diff --git a/services/surfaceflinger/DisplayHardware/ComposerHal.cpp b/services/surfaceflinger/DisplayHardware/ComposerHal.cpp
index c707e3c..03b714f 100644
--- a/services/surfaceflinger/DisplayHardware/ComposerHal.cpp
+++ b/services/surfaceflinger/DisplayHardware/ComposerHal.cpp
@@ -31,6 +31,8 @@
 
 namespace Hwc2 {
 
+Composer::~Composer() = default;
+
 namespace {
 
 class BufferHandle {
@@ -103,6 +105,8 @@
 
 } // anonymous namespace
 
+namespace impl {
+
 Composer::CommandWriter::CommandWriter(uint32_t initialMaxSize)
     : CommandWriterBase(initialMaxSize) {}
 
@@ -186,6 +190,8 @@
     }
 }
 
+Composer::~Composer() = default;
+
 std::vector<IComposer::Capability> Composer::getCapabilities()
 {
     std::vector<IComposer::Capability> capabilities;
@@ -1118,6 +1124,8 @@
     *state = data.presentOrValidateState;
 }
 
+} // namespace impl
+
 } // namespace Hwc2
 
 } // namespace android
diff --git a/services/surfaceflinger/DisplayHardware/ComposerHal.h b/services/surfaceflinger/DisplayHardware/ComposerHal.h
index 3d9993e..4372362 100644
--- a/services/surfaceflinger/DisplayHardware/ComposerHal.h
+++ b/services/surfaceflinger/DisplayHardware/ComposerHal.h
@@ -58,6 +58,118 @@
 using android::hardware::hidl_vec;
 using android::hardware::hidl_handle;
 
