ActivityManagerService解读之Activity启动三探--Activity中Task与Stack

简介

ActivityManagerService中对Activity的管理都是以Task的形式，任务Task是指在执行特定作业时与用户交互的一系列 Activity，这些 Activity 按照各自的打开顺序排列在堆栈Stack中，AMS中分别以TaskRecord和ActivityStack表示，Activity则用ActivityRecord表示。因此我们也可以这么认为ActivityManagerService对Activity的管理，其实真正实现上来说是对ActivityStack，TaskRecord和ActivityRecord这三个数据结构的管理。更多详细的Task，Stack信息我们可以参考Google官网中Understand Tasks and Back Stack。
通常我们可以通过如下命令获取Android系统中Stack和Task的一些基本信息：

adb shell am stack list
Stack id=1 bounds=[0,0][240,320] displayId=0 userId=0taskId=142: com.android.settings/com.android.settings.Settings bounds=[0,0][240,320] userId=0 visible=true topActivity=ComponentInfo{com.android.settings/com.android.settings.Settings}Stack id=0 bounds=[0,0][240,320] displayId=0 userId=0taskId=139: com.android.launcher3/com.android.launcher3.Launcher bounds=[0,0][240,320] userId=0 visible=false topActivity=ComponentInfo{com.android.launcher3/com.android.launcher3.Launcher}

如果我们想要获取对应Stack中Task以及Task中Activity的详细信息，比如Task中Activity的数量，Activity的启动Intent，Activity的启动模式等等，我们可以通过如下命令：

