Android 7.1 APP 啓動流程分析

本文是基於 Android 7.1 系統進行探討的.

我們都知道Launcher 其實也是一個APP ,安裝好的應用的快捷方式都被放在了Launcher中.很多的廠家或者廠商都在定製自己的Launcher,目前我們知道Android現在使用的是Launcher3的版本,

總體創建流程如下

 

下圖是應用層創建Activity的過程

 

我們可以在如下路徑找到Launcher.java

packages/apps/Launcher3/src/com/android/launcher3/Launcher.java

可以查看到 Launcher.java 中的方法就是創建圖標的方法. 由此可以知道 圖標的點擊事件放在了本 favorite.setOnClickListener(this);

    public View createShortcut(ViewGroup parent, ShortcutInfo info) {
        BubbleTextView favorite = (BubbleTextView) getLayoutInflater().inflate(R.layout.app_icon,
                parent, false);
        favorite.applyFromShortcutInfo(info, mIconCache);
        favorite.setCompoundDrawablePadding(mDeviceProfile.iconDrawablePaddingPx);
        favorite.setOnClickListener(this);
        favorite.setOnFocusChangeListener(mFocusHandler);
        return favorite;
    }

我們查看到 Launcher.java 中的onClick方法 可以查看到 如下監聽時間發現走的是 onClickAppShortcut(v); 

  public void onClick(View v) {
        // Make sure that rogue clicks don't get through while allapps is launching, or after the
        // view has detached (it's possible for this to happen if the view is removed mid touch).
........省略代碼.....

        Object tag = v.getTag();
        if (tag instanceof ShortcutInfo) {
            //啓動桌面圖標
            onClickAppShortcut(v);
        } else if (tag instanceof FolderInfo) {
            if (v instanceof FolderIcon) {
                onClickFolderIcon(v);
            }
        } else if ((FeatureFlags.LAUNCHER3_ALL_APPS_PULL_UP && v instanceof PageIndicator) ||
                (v == mAllAppsButton && mAllAppsButton != null)) {
            onClickAllAppsButton(v);
        } else if (tag instanceof AppInfo) {
            startAppShortcutOrInfoActivity(v);
        } else if (tag instanceof LauncherAppWidgetInfo) {
            if (v instanceof PendingAppWidgetHostView) {
                onClickPendingWidget((PendingAppWidgetHostView) v);
            }
        }
    }

查看onClickAppShortcut(v); 我們可以查看到調用的是   startAppShortcutOrInfoActivity(v); 我們繼續查看 

   protected void onClickAppShortcut(final View v) {
        if (LOGD) Log.d(TAG, "onClickAppShortcut");
...........省略代碼........

        // Start activities
        startAppShortcutOrInfoActivity(v);
    }

查看 startAppShortcutOrInfoActivity(v);方法

   private void startAppShortcutOrInfoActivity(View v) {
        ItemInfo item = (ItemInfo) v.getTag();
        Intent intent = item.getIntent();
        if (intent == null) {
            throw new IllegalArgumentException("Input must have a valid intent");
        }
        //啓動Activity 
        boolean success = startActivitySafely(v, intent, item);
        getUserEventDispatcher().logAppLaunch(v, intent);

        if (success && v instanceof BubbleTextView) {
            mWaitingForResume = (BubbleTextView) v;
            mWaitingForResume.setStayPressed(true);
        }
    }

緊接着我們查看到 startActivitySafely 方法被調用startActivity 方法也就是調用的我們Activity.java中的方法

    public boolean startActivitySafely(View v, Intent intent, ItemInfo item) {
         .....省略代碼......
        // Prepare intent
        //添加  FLAG_ACTIVITY_NEW_TASK
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        if (v != null) {
            intent.setSourceBounds(getViewBounds(v));
        }
        .....省略代碼......
        //啓動 Activity
         startActivity(intent, optsBundle);
       
        return false;
    }

我們從startActivitySafely 可以看到 添加了 Intent.FLAG_ACTIVITY_NEW_TASK 這個Flag 也調用了 startActivity 這個方法.到這裏就又回到了Activity的startActivity()方法，也就是Activity的啓動流程

frameworks/base/core/java/android/app/Activity.java

    public void startActivityAsUser(Intent intent, Bundle options, UserHandle user) {
        ......省略代碼.....
        Instrumentation.ActivityResult ar =
                mInstrumentation.execStartActivity(
                        this, mMainThread.getApplicationThread(), mToken, this,
                        intent, -1, options, user);
       ......省略代碼.....
        cancelInputsAndStartExitTransition(options);
    }

