libgui: Add Surface::getLastDequeueStartTime

Adds the getLastDequeueStartTime method, which allows the caller to
determine whether the last dequeueBuffer call fell into a given time
window.

Bug: 62213889
Test: SurfaceTest.TestGetLastDequeueStartTime in libgui_test
Change-Id: I1684deb09273745a3adc751554624d2257fa890e

3 files changed, 33 insertions, 3 deletions

diff --git a/include/gui/Surface.h b/include/gui/Surface.h
index 8b1d1069b3..e8dc83e951 100644
--- a/include/gui/Surface.h
+++ b/include/gui/Surface.h
@@ -160,6 +160,9 @@ public:
 
     status_t getUniqueId(uint64_t* outId) const;
 
+    // Returns the CLOCK_MONOTONIC start time of the last dequeueBuffer call
+    nsecs_t getLastDequeueStartTime() const;
+
 protected:
     virtual ~Surface();
 
@@ -421,6 +424,9 @@ protected:
     nsecs_t mLastDequeueDuration = 0;
     nsecs_t mLastQueueDuration = 0;
 
+    // Stores the time right before we call IGBP::dequeueBuffer
+    nsecs_t mLastDequeueStartTime = 0;
+
     Condition mQueueBufferCondition;
 
     uint64_t mNextFrameNumber = 1;
diff --git a/libs/gui/Surface.cpp b/libs/gui/Surface.cpp
index 6583a622f5..7b2b5c37f1 100644
--- a/libs/gui/Surface.cpp
+++ b/libs/gui/Surface.cpp
@@ -501,13 +501,13 @@ int Surface::dequeueBuffer(android_native_buffer_t** buffer, int* fenceFd) {
 
     int buf = -1;
     sp<Fence> fence;
-    nsecs_t now = systemTime();
+    nsecs_t startTime = systemTime();
 
     FrameEventHistoryDelta frameTimestamps;
     status_t result = mGraphicBufferProducer->dequeueBuffer(&buf, &fence,
             reqWidth, reqHeight, reqFormat, reqUsage,
             enableFrameTimestamps ? &frameTimestamps : nullptr);
-    mLastDequeueDuration = systemTime() - now;
+    mLastDequeueDuration = systemTime() - startTime;
 
     if (result < 0) {
         ALOGV("dequeueBuffer: IGraphicBufferProducer::dequeueBuffer"
@@ -524,6 +524,9 @@ int Surface::dequeueBuffer(android_native_buffer_t** buffer, int* fenceFd) {
 
     Mutex::Autolock lock(mMutex);
 
+    // Write this while holding the mutex
+    mLastDequeueStartTime = startTime;
+
     sp<GraphicBuffer>& gbuf(mSlots[buf].buffer);
 
     // this should never happen
@@ -1699,6 +1702,11 @@ status_t Surface::getUniqueId(uint64_t* outId) const {
     return mGraphicBufferProducer->getUniqueId(outId);
 }
 
+nsecs_t Surface::getLastDequeueStartTime() const {
+    Mutex::Autolock lock(mMutex);
+    return mLastDequeueStartTime;
+}
+
 status_t Surface::getAndFlushRemovedBuffers(std::vector<sp<GraphicBuffer>>* out) {
     if (out == nullptr) {
         ALOGE("%s: out must not be null!", __FUNCTION__);
diff --git a/libs/gui/tests/Surface_test.cpp b/libs/gui/tests/Surface_test.cpp
index fcaa23a4e5..81820def1c 100644
--- a/libs/gui/tests/Surface_test.cpp
+++ b/libs/gui/tests/Surface_test.cpp
@@ -393,6 +393,22 @@ TEST_F(SurfaceTest, GetAndFlushRemovedBuffers) {
     ASSERT_LE(removedBuffers.size(), 1u);
 }
 
+TEST_F(SurfaceTest, TestGetLastDequeueStartTime) {
+    sp<ANativeWindow> anw(mSurface);
+    ASSERT_EQ(NO_ERROR, native_window_api_connect(anw.get(), NATIVE_WINDOW_API_CPU));
+
+    ANativeWindowBuffer* buffer = nullptr;
+    int32_t fenceFd = -1;
+
+    nsecs_t before = systemTime(CLOCK_MONOTONIC);
+    anw->dequeueBuffer(anw.get(), &buffer, &fenceFd);
+    nsecs_t after = systemTime(CLOCK_MONOTONIC);
+
+    nsecs_t lastDequeueTime = mSurface->getLastDequeueStartTime();
+    ASSERT_LE(before, lastDequeueTime);
+    ASSERT_GE(after, lastDequeueTime);
+}
+
 class FakeConsumer : public BnConsumerListener {
 public:
     void onFrameAvailable(const BufferItem& /*item*/) override {}
@@ -1568,4 +1584,4 @@ TEST_F(GetFrameTimestampsTest, PresentUnsupportedNoSync) {
     EXPECT_EQ(-1, outDisplayPresentTime);
 }
 
-}
+} // namespace android