概述

WMS作为系统的一个关键服务其是在SystemServer.java::startOtherServices中启动的
WMS主要有下面几个作用:
1：应用程序通过WMS向SurfaceFinger申请surface,surface代表的是绘图表面，应用程序绘制都必须在绘图表面上.
2：管理窗口的层级，一个窗口一般在WMS端都是一个WindowState，其是有层级区分的，其有baseLayer和subLayer两个值共同确定.
3：窗口动画：WindowAnimator

WMS的启动

WindowManagerService.java的创建

 wm = WindowManagerService.main(context, inputManager, !mFirstBoot, mOnlyCore,
                    new PhoneWindowManager(), mActivityManagerService.mActivityTaskManager);//taskManager对象
ServiceManager.addService(Context.WINDOW_SERVICE, wm, /* allowIsolated= */ false,
 ServiceManager.addService(Context.INPUT_SERVICE, inputManager,
                    /* allowIsolated= */ false, DUMP_FLAG_PRIORITY_CRITICAL);
 mActivityManagerService.setWindowManager(wm);//ams持有wms对象
  wm.onInitReady();//准备初始化

其中上面有一个比较重要的对象PhoneWindowManager,主要是负责窗口管理的各种策略

WindowManagerService.java::main

   public static WindowManagerService main(final Context context, final InputManagerService im,
            final boolean showBootMsgs, final boolean onlyCore, WindowManagerPolicy policy,
            ActivityTaskManagerService atm) {
        return main(context, im, showBootMsgs, onlyCore, policy, atm,
                SurfaceControl.Transaction::new);//调用的内部的main方法
    }
    public static WindowManagerService main(final Context context, final InputManagerService im,
            final boolean showBootMsgs, final boolean onlyCore, WindowManagerPolicy policy,
            ActivityTaskManagerService atm, TransactionFactory transactionFactory) {
        DisplayThread.getHandler().runWithScissors(() ->
                sInstance = new WindowManagerService(context, im, showBootMsgs, onlyCore, policy,
                        atm, transactionFactory), 0);//wms是运行在android.display线程
        return sInstance;
    }