ACTIVITY MANAGER ACTIVITIES (dumpsys activity activities)
Display #0 (activities from top to bottom):Stack #1:mFullscreen=trueisSleeping=falsemBounds=nullTask id #142mFullscreen=truemBounds=nullmMinWidth=-1mMinHeight=-1mLastNonFullscreenBounds=null* TaskRecord{32da96f #142 A=com.android.settings U=0 StackId=1 sz=1}userId=0 effectiveUid=1000 mCallingUid=u0a14 mUserSetupComplete=true mCallingPackage=com.android.launcher3affinity=com.android.settingsintent={act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.android.settings/.Settings}origActivity=com.android.settings/.SettingsrealActivity=com.android.settings/.SettingsautoRemoveRecents=false isPersistable=true numFullscreen=1 taskType=0 mTaskToReturnTo=1rootWasReset=true mNeverRelinquishIdentity=true mReuseTask=false mLockTaskAuth=LOCK_TASK_AUTH_PINNABLEActivities=[ActivityRecord{f46fe89 u0 com.android.settings/.Settings t142}]askedCompatMode=false inRecents=true isAvailable=truelastThumbnail=null lastThumbnailFile=/data/system_ce/0/recent_images/142_task_thumbnail.pngstackId=1hasBeenVisible=true mResizeMode=RESIZE_MODE_RESIZEABLE_VIA_SDK_VERSION mSupportsPictureInPicture=false isResizeable=true firstActiveTime=1672808557 lastActiveTime=1672809402 (inactive for 223s)* Hist #0: ActivityRecord{f46fe89 u0 com.android.settings/.Settings t142}packageName=com.android.settings processName=com.android.settingslaunchedFromUid=10014 launchedFromPackage=com.android.launcher3 userId=0app=ProcessRecord{218dd1e 2581:com.android.settings/1000}Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.android.settings/.Settings bnds=[159,155][237,242] }frontOfTask=true task=TaskRecord{32da96f #142 A=com.android.settings U=0 StackId=1 sz=1}taskAffinity=com.android.settingsrealActivity=com.android.settings/.SettingsbaseDir=/system/priv-app/Settings/Settings.apkdataDir=/data/user_de/0/com.android.settingsstateNotNeeded=false componentSpecified=true mActivityType=0compat={160dpi always-compat} labelRes=0x7f120b06 icon=0x7f0800df theme=0x7f1301c8mLastReportedConfigurations:mGlobalConfig={1.0 ?mcc?mnc [en_US] ldltr sw240dp w240dp h248dp 160dpi smll port -touch -keyb/v/h -nav/h appBounds=Rect(0, 0 - 240, 272) s.4}mOverrideConfig={1.0 ?mcc?mnc [en_US] ldltr sw240dp w240dp h248dp 160dpi smll port -touch -keyb/v/h -nav/h appBounds=Rect(0, 0 - 240, 272) s.4}CurrentConfiguration={1.0 ?mcc?mnc [en_US] ldltr sw240dp w240dp h248dp 160dpi smll port -touch -keyb/v/h -nav/h appBounds=Rect(0, 0 - 240, 272) s.4}taskDescription: iconFilename=/data/system_ce/0/recent_images/142_activity_icon_1672808529.png label="null" primaryColor=fff5f5f5backgroundColor=fffafafastatusBarColor=ff757575navigationBarColor=ff000000launchFailed=false launchCount=1 lastLaunchTime=-3m44s281mshaveState=false icicle=nullstate=RESUMED stopped=false delayedResume=false finishing=falsekeysPaused=false inHistory=true visible=true sleeping=false idle=true mStartingWindowState=STARTING_WINDOW_SHOWNfullscreen=true noDisplay=false immersive=false launchMode=2frozenBeforeDestroy=false forceNewConfig=falsemActivityType=APPLICATION_ACTIVITY_TYPEwaitingVisible=false nowVisible=true lastVisibleTime=-3m40s512msresizeMode=RESIZE_MODE_RESIZEABLE_VIA_SDK_VERSIONmLastReportedMultiWindowMode=false mLastReportedPictureInPictureMode=falseRunning activities (most recent first):TaskRecord{32da96f #142 A=com.android.settings U=0 StackId=1 sz=1}Run #0: ActivityRecord{f46fe89 u0 com.android.settings/.Settings t142}mResumedActivity: ActivityRecord{f46fe89 u0 com.android.settings/.Settings t142}Stack #0:mFullscreen=trueisSleeping=falsemBounds=nullTask id #139mFullscreen=truemBounds=nullmMinWidth=-1mMinHeight=-1mLastNonFullscreenBounds=null* TaskRecord{b1b0e06 #139 I=com.android.launcher3/.Launcher U=0 StackId=0 sz=1}userId=0 effectiveUid=u0a14 mCallingUid=1000 mUserSetupComplete=true mCallingPackage=nullintent={act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10000100 cmp=com.android.launcher3/.Launcher}realActivity=com.android.launcher3/.LauncherautoRemoveRecents=false isPersistable=true numFullscreen=1 taskType=1 mTaskToReturnTo=0rootWasReset=false mNeverRelinquishIdentity=true mReuseTask=false mLockTaskAuth=LOCK_TASK_AUTH_PINNABLEActivities=[ActivityRecord{1f09444 u0 com.android.launcher3/.Launcher t139}]askedCompatMode=false inRecents=true isAvailable=truelastThumbnail=null lastThumbnailFile=/data/system_ce/0/recent_images/139_task_thumbnail.pngstackId=0hasBeenVisible=true mResizeMode=RESIZE_MODE_RESIZEABLE mSupportsPictureInPicture=false isResizeable=true firstActiveTime=1667109722 lastActiveTime=1672808679 (inactive for 224s)* Hist #0: ActivityRecord{1f09444 u0 com.android.launcher3/.Launcher t139}packageName=com.android.launcher3 processName=com.android.launcher3launchedFromUid=0 launchedFromPackage=null userId=0app=ProcessRecord{31ae0ef 3012:com.android.launcher3/u0a14}Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10000100 cmp=com.android.launcher3/.Launcher }frontOfTask=true task=TaskRecord{b1b0e06 #139 I=com.android.launcher3/.Launcher U=0 StackId=0 sz=1}taskAffinity=nullrealActivity=com.android.launcher3/.LauncherbaseDir=/system/priv-app/Launcher3Go/Launcher3Go.apkdataDir=/data/user/0/com.android.launcher3stateNotNeeded=true componentSpecified=false mActivityType=1compat={160dpi always-compat} labelRes=0x7f0c000d icon=0x7f020021 theme=0x7f120002mLastReportedConfigurations:mGlobalConfig={1.0 ?mcc?mnc [en_US] ldltr sw240dp w240dp h248dp 160dpi smll port -touch -keyb/v/h -nav/h appBounds=Rect(0, 0 - 240, 272) s.4}mOverrideConfig={1.0 ?mcc?mnc [en_US] ldltr sw240dp w240dp h248dp 160dpi smll port -touch -keyb/v/h -nav/h appBounds=Rect(0, 0 - 240, 272) s.4}CurrentConfiguration={1.0 ?mcc?mnc [en_US] ldltr sw240dp w240dp h248dp 160dpi smll port -touch -keyb/v/h -nav/h appBounds=Rect(0, 0 - 240, 272) s.4}taskDescription: iconFilename=null label="null" primaryColor=fff5f5f5backgroundColor=fffafafastatusBarColor=0navigationBarColor=0launchFailed=false launchCount=0 lastLaunchTime=-1h38m41s610mshaveState=true icicle=Bundle[mParcelledData.dataSize=4096]state=STOPPED stopped=true delayedResume=false finishing=falsekeysPaused=false inHistory=true visible=false sleeping=false idle=true mStartingWindowState=STARTING_WINDOW_NOT_SHOWNfullscreen=true noDisplay=false immersive=false launchMode=2frozenBeforeDestroy=false forceNewConfig=falsemActivityType=HOME_ACTIVITY_TYPEwaitingVisible=false nowVisible=false lastVisibleTime=-43m15s482msresizeMode=RESIZE_MODE_RESIZEABLEmLastReportedMultiWindowMode=false mLastReportedPictureInPictureMode=falseRunning activities (most recent first):TaskRecord{b1b0e06 #139 I=com.android.launcher3/.Launcher U=0 StackId=0 sz=1}Run #0: ActivityRecord{1f09444 u0 com.android.launcher3/.Launcher t139}mLastPausedActivity: ActivityRecord{1f09444 u0 com.android.launcher3/.Launcher t139}
Display #1 (activities from top to bottom):ResumedActivity: ActivityRecord{f46fe89 u0 com.android.settings/.Settings t142}mFocusedStack=ActivityStack{4f3c6a8 stackId=1, 1 tasks} mLastFocusedStack=ActivityStack{4f3c6a8 stackId=1, 1 tasks}mCurTaskIdForUser={0=142}mUserStackInFront={}mStacks={0=ActivityStack{7020d13 stackId=0, 1 tasks}, 1=ActivityStack{4f3c6a8 stackId=1, 1 tasks}}mLockTaskModeState=NONE  mLockTaskPackages (userId:packages)=0:[]mLockTaskModeTasks[]KeyguardController:mKeyguardShowing=falsemKeyguardGoingAway=falsemOccluded=falsemDismissingKeyguardActivity=nullmDismissalRequested=falsemVisibilityTransactionDepth=0

