android ActivityManagerService 源码分析----Activity管理(二)

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    上篇文章分析完了task的创建或者复用，接下来接着分析activity在启动过程中还有哪些工作需要去完成？首先给出整个activity的过程图。

    

1. Starting Window

    当该activity运行在新的task中或者进程中时，需要在activity显示之前显示一个Starting Window。如上图所示的setAppStartingWindow()方法，这个Starting Window上并没有绘制任何的view，它就是一个空白的Window，但是WMS赋予了它一个animation。这个Starting Window的处理过程需要注意几点：

    ·1. 在AMS请求WMS启动Starting Window时，这个过程是被置在WMS的消息队列中，也就是说这个过程是一个异步的过程，并且需要将其置在WMS消息队列的队首。

     一般情况下，Starting Window是在activity Window之前显示的，但是由于是异步过程，因此从理论上来说activity Window较早显示是有可能的，如果这样的话，Starting Window将会被清除而不再显示。例如在addStartingWindow()@PhoneWindowManager.java方法调用addView之前做一个sleep操作，结果就可能不显示Starting Window。

setAppStartingWindow()@WindowManagerService.java

 

// The previous app was getting ready to show a
// starting window, but hasn't yet done so.  Steal it!
if (DEBUG_STARTING_WINDOW) Slog.v(TAG,
        "Moving pending starting from " + ttoken
        + " to " + wtoken);
wtoken.startingData = ttoken.startingData;
ttoken.startingData = null;
ttoken.startingMoved = true;
Message m = mH.obtainMessage(H.ADD_STARTING, wtoken);
// Note: we really want to do sendMessageAtFrontOfQueue() because we
// want to process the message ASAP, before any other queued
// messages.
mH.sendMessageAtFrontOfQueue(m);
return;

    2. Starting Window是设置了Animation的

 

addStartingWindow()@PhoneWindowManager.java

 

final WindowManager.LayoutParams params = win.getAttributes();
params.token = appToken;
params.packageName = packageName;
params.windowAnimations = win.getWindowStyle().getResourceId(
        com.android.internal.R.styleable.Window_windowAnimationStyle, 0);
params.setTitle("Starting " + packageName);

    3. Starting Window同普通的activity Window一样，均为一个PhoneWindow，其中包看着DecorView和ViewRoot。

 

addStartingWindow()@PhoneWindowManager.java

 

        try {
            Context context = mContext;
            boolean setTheme = false;
            //Log.i(TAG, "addStartingWindow " + packageName + ": nonLocalizedLabel="
            //        + nonLocalizedLabel + " theme=" + Integer.toHexString(theme));
            if (theme != 0 || labelRes != 0) {
                try {
                    context = context.createPackageContext(packageName, 0);
                    if (theme != 0) {
                        context.setTheme(theme);
                        setTheme = true;
                    }
                } catch (PackageManager.NameNotFoundException e) {
                    // Ignore
                }
            }
            if (!setTheme) {
                context.setTheme(com.android.internal.R.style.Theme);
            }
            //创建PhoneWindow
            Window win = PolicyManager.makeNewWindow(context);
            if (win.getWindowStyle().getBoolean(
                    com.android.internal.R.styleable.Window_windowDisablePreview, false)) {
                return null;
            }

            Resources r = context.getResources();
            win.setTitle(r.getText(labelRes, nonLocalizedLabel));

            win.setType(
                WindowManager.LayoutParams.TYPE_APPLICATION_STARTING);
            // Force the window flags: this is a fake window, so it is not really
            // touchable or focusable by the user.  We also add in the ALT_FOCUSABLE_IM
            // flag because we do know that the next window will take input
            // focus, so we want to get the IME window up on top of us right away.
            win.setFlags(
                WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE|
                WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE|
                WindowManager.LayoutParams.FLAG_ALT_FOCUSABLE_IM,
                WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE|
                WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE|
                WindowManager.LayoutParams.FLAG_ALT_FOCUSABLE_IM);

            win.setLayout(WindowManager.LayoutParams.MATCH_PARENT,
                                WindowManager.LayoutParams.MATCH_PARENT);

            final WindowManager.LayoutParams params = win.getAttributes();
            params.token = appToken;
            params.packageName = packageName;
            params.windowAnimations = win.getWindowStyle().getResourceId(
                    com.android.internal.R.styleable.Window_windowAnimationStyle, 0);
            params.setTitle("Starting " + packageName);