WindowManagerService

private WindowManagerService(Context context, InputManagerService inputManager,
            boolean showBootMsgs, boolean onlyCore, WindowManagerPolicy policy,
            ActivityTaskManagerService atm, TransactionFactory transactionFactory) {
        installLock(this, INDEX_WINDOW);
        mGlobalLock = atm.getGlobalLock();
        mAtmService = atm;
        mContext = context;
        mAllowBootMessages = showBootMsgs;
        mOnlyCore = onlyCore;
        mLimitedAlphaCompositing = context.getResources().getBoolean(
                com.android.internal.R.bool.config_sf_limitedAlpha);
        mHasPermanentDpad = context.getResources().getBoolean(
                com.android.internal.R.bool.config_hasPermanentDpad);
        mInTouchMode = context.getResources().getBoolean(
                com.android.internal.R.bool.config_defaultInTouchMode);
        mDrawLockTimeoutMillis = context.getResources().getInteger(
                com.android.internal.R.integer.config_drawLockTimeoutMillis);
        mAllowAnimationsInLowPowerMode = context.getResources().getBoolean(
                com.android.internal.R.bool.config_allowAnimationsInLowPowerMode);
        mMaxUiWidth = context.getResources().getInteger(
                com.android.internal.R.integer.config_maxUiWidth);
        mDisableTransitionAnimation = context.getResources().getBoolean(
                com.android.internal.R.bool.config_disableTransitionAnimation);
        mPerDisplayFocusEnabled = context.getResources().getBoolean(
                com.android.internal.R.bool.config_perDisplayFocusEnabled);
        mLowRamTaskSnapshotsAndRecents = context.getResources().getBoolean(
                com.android.internal.R.bool.config_lowRamTaskSnapshotsAndRecents);
        mInputManager = inputManager; // Must be before createDisplayContentLocked.
        mDisplayManagerInternal = LocalServices.getService(DisplayManagerInternal.class);
        mDisplayWindowSettings = new DisplayWindowSettings(this);
        mTransactionFactory = transactionFactory;
        mTransaction = mTransactionFactory.make();
        mPolicy = policy;
        mAnimator = new WindowAnimator(this);//窗口动画，管理系统里所有的动画
        mRoot = new RootWindowContainer(this);//总管家,对应于ActivityDisplay,用来管理DisplayContent
        mWindowPlacerLocked = new WindowSurfacePlacer(this);
        mTaskSnapshotController = new TaskSnapshotController(this);
        mWindowTracing = WindowTracing.createDefaultAndStartLooper(this,
                Choreographer.getInstance());
        LocalServices.addService(WindowManagerPolicy.class, mPolicy);
        mDisplayManager = (DisplayManager)context.getSystemService(Context.DISPLAY_SERVICE);
        mKeyguardDisableHandler = KeyguardDisableHandler.create(mContext, mPolicy, mH);
        mPowerManager = (PowerManager)context.getSystemService(Context.POWER_SERVICE);
        mPowerManagerInternal = LocalServices.getService(PowerManagerInternal.class);
        if (mPowerManagerInternal != null) {//电源管理相关的服务
            mPowerManagerInternal.registerLowPowerModeObserver(
                    new PowerManagerInternal.LowPowerModeListener() {//注册监听
                @Override
                public int getServiceType() {
                    return ServiceType.ANIMATION;
                }
                @Override
                public void onLowPowerModeChanged(PowerSaveState result) {
                    synchronized (mGlobalLock) {//低电量模式
                        final boolean enabled = result.batterySaverEnabled;
                        if (mAnimationsDisabled != enabled && !mAllowAnimationsInLowPowerMode) {
                            mAnimationsDisabled = enabled;
                            dispatchNewAnimatorScaleLocked(null);
                        }
                    }
                }
            });
            mAnimationsDisabled = mPowerManagerInternal
                    .getLowPowerState(ServiceType.ANIMATION).batterySaverEnabled;
        }
        mScreenFrozenLock = mPowerManager.newWakeLock(
                PowerManager.PARTIAL_WAKE_LOCK, "SCREEN_FROZEN");
        mScreenFrozenLock.setReferenceCounted(false);
        mActivityManager = ActivityManager.getService();
        mActivityTaskManager = ActivityTaskManager.getService();
        mAmInternal = LocalServices.getService(ActivityManagerInternal.class);
        mAtmInternal = LocalServices.getService(ActivityTaskManagerInternal.class);
        mAppOps = (AppOpsManager)context.getSystemService(Context.APP_OPS_SERVICE);
        AppOpsManager.OnOpChangedInternalListener opListener =
                new AppOpsManager.OnOpChangedInternalListener() {
                    @Override public void onOpChanged(int op, String packageName) {
                        updateAppOpsState();
