Add a callback for rendernode parentcount=0

Bug: 27709981
Fixes: 22565656

Change-Id: I1cb4461baf9069dc4e7ca6de10d5862578c107f4
diff --git a/libs/hwui/Android.mk b/libs/hwui/Android.mk
index 1f17851..be816f78 100644
--- a/libs/hwui/Android.mk
+++ b/libs/hwui/Android.mk
@@ -252,6 +252,7 @@
     tests/unit/LinearAllocatorTests.cpp \
     tests/unit/MatrixTests.cpp \
     tests/unit/OffscreenBufferPoolTests.cpp \
+    tests/unit/RenderNodeTests.cpp \
     tests/unit/SkiaBehaviorTests.cpp \
     tests/unit/StringUtilsTests.cpp \
     tests/unit/TextDropShadowCacheTests.cpp \
diff --git a/libs/hwui/RenderNode.cpp b/libs/hwui/RenderNode.cpp
index 61441ce..f6f92f7 100644
--- a/libs/hwui/RenderNode.cpp
+++ b/libs/hwui/RenderNode.cpp
@@ -68,7 +68,7 @@
 }
 
 RenderNode::~RenderNode() {
-    deleteDisplayList();
+    deleteDisplayList(nullptr);
     delete mStagingDisplayList;
 #if HWUI_NEW_OPS
     LOG_ALWAYS_FATAL_IF(mLayer, "layer missed detachment!");
@@ -88,7 +88,7 @@
     // If mParentCount == 0 we are the sole reference to this RenderNode,
     // so immediately free the old display list
     if (!mParentCount && !mStagingDisplayList) {
-        deleteDisplayList();
+        deleteDisplayList(nullptr);
     }
 }
 
@@ -462,7 +462,7 @@
 }
 #endif
 
-void RenderNode::syncDisplayList() {
+void RenderNode::syncDisplayList(TreeObserver* observer) {
     // Make sure we inc first so that we don't fluctuate between 0 and 1,
     // which would thrash the layer cache
     if (mStagingDisplayList) {
@@ -470,7 +470,7 @@
             child->renderNode->incParentRefCount();
         }
     }
-    deleteDisplayList();
+    deleteDisplayList(observer);
     mDisplayList = mStagingDisplayList;
     mStagingDisplayList = nullptr;
     if (mDisplayList) {
@@ -486,15 +486,15 @@
         // Damage with the old display list first then the new one to catch any
         // changes in isRenderable or, in the future, bounds
         damageSelf(info);
-        syncDisplayList();
+        syncDisplayList(info.observer);
         damageSelf(info);
     }
 }
 
-void RenderNode::deleteDisplayList() {
+void RenderNode::deleteDisplayList(TreeObserver* observer) {
     if (mDisplayList) {
         for (auto&& child : mDisplayList->getChildren()) {
-            child->renderNode->decParentRefCount();
+            child->renderNode->decParentRefCount(observer);
         }
     }
     delete mDisplayList;
@@ -526,32 +526,35 @@
     }
 }
 
-void RenderNode::destroyHardwareResources() {
+void RenderNode::destroyHardwareResources(TreeObserver* observer) {
     if (mLayer) {
         destroyLayer(mLayer);
         mLayer = nullptr;
     }
     if (mDisplayList) {
         for (auto&& child : mDisplayList->getChildren()) {
-            child->renderNode->destroyHardwareResources();
+            child->renderNode->destroyHardwareResources(observer);
         }
         if (mNeedsDisplayListSync) {
             // Next prepare tree we are going to push a new display list, so we can
             // drop our current one now
-            deleteDisplayList();
+            deleteDisplayList(observer);
         }
     }
 }
 