+class Composer {
+public:
+    virtual ~Composer() = 0;
+
+    virtual std::vector<IComposer::Capability> getCapabilities() = 0;
+    virtual std::string dumpDebugInfo() = 0;
+
+    virtual void registerCallback(const sp<IComposerCallback>& callback) = 0;
+
+    // Returns true if the connected composer service is running in a remote
+    // process, false otherwise. This will return false if the service is
+    // configured in passthrough mode, for example.
+    virtual bool isRemote() = 0;
+
+    // Reset all pending commands in the command buffer. Useful if you want to
+    // skip a frame but have already queued some commands.
+    virtual void resetCommands() = 0;
+
+    // Explicitly flush all pending commands in the command buffer.
+    virtual Error executeCommands() = 0;
+
+    virtual uint32_t getMaxVirtualDisplayCount() = 0;
+    virtual bool isUsingVrComposer() const = 0;
+    virtual Error createVirtualDisplay(uint32_t width, uint32_t height, PixelFormat* format,
+                                       Display* outDisplay) = 0;
+    virtual Error destroyVirtualDisplay(Display display) = 0;
+
+    virtual Error acceptDisplayChanges(Display display) = 0;
+
+    virtual Error createLayer(Display display, Layer* outLayer) = 0;
+    virtual Error destroyLayer(Display display, Layer layer) = 0;
+
+    virtual Error getActiveConfig(Display display, Config* outConfig) = 0;
+    virtual Error getChangedCompositionTypes(
+            Display display, std::vector<Layer>* outLayers,
+            std::vector<IComposerClient::Composition>* outTypes) = 0;
+    virtual Error getColorModes(Display display, std::vector<ColorMode>* outModes) = 0;
+    virtual Error getDisplayAttribute(Display display, Config config,
+                                      IComposerClient::Attribute attribute, int32_t* outValue) = 0;
+    virtual Error getDisplayConfigs(Display display, std::vector<Config>* outConfigs) = 0;
+    virtual Error getDisplayName(Display display, std::string* outName) = 0;
+
+    virtual Error getDisplayRequests(Display display, uint32_t* outDisplayRequestMask,
+                                     std::vector<Layer>* outLayers,
+                                     std::vector<uint32_t>* outLayerRequestMasks) = 0;
+
+    virtual Error getDisplayType(Display display, IComposerClient::DisplayType* outType) = 0;
+    virtual Error getDozeSupport(Display display, bool* outSupport) = 0;
+    virtual Error getHdrCapabilities(Display display, std::vector<Hdr>* outTypes,
+                                     float* outMaxLuminance, float* outMaxAverageLuminance,
+                                     float* outMinLuminance) = 0;
+
+    virtual Error getReleaseFences(Display display, std::vector<Layer>* outLayers,
+                                   std::vector<int>* outReleaseFences) = 0;
+
+    virtual Error presentDisplay(Display display, int* outPresentFence) = 0;
+
+    virtual Error setActiveConfig(Display display, Config config) = 0;
+
+    /*
+     * The composer caches client targets internally.  When target is nullptr,
+     * the composer uses slot to look up the client target from its cache.
+     * When target is not nullptr, the cache is updated with the new target.
+     */
+    virtual Error setClientTarget(Display display, uint32_t slot, const sp<GraphicBuffer>& target,
+                                  int acquireFence, Dataspace dataspace,
+                                  const std::vector<IComposerClient::Rect>& damage) = 0;
+    virtual Error setColorMode(Display display, ColorMode mode) = 0;
+    virtual Error setColorTransform(Display display, const float* matrix, ColorTransform hint) = 0;
+    virtual Error setOutputBuffer(Display display, const native_handle_t* buffer,
+                                  int releaseFence) = 0;
+    virtual Error setPowerMode(Display display, IComposerClient::PowerMode mode) = 0;
+    virtual Error setVsyncEnabled(Display display, IComposerClient::Vsync enabled) = 0;
+
+    virtual Error setClientTargetSlotCount(Display display) = 0;
+
+    virtual Error validateDisplay(Display display, uint32_t* outNumTypes,
+                                  uint32_t* outNumRequests) = 0;
+
+    virtual Error presentOrValidateDisplay(Display display, uint32_t* outNumTypes,
+                                           uint32_t* outNumRequests, int* outPresentFence,
+                                           uint32_t* state) = 0;
+
+    virtual Error setCursorPosition(Display display, Layer layer, int32_t x, int32_t y) = 0;
+    /* see setClientTarget for the purpose of slot */
+    virtual Error setLayerBuffer(Display display, Layer layer, uint32_t slot,
+                                 const sp<GraphicBuffer>& buffer, int acquireFence) = 0;
+    virtual Error setLayerSurfaceDamage(Display display, Layer layer,
+                                        const std::vector<IComposerClient::Rect>& damage) = 0;
+    virtual Error setLayerBlendMode(Display display, Layer layer,
+                                    IComposerClient::BlendMode mode) = 0;
+    virtual Error setLayerColor(Display display, Layer layer,
+                                const IComposerClient::Color& color) = 0;
+    virtual Error setLayerCompositionType(Display display, Layer layer,
+                                          IComposerClient::Composition type) = 0;
+    virtual Error setLayerDataspace(Display display, Layer layer, Dataspace dataspace) = 0;
+    virtual Error setLayerDisplayFrame(Display display, Layer layer,
+                                       const IComposerClient::Rect& frame) = 0;
+    virtual Error setLayerPlaneAlpha(Display display, Layer layer, float alpha) = 0;
+    virtual Error setLayerSidebandStream(Display display, Layer layer,
+                                         const native_handle_t* stream) = 0;
+    virtual Error setLayerSourceCrop(Display display, Layer layer,
+                                     const IComposerClient::FRect& crop) = 0;
+    virtual Error setLayerTransform(Display display, Layer layer, Transform transform) = 0;
+    virtual Error setLayerVisibleRegion(Display display, Layer layer,
+                                        const std::vector<IComposerClient::Rect>& visible) = 0;
+    virtual Error setLayerZOrder(Display display, Layer layer, uint32_t z) = 0;
+    virtual Error setLayerInfo(Display display, Layer layer, uint32_t type, uint32_t appId) = 0;
+};
+
+namespace impl {
+
 class CommandReader : public CommandReaderBase {
 public:
     ~CommandReader();
@@ -134,123 +246,111 @@
 };
 
