(IApplicationThread.descriptor);
data.writeStrongBinder(token);
data.writeInt(finished ? 1 : 0);
data.writeInt(userLeaving ? 1 :0);
data.writeInt(configChanges);
mRemote.transact(SCHEDULE_PAUSE_ACTIVITY_TRANSACTION, data, null,
IBinder.FLAG_ONEWAY);
data.recycle();
}
Launcher進入Pause狀態
以上過程都在Laucher完成
13 ApplicationThread.scedulePauseActivity
binder指向ActivityRecord
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Bundle state, List<ResultInfo> pendingResults,
List<Intent> pendingNewIntents, boolean notResumed, boolean isForward) {ActivityClientRecord r = new ActivityClientRecord();
r.token = token;
r.ident = ident;
r.intent = intent;
r.activityInfo = info;
r.state = state;
r.pendingResults = pendingResults;
r.pendingIntents = pendingNewIntents;
r.startsNotResumed = notResumed;
r.isForward = isForward;
queueOrSendMessage(H.LAUNCH_ACTIVITY, r);
}
14 ActivityThread.queueOrSendMessage
mH處理主線程pause操作
15 ActivityThread.handleMessage
16 ActivityThread.handlePauseActivity
通知Launcher 用戶離開
通知Launcher onPause
queueWork wait數據寫入（以備onResume恢復）
通知ActivityManagerService pause
private final void handlePauseActivity(IBinder token, boolean finished,
boolean userLeaving, int configChanges) {ActivityClientRecord r = mActivities.get(token);
if (r != null) {//Slog.v(TAG, "userLeaving=" + userLeaving + " handling pause of " + r);
if (userLeaving) {performUserLeavingActivity(r);
}
r.activity.mConfigChangeFlags |= configChanges;
Bundle state = performPauseActivity(token, finished, true);
// Make sure any pending writes are now committed.
QueuedWork.waitToFinish();
// Tell the activity manager we have paused.
try {ActivityManagerNative.getDefault().activityPaused(token, state);
} catch (RemoteException ex) {}
}
}
版本變化
8.0
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);
if (userLeaving) {performUserLeavingActivity(r);
}
r.activity.mConfigChangeFlags |= configChanges;
performPauseActivity(token, finished, r.isPreHoneycomb(), "handlePauseActivity");
// Make sure any pending writes are now committed.
if (r.isPreHoneycomb()) {QueuedWork.waitToFinish();
}
// Tell the activity manager we have paused.
if (!dontReport) { try {ActivityManager.getService().activityPaused(token);
} catch (RemoteException ex) {throw ex.rethrowFromSystemServer();
}
}
mSomeActivitiesChanged = true;
}
}
17 ActivityManagerProxy.activityPaused
parcel封裝數據
mRemote通知ActivityManagerService(IPC)
public void activityPaused(IBinder token, Bundle state) throws RemoteException
{Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(token);
data.writeBundle(state);
mRemote.transact(ACTIVITY_PAUSED_TRANSACTION, data, reply, 0);
reply.readException();
data.recycle();
reply.recycle();
}
AMS準備啓動新進程
18 ActivityManagerService.activityPaused
public final void activityPaused(IBinder token, Bundle icicle) {// Refuse possible leaked file descriptors
if (icicle != null && icicle.hasFileDescriptors()) { throw new IllegalArgumentException("File descriptors passed in Bundle");}
final long origId = Binder.clearCallingIdentity();
mMainStack.activityPaused(token, icicle, false);
Binder.restoreCallingIdentity(origId);
}
19 ActivityStack.activityPaused
移除超時
獲取stack中的ActivityRecord
public final void activityPaused(IBinder token, Bundle icicle) {// Refuse possible leaked file descriptors
if (icicle != null && icicle.hasFileDescriptors()) { throw new IllegalArgumentException("File descriptors passed in Bundle");}
final long origId = Binder.clearCallingIdentity();
mMainStack.activityPaused(token, icicle, false);