-void RenderNode::decParentRefCount() {
+void RenderNode::decParentRefCount(TreeObserver* observer) {
     LOG_ALWAYS_FATAL_IF(!mParentCount, "already 0!");
     mParentCount--;
     if (!mParentCount) {
+        if (observer) {
+            observer->onMaybeRemovedFromTree(this);
+        }
         // If a child of ours is being attached to our parent then this will incorrectly
         // destroy its hardware resources. However, this situation is highly unlikely
         // and the failure is "just" that the layer is re-created, so this should
         // be safe enough
-        destroyHardwareResources();
+        destroyHardwareResources(observer);
     }
 }
 
diff --git a/libs/hwui/RenderNode.h b/libs/hwui/RenderNode.h
index 8381925..b0136cf 100644
--- a/libs/hwui/RenderNode.h
+++ b/libs/hwui/RenderNode.h
@@ -68,6 +68,7 @@
 class SaveOp;
 class RestoreToCountOp;
 class TreeInfo;
+class TreeObserver;
 
 namespace proto {
 class RenderNode;
@@ -154,6 +155,14 @@
         }
     }
 
+    VirtualLightRefBase* getUserContext() const {
+        return mUserContext.get();
+    }
+
+    void setUserContext(VirtualLightRefBase* context) {
+        mUserContext = context;
+    }
+
     bool isPropertyFieldDirty(DirtyPropertyMask field) const {
         return mDirtyPropertyFields & field;
     }
@@ -187,7 +196,7 @@
     }
 
     ANDROID_API virtual void prepareTree(TreeInfo& info);
-    void destroyHardwareResources();
+    void destroyHardwareResources(TreeObserver* observer);
 
     // UI thread only!
     ANDROID_API void addAnimator(const sp<BaseRenderNodeAnimator>& animator);
@@ -232,6 +241,12 @@
         mPositionListener.reset(listener);
     }
 
+    // This is only modified in MODE_FULL, so it can be safely accessed
+    // on the UI thread.
+    ANDROID_API bool hasParents() {
+        return mParentCount;
+    }
+
 private:
     typedef key_value_pair_t<float, DrawRenderNodeOp*> ZDrawRenderNodeOpPair;
 
@@ -291,7 +306,7 @@
 
 
     void syncProperties();
-    void syncDisplayList();
+    void syncDisplayList(TreeObserver* observer);
 
     void prepareTreeImpl(TreeInfo& info, bool functorsNeedLayer);
     void pushStagingPropertiesChanges(TreeInfo& info);
@@ -302,13 +317,14 @@
 #endif
     void prepareLayer(TreeInfo& info, uint32_t dirtyMask);
     void pushLayerUpdate(TreeInfo& info);
-    void deleteDisplayList();
+    void deleteDisplayList(TreeObserver* observer);
     void damageSelf(TreeInfo& info);
 
     void incParentRefCount() { mParentCount++; }
-    void decParentRefCount();
+    void decParentRefCount(TreeObserver* observer);
 
     String8 mName;
+    sp<VirtualLightRefBase> mUserContext;
 
     uint32_t mDirtyPropertyFields;
     RenderProperties mProperties;
diff --git a/libs/hwui/TreeInfo.h b/libs/hwui/TreeInfo.h
index accd303..a43e544 100644
--- a/libs/hwui/TreeInfo.h
+++ b/libs/hwui/TreeInfo.h
@@ -32,6 +32,7 @@
 class DamageAccumulator;
 class LayerUpdateQueue;
 class OpenGLRenderer;
+class RenderNode;
 class RenderState;
 
 class ErrorHandler {
@@ -41,6 +42,17 @@
     ~ErrorHandler() {}
 };
 
+class TreeObserver {
+public:
+    // Called when a RenderNode's parent count hits 0.
+    // Due to the unordered nature of tree pushes, once prepareTree
+    // is finished it is possible that the node was "resurrected" and has
+    // a non-zero parent count.
+    virtual void onMaybeRemovedFromTree(RenderNode* node) {}
+protected:
+    ~TreeObserver() {}
+};
+
 // This would be a struct, but we want to PREVENT_COPY_AND_ASSIGN
 class TreeInfo {
     PREVENT_COPY_AND_ASSIGN(TreeInfo);
@@ -86,6 +98,10 @@
 #endif
     ErrorHandler* errorHandler = nullptr;
 