 // Composer is a wrapper to IComposer, a proxy to server-side composer.
-class Composer {
+class Composer final : public Hwc2::Composer {
 public:
     Composer(const std::string& serviceName);
+    ~Composer() override;
 
-    std::vector<IComposer::Capability> getCapabilities();
-    std::string dumpDebugInfo();
+    std::vector<IComposer::Capability> getCapabilities() override;
+    std::string dumpDebugInfo() override;
 
-    void registerCallback(const sp<IComposerCallback>& callback);
+    void registerCallback(const sp<IComposerCallback>& callback) override;
 
     // Returns true if the connected composer service is running in a remote
     // process, false otherwise. This will return false if the service is
     // configured in passthrough mode, for example.
-    bool isRemote();
+    bool isRemote() override;
 
     // Reset all pending commands in the command buffer. Useful if you want to
     // skip a frame but have already queued some commands.
-    void resetCommands();
+    void resetCommands() override;
 
     // Explicitly flush all pending commands in the command buffer.
-    Error executeCommands();
+    Error executeCommands() override;
 
-    uint32_t getMaxVirtualDisplayCount();
-    bool isUsingVrComposer() const { return mIsUsingVrComposer; }
-    Error createVirtualDisplay(uint32_t width, uint32_t height,
-            PixelFormat* format, Display* outDisplay);
-    Error destroyVirtualDisplay(Display display);
+    uint32_t getMaxVirtualDisplayCount() override;
+    bool isUsingVrComposer() const override { return mIsUsingVrComposer; }
+    Error createVirtualDisplay(uint32_t width, uint32_t height, PixelFormat* format,
+                               Display* outDisplay) override;
+    Error destroyVirtualDisplay(Display display) override;
 
-    Error acceptDisplayChanges(Display display);
+    Error acceptDisplayChanges(Display display) override;
 
-    Error createLayer(Display display, Layer* outLayer);
-    Error destroyLayer(Display display, Layer layer);
+    Error createLayer(Display display, Layer* outLayer) override;
+    Error destroyLayer(Display display, Layer layer) override;
 
-    Error getActiveConfig(Display display, Config* outConfig);
-    Error getChangedCompositionTypes(Display display,
-            std::vector<Layer>* outLayers,
-            std::vector<IComposerClient::Composition>* outTypes);
-    Error getColorModes(Display display, std::vector<ColorMode>* outModes);
-    Error getDisplayAttribute(Display display, Config config,
-            IComposerClient::Attribute attribute, int32_t* outValue);
+    Error getActiveConfig(Display display, Config* outConfig) override;
+    Error getChangedCompositionTypes(Display display, std::vector<Layer>* outLayers,
+                                     std::vector<IComposerClient::Composition>* outTypes) override;
+    Error getColorModes(Display display, std::vector<ColorMode>* outModes) override;
+    Error getDisplayAttribute(Display display, Config config, IComposerClient::Attribute attribute,
+                              int32_t* outValue) override;
     Error getDisplayConfigs(Display display, std::vector<Config>* outConfigs);
-    Error getDisplayName(Display display, std::string* outName);
+    Error getDisplayName(Display display, std::string* outName) override;
 
     Error getDisplayRequests(Display display, uint32_t* outDisplayRequestMask,
-            std::vector<Layer>* outLayers,
-            std::vector<uint32_t>* outLayerRequestMasks);
+                             std::vector<Layer>* outLayers,
+                             std::vector<uint32_t>* outLayerRequestMasks) override;
 