                    }
                };
        mAppOps.startWatchingMode(OP_SYSTEM_ALERT_WINDOW, null, opListener);
        mAppOps.startWatchingMode(AppOpsManager.OP_TOAST_WINDOW, null, opListener);
        mPmInternal = LocalServices.getService(PackageManagerInternal.class);
        final IntentFilter suspendPackagesFilter = new IntentFilter();
        suspendPackagesFilter.addAction(Intent.ACTION_PACKAGES_SUSPENDED);
        suspendPackagesFilter.addAction(Intent.ACTION_PACKAGES_UNSUSPENDED);
        context.registerReceiverAsUser(new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                final String[] affectedPackages =
                        intent.getStringArrayExtra(Intent.EXTRA_CHANGED_PACKAGE_LIST);
                final boolean suspended =
                        Intent.ACTION_PACKAGES_SUSPENDED.equals(intent.getAction());
                updateHiddenWhileSuspendedState(new ArraySet<>(Arrays.asList(affectedPackages)),
                        suspended);
            }
        }, UserHandle.ALL, suspendPackagesFilter, null, null);
        final ContentResolver resolver = context.getContentResolver();
        // Get persisted window scale setting
        mWindowAnimationScaleSetting = Settings.Global.getFloat(resolver,
                Settings.Global.WINDOW_ANIMATION_SCALE, mWindowAnimationScaleSetting);//窗口动画缩放的比例
        mTransitionAnimationScaleSetting = Settings.Global.getFloat(resolver,
                Settings.Global.TRANSITION_ANIMATION_SCALE,
                context.getResources().getFloat(
                        R.dimen.config_appTransitionAnimationDurationScaleDefault));
        setAnimatorDurationScale(Settings.Global.getFloat(resolver,
                Settings.Global.ANIMATOR_DURATION_SCALE, mAnimatorDurationScaleSetting));//动画时长缩放比例
        mForceDesktopModeOnExternalDisplays = Settings.Global.getInt(resolver,
                DEVELOPMENT_FORCE_DESKTOP_MODE_ON_EXTERNAL_DISPLAYS, 0) != 0;
        IntentFilter filter = new IntentFilter();
        // Track changes to DevicePolicyManager state so we can enable/disable keyguard.
        filter.addAction(ACTION_DEVICE_POLICY_MANAGER_STATE_CHANGED);
        mContext.registerReceiverAsUser(mBroadcastReceiver, UserHandle.ALL, filter, null, null);
        mLatencyTracker = LatencyTracker.getInstance(context);
        mSettingsObserver = new SettingsObserver();
        mHoldingScreenWakeLock = mPowerManager.newWakeLock(
                PowerManager.SCREEN_BRIGHT_WAKE_LOCK | PowerManager.ON_AFTER_RELEASE, TAG_WM);
        mHoldingScreenWakeLock.setReferenceCounted(false);
        mSurfaceAnimationRunner = new SurfaceAnimationRunner(mPowerManagerInternal);
        mAllowTheaterModeWakeFromLayout = context.getResources().getBoolean(
            com.android.internal.R.bool.config_allowTheaterModeWakeFromWindowLayout);
        mTaskPositioningController = new TaskPositioningController(
                this, mInputManager, mActivityTaskManager, mH.getLooper());
        mDragDropController = new DragDropController(this, mH.getLooper());
        mSystemGestureExclusionLimitDp = Math.max(MIN_GESTURE_EXCLUSION_LIMIT_DP,
                DeviceConfig.getInt(DeviceConfig.NAMESPACE_WINDOW_MANAGER,
                        KEY_SYSTEM_GESTURE_EXCLUSION_LIMIT_DP, 0));
        mSystemGestureExcludedByPreQStickyImmersive =
      DeviceConfig.getBoolean(DeviceConfig.NAMESPACE_WINDOW_MANAGER,
             KEY_SYSTEM_GESTURES_EXCLUDED_BY_PRE_Q_STICKY_IMMERSIVE, false);
     DeviceConfig.addOnPropertiesChangedListener(DeviceConfig.NAMESPACE_WINDOW_MANAGER,
                new HandlerExecutor(mH), properties -> {
                    synchronized (mGlobalLock) {
                        final int exclusionLimitDp = Math.max(MIN_GESTURE_EXCLUSION_LIMIT_DP,
                                properties.getInt(KEY_SYSTEM_GESTURE_EXCLUSION_LIMIT_DP, 0));
                        final boolean excludedByPreQSticky = DeviceConfig.getBoolean(
                                DeviceConfig.NAMESPACE_WINDOW_MANAGER,
                                KEY_SYSTEM_GESTURES_EXCLUDED_BY_PRE_Q_STICKY_IMMERSIVE, false);
                        if (mSystemGestureExcludedByPreQStickyImmersive != excludedByPreQSticky
                                || mSystemGestureExclusionLimitDp != exclusionLimitDp) {
                            mSystemGestureExclusionLimitDp = exclusionLimitDp;
                            mSystemGestureExcludedByPreQStickyImmersive = excludedByPreQSticky;
                           mRoot.forAllDisplays(DisplayContent::updateSystemGestureExclusionLimit);
                        }
                    }
                });
        LocalServices.addService(WindowManagerInternal.class, new LocalService());
    }

