From 5c259c0e07395b7d80a43a36d500ba6412606689 Mon Sep 17 00:00:00 2001
From: Patrick Williams <pdwilliams@google.com>
Date: Mon, 7 Nov 2022 23:47:01 +0000
Subject: SF: Use strong pointers to Layer when moving snapshot

Bug: 258009724
Test: presubmits
Change-Id: Ie5c22a08bf8539a5ea3f8fb9d72bdaa1a1477e91
---
 services/surfaceflinger/Layer.cpp          |  9 ++++++---
 services/surfaceflinger/SurfaceFlinger.cpp | 17 ++++++++++++-----
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 3478eaaa92..799d79f300 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -3965,14 +3965,17 @@ void Layer::updateRelativeMetadataSnapshot(const LayerMetadata& relativeLayerMet
 }
 
 LayerSnapshotGuard::LayerSnapshotGuard(Layer* layer) : mLayer(layer) {
-    if (mLayer) {
-        mLayer->mLayerFE->mSnapshot = std::move(mLayer->mSnapshot);
-    }
+    LOG_ALWAYS_FATAL_IF(!mLayer, "LayerSnapshotGuard received a null layer.");
+    mLayer->mLayerFE->mSnapshot = std::move(mLayer->mSnapshot);
+    LOG_ALWAYS_FATAL_IF(!mLayer->mLayerFE->mSnapshot,
+                        "LayerFE snapshot null after taking ownership from layer");
 }
 
 LayerSnapshotGuard::~LayerSnapshotGuard() {
     if (mLayer) {
         mLayer->mSnapshot = std::move(mLayer->mLayerFE->mSnapshot);
+        LOG_ALWAYS_FATAL_IF(!mLayer->mSnapshot,
+                            "Layer snapshot null after taking ownership from LayerFE");
     }
 }
 
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 53066024d0..b930231f73 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -2182,13 +2182,14 @@ void SurfaceFlinger::composite(TimePoint frameTime, VsyncId vsyncId)
 
     refreshArgs.updatingOutputGeometryThisFrame = mVisibleRegionsDirty;
     refreshArgs.updatingGeometryThisFrame = mGeometryDirty.exchange(false) || mVisibleRegionsDirty;
-    std::vector<Layer*> layers;
+    std::vector<sp<Layer>> layers;
 
     mDrawingState.traverseInZOrder([&refreshArgs, &layers](Layer* layer) {
+        auto strongLayer = sp<Layer>::fromExisting(layer);
         if (auto layerFE = layer->getCompositionEngineLayerFE()) {
             layer->updateSnapshot(refreshArgs.updatingGeometryThisFrame);
             refreshArgs.layers.push_back(layerFE);
-            layers.push_back(layer);
+            layers.push_back(std::move(strongLayer));
         }
     });
     refreshArgs.blursAreExpensive = mBlursAreExpensive;
@@ -2220,8 +2221,8 @@ void SurfaceFlinger::composite(TimePoint frameTime, VsyncId vsyncId)
 
     {
         std::vector<LayerSnapshotGuard> layerSnapshotGuards;
-        for (Layer* layer : layers) {
-            layerSnapshotGuards.emplace_back(layer);
+        for (auto& layer : layers) {
+            layerSnapshotGuards.emplace_back(layer.get());
         }
         mCompositionEngine->present(refreshArgs);
     }
@@ -3327,7 +3328,12 @@ void SurfaceFlinger::updateCursorAsync() {
 
     std::vector<LayerSnapshotGuard> layerSnapshotGuards;
     mDrawingState.traverse([&layerSnapshotGuards](Layer* layer) {
-        if (layer->getLayerSnapshot()->compositionType ==
+        auto strongLayer = sp<Layer>::fromExisting(layer);
+        const LayerSnapshot* snapshot = layer->getLayerSnapshot();
+        if (!snapshot) {
+            LOG_ALWAYS_FATAL("Layer snapshot unexpectedly null");
+        }
+        if (snapshot->compositionType ==
             aidl::android::hardware::graphics::composer3::Composition::CURSOR) {
             layer->updateSnapshot(false /* updateGeometry */);
             layerSnapshotGuards.emplace_back(layer);
@@ -6461,6 +6467,7 @@ ftl::SharedFuture<FenceResult> SurfaceFlinger::renderScreenImpl(
     std::vector<Layer*> renderedLayers;
     bool disableBlurs = false;
     traverseLayers([&](Layer* layer) FTL_FAKE_GUARD(kMainThreadContext) {
+        auto strongLayer = sp<Layer>::fromExisting(layer);
         auto layerFE = layer->getCompositionEngineLayerFE();
         if (!layerFE) {
             return;
-- 
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