-    Error getDisplayType(Display display,
-            IComposerClient::DisplayType* outType);
-    Error getDozeSupport(Display display, bool* outSupport);
-    Error getHdrCapabilities(Display display, std::vector<Hdr>* outTypes,
-            float* outMaxLuminance, float* outMaxAverageLuminance,
-            float* outMinLuminance);
+    Error getDisplayType(Display display, IComposerClient::DisplayType* outType) override;
+    Error getDozeSupport(Display display, bool* outSupport) override;
+    Error getHdrCapabilities(Display display, std::vector<Hdr>* outTypes, float* outMaxLuminance,
+                             float* outMaxAverageLuminance, float* outMinLuminance) override;
 
     Error getReleaseFences(Display display, std::vector<Layer>* outLayers,
-            std::vector<int>* outReleaseFences);
+                           std::vector<int>* outReleaseFences) override;
 
-    Error presentDisplay(Display display, int* outPresentFence);
+    Error presentDisplay(Display display, int* outPresentFence) override;
 
-    Error setActiveConfig(Display display, Config config);
+    Error setActiveConfig(Display display, Config config) override;
 
     /*
      * The composer caches client targets internally.  When target is nullptr,
      * the composer uses slot to look up the client target from its cache.
      * When target is not nullptr, the cache is updated with the new target.
      */
-    Error setClientTarget(Display display, uint32_t slot,
-            const sp<GraphicBuffer>& target,
-            int acquireFence, Dataspace dataspace,
-            const std::vector<IComposerClient::Rect>& damage);
-    Error setColorMode(Display display, ColorMode mode);
-    Error setColorTransform(Display display, const float* matrix,
-            ColorTransform hint);
+    Error setClientTarget(Display display, uint32_t slot, const sp<GraphicBuffer>& target,
+                          int acquireFence, Dataspace dataspace,
+                          const std::vector<IComposerClient::Rect>& damage) override;
+    Error setColorMode(Display display, ColorMode mode) override;
+    Error setColorTransform(Display display, const float* matrix, ColorTransform hint) override;
     Error setOutputBuffer(Display display, const native_handle_t* buffer,
-            int releaseFence);
-    Error setPowerMode(Display display, IComposerClient::PowerMode mode);
-    Error setVsyncEnabled(Display display, IComposerClient::Vsync enabled);
+                          int releaseFence) override;
+    Error setPowerMode(Display display, IComposerClient::PowerMode mode) override;
+    Error setVsyncEnabled(Display display, IComposerClient::Vsync enabled) override;
 
-    Error setClientTargetSlotCount(Display display);
+    Error setClientTargetSlotCount(Display display) override;
 
     Error validateDisplay(Display display, uint32_t* outNumTypes,
-            uint32_t* outNumRequests);
+                          uint32_t* outNumRequests) override;
 
-    Error presentOrValidateDisplay(Display display, uint32_t* outNumTypes,
-                                   uint32_t* outNumRequests,
-                                   int* outPresentFence,
-                                   uint32_t* state);
+    Error presentOrValidateDisplay(Display display, uint32_t* outNumTypes, uint32_t* outNumRequests,
+                                   int* outPresentFence, uint32_t* state) override;
 
