Android P图形架构之DisplayManagerService解析

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顾名思义，DisplayManagerService是一个用于管理显示的服务。

源码：
\frameworks\base\services\java\com\android\server\SystemServer.java
\frameworks\base\services\core\java\com\android\server\display\DisplayManagerService.java
\frameworks\base\services\core\java\com\android\server\display\DisplayDevice.java
\frameworks\base\services\core\java\com\android\server\display\LogicalDisplay.java

作用：

管理显示器的全局生命周期，决定如何根据当前连接的物理显示设备配置逻辑显示，在状态更改时向系统和应用程序发送通知等
显示管理服务依赖于DisplayAdapter（LocalDisplayAdapter，OverlayDisplayAdapter，WifiDisplayAdapter）用于发现和配置连接到系统的物理显示设备
设备连接的方式都有单独的DisplayAdapter，一个本地显示器的适配器，用于模拟无头系统（不接显示器）的非功能显示；一个用于开发的模拟overlay显示器；一个用wifi显示器
显示适配器仅与显示管理器服务弱耦合
显示适配器通过显示管理器服务注册的DisplayAdapter.Listener异步地将显示设备状态的变化传送到显示管理器服务

启动过程：
DisplayManagerService是在SystemServer中启动的。
\frameworks\base\services\java\com\android\server\SystemServer.java

private void startBootstrapServices() {//...// Display manager is needed to provide display metrics before package manager// starts up.traceBeginAndSlog("StartDisplayManager");mDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class);traceEnd();//...
}

代码分析：

LocalDisplayAdapter

DisplayManagerService的onStart()中发送了消息MSG_REGISTER_DEFAULT_DISPLAY_ADAPTERS，去执行了registerDefaultDisplayAdapters()，初始化了主屏显示器适配器LocalDisplayAdapter

@Override
public void onStart() {// We need to pre-load the persistent data store so it's ready before the default display// adapter is up so that we have it's configuration. We could load it lazily, but since// we're going to have to read it in eventually we may as well do it here rather than after// we've waited for the display to register itself with us.
synchronized(mSyncRoot) {
mPersistentDataStore.loadIfNeeded();
loadStableDisplayValuesLocked();}mHandler.sendEmptyMessage(MSG_REGISTER_DEFAULT_DISPLAY_ADAPTERS);publishBinderService(Context.DISPLAY_SERVICE, new BinderService(),true /*allowIsolated*/);publishLocalService(DisplayManagerInternal.class, new LocalService());publishLocalService(DisplayTransformManager.class, new DisplayTransformManager());
}//加载LocalDisplayAdapter和getVirtualDisplayAdapter
private void registerDefaultDisplayAdapters() {// Register default display adapters.synchronized (mSyncRoot) {// main display adapterregisterDisplayAdapterLocked(new LocalDisplayAdapter(mSyncRoot, mContext, mHandler, mDisplayAdapterListener));// Standalone VR devices rely on a virtual display as their primary display for// 2D UI. We register virtual display adapter along side the main display adapter// here so that it is ready by the time the system sends the home Intent for// early apps like SetupWizard/Launcher. In particular, SUW is displayed using// the virtual display inside VR before any VR-specific apps even run.mVirtualDisplayAdapter = mInjector.getVirtualDisplayAdapter(mSyncRoot, mContext,mHandler, mDisplayAdapterListener);if (mVirtualDisplayAdapter != null) {registerDisplayAdapterLocked(mVirtualDisplayAdapter);}}
}

registerDisplayAdapterLocked把适配器放入了mDisplayAdapters中，并且执行了LocalDisplayAdapter的registerLocked();

// List of all currently registered display adapters.
private final ArrayList<DisplayAdapter> mDisplayAdapters = new ArrayList<DisplayAdapter>();private void registerDisplayAdapterLocked(DisplayAdapter adapter) {mDisplayAdapters.add(adapter);adapter.registerLocked();
}

LocalDisplayAdapter中则去调用SurfaceFlinger获取物理显示屏的信息，并返回给DisplayManagerService，最终执行了handleDisplayDeviceAddedLocked()，来添加显示器设备。
\frameworks\base\services\core\java\com\android\server\display\LocalDisplayAdapter.java

@Override
public void registerLocked() {super.registerLocked();mHotplugReceiver = new HotplugDisplayEventReceiver(getHandler().getLooper());for (int builtInDisplayId : BUILT_IN_DISPLAY_IDS_TO_SCAN) {tryConnectDisplayLocked(builtInDisplayId);}
}

添加显示器：

// List of all currently connected display devices.
private final ArrayList<DisplayDevice> mDisplayDevices = new ArrayList<DisplayDevice>();private void handleDisplayDeviceAddedLocked(DisplayDevice device) {DisplayDeviceInfo info = device.getDisplayDeviceInfoLocked();if (mDisplayDevices.contains(device)) {Slog.w(TAG, "Attempted to add already added display device: " + info);return;}Slog.i(TAG, "Display device added: " + info);device.mDebugLastLoggedDeviceInfo = info;mDisplayDevices.add(device);LogicalDisplay display = addLogicalDisplayLocked(device);Runnable work = updateDisplayStateLocked(device);if (work != null) {work.run();}scheduleTraversalLocked(false);
}

handleDisplayDeviceAddedLocked()会将显示器设备统一放到mDisplayDevices中，并且执行了addLogicalDisplayLocked()，作用是在一个显示设备中添加逻辑显示，assignDisplayIdLocked()分配一个displayId，并且放入mLogicalDisplays中。