            WindowManagerImpl wm = (WindowManagerImpl)
                    context.getSystemService(Context.WINDOW_SERVICE);
            View view = win.getDecorView();

            if (win.isFloating()) {
                // Whoops, there is no way to display an animation/preview
                // of such a thing!  After all that work...  let's skip it.
                // (Note that we must do this here because it is in
                // getDecorView() where the theme is evaluated...  maybe
                // we should peek the floating attribute from the theme
                // earlier.)
                return null;
            }

            if (localLOGV) Log.v(
                TAG, "Adding starting window for " + packageName
                + " / " + appToken + ": "
                + (view.getParent() != null ? view : null));
<span style="white-space: pre;">  </span>    //向WindowManager addView
            wm.addView(view, params);

            // Only return the view if it was successfully added to the
            // window manager... which we can tell by it having a parent.
            return view.getParent() != null ? view : null;
        }

    

 

2. 启动新进程

    如果新启动的activity需要运行在新的进程中，那么这个流程就涉及到了一个新进程的启动，由于画图的局限性，这个过程在上图中没有体现出来。

    所有的ProcessRecord被存储在mProcessNames变量中,以当前的进程的名字为索引。

@ActivityManagerService.java

 

final ProcessMap<ProcessRecord> mProcessNames
        = new ProcessMap<ProcessRecord>();

 

  进程名字的确定有如下规则： 

①如果Activity设置了android:process属性，则processName为属性设置的值；    

 

@ComponentInfo.java

 

public String processName;

   ②如果Activity没有设置android:process属性，那么Activity的processName为Application的processName。如果Application设置了process属性，那么processName为该值；如果没有设置，processName为Package的名字，即

 

@PackageItemInfo.java

 

public String packageName;

整个进程启动的过程前面有一篇文章介绍过，就不在介绍。

3. Application Transition

    Application Transition是android在实现窗口切换过程中，为了提供更好的用户体验和特定的指示，来呈现出的过渡效果。一般情况下，Application Transition是一个动画效果。

    Application Transition有两种，一种是启动activity时的Transition动画，一种是启动一些widget时的Transition动画。

    Transition类型的设置通过函数prepareAppTransition()@WindowManagerService.java来进行.

    设置完Transition类型之后,通过executeAppTransition()@WindowManagerService.java函数来执行这个Transition。

   prepareAppTransition()-->executeAppTransition()-->performLayoutAndPlaceSurfacesLocked();

   具体的Transition的animation绘制过程在分析WMS再做分析。

   

3.1 activity Transition

    当启动一个activity时，系统会给它的window呈现提供一个animation，这个animation可以在frameworks/base/core/res/res/values/styles.xml中进行设置

 

<!-- Standard animations for a full-screen window or activity. -->
<style name="Animation.Activity">
    <item name="activityOpenEnterAnimation">@anim/activity_open_enter</item>
    <item name="activityOpenExitAnimation">@anim/activity_open_exit</item>
    <item name="activityCloseEnterAnimation">@anim/activity_close_enter</item>
    <item name="activityCloseExitAnimation">@anim/activity_close_exit</item>
    <item name="taskOpenEnterAnimation">@anim/task_open_enter</item>
    <item name="taskOpenExitAnimation">@anim/task_open_exit</item>
    <item name="taskCloseEnterAnimation">@anim/task_close_enter</item>
    <item name="taskCloseExitAnimation">@anim/task_close_exit</item>
    <item name="taskToFrontEnterAnimation">@anim/task_open_enter</item>
    <item name="taskToFrontExitAnimation">@anim/task_open_exit</item>
    <item name="taskToBackEnterAnimation">@anim/task_close_enter</item>
    <item name="taskToBackExitAnimation">@anim/task_close_exit</item>
    <item name="wallpaperOpenEnterAnimation">@anim/wallpaper_open_enter</item>
    <item name="wallpaperOpenExitAnimation">@anim/wallpaper_open_exit</item>
    <item name="wallpaperCloseEnterAnimation">@anim/wallpaper_close_enter</item>
    <item name="wallpaperCloseExitAnimation">@anim/wallpaper_close_exit</item>
    <item name="wallpaperIntraOpenEnterAnimation">@anim/wallpaper_intra_open_enter</item>
    <item name="wallpaperIntraOpenExitAnimation">@anim/wallpaper_intra_open_exit</item>
    <item name="wallpaperIntraCloseEnterAnimation">@anim/wallpaper_intra_close_enter</item>
    <item name="wallpaperIntraCloseExitAnimation">@anim/wallpaper_intra_close_exit</item>
</style>

 

    activity启动的animation根据当前的activity所在的task状态有所不同，从上面的xml中的animation定义中就可以看出，它的分类：

    ★ 如果启动的activity运行在原来的task中，那么使用animation activityOpenEnterAnimation/activityOpenExitAnimation;