Binder.restoreCallingIdentity(origId);
}
20 ActivityStack.completePauseLocked
使pre指向mPausingActivity，並置空mPausingActivity，表示已完成pause
非睡眠和關閉狀態執行resume
private final void completePauseLocked() {ActivityRecord prev = mPausingActivity;
if (DEBUG_PAUSE) Slog.v(TAG, "Complete pause: " + prev);
if (prev != null) { if (prev.finishing) {if (DEBUG_PAUSE) Slog.v(TAG, "Executing finish of activity: " + prev);
prev = finishCurrentActivityLocked(prev, FINISH_AFTER_VISIBLE);
} else if (prev.app != null) {if (DEBUG_PAUSE) Slog.v(TAG, "Enqueueing pending stop: " + prev);
if (prev.waitingVisible) {prev.waitingVisible = false;
mWaitingVisibleActivities.remove(prev);
if (DEBUG_SWITCH || DEBUG_PAUSE) Slog.v(
TAG, "Complete pause, no longer waiting: " + prev);
}
if (prev.configDestroy) {destroyActivityLocked(prev, true);
} else {mStoppingActivities.add(prev);
if (mStoppingActivities.size() > 3) {// If we already have a few activities waiting to stop,
// then give up on things going idle and start clearing
// them out.
if (DEBUG_PAUSE) Slog.v(TAG, "To many pending stops, forcing idle");
Message msg = Message.obtain();
msg.what = IDLE_NOW_MSG;
mHandler.sendMessage(msg);
}
}
} else {if (DEBUG_PAUSE) Slog.v(TAG, "App died during pause, not stopping: " + prev);
prev = null;
}
mPausingActivity = null;
}
if (!mService.mSleeping && !mService.mShuttingDown) {resumeTopActivityLocked(prev);
} else { if (mGoingToSleep.isHeld()) {mGoingToSleep.release();
}
if (mService.mShuttingDown) {mService.notifyAll();
}
}
}
21 ActivityStack.resumeActivityLocked
此時mResumeAcitivity爲空，並且未啓動新的app進程，執行startSpecificActivityLocked
final boolean resumeTopActivityLocked(ActivityRecord prev) {...
if (mResumedActivity != null) {if (DEBUG_SWITCH) Slog.v(TAG, "Skip resume: need to start pausing");
startPausingLocked(userLeaving, false);
return true;
}
if (next.app != null && next.app.thread != null) {...
next.app.thread.scheduleResumeActivity(next,
mService.isNextTransitionForward());
pauseIfSleepingLocked();
...
} else {startSpecificActivityLocked(next, true, false);
return true;
}
}
22 ActivityStack.startSpecificActivityLocked
根據應用進程名稱和用戶id(每個activity相對應)啓動Activity，如果不存在創建相應進程，根Activity在此處初次創建進程
private final void startSpecificActivityLocked(ActivityRecord r,
boolean andResume, boolean checkConfig) {// Is this activity's application already running?
Proce***ecord app = mService.getProce***ecordLocked(r.processName,
r.info.applicationInfo.uid);
...
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);
}
// 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);
}
23 ActivityManagerService.startProcessLocked
newProce***ecordLocked 保存進程對應record
重載函數創建進程
發送PROC_START_TIMEOUT_MSG 新進程要求20毫秒內啓動完成 否則超時
Process.start
private final void startProcessLocked(Proce***ecord app,
String hostingType, String hostingNameStr) {...
int pid = Process.start("android.app.ActivityThread",mSimpleProcessManagement ? app.processName : null, uid, uid,
gids, debugFlags, null);
if (pid == 0 || pid == MY_PID) {// Processes are being emulated with threads.
app.pid = MY_PID;
app.removed = false;
mStartingProcesses.add(app);
} else if (pid > 0) {app.pid = pid;
app.removed = false;
synchronized (mPidsSelfLocked) {this.mPidsSelfLocked.put(pid, app);
Message msg = mHandler.obtainMessage(PROC_START_TIMEOUT_MSG);
msg.obj = app;
mHandler.sendMessageDelayed(msg, PROC_START_TIMEOUT);
}
} else {app.pid = 0;
RuntimeException e = new RuntimeException(
"Failure starting process " + app.processName
+ ": returned pid=" + pid);
Slog.e(TAG, e.getMessage(), e);
}
...