PhoneWindowManager的初始化

   traceBeginAndSlog("WindowManagerServiceOnInitReady");
   wm.onInitReady();
   traceEnd();
   public void onInitReady() {
        initPolicy();
        // Add ourself to the Watchdog monitors.
        Watchdog.getInstance().addMonitor(this);//watchdog机制，添加一个监视锁
        openSurfaceTransaction();
        try {
            createWatermarkInTransaction();
        } finally {
            closeSurfaceTransaction("createWatermarkInTransaction");
        }
        showEmulatorDisplayOverlayIfNeeded();
    }
    private void initPolicy() {
        UiThread.getHandler().runWithScissors(new Runnable() {
            @Override
            public void run() {
                WindowManagerPolicyThread.set(Thread.currentThread(), Looper.myLooper());
                mPolicy.init(mContext, WindowManagerService.this, WindowManagerService.this);//运行在android.ui线程
            }
        }, 0);
    }

PhoneWindowManager::init

 public void init(Context context, IWindowManager windowManager,
            WindowManagerFuncs windowManagerFuncs) {
        mContext = context;
        mWindowManager = windowManager;
        mWindowManagerFuncs = windowManagerFuncs;
        mWindowManagerInternal = LocalServices.getService(WindowManagerInternal.class);
        mActivityManagerInternal = LocalServices.getService(ActivityManagerInternal.class);
        mActivityTaskManagerInternal = LocalServices.getService(ActivityTaskManagerInternal.class);
        mInputManagerInternal = LocalServices.getService(InputManagerInternal.class);
        mDreamManagerInternal = LocalServices.getService(DreamManagerInternal.class);
        mPowerManagerInternal = LocalServices.getService(PowerManagerInternal.class);
        mAppOpsManager = mContext.getSystemService(AppOpsManager.class);
        mHandler = new PolicyHandler();
        mWakeGestureListener = new MyWakeGestureListener(mContext, mHandler);
        mSettingsObserver = new SettingsObserver(mHandler);
        mSettingsObserver.observe();
        mShortcutManager = new ShortcutManager(context);
        mPowerManager = (PowerManager)context.getSystemService(Context.POWER_SERVICE);
        mBroadcastWakeLock = mPowerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
                "PhoneWindowManager.mBroadcastWakeLock");
        mPowerKeyWakeLock = mPowerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
                "PhoneWindowManager.mPowerKeyWakeLock");
        mEnableShiftMenuBugReports = "1".equals(SystemProperties.get("ro.debuggable"));
        mAllowStartActivityForLongPressOnPowerDuringSetup = 
        readConfigurationDependentBehaviors();
        if (mLidControlsDisplayFold) {
            mDisplayFoldController = DisplayFoldController.create(context, DEFAULT_DISPLAY);
        } else if (SystemProperties.getBoolean("persist.debug.force_foldable", false)) {
            mDisplayFoldController = DisplayFoldController.createWithProxSensor(context,
                    DEFAULT_DISPLAY);
        }
        mAccessibilityManager = (AccessibilityManager) context.getSystemService(
                Context.ACCESSIBILITY_SERVICE);
        // register for dock events
        .............................................
        mWindowManagerInternal.registerAppTransitionListener(new AppTransitionListener() {
            @Override
            public int onAppTransitionStartingLocked(int transit, long duration,
                    long statusBarAnimationStartTime, long statusBarAnimationDuration) {
                return handleStartTransitionForKeyguardLw(transit, duration);
            }
            @Override
            public void onAppTransitionCancelledLocked(int transit) {
                handleStartTransitionForKeyguardLw(transit, 0 /* duration */);
            }
        });
        mKeyguardDelegate = new KeyguardServiceDelegate(mContext,
                new StateCallback() {
                    @Override
                    public void onTrustedChanged() {
                        mWindowManagerFuncs.notifyKeyguardTrustedChanged();
                    }
                    @Override
                    public void onShowingChanged() {
                        mWindowManagerFuncs.onKeyguardShowingAndNotOccludedChanged();
                    }
                });
    }