    ★ 如果启动的activity运行在新的task中，那么使用animation taskOpenEnterAnimation/taskOpenExitAnimation;

    ★ 如果结束的activity结束之后原来的task还存在，那么使用activityCloseEnterAnimation/activityCloseExitAnimation;

    ★ 如果结束的activity结束之后原来的task将不存在，也即次activity为task最后的activity，那么使用taskCloseEnterAnimation/taskCloseExitAnimation;

    ★ 一些特定的情况下，AMS需要将某个task move到最前面，例如上一篇文章中的task reparenting过程，此时使用taskToFrontEnterAnimation/taskToFrontExitAnimation;

    ★ 一些特定的情况下，AMS需要将某个task move到最底端，此时使用taskToBackEnterAnimation/taskToBackExitAnimation;

    ★ 如果当前的activity使用的theme中的参数android:windowShowWallpaper为true，此时的activity应该以当前的壁纸为背景，并且前一个显示的activity的背景不是当前的壁纸，此时使用wallpaperOpenEnterAnimation/wallpaperOpenExitAnimation/wallpaperCloseEnterAnimation/wallpaperCloseExitAnimation,

如下面activity所示：

    

    ★ 如果当前的activity使用的theme中的参数android:windowShowWallpaper为true，此时的activity应该以当前的壁纸为背景，并且前一个显示的activity的背景是当前的壁纸，此时使用wallpaperIntraOpenEnterAnimation/wallpaperIntraOpenExitAnimation/wallpaperIntraCloseEnterAnimation/wallpaperIntraCloseExitAnimation.

下面代码即是判断当前应该选择那些带有wallpaper的Transition类型。

performLayoutAndPlaceSurfacesLockedInner()@WindowManagerService.java

 

final int NC = mClosingApps.size();
 NN = NC + mOpeningApps.size();
 for (i=0; i<NN; i++) {
     AppWindowToken wtoken;
     int mode;
     if (i < NC) {
         wtoken = mClosingApps.get(i);
         mode = 1;
     } else {
         wtoken = mOpeningApps.get(i-NC);
         mode = 2;
     }
     if (mLowerWallpaperTarget != null) {
         if (mLowerWallpaperTarget.mAppToken == wtoken
                 || mUpperWallpaperTarget.mAppToken == wtoken) {
             foundWallpapers |= mode;
         }
     }
     if (wtoken.appFullscreen) {
         WindowState ws = wtoken.findMainWindow();
         if (ws != null) {
             // If this is a compatibility mode
             // window, we will always use its anim.
             if ((ws.mAttrs.flags&FLAG_COMPATIBLE_WINDOW) != 0) {
                 animLp = ws.mAttrs;
                 animToken = ws.mAppToken;
                 bestAnimLayer = Integer.MAX_VALUE;
             } else if (ws.mLayer > bestAnimLayer) {
                 animLp = ws.mAttrs;
                 animToken = ws.mAppToken;
                 bestAnimLayer = ws.mLayer;
             }
         }
     }
 }

 if (foundWallpapers == 3) {
     if (DEBUG_APP_TRANSITIONS) Slog.v(TAG,
             "Wallpaper animation!");
     switch (transit) {
         case WindowManagerPolicy.TRANSIT_ACTIVITY_OPEN:
         case WindowManagerPolicy.TRANSIT_TASK_OPEN:
         case WindowManagerPolicy.TRANSIT_TASK_TO_FRONT:
             transit = WindowManagerPolicy.TRANSIT_WALLPAPER_INTRA_OPEN;
             break;
         case WindowManagerPolicy.TRANSIT_ACTIVITY_CLOSE:
         case WindowManagerPolicy.TRANSIT_TASK_CLOSE:
         case WindowManagerPolicy.TRANSIT_TASK_TO_BACK:
             transit = WindowManagerPolicy.TRANSIT_WALLPAPER_INTRA_CLOSE;
             break;
     }
     if (DEBUG_APP_TRANSITIONS) Slog.v(TAG,
             "New transit: " + transit);
 } else if (oldWallpaper != null) {
     // We are transitioning from an activity with
     // a wallpaper to one without.
     transit = WindowManagerPolicy.TRANSIT_WALLPAPER_CLOSE;
     if (DEBUG_APP_TRANSITIONS) Slog.v(TAG,
             "New transit away from wallpaper: " + transit);
 } else if (mWallpaperTarget != null) {
     // We are transitioning from an activity without
     // a wallpaper to now showing the wallpaper
     transit = WindowManagerPolicy.TRANSIT_WALLPAPER_OPEN;
     if (DEBUG_APP_TRANSITIONS) Slog.v(TAG,
             "New transit into wallpaper: " + transit);
 }