 查看到調用到了Instrumentation.java 中的 execStartActivity 方法

frameworks/base/core/java/android/app/Instrumentation.java

    public ActivityResult execStartActivity(
            Context who, IBinder contextThread, IBinder token, Activity target,
            Intent intent, int requestCode, Bundle options) {
   ..... 省略代碼 ....
        try {
            intent.migrateExtraStreamToClipData();
            intent.prepareToLeaveProcess(who);
            int result = ActivityManagerNative.getDefault()
                .startActivity(whoThread, who.getBasePackageName(), intent,
                        intent.resolveTypeIfNeeded(who.getContentResolver()),
                        token, target != null ? target.mEmbeddedID : null,
                        requestCode, 0, null, options);
            checkStartActivityResult(result, intent);
        } catch (RemoteException e) {
            throw new RuntimeException("Failure from system", e);
        }
        return null;
    }

  查看到調用到了ActivityManagerService.jav 中的 startActivity 方法

frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

    @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);
    }

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, IActivityManager.WaitResult outResult, Configuration config,
            Bundle bOptions, boolean ignoreTargetSecurity, int userId,
            IActivityContainer iContainer, TaskRecord inTask) {
            ....省略代碼....
            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);
    }

   final 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) {
        ....省略代碼.....
        try {
            mService.mWindowManager.deferSurfaceLayout();
            err = startActivityUnchecked(r, sourceRecord, voiceSession, voiceInteractor, startFlags,
                    true, options, inTask);
        } finally {
            mService.mWindowManager.continueSurfaceLayout();
        }
        postStartActivityUncheckedProcessing(r, err, stack.mStackId, mSourceRecord, mTargetStack);
        return err;
    }

frameworks\base\services\core\java\com\android\server\am\ActivityStack.java

    private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
            IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
            int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask) {
                ....省略代碼....
                mSupervisor.resumeFocusedStackTopActivityLocked(mTargetStack, mStartActivity,
                        mOptions);
                ....省略代碼....
        return START_SUCCESS;
    }

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);
        }
        ...省略代碼...
    }

frameworks/base/services/core/java/com/android/server/am/ActivityStack.java

    boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
            ...省略代碼...
            result = resumeTopActivityInnerLocked(prev, options);
            ...省略代碼...
    }

    private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {
       ...省略代碼...
       mStackSupervisor.startSpecificActivityLocked(next, true, false);
       ...省略代碼...
        return true;
    }

到此處我們可以查看到如果應用已經啓動 就直接開始創建Activity進行底層通訊.如果進程未啓動需要創建進行 

frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java

    void startSpecificActivityLocked(ActivityRecord r,
            boolean andResume, boolean checkConfig) {
        
        if (app != null && app.thread != null) {
            //進程已經創建
            try {
                //創建Activity
                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.
        }
        //進程不存在需要先創建進程
        mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
                "activity", r.intent.getComponent(), false, false, true);
    }

進程已經存在的情況 

    final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
            boolean andResume, boolean checkConfig) throws RemoteException {
            ...省略代碼...
            app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
                    System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration),
                    new Configuration(task.mOverrideConfig), r.compat, r.launchedFromPackage,
                    task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results,
                    newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo);
            ...省略代碼...
    }

frameworks/base/core/java/android/app/IApplicationThread.java

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) throws RemoteException;

frameworks/base/core/java/android/app/ApplicationThreadNative.java

    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) throws RemoteException {
             ...省略代碼...
        mRemote.transact(SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION, data, null,
                IBinder.FLAG_ONEWAY);
            ...省略代碼...
    }

    @Override
    public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
            throws RemoteException {
        switch (code) {
        ...省略代碼...
        case SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION:
        {
           ...省略代碼...
            //調用的是 ActivityThread.java中的 內部類 ApplicationThread
            //scheduleLaunchActivity
            scheduleLaunchActivity(intent, b, ident, info, curConfig, overrideConfig, compatInfo,
                    referrer, voiceInteractor, procState, state, persistentState, ri, pi,
                    notResumed, isForward, profilerInfo);
           ...省略代碼...
        }
       ...省略代碼...
    }

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) {

            sendMessage(H.LAUNCH_ACTIVITY, r);
        }

   public void handleMessage(Message msg) {
            if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
            switch (msg.what) {
                case LAUNCH_ACTIVITY: {
                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
                    final ActivityClientRecord r = (ActivityClientRecord) msg.obj;

                    r.packageInfo = getPackageInfoNoCheck(
                            r.activityInfo.applicationInfo, r.compatInfo);
                    handleLaunchActivity(r, null, "LAUNCH_ACTIVITY");
                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
                } break;
                ...省略代碼...
        }

    private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) {
        
        ...省略代碼...
        //不可見 on
        Activity a = performLaunchActivity(r, customIntent);
        ...省略代碼...
        //Activity可見 
        handleResumeActivity(r.token, false, r.isForward,
                    !r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);
    }