-    Error setCursorPosition(Display display, Layer layer,
-            int32_t x, int32_t y);
+    Error setCursorPosition(Display display, Layer layer, int32_t x, int32_t y) override;
     /* see setClientTarget for the purpose of slot */
     Error setLayerBuffer(Display display, Layer layer, uint32_t slot,
-            const sp<GraphicBuffer>& buffer, int acquireFence);
+                         const sp<GraphicBuffer>& buffer, int acquireFence) override;
     Error setLayerSurfaceDamage(Display display, Layer layer,
-            const std::vector<IComposerClient::Rect>& damage);
-    Error setLayerBlendMode(Display display, Layer layer,
-            IComposerClient::BlendMode mode);
-    Error setLayerColor(Display display, Layer layer,
-            const IComposerClient::Color& color);
+                                const std::vector<IComposerClient::Rect>& damage) override;
+    Error setLayerBlendMode(Display display, Layer layer, IComposerClient::BlendMode mode) override;
+    Error setLayerColor(Display display, Layer layer, const IComposerClient::Color& color) override;
     Error setLayerCompositionType(Display display, Layer layer,
-            IComposerClient::Composition type);
-    Error setLayerDataspace(Display display, Layer layer,
-            Dataspace dataspace);
+                                  IComposerClient::Composition type) override;
+    Error setLayerDataspace(Display display, Layer layer, Dataspace dataspace) override;
     Error setLayerDisplayFrame(Display display, Layer layer,
-            const IComposerClient::Rect& frame);
-    Error setLayerPlaneAlpha(Display display, Layer layer,
-            float alpha);
+                               const IComposerClient::Rect& frame) override;
+    Error setLayerPlaneAlpha(Display display, Layer layer, float alpha) override;
     Error setLayerSidebandStream(Display display, Layer layer,
-            const native_handle_t* stream);
+                                 const native_handle_t* stream) override;
     Error setLayerSourceCrop(Display display, Layer layer,
-            const IComposerClient::FRect& crop);
-    Error setLayerTransform(Display display, Layer layer,
-            Transform transform);
+                             const IComposerClient::FRect& crop) override;
+    Error setLayerTransform(Display display, Layer layer, Transform transform) override;
     Error setLayerVisibleRegion(Display display, Layer layer,
-            const std::vector<IComposerClient::Rect>& visible);
-    Error setLayerZOrder(Display display, Layer layer, uint32_t z);
-    Error setLayerInfo(Display display, Layer layer, uint32_t type,
-                       uint32_t appId);
+                                const std::vector<IComposerClient::Rect>& visible) override;
+    Error setLayerZOrder(Display display, Layer layer, uint32_t z) override;
+    Error setLayerInfo(Display display, Layer layer, uint32_t type, uint32_t appId) override;
+
 private:
     class CommandWriter : public CommandWriterBase {
     public:
@@ -287,6 +387,8 @@
     const bool mIsUsingVrComposer;
 };
 
+} // namespace impl
+
 } // namespace Hwc2
 
 } // namespace android
diff --git a/services/surfaceflinger/DisplayHardware/HWC2.cpp b/services/surfaceflinger/DisplayHardware/HWC2.cpp
index 070b691..bcba35f 100644
--- a/services/surfaceflinger/DisplayHardware/HWC2.cpp
+++ b/services/surfaceflinger/DisplayHardware/HWC2.cpp
@@ -84,12 +84,7 @@
 
 // Device methods
 
-Device::Device(const std::string& serviceName)
-  : mComposer(std::make_unique<Hwc2::Composer>(serviceName)),
-    mCapabilities(),
-    mDisplays(),
-    mRegisteredCallback(false)
-{
+Device::Device(std::unique_ptr<android::Hwc2::Composer> composer) : mComposer(std::move(composer)) {
     loadCapabilities();
 }
 
diff --git a/services/surfaceflinger/DisplayHardware/HWC2.h b/services/surfaceflinger/DisplayHardware/HWC2.h
index 7b98b3e..aade4e0 100644
--- a/services/surfaceflinger/DisplayHardware/HWC2.h
+++ b/services/surfaceflinger/DisplayHardware/HWC2.h
@@ -78,9 +78,7 @@
 class Device
 {
 public:
-    // Service name is expected to be 'default' or 'vr' for normal use.
-    // 'vr' will slightly modify the behavior of the mComposer.
-    Device(const std::string& serviceName);
+    explicit Device(std::unique_ptr<android::Hwc2::Composer> composer);
 
     void registerCallback(ComposerCallback* callback, int32_t sequenceId);
 