至于为什么使用如上命令就能获取这么多的信息，建议还是去多多的阅读系统源码，或许我们可以找到我们想要的答案。

ActivityManagerService中的Stack

Android系统中一些常用的Stack

Name	Value	Description
HOME_STACK_ID	0	一般HomeActivity所在的Stack，就是Launcher所在的Stack
FULLSCREEN_WORKSPACE_STACK_ID	1	正常情况下，我们启动的Activity都在这个Stack
FREEFORM_WORKSPACE_STACK_ID	2	自由模式下，一般平板中会使用
DOCKED_STACK_ID	3	进入分屏模式后，新创建的便是该类型的Stack
PINNED_STACK_ID	4	画中画模式下，处于画中画Activity所在的Stack
RECENTS_STACK_ID	5	SystemUI的RecentActivity所在的Stack
ASSISTANT_STACK_ID	6	有Android assistant启动的Activity都在此Stack，国内手机貌似很少使用该Stack

从这些常用的Stack的作用上来看，我们可以简单的理解Android更多的会根据各种不同的行为和场景来区分不同的ActivityStack。从之前的dump信息我们便可以断定ActivityStack中主要存放的就是各种Task，对应的便是TaskRecord，实际Android代码中也确实如此。对于ActivityStack的各种管理，Android又抽象出ActivityStackSupervisor类，我们从命名中也可以看出该类专门负责ActivityStack的管理。后续Activity的启动流程分析中，我们将更多的接触并分析该类。一般Android系统启动时，开机启动到Launcher界面，便会创建HOME_STACK_ID Stack（下面便是开机的Trace Log，可以结合Trace和代码具体理一下这个创建的过程，这里就不再细述了）专门用于存放Home Activity。