進程不存在的情況

mService的類型是ActivityManagerService（AMS），我們來看ActivityManagerService的startProcessLocked()方法：

private boolean startProcessLocked(String hostingType, String hostingNameStr, String entryPoint,
                                   ProcessRecord app, int uid, int[] gids, int runtimeFlags, int mountExternal,
                                   String seInfo, String requiredAbi, String instructionSet, String invokeWith,
                                   long startTime) {
    // ...
    final ProcessStartResult startResult = startProcess(app.hostingType, entryPoint,
            app, app.startUid, gids, runtimeFlags, mountExternal, app.seInfo,
            requiredAbi, instructionSet, invokeWith, app.startTime);
    // ...
}

經過一系列調用最終執行了Process.start()方法：

public static final ProcessStartResult start(final String processClass,
                                             final String niceName,
                                             int uid, int gid, int[] gids,
                                             int runtimeFlags, int mountExternal,
                                             int targetSdkVersion,
                                             String seInfo,
                                             String abi,
                                             String instructionSet,
                                             String appDataDir,
                                             String invokeWith,
                                             String[] zygoteArgs) {
    return zygoteProcess.start(processClass, niceName, uid, gid, gids,
            runtimeFlags, mountExternal, targetSdkVersion, seInfo,
            abi, instructionSet, appDataDir, invokeWith, zygoteArgs);
}

接着又調用了ZygoteProcess的start()方法：

public final Process.ProcessStartResult start(final String processClass,
                                              final String niceName,
                                              int uid, int gid, int[] gids,
                                              int runtimeFlags, int mountExternal,
                                              int targetSdkVersion,
                                              String seInfo,
                                              String abi,
                                              String instructionSet,
                                              String appDataDir,
                                              String invokeWith,
                                              String[] zygoteArgs) {
....略代碼...
        return startViaZygote(processClass, niceName, uid, gid, gids,
                runtimeFlags, mountExternal, targetSdkVersion, seInfo,
                abi, instructionSet, appDataDir, invokeWith, false /* startChildZygote */,
                zygoteArgs);
....略代碼...
  
}

private Process.ProcessStartResult startViaZygote(final String processClass,
                                                  final String niceName,
                                                  final int uid, final int gid,
                                                  final int[] gids,
                                                  int runtimeFlags, int mountExternal,
                                                  int targetSdkVersion,
                                                  String seInfo,
                                                  String abi,
                                                  String instructionSet,
                                                  String appDataDir,
                                                  String invokeWith,
                                                  boolean startChildZygote,
                                                  String[] extraArgs)
        throws ZygoteStartFailedEx {
    ....略代碼...
    return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi), argsForZygote);
}

private static Process.ProcessStartResult zygoteSendArgsAndGetResult(
        ZygoteState zygoteState, ArrayList<String> args)
        throws ZygoteStartFailedEx {
   ....略代碼...
    for (int i = 0; i < sz; i++) {
        String arg = args.get(i);
        writer.write(arg);
        writer.newLine();
    }
....略代碼...
    writer.flush();
....略代碼...
    result.pid = inputStream.readInt();
    result.usingWrapper = inputStream.readBoolean();
....略代碼...
    return result;
}

這裏又是經過了一系列的調用，最終執行了zygoteSendArgsAndGetResult()方法，該方法的作用就是創建App進程。關於App進程的創建，我粗略地閱讀了一下網上的相關文章，簡單介紹一下，Android中有一個重要的進程Zygote，翻譯爲受精卵進程，所有的應用程序進程都是通過Zygote進程fork得來的。流程簡單來說就是通過Binder請求AMS進程，然後AMS再發送Socket消息給Zygote進程，最後統一由Zygote進程fork出應用進程

進程創建完成後，就會執行ActivityThread的main()方法，它是應用程序的入口方法之後就是和ActivityManagerService.java 的一些交互工作.

public static void main(String[] args) {
    ...省略代碼...
    // 創建主線程Looper
    Looper.prepareMainLooper();
    ...省略代碼...
    // 核心代碼
    ActivityThread thread = new ActivityThread();
    thread.attach(false, startSeq);
    ...省略代碼...
      // 開啓消息循環
    Looper.loop();
     ...省略代碼...
}