@@ -119,7 +117,7 @@
     std::unique_ptr<android::Hwc2::Composer> mComposer;
     std::unordered_set<Capability> mCapabilities;
     std::unordered_map<hwc2_display_t, std::unique_ptr<Display>> mDisplays;
-    bool mRegisteredCallback;
+    bool mRegisteredCallback = false;
 };
 
 // Convenience C++ class to access hwc2_device_t Display functions directly.
diff --git a/services/surfaceflinger/DisplayHardware/HWComposer.cpp b/services/surfaceflinger/DisplayHardware/HWComposer.cpp
index 7eb3998..2cafd8e 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.cpp
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.cpp
@@ -59,25 +59,10 @@
 
 // ---------------------------------------------------------------------------
 
-HWComposer::HWComposer(const std::string& serviceName)
-    : mHwcDevice(),
-      mDisplayData(2),
-      mFreeDisplaySlots(),
-      mHwcDisplaySlots(),
-      mCBContext(),
-      mVSyncCounts(),
-      mRemainingHwcVirtualDisplays(0)
-{
-    for (size_t i=0 ; i<HWC_NUM_PHYSICAL_DISPLAY_TYPES ; i++) {
-        mLastHwVSync[i] = 0;
-        mVSyncCounts[i] = 0;
-    }
+HWComposer::HWComposer(std::unique_ptr<android::Hwc2::Composer> composer)
+      : mHwcDevice(std::make_unique<HWC2::Device>(std::move(composer))) {}
 
-    mHwcDevice = std::make_unique<HWC2::Device>(serviceName);
-    mRemainingHwcVirtualDisplays = mHwcDevice->getMaxVirtualDisplayCount();
-}
-
-HWComposer::~HWComposer() {}
+HWComposer::~HWComposer() = default;
 
 void HWComposer::registerCallback(HWC2::ComposerCallback* callback,
                                   int32_t sequenceId) {
diff --git a/services/surfaceflinger/DisplayHardware/HWComposer.h b/services/surfaceflinger/DisplayHardware/HWComposer.h
index 2e4f5d4..abb0fcb 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.h
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.h
@@ -59,12 +59,14 @@
 class Region;
 class String8;
 
+namespace Hwc2 {
+class Composer;
+} // namespace Hwc2
+
 class HWComposer
 {
 public:
-    // Uses the named composer service. Valid choices for normal use
-    // are 'default' and 'vr'.
-    HWComposer(const std::string& serviceName);
+    explicit HWComposer(std::unique_ptr<android::Hwc2::Composer> composer);
 
     ~HWComposer();
 
@@ -199,19 +201,20 @@
     };
 
     std::unique_ptr<HWC2::Device>   mHwcDevice;
-    std::vector<DisplayData>        mDisplayData;
+    std::vector<DisplayData> mDisplayData{HWC_NUM_PHYSICAL_DISPLAY_TYPES};
     std::set<size_t>                mFreeDisplaySlots;
     std::unordered_map<hwc2_display_t, int32_t> mHwcDisplaySlots;
     // protect mDisplayData from races between prepare and dump
     mutable Mutex mDisplayLock;
 
-    cb_context*                     mCBContext;
-    size_t                          mVSyncCounts[HWC_NUM_PHYSICAL_DISPLAY_TYPES];
-    uint32_t                        mRemainingHwcVirtualDisplays;
+    cb_context* mCBContext = nullptr;
+    size_t mVSyncCounts[HWC_NUM_PHYSICAL_DISPLAY_TYPES]{0, 0};
+    uint32_t mRemainingHwcVirtualDisplays{mHwcDevice->getMaxVirtualDisplayCount()};
 
     // protected by mLock
     mutable Mutex mLock;
-    mutable std::unordered_map<int32_t, nsecs_t> mLastHwVSync;
+    mutable std::unordered_map<int32_t, nsecs_t> mLastHwVSync{
+            {{HWC_DISPLAY_PRIMARY, 0}, {HWC_DISPLAY_EXTERNAL, 0}}};
 
     // thread-safe
     mutable Mutex mVsyncLock;