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追踪Android源码演变——Activity启动全流程

发布时间:2020-07-20 08:44:41 来源:网络 阅读:690 作者:星恒Android 栏目:移动开发

主要参考的源码为Android2.3与8.0,从姜饼到奥瑞奥,Activity的主要逻辑并没有根本性的改变,更多是做了一些封装和优化,下文会在版本变化中对相关变化的代码进行对比和说明。

Launcher发送start请求

1 Launcher.startActivitySafely

系统启动时 PackageManagerService 解析 Androidmainfest文件, 会获取启动需要的laucher等信息,详情见《安卓源码分析与演变——PackageManager全流程》

之后根据flag走相应的启动流程

 

 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 监护系统和应用交互

ActivityThread 每个应用进程启动持有,拥有ApplicationThread变量(Binder本地对象),作为参数传递给ActivityManagerService,通知组件进入

paused状态

Activity的mToken为Ibinder(代理对象),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;
    }


版本变化

2.3版本

ActivityManagerNative.getDefalt获取ActivityManagerService的代理对象,封装为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类,直接获取封装过的单例aidl接口IActivityManager,包括startservice等大量方法

调用asInterface()将服务端的Binder对象转换为客户端所需要的AIDL接口类型。如果客户端和服务端在同一个进程他返回的就是服务端Stub对象本身,否则返回封装的Stub.proxy对象。

 

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实质上是管理缓存的Ibinder对象
 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

参数传递为Parcel,反序列化对象

通过ActivityManagerProxy的mRemote发送START_ACTIVITY_TRANSACTION,即进程间通信请求

(Proxy类实现IActivityManager接口,而8.0将中转的代理类去除,精简了流程)

 

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处理start请求并发送paused

ActivityManagerService.startActivity

成员函数ActivityStack处理IPC请求,启动组件

 

 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);
    }

版本变化

8.0 使用了ActivityStarter,封装了ActivityStack、ActivityRecord、flag,intent相关的处理

 

 @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获取Caller对应的Proce***ecord对象,该对象指向Launcher所在进程,获取pid和uid

从mHistory寻找ActivityRecord信息,保存变量sourceActivity


 


9 ActivityStack.startActivityUnCheckedLocked

判断标志位,是否新task,是否用户操作,根据taskAffinity属性判断新Activity的task组归属

重载方法startActivityLocked,加入栈顶,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

如果将要启动的Activity已经resume或者pause直接返回,否则通知进入pause状态准备启动

 

 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;
        }

        ...
        }
版本变化

8.0

ActivityStackSupervisor封装了ActivityStack有关的方法

 

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

调用AMP通知主Activity,进入pause状态。延时发送handler超时消息


 

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发往Laucher组件(异步请求)

 

   
    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进入Pause状态

追踪Android源码演变——Activity启动全流程

以上过程都在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处理主线程pause操作

15 ActivityThread.handleMessage
16 ActivityThread.handlePauseActivity

通知Launcher 用户离开

通知Launcher onPause

queueWork wait数据写入(以备onResume恢复)

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) {
            }
        }
    }
版本变化

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封装数据

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准备启动新进程

追踪Android源码演变——Activity启动全流程

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

移除超时

获取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,并置空mPausingActivity,表示已完成pause

非睡眠和关闭状态执行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

此时mResumeAcitivity为空,并且未启动新的app进程,执行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

根据应用进程名称和用户id(每个activity相对应)启动Activity,如果不存在创建相应进程,根Activity在此处初次创建进程

 

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 保存进程对应record

重载函数创建进程

发送PROC_START_TIMEOUT_MSG 新进程要求20毫秒内启动完成 否则超时

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);
            }
     ...
 }

新应用进程启动

24 ActivityThread.main

main方法-looper.prepare-thread.attach-looper.loop-thread.detach

thread为ActivityThread,内部初始化ApplicationThread(binder本地对象,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();
    }

追踪Android源码演变——Activity启动全流程

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 即可以通过该对象与app进行通信

进程启动完成 移除超时msg

获取顶端 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准备启动ac

Proce***ecord.thread指向IApplicationThread(IPC),ActivityManagerService 即可以通过该对象与app进行通信

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();
    }

主线程启动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);
        }

封装ActivityClientRecord信息,主线程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 已加载的apk信息

把它赋予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启动activity并恢复状态

mActivities.put(r.token, r); 将toke和ActivityClientRecord对应保存

注意:ActivityClientRecord的token是Binder代理对象,指向ActivityManagerService中的ActivityRecord,双方只是在不同进程使用。

 

 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

来到大家最熟悉的方法了,流程完结。


总结

1、Launcher组件、MainActivity组件、AMS(ActivityManagerService),这三者的交互为核心,而这三者分属不同进程,以Binder作为通信工具进行交互。

2、主流程:Launcher通知AMS并等待启动——AMS准备启动MainActivity——创建新进程——AMS通知新进程ActivityThread启动MainActivity

3、ActivityManagerNative通过ServiceManager获得AMS的代理对象,实现应用与AMS通信;AMS通过ApplicationThreadProxy获取Launcher代理对象,实现AMS与应用通信。


追踪Android源码演变——Activity启动全流程


向AI问一下细节

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