// List of all logical displays indexed by logical display id.
private final SparseArray<LogicalDisplay> mLogicalDisplays = new SparseArray<LogicalDisplay>();// Adds a new logical display based on the given display device.
// Sends notifications if needed.
private LogicalDisplay addLogicalDisplayLocked(DisplayDevice device) {DisplayDeviceInfo deviceInfo = device.getDisplayDeviceInfoLocked();boolean isDefault = (deviceInfo.flags& DisplayDeviceInfo.FLAG_DEFAULT_DISPLAY) != 0;if (isDefault && mLogicalDisplays.get(Display.DEFAULT_DISPLAY) != null) {Slog.w(TAG, "Ignoring attempt to add a second default display: " + deviceInfo);isDefault = false;}if (!isDefault && mSingleDisplayDemoMode) {Slog.i(TAG, "Not creating a logical display for a secondary display "+ " because single display demo mode is enabled: " + deviceInfo);return null;}final int displayId = assignDisplayIdLocked(isDefault);final int layerStack = assignLayerStackLocked(displayId);LogicalDisplay display = new LogicalDisplay(displayId, layerStack, device);display.updateLocked(mDisplayDevices);if (!display.isValidLocked()) {// This should never happen currently.Slog.w(TAG, "Ignoring display device because the logical display "+ "created from it was not considered valid: " + deviceInfo);return null;}configureColorModeLocked(display, device);if (isDefault) {recordStableDisplayStatsIfNeededLocked(display);recordTopInsetLocked(display);}mLogicalDisplays.put(displayId, display);// Wake up waitForDefaultDisplay.if (isDefault) {mSyncRoot.notifyAll();}sendDisplayEventLocked(displayId, DisplayManagerGlobal.EVENT_DISPLAY_ADDED);return display;
}

OverlayDisplayAdapter、WifiDisplayAdapter

DisplayManagerService的systemReady()中，发送了MSG_REGISTER_ADDITIONAL_DISPLAY_ADAPTERS，并执行了registerAdditionalDisplayAdapters()，在registerAdditionalDisplayAdapters中完成了OverlayDisplayAdapter和WifiDisplayAdapter的注册。

/*** Called when the system is ready to go.*/
public void systemReady(boolean safeMode, boolean onlyCore) {synchronized (mSyncRoot) {mSafeMode = safeMode;mOnlyCore = onlyCore;mSystemReady = true;// Just in case the top inset changed before the system was ready. At this point, any// relevant configuration should be in place.recordTopInsetLocked(mLogicalDisplays.get(Display.DEFAULT_DISPLAY));}mHandler.sendEmptyMessage(MSG_REGISTER_ADDITIONAL_DISPLAY_ADAPTERS);mHandler.sendEmptyMessage(MSG_REGISTER_BRIGHTNESS_TRACKER);
}private void registerAdditionalDisplayAdapters() {synchronized (mSyncRoot) {if (shouldRegisterNonEssentialDisplayAdaptersLocked()) {registerOverlayDisplayAdapterLocked();registerWifiDisplayAdapterLocked();}}
}

跟LocalDisplayAdapter流程类似:

private void registerOverlayDisplayAdapterLocked() {registerDisplayAdapterLocked(new OverlayDisplayAdapter(mSyncRoot, mContext, mHandler, mDisplayAdapterListener, mUiHandler));
}private void registerWifiDisplayAdapterLocked() {if (mContext.getResources().getBoolean(com.android.internal.R.bool.config_enableWifiDisplay)|| SystemProperties.getInt(FORCE_WIFI_DISPLAY_ENABLE, -1) == 1) {mWifiDisplayAdapter = new WifiDisplayAdapter(mSyncRoot, mContext, mHandler, mDisplayAdapterListener,mPersistentDataStore);registerDisplayAdapterLocked(mWifiDisplayAdapter);}
}

VirtualDisplayAdapter

在加载LocalDisplayAdapter的时候就加载了虚拟显示适配器，因为虚拟显示必须依赖于物理屏。
DisplayManagerService的onstart()中执行的，getVirtualDisplayAdapter()，加载虚拟屏。

private void registerDefaultDisplayAdapters() {// Register default display adapters.synchronized (mSyncRoot) {// main display adapterregisterDisplayAdapterLocked(new LocalDisplayAdapter(mSyncRoot, mContext, mHandler, mDisplayAdapterListener));// Standalone VR devices rely on a virtual display as their primary display for// 2D UI. We register virtual display adapter along side the main display adapter// here so that it is ready by the time the system sends the home Intent for// early apps like SetupWizard/Launcher. In particular, SUW is displayed using// the virtual display inside VR before any VR-specific apps even run.mVirtualDisplayAdapter = mInjector.getVirtualDisplayAdapter(mSyncRoot, mContext,mHandler, mDisplayAdapterListener);if (mVirtualDisplayAdapter != null) {registerDisplayAdapterLocked(mVirtualDisplayAdapter);}}
}@VisibleForTesting
static class Injector {VirtualDisplayAdapter getVirtualDisplayAdapter(SyncRoot syncRoot, Context context,Handler handler, DisplayAdapter.Listener displayAdapterListener) {return new VirtualDisplayAdapter(syncRoot, context, handler, displayAdapterListener);}long getDefaultDisplayDelayTimeout() {return WAIT_FOR_DEFAULT_DISPLAY_TIMEOUT;}
}