01-20 23:40:35.110  1964  1964 D ABM_TRACE_MAIN: java.lang.Throwable
01-20 23:40:35.110  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityStack.<init>(ActivityStack.java:458)
01-20 23:40:35.110  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityStackSupervisor.createStack(ActivityStackSupervisor.java:2657)
01-20 23:40:35.110  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityStackSupervisor.createStackOnDisplay(ActivityStackSupervisor.java:2648)
01-20 23:40:35.110  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityStackSupervisor.getStack(ActivityStackSupervisor.java:2251)
01-20 23:40:35.110  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityStackSupervisor.setWindowManager(ActivityStackSupervisor.java:689)
01-20 23:40:35.110  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityManagerService.setWindowManager(ActivityManagerService.java:2629)
01-20 23:40:35.110  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.SystemServer.startOtherServices(SystemServer.java:861)
01-20 23:40:35.110  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.SystemServer.run(SystemServer.java:398)
01-20 23:40:35.110  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.SystemServer.main(SystemServer.java:274)
01-20 23:40:35.110  1964  1964 D ABM_TRACE_MAIN:    at java.lang.reflect.Method.invoke(Native Method)
01-20 23:40:35.110  1964  1964 D ABM_TRACE_MAIN:    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
01-20 23:40:35.110  1964  1964 D ABM_TRACE_MAIN:    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:787)
01-20 23:40:35.129  1964  1964 I wm_stack_created: 0
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN: java.lang.Throwable
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityStackSupervisor$ActivityDisplay.attachStack(ActivityStackSupervisor.java:4749)
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityStack.postAddToDisplay(ActivityStack.java:514)
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityStack.<init>(ActivityStack.java:472)
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityStackSupervisor.createStack(ActivityStackSupervisor.java:2657)
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityStackSupervisor.createStackOnDisplay(ActivityStackSupervisor.java:2648)
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityStackSupervisor.getStack(ActivityStackSupervisor.java:2251)
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityStackSupervisor.setWindowManager(ActivityStackSupervisor.java:689)
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.am.ActivityManagerService.setWindowManager(ActivityManagerService.java:2629)
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.SystemServer.startOtherServices(SystemServer.java:861)
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.SystemServer.run(SystemServer.java:398)
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at com.android.server.SystemServer.main(SystemServer.java:274)
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at java.lang.reflect.Method.invoke(Native Method)
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
01-20 23:40:35.140  1964  1964 D ABM_TRACE_MAIN:    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:787)
01-20 23:40:35.141  1964  1964 V ABM_Log : attachStack: attaching ActivityStack{abbc88a stackId=0, 0 tasks} to displayId=0 position=0

一般我们可以通过event log可以获取ActivityStack的创建与销毁

wm_stack_created (StackId|1|5)
wm_task_removed (TaskId|1|5),(Reason|3)

虽然这是WindowManagerService相关的Log，但是Window在组织和管理各种窗口时ActivityManagerService管理Activity一样都是通过各种堆栈形式的，并且WindowManagerService里面对应的堆栈顺序都是和ActivityManagerService中保持一致的，他们在Activity启动时创建的顺序也是一前一后的，其中相关的数据结构的对应关系如下：

ActivityStack    TaskStack
TaskRecord  Task
ActivityRecord  APPWindowToken

一般我们在创建Activity时，根据不同功能的需要，创建对应或使用不同的ActivityStack，一般使用ActivityStackSupervisor.getStack去获取，如果不存在便创建新的。对应的当我们Activity销毁的时候，Android系统会从该Activity所在的Task中移除该Activity，如果该Activity是lastActivity，系统还会从ActivityStack中移除该Task，如果从ActivityStack移除完该Task之后，ActivityStack中不存在任何Task，系统还会将该ActivityStack销毁回收。

ActivityManagerService中的Task

Activity启动过程中，对于ActivityStack应用开发者很少接触，我们也可以不去关注它的创建与销毁，更多的这都是系统完成的。通过前文ActivityManagerService解读之Activity启动再探所述，我们知道可以更多的使用不同的启动模式，外加各种Task属性和设置不同的Intent flag来影响Activity Task的创建管理行为。比如每次需要Activity创建单独的Task时您可以使用singleInstance模式，等等（更多关于启动模式和Task属性以及不同intent flag请参阅ActivityManagerService解读之Activity启动再探一文）。当我们启动Activity或者销毁Activity时，系统为该Activity创建Task或者销毁Task时候，我们一般会看见如下Log：

wm_task_created (TaskId|1|5),(StackId|1|5)
am_create_task (User|1|5),(Task ID|1|5)wm_task_removed (TaskId|1|5),(Reason|3)

Task是从用户角度来管理Activity的，Android系统更多的是根据用户的操作来将一系列Activity按启动顺序放于同一个Task中，这些Activity可以来自不同的应用，因为从用户角度来说，这些操作只是为自己服务而已，用户并不知道他们来自不同的应用。

写在最后

ActivityStack和TaskRecord是ActivityManagerService管理Activity的两个相当重要的数据，了解他们的作用对分析Activity启动大有作用，懂得Activity启动流程，在日常项目开发中才能应对各种需求，实施各种不同的应对方案，比如最近很火的插件技术，想要插件话Activity，必须得了解Activity的启动流程，又比如优化应用的启动速度等等。