+    // Optional, may be nullptr. Used to allow things to observe interesting
+    // tree state changes
+    TreeObserver* observer = nullptr;
+
     // Frame number for use with synchronized surfaceview position updating
     int64_t frameNumber = -1;
     int32_t windowInsetLeft = 0;
diff --git a/libs/hwui/renderthread/CanvasContext.cpp b/libs/hwui/renderthread/CanvasContext.cpp
index 6933b2f..63fa788 100644
--- a/libs/hwui/renderthread/CanvasContext.cpp
+++ b/libs/hwui/renderthread/CanvasContext.cpp
@@ -576,7 +576,7 @@
 
 static void destroyPrefetechedNode(RenderNode* node) {
     ALOGW("Incorrectly called buildLayer on View: %s, destroying layer...", node->getName());
-    node->destroyHardwareResources();
+    node->destroyHardwareResources(nullptr);
     node->decStrong(nullptr);
 }
 
@@ -641,7 +641,7 @@
     if (mEglManager.hasEglContext()) {
         freePrefetechedLayers();
         for (const sp<RenderNode>& node : mRenderNodes) {
-            node->destroyHardwareResources();
+            node->destroyHardwareResources(nullptr);
         }
         Caches& caches = Caches::getInstance();
         // Make sure to release all the textures we were owning as there won't
diff --git a/libs/hwui/tests/common/TestUtils.h b/libs/hwui/tests/common/TestUtils.h
index 2d1e2e9..5492035 100644
--- a/libs/hwui/tests/common/TestUtils.h
+++ b/libs/hwui/tests/common/TestUtils.h
@@ -218,7 +218,7 @@
 private:
     static void syncHierarchyPropertiesAndDisplayListImpl(RenderNode* node) {
         node->syncProperties();
-        node->syncDisplayList();
+        node->syncDisplayList(nullptr);
         auto displayList = node->getDisplayList();
         if (displayList) {
             for (auto&& childOp : displayList->getChildren()) {
diff --git a/libs/hwui/tests/unit/RenderNodeTests.cpp b/libs/hwui/tests/unit/RenderNodeTests.cpp
new file mode 100644
index 0000000..7c57a50
--- /dev/null
+++ b/libs/hwui/tests/unit/RenderNodeTests.cpp
@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+
+#include "RenderNode.h"
+#include "TreeInfo.h"
+#include "tests/common/TestUtils.h"
+#include "utils/Color.h"
+
+using namespace android;
+using namespace android::uirenderer;
+
+TEST(RenderNode, hasParents) {
+    auto child = TestUtils::createNode(0, 0, 200, 400,
+            [](RenderProperties& props, TestCanvas& canvas) {
+        canvas.drawColor(Color::Red_500, SkXfermode::kSrcOver_Mode);
+    });
+    auto parent = TestUtils::createNode(0, 0, 200, 400,
+            [&child](RenderProperties& props, TestCanvas& canvas) {
+        canvas.drawRenderNode(child.get());
+    });
+
+    TestUtils::syncHierarchyPropertiesAndDisplayList(parent);
+
+    EXPECT_TRUE(child->hasParents()) << "Child node has no parent";
+    EXPECT_FALSE(parent->hasParents()) << "Root node shouldn't have any parents";
+
+    TestUtils::recordNode(*parent, [](TestCanvas& canvas) {
+        canvas.drawColor(Color::Amber_500, SkXfermode::kSrcOver_Mode);
+    });
+
+    EXPECT_TRUE(child->hasParents()) << "Child should still have a parent";
+    EXPECT_FALSE(parent->hasParents()) << "Root node shouldn't have any parents";
+
+    TestUtils::syncHierarchyPropertiesAndDisplayList(parent);
+
+    EXPECT_FALSE(child->hasParents()) << "Child should be removed";
+    EXPECT_FALSE(parent->hasParents()) << "Root node shouldn't have any parents";
+}