}
新應用進程啓動
24 ActivityThread.main
main方法-looper.prepare-thread.attach-looper.loop-thread.detach
thread爲ActivityThread，內部初始化ApplicationThread（binder本地對象，ActivityManagerService通信）
public static final void main(String[] args) {SamplingProfilerIntegration.start();
Process.setArgV0("<pre-initialized>");Looper.prepareMainLooper();
if (sMainThreadHandler == null) {sMainThreadHandler = new Handler();
}
ActivityThread thread = new ActivityThread();
thread.attach(false);
if (false) {Looper.myLooper().setMessageLogging(new
LogPrinter(Log.DEBUG, "ActivityThread"));
}
Looper.loop();
if (Process.supportsProcesses()) { throw new RuntimeException("Main thread loop unexpectedly exited");}
thread.detach();
String name = (thread.mInitialApplication != null)
? thread.mInitialApplication.getPackageName()
: "<unknown>";
Slog.i(TAG, "Main thread of " + name + " is now exiting");
}
25 ActivityThread.attachApplication
public void attachApplication(IApplicationThread app) throws RemoteException
{Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(app.asBinder());
mRemote.transact(ATTACH_APPLICATION_TRANSACTION, data, reply, 0);
reply.readException();
data.recycle();
reply.recycle();
}
26 ActivityManagerService.attachApplication
public final void attachApplication(IApplicationThread thread) { synchronized (this) {int callingPid = Binder.getCallingPid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid);
Binder.restoreCallingIdentity(origId);
}
}
27 ActivityManagerService attachApplicationLocked
使Proce***ecord.thread指向IApplicationThread（IPC），ActivityManagerService 即可以通過該對象與app進行通信
進程啓動完成 移除超時msg
獲取頂端 ActivityRecord，realStartActivityLocked
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {Proce***ecord app;
...
app.thread = thread;
app.curAdj = app.setAdj = -100;
app.curSchedGroup = Process.THREAD_GROUP_DEFAULT;
app.setSchedGroup = Process.THREAD_GROUP_BG_NONINTERACTIVE;
app.forcingToForeground = null;
app.foregroundServices = false;
app.debugging = false;
mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app);
...
// See if the top visible activity is waiting to run in this process...
ActivityRecord hr = mMainStack.topRunningActivityLocked(null);
if (hr != null && normalMode) {if (hr.app == null && app.info.uid == hr.info.applicationInfo.uid
&& processName.equals(hr.processName)) { try { if (mMainStack.realStartActivityLocked(hr, app, true, true)) {didSomething = true;
}
} catch (Exception e) {Slog.w(TAG, "Exception in new application when starting activity "
+ hr.intent.getComponent().flattenToShortString(), e);
badApp = true;
}
} else {mMainStack.ensureActivitiesVisibleLocked(hr, null, processName, 0);
}
}
}
29 ActivityStack.realStartActivityLocked
final boolean realStartActivityLocked(ActivityRecord r,
Proce***ecord app, boolean andResume, boolean checkConfig)
throws RemoteException {...
r.app = app;
if (localLOGV) Slog.v(TAG, "Launching: " + r);
int idx = app.activities.indexOf(r);
if (idx < 0) {app.activities.add(r);
}
...
mService.ensurePackageDexOpt(r.intent.getComponent().getPackageName());
app.thread.scheduleLaunchActivity(new Intent(r.intent), r,
System.identityHashCode(r),
r.info, r.icicle, results, newIntents, !andResume,
mService.isNextTransitionForward());
...