 

3.2 widget  Transition

    每个widget在启动时的animation和activity不一样,并且在frameworks/base/core/res/res/values/styles.xml中可以设置不同widget。

    

 

private boolean applyAnimationLocked(WindowState win,
        int transit, boolean isEntrance) {
    if (win.mLocalAnimating && win.mAnimationIsEntrance == isEntrance) {
        // If we are trying to apply an animation, but already running
        // an animation of the same type, then just leave that one alone.
        return true;
    }

    // Only apply an animation if the display isn't frozen.  If it is
    // frozen, there is no reason to animate and it can cause strange
    // artifacts when we unfreeze the display if some different animation
    // is running.
    if (!mDisplayFrozen && mPolicy.isScreenOn()) {
        int anim = mPolicy.selectAnimationLw(win, transit);
        int attr = -1;
        Animation a = null;
        if (anim != 0) {
            a = AnimationUtils.loadAnimation(mContext, anim);
        } else {
            switch (transit) {
                case WindowManagerPolicy.TRANSIT_ENTER:
                    attr = com.android.internal.R.styleable.WindowAnimation_windowEnterAnimation;
                    break;
                case WindowManagerPolicy.TRANSIT_EXIT:
                    attr = com.android.internal.R.styleable.WindowAnimation_windowExitAnimation;
                    break;
                case WindowManagerPolicy.TRANSIT_SHOW:
                    attr = com.android.internal.R.styleable.WindowAnimation_windowShowAnimation;
                    break;
                case WindowManagerPolicy.TRANSIT_HIDE:
                    attr = com.android.internal.R.styleable.WindowAnimation_windowHideAnimation;
                    break;
            }
            if (attr >= 0) {
                a = loadAnimation(win.mAttrs, attr);
            }
        }
        if (DEBUG_ANIM) Slog.v(TAG, "applyAnimation: win=" + win
                + " anim=" + anim + " attr=0x" + Integer.toHexString(attr)
                + " mAnimation=" + win.mAnimation
                + " isEntrance=" + isEntrance);
        if (a != null) {
            if (DEBUG_ANIM) {
                RuntimeException e = null;
                if (!HIDE_STACK_CRAWLS) {
                    e = new RuntimeException();
                    e.fillInStackTrace();
                }
                Slog.v(TAG, "Loaded animation " + a + " for " + win, e);
            }
            win.setAnimation(a);
            win.mAnimationIsEntrance = isEntrance;
        }
    } else {
        win.clearAnimation();
    }

    return win.mAnimation != null;
}

 

4. Activity启动

    文章的前面的内容中分析的一直是AMS对一个新启动的activity的管理，activity在AMS中的形态是以ActivityRecord的形式来管理的，下面的时序图中则是描绘了应用中一个activity的创建并启动的过程。

 

5. Activity pausing过程

    Activity pausing过程有3种情况：

    1. 第一种情况是从一个activity启动另一个activity的同时，也伴随着前一个activity的pause过程。

resumeTopActivityLocked()@ActivityStack.java

 

// 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;
}

 

    2. 第二种情况是当PowerManagerService要求AMS休眠或者设备shutDown时；

@ActivityStack.java

 

void pauseIfSleepingLocked() {
    if (mService.mSleeping || mService.mShuttingDown) {
        if (!mGoingToSleep.isHeld()) {
            mGoingToSleep.acquire();
            if (mLaunchingActivity.isHeld()) {
                mLaunchingActivity.release();
                mService.mHandler.removeMessages(LAUNCH_TIMEOUT_MSG);
            }
        }

        // If we are not currently pausing an activity, get the current
        // one to pause.  If we are pausing one, we will just let that stuff
        // run and release the wake lock when all done.
        if (mPausingActivity == null) {
            if (DEBUG_PAUSE) Slog.v(TAG, "Sleep needs to pause...");
            if (DEBUG_USER_LEAVING) Slog.v(TAG, "Sleep => pause with userLeaving=false");
            startPausingLocked(false, true);
        }
    }
}

 

    3.第三种情况是一个activity finish过程中。这个下面再介绍。

下图为第一种情况的时序图，整个pausing过程的是相同的，因此以一种情况的时序图来体现activity的pausing过程。

 

6. Activity Stoping 过程

     我们知道，当Activity不可见时会执行stoping的过程，下面我们就来分析以下一个activity是怎么来进行stop的。下面给出整个stop过程的时序图：

    

