Maintain the active buffer when clearing buffer slots

When an app discards graphic buffers, for example when a MediaCodec
disconnects from a surface, those buffers will be uncached and removed
from HWC buffer slots. The active buffer, however, should still remain
active until the next buffer is queued up.

Bug: 262037933
Bug: 258196272
Test: atest OutputLayerUncacheBufferTest
Test: atest VtsHalGraphicsComposer3_TargetTest
Test: atest VtsHalGraphicsComposerV2_2TargetTest
Change-Id: I7c4eefb17e8bad694d698f9ad6d1d289f4af8d2c
diff --git a/services/surfaceflinger/CompositionEngine/tests/HwcBufferCacheTest.cpp b/services/surfaceflinger/CompositionEngine/tests/HwcBufferCacheTest.cpp
index cf72e8f..c5fb594 100644
--- a/services/surfaceflinger/CompositionEngine/tests/HwcBufferCacheTest.cpp
+++ b/services/surfaceflinger/CompositionEngine/tests/HwcBufferCacheTest.cpp
@@ -115,20 +115,20 @@
     EXPECT_EQ(cache.uncache(mBuffer2->getId()), UINT32_MAX);
 }
 
-TEST_F(HwcBufferCacheTest, getHwcSlotAndBufferForOverride_whenCached_returnsSameSlotAndNullBuffer) {
+TEST_F(HwcBufferCacheTest, getOverrideHwcSlotAndBuffer_whenCached_returnsSameSlotAndNullBuffer) {
     HwcBufferCache cache;
     sp<GraphicBuffer> outBuffer;
 
-    HwcSlotAndBuffer originalSlotAndBuffer = cache.getHwcSlotAndBufferForOverride(mBuffer1);
+    HwcSlotAndBuffer originalSlotAndBuffer = cache.getOverrideHwcSlotAndBuffer(mBuffer1);
     EXPECT_NE(originalSlotAndBuffer.slot, UINT32_MAX);
     EXPECT_EQ(originalSlotAndBuffer.buffer, mBuffer1);
 
-    HwcSlotAndBuffer finalSlotAndBuffer = cache.getHwcSlotAndBufferForOverride(mBuffer1);
+    HwcSlotAndBuffer finalSlotAndBuffer = cache.getOverrideHwcSlotAndBuffer(mBuffer1);
     EXPECT_EQ(finalSlotAndBuffer.slot, originalSlotAndBuffer.slot);
     EXPECT_EQ(finalSlotAndBuffer.buffer, nullptr);
 }
 
-TEST_F(HwcBufferCacheTest, getHwcSlotAndBufferForOverride_whenSlotsFull_returnsIndependentSlot) {
+TEST_F(HwcBufferCacheTest, getOverrideHwcSlotAndBuffer_whenSlotsFull_returnsIndependentSlot) {
     HwcBufferCache cache;
     sp<GraphicBuffer> outBuffer;
 
@@ -149,7 +149,7 @@
 
     sp<GraphicBuffer> overrideBuffer =
             sp<GraphicBuffer>::make(1u, 1u, HAL_PIXEL_FORMAT_RGBA_8888, 1u, 0u);
-    HwcSlotAndBuffer overrideSlotAndBuffer = cache.getHwcSlotAndBufferForOverride(overrideBuffer);
+    HwcSlotAndBuffer overrideSlotAndBuffer = cache.getOverrideHwcSlotAndBuffer(overrideBuffer);
     // expect us to have a slot number
     EXPECT_NE(overrideSlotAndBuffer.slot, UINT32_MAX);
     // expect this to be the first time we cached the buffer
@@ -173,7 +173,7 @@
     HwcBufferCache cache;
     sp<GraphicBuffer> outBuffer;
 
-    HwcSlotAndBuffer hwcSlotAndBuffer = cache.getHwcSlotAndBufferForOverride(mBuffer1);
+    HwcSlotAndBuffer hwcSlotAndBuffer = cache.getOverrideHwcSlotAndBuffer(mBuffer1);
     ASSERT_NE(hwcSlotAndBuffer.slot, UINT32_MAX);
 