return true;
}
ActivityRecord加入app的ac列表
app.thread準備啓動ac
（Proce***ecord.thread指向IApplicationThread（IPC），ActivityManagerService 即可以通過該對象與app進行通信）
29 ApplicationThreadNative.scheduleLaunchActivity
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Bundle state, List<ResultInfo> pendingResults,
List<Intent> pendingNewIntents, boolean notResumed, boolean isForward)
throws RemoteException {Parcel data = Parcel.obtain();
data.writeInterfaceToken(IApplicationThread.descriptor);
intent.writeToParcel(data, 0);
data.writeStrongBinder(token);
data.writeInt(ident);
info.writeToParcel(data, 0);
data.writeBundle(state);
data.writeTypedList(pendingResults);
data.writeTypedList(pendingNewIntents);
data.writeInt(notResumed ? 1 : 0);
data.writeInt(isForward ? 1 : 0);
mRemote.transact(SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION, data, null,
IBinder.FLAG_ONEWAY);
data.recycle();
}
主線程啓動Activity
30 ActivityThread.ApplicationThread.scheduleLaunchActivity
// we use token to identify this activity without having to send the
// activity itself back to the activity manager. (matters more with ipc)
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Bundle state, List<ResultInfo> pendingResults,
List<Intent> pendingNewIntents, boolean notResumed, boolean isForward) {ActivityClientRecord r = new ActivityClientRecord();
r.token = token;
r.ident = ident;
r.intent = intent;
r.activityInfo = info;
r.state = state;
r.pendingResults = pendingResults;
r.pendingIntents = pendingNewIntents;
r.startsNotResumed = notResumed;
r.isForward = isForward;
queueOrSendMessage(H.LAUNCH_ACTIVITY, r);
}
封裝ActivityClientRecord信息，主線程LAUNCH_ACTIVITY
31 ActivityThread.queueOrSendMessage
32 HandleMsg
public void handleMessage(Message msg) {if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + msg.what);
switch (msg.what) { case LAUNCH_ACTIVITY: {ActivityClientRecord r = (ActivityClientRecord)msg.obj;
r.packageInfo = getPackageInfoNoCheck(
r.activityInfo.applicationInfo);
handleLaunchActivity(r, null);
} break;
}
}
getPackageInfoNoCheck，返回LoadedApk 已加載的apk信息
把它賦予ActivityClientRecord
33 handleLaunchActivity
private final void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {// If we are getting ready to gc after going to the background, well
// we are back active so skip it.
unscheduleGcIdler();
if (localLOGV) Slog.v(
TAG, "Handling launch of " + r);
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {r.createdConfig = new Configuration(mConfiguration);
Bundle oldState = r.state;
handleResumeActivity(r.token, false, r.isForward);
...
}
34 performLaunchActivity
初始化context和application
mInstrumentation.callActivityOnCreate啓動activity並恢復狀態
mActivities.put(r.token, r); 將toke和ActivityClientRecord對應保存
注意：ActivityClientRecord的token是Binder代理對象，指向ActivityManagerService中的ActivityRecord，雙方只是在不同進程使用。
private final Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) { // System.out.println("##### [" + System.currentTimeMillis() + "] ActivityThread.performLaunchActivity(" + r + ")");ActivityInfo aInfo = r.activityInfo;
if (r.packageInfo == null) {r.packageInfo = getPackageInfo(aInfo.applicationInfo,
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 activity = null;
try {java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
r.intent.setExtrasClassLoader(cl);
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);
}
}
try {Application app = r.packageInfo.makeApplication(false, mInstrumentation);
。。。
mInstrumentation.callActivityOnCreate(activity, r.state);
...
35 MainActivity.onCreate
來到大家最熟悉的方法了，流程完結。
總結
1、Launcher組件、MainActivity組件、AMS（ActivityManagerService），這三者的交互爲核心，而這三者分屬不同進程，以Binder作爲通信工具進行交互。
2、主流程：Launcher通知AMS並等待啓動——AMS準備啓動MainActivity——創建新進程——AMS通知新進程ActivityThread啓動MainActivity
3、ActivityManagerNative通過ServiceManager獲得AMS的代理對象，實現應用與AMS通信；AMS通過ApplicationThreadProxy獲取Launcher代理對象，實現AMS與應用通信。