    在stop中有一个很重要的概念就是activity idle状态，不论是activity被新启动的activity完全覆盖，还是activity被finish，也就是activity的stop过程以及finsh过程，均是在最新被resume的activity已经resume完成之后才去处理。

    我们可以想象一下，每个应用程序的主线程ActivityThread中，当没有任何的消息待处理时，此时我们可以认为此时的已被resumed的activity状态时空闲的，没有任何的人机交互。因此android设计者将前一个被完全覆盖不可见的或者finish的activity的stop或finish操作放在此时来处理。这样做是合情合理，毕竟stop或者finish一个activity以及显示新的activity之间的关系是同步，是必须有先后顺序的，为了达到更好的用户体验，理所当然应该是先显示新的activity，然后采取stop或者finish旧的activity。为了实现这个目的，android设计者使用了MessageQueue的这个IdleHandler机制。

    首先，我们看一下MessageQueue的IdleHandler机制。

next ()@MessageQueue.java

 

// Run the idle handlers.
// We only ever reach this code block during the first iteration.
for (int i = 0; i < pendingIdleHandlerCount; i++) {
    final IdleHandler idler = mPendingIdleHandlers[i];
    mPendingIdleHandlers[i] = null; // release the reference to the handler

    boolean keep = false;
    try {
        keep = idler.queueIdle();
    } catch (Throwable t) {
        Log.wtf("MessageQueue", "IdleHandler threw exception", t);
    }

    if (!keep) {
        synchronized (this) {
            mIdleHandlers.remove(idler);
        }
    }
}

    在ActivityThread线程的Looper中，Looper会不停的去查找消息队列中是否有消息需要处理，如果没有任何的消息待处理，那么将查看当前的消息队列是否有IdleHandler注册，如果有逐个执行这些IdleHandler。
    明白了IdleHandler的机制，回过头来了看ActivityThread的IdleHandler的注册过程，代码如下。

 

handleResumeActivity()@ActivityThread.java

 

r.nextIdle = mNewActivities;
mNewActivities = r;
if (localLOGV) Slog.v(
    TAG, "Scheduling idle handler for " + r);
Looper.myQueue().addIdleHandler(new Idler());

 

7. Activity finishing过程

    用户从application结束当前的activity，如按back键；

   

    如同activity不可见时的处理一样，activity的finishing过程同样是在新的activity被resume之后才去执行，但是存在一种情况，当mHistory栈中存在多个(多于4个)activity时，假如此时user以很快的速度去按back键，并且在第一个需resume的activity尚未被resume完成时，已经被user触发了多次back键，此时应该怎么处理finish过程呢？

    按照上面的逻辑来看，user不停的以很快的速度去触发back键，直到回到home activity，这种情况下ActivityThread的Looper一直会有消息需要处理，根本不可能去处理它的IdleHandler，也就不可能去处理各个activity的finish过程，直到回到home activity之后才能有空闲去处理。我们可以想象一下如果按照这个逻辑去操作的话，会有什么问题？

    设想一下，我们累计了多个activity在ActivityThread的Looper在idle状态下处理，那么这个过程将是比较长的，假如此时又有user触发了启动actibity的操作，那么ActivityThread将会同时处理累计的activity的finish过程，同时又需要处理activity的启动过程，那么这么做的结果只能是给用户带来系统很慢的用户体验。因此上面的finish逻辑需要进行一定的矫正与修改。

    AMS在累计的activity超过3个时，就会强制调用Idle处理操作。这么做就有效的消耗了累计的activity的finish过程，就很大程度上减轻了上述所说的问题。

finishCurrentActivityLocked()@ActivityStack.java

 

// First things first: if this activity is currently visible,
// and the resumed activity is not yet visible, then hold off on
// finishing until the resumed one becomes visible.
if (mode == FINISH_AFTER_VISIBLE && r.nowVisible) {
    if (!mStoppingActivities.contains(r)) {
        mStoppingActivities.add(r);
        Slog.d(TAG, "finishCurrentActivityLocked mStoppingActivities size:" + mStoppingActivities.size());
        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.
            Message msg = Message.obtain();
            msg.what = IDLE_NOW_MSG;
            mHandler.sendMessage(msg);
        }
    }
    r.state = ActivityState.STOPPING;
    mService.updateOomAdjLocked();
    return r;
}

    同样的问题也存在与activity启动过程中，假如user以很快的速度去不停的启动activity，那么被覆盖的activity的stop过程很上述的finish过程一样，也会不停的累计，出现相同的问题。解决的思路也是一致的。
completePauseLocked()@ActivityStack.java

 

 

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);
}