WindowManagerService::displayReady

traceBeginAndSlog("MakeDisplayReady");
      try {
          wm.displayReady();
      } catch (Throwable e) {
        reportWtf("making display ready", e);
     }
     traceEnd();
  public void displayReady() {
        synchronized (mGlobalLock) {
            if (mMaxUiWidth > 0) {
                mRoot.forAllDisplays(displayContent -> displayContent.setMaxUiWidth(mMaxUiWidth));
            }
            final boolean changed = applyForcedPropertiesForDefaultDisplay();
            mAnimator.ready();//WindowAnimator
            mDisplayReady = true;
            if (changed) {
                reconfigureDisplayLocked(getDefaultDisplayContentLocked());
            }
            mIsTouchDevice = mContext.getPackageManager().hasSystemFeature(
                    PackageManager.FEATURE_TOUCHSCREEN);
        }
        try {
            mActivityTaskManager.updateConfiguration(null);
        } catch (RemoteException e) {
        }
        updateCircularDisplayMaskIfNeeded();
    }

WindowManagerService::systemReady

    traceBeginAndSlog("MakeWindowManagerServiceReady");
        try {
            wm.systemReady();
        } catch (Throwable e) {
            reportWtf("making Window Manager Service ready", e);
        }
        traceEnd();
 public void systemReady() {
        mSystemReady = true;
        mPolicy.systemReady();//PhoneWindowManager对象
        mRoot.forAllDisplayPolicies(DisplayPolicy::systemReady);
        mTaskSnapshotController.systemReady();
        mHasWideColorGamutSupport = queryWideColorGamutSupport();
        mHasHdrSupport = queryHdrSupport();
        UiThread.getHandler().post(mSettingsObserver::updateSystemUiSettings);
        UiThread.getHandler().post(mSettingsObserver::updatePointerLocation);
        IVrManager vrManager = IVrManager.Stub.asInterface(
                ServiceManager.getService(Context.VR_SERVICE));
        if (vrManager != null) {
            try {
                final boolean vrModeEnabled = vrManager.getVrModeState();
                synchronized (mGlobalLock) {
                    vrManager.registerListener(mVrStateCallbacks);
                    if (vrModeEnabled) {
                        mVrModeEnabled = vrModeEnabled;
                        mVrStateCallbacks.onVrStateChanged(vrModeEnabled);
                    }
                }
            } catch (RemoteException e) {
                // Ignore, we cannot do anything if we failed to register VR mode listener
            }
        }
    }

PhoneWindowManager.java::systemReady

 public void systemReady() {
        // In normal flow, systemReady is called before other system services are ready.
        // So it is better not to bind keyguard here.
        mKeyguardDelegate.onSystemReady();//keyguard
        mVrManagerInternal = LocalServices.getService(VrManagerInternal.class);
        if (mVrManagerInternal != null) {
          mVrManagerInternal.addPersistentVrModeStateListener(mPersistentVrModeListener);
        }
        readCameraLensCoverState();
        updateUiMode();
        mDefaultDisplayRotation.updateOrientationListener();
        synchronized (mLock) {
            mSystemReady = true;
            mHandler.post(new Runnable() {
                @Override
                public void run() {
                    updateSettings();
                }
            });
            // If this happens, for whatever reason, systemReady came later than systemBooted.
            // And keyguard should be already bound from systemBooted
            if (mSystemBooted) {
                mKeyguardDelegate.onBootCompleted();
            }
        }
        mAutofillManagerInternal = LocalServices.getService(AutofillManagerInternal.class);
    }

WindowManagerService.java中重要的变量

• WindowManagerPolicy mPolicy
  对应的实现类PhoneWindowManager,主要是窗口管理的策略和按键的处理

• final ActivityManagerInternal mAmInternal;
  对应的是AMS,持有AMS对象

• final ActivityTaskManagerInternal mAtmInternal;
  管理Task的，android10.0新增

• final ArraySet<Session> mSessions = new ArraySet<>();
  会话，主要是建立和surfaceFinger的连接

• final WindowHashMap mWindowMap = new WindowHashMap();
  缓存windowstate

AMS,WMS之间数据是对应的,通过token值可以在AMS,WMS,应用程序之后来唯一确定一组Window,token是关联着一组窗口的，可能有多个WindowState的token值是相同的.

小结

整个启动过程涉及3个线程: system_server主线程, “android.display”, “android.ui”, 整个过程是采用阻塞方式(利用Handler.runWithScissors)执行的. 其中WindowManagerService.mH的Looper运行在 “android.display”进程，也就意味着WMS.H.handleMessage()在该线程执行。