     EXPECT_EQ(cache.uncache(mBuffer1->getId()), hwcSlotAndBuffer.slot);
@@ -184,7 +184,7 @@
     HwcBufferCache cache;
     sp<GraphicBuffer> outBuffer;
 
-    HwcSlotAndBuffer hwcSlotAndBuffer = cache.getHwcSlotAndBufferForOverride(mBuffer1);
+    HwcSlotAndBuffer hwcSlotAndBuffer = cache.getOverrideHwcSlotAndBuffer(mBuffer1);
     ASSERT_NE(hwcSlotAndBuffer.slot, UINT32_MAX);
 
     EXPECT_EQ(cache.uncache(mBuffer2->getId()), UINT32_MAX);
diff --git a/services/surfaceflinger/CompositionEngine/tests/MockHWC2.h b/services/surfaceflinger/CompositionEngine/tests/MockHWC2.h
index c7f9c69..b0b1a02 100644
--- a/services/surfaceflinger/CompositionEngine/tests/MockHWC2.h
+++ b/services/surfaceflinger/CompositionEngine/tests/MockHWC2.h
@@ -56,7 +56,7 @@
     MOCK_METHOD3(setBuffer,
                  Error(uint32_t, const android::sp<android::GraphicBuffer>&,
                        const android::sp<android::Fence>&));
-    MOCK_METHOD1(clearBufferSlot, Error(uint32_t));
+    MOCK_METHOD2(setBufferSlotsToClear, Error(const std::vector<uint32_t>&, uint32_t));
     MOCK_METHOD1(setSurfaceDamage, Error(const android::Region&));
     MOCK_METHOD1(setBlendMode, Error(hal::BlendMode));
     MOCK_METHOD1(setColor, Error(aidl::android::hardware::graphics::composer3::Color));
diff --git a/services/surfaceflinger/CompositionEngine/tests/OutputLayerTest.cpp b/services/surfaceflinger/CompositionEngine/tests/OutputLayerTest.cpp
index f2128c9..0edc226 100644
--- a/services/surfaceflinger/CompositionEngine/tests/OutputLayerTest.cpp
+++ b/services/surfaceflinger/CompositionEngine/tests/OutputLayerTest.cpp
@@ -1361,19 +1361,21 @@
     Mock::VerifyAndClearExpectations(&mHwcLayer);
 
     // buffer slots are cleared in HWC
-    EXPECT_CALL(mHwcLayer, clearBufferSlot(/*slot*/ 0));
-    EXPECT_CALL(mHwcLayer, clearBufferSlot(/*slot*/ 1));
+    std::vector<uint32_t> slotsToClear = {0, 1};
+    EXPECT_CALL(mHwcLayer,
+                setBufferSlotsToClear(/*slotsToClear*/ slotsToClear, /*activeBufferSlot*/ 1));
     mOutputLayer.uncacheBuffers({kBuffer1->getId(), kBuffer2->getId()});
     Mock::VerifyAndClearExpectations(&mHwcLayer);
 
-    // slot 1 is reused for Buffer1
+    // rather than allocating a new slot, the active buffer slot (slot 1) is reused first to free
+    // the memory as soon as possible
     mLayerFEState.buffer = kBuffer1;
     EXPECT_CALL(mHwcLayer, setBuffer(/*slot*/ 1, kBuffer1, kFence));
     mOutputLayer.writeStateToHWC(/*includeGeometry*/ false, /*skipLayer*/ false, 0,
                                  /*zIsOverridden*/ false, /*isPeekingThrough*/ false);
     Mock::VerifyAndClearExpectations(&mHwcLayer);
 
-    // slot 0 is reused for Buffer2
+    // rather than allocating a new slot, slot 0 is reused
     mLayerFEState.buffer = kBuffer2;
     EXPECT_CALL(mHwcLayer, setBuffer(/*slot*/ 0, kBuffer2, kFence));
     mOutputLayer.writeStateToHWC(/*includeGeometry*/ false, /*skipLayer*/ false, 0,