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

1 files changed, 10 insertions, 2 deletions

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__);