commit a4650a50a0b35e9e4342d6600b6eb24fd94bb8e5
author Dan Stoza <stoza@google.com> Tue May 12 12:56:16 2015 -0700
committer Dan Stoza <stoza@google.com> Tue May 12 13:10:17 2015 -0700
tree 756ed49e76eb52abc3b1e8ec7cb962b9a627fcc6
parent 2a7dde58036e02b2417e49c8965d4a518d981b0b

Fix PTS handling for buffer replacement

This changes the way that SurfaceFlinger's shadow buffer management
works such that instead of tracking the size of the shadow queue in the
BufferQueue, SF tracks the last frame number it has seen, and passes
that into the acquireBuffer call. BufferQueueConsumer then ensures that
it never returns a buffer newer than that frame number, even if that
means that it must return PRESENT_LATER for an otherwise valid buffer.

Change-Id: I3fcb45f683ed660c3f18a8b85ae1f8a962ba6f0e

libs/gui/BufferQueueConsumer.cpp

diff --git a/libs/gui/BufferQueueConsumer.cpp b/libs/gui/BufferQueueConsumer.cpp
index 336ddb6..4174676 100644
--- a/libs/gui/BufferQueueConsumer.cpp
+++ b/libs/gui/BufferQueueConsumer.cpp
@@ -36,7 +36,7 @@
 BufferQueueConsumer::~BufferQueueConsumer() {}
 
 status_t BufferQueueConsumer::acquireBuffer(BufferItem* outBuffer,
-        nsecs_t expectedPresent) {
+        nsecs_t expectedPresent, uint64_t maxFrameNumber) {
     ATRACE_CALL();
     Mutex::Autolock lock(mCore->mMutex);
 
@@ -89,17 +89,12 @@
         // the timestamps are being auto-generated by Surface. If the app isn't
         // generating timestamps explicitly, it probably doesn't want frames to
         // be discarded based on them.
-        //
-        // If the consumer is shadowing our queue, we also make sure that we
-        // don't drop so many buffers that the consumer hasn't received the
-        // onFrameAvailable callback for the buffer it acquires. That is, we
-        // want the buffer we return to be in the consumer's shadow queue.
-        size_t droppableBuffers = mCore->mConsumerShadowQueueSize > 1 ?
-                mCore->mConsumerShadowQueueSize - 1 : 0;
         while (mCore->mQueue.size() > 1 && !mCore->mQueue[0].mIsAutoTimestamp) {
-            if (mCore->mConsumerHasShadowQueue && droppableBuffers == 0) {
-                BQ_LOGV("acquireBuffer: no droppable buffers in consumer's"
-                        " shadow queue, continuing");
+            const BufferItem& bufferItem(mCore->mQueue[1]);
+
+            // If dropping entry[0] would leave us with a buffer that the
+            // consumer is not yet ready for, don't drop it.
+            if (maxFrameNumber && bufferItem.mFrameNumber > maxFrameNumber) {
                 break;
             }
 
@@ -112,7 +107,6 @@
             //
             // We may want to add an additional criterion: don't drop the
             // earlier buffer if entry[1]'s fence hasn't signaled yet.
-            const BufferItem& bufferItem(mCore->mQueue[1]);
             nsecs_t desiredPresent = bufferItem.mTimestamp;
             if (desiredPresent < expectedPresent - MAX_REASONABLE_NSEC ||
                     desiredPresent > expectedPresent) {
@@ -137,18 +131,22 @@
             }
             mCore->mQueue.erase(front);
             front = mCore->mQueue.begin();
-            --droppableBuffers;
         }
 
-        // See if the front buffer is due
+        // See if the front buffer is ready to be acquired
         nsecs_t desiredPresent = front->mTimestamp;
-        if (desiredPresent > expectedPresent &&
-                desiredPresent < expectedPresent + MAX_REASONABLE_NSEC) {
+        bool bufferIsDue = desiredPresent <= expectedPresent ||
+                desiredPresent > expectedPresent + MAX_REASONABLE_NSEC;
+        bool consumerIsReady = maxFrameNumber > 0 ?
+                front->mFrameNumber <= maxFrameNumber : true;
+        if (!bufferIsDue || !consumerIsReady) {
             BQ_LOGV("acquireBuffer: defer desire=%" PRId64 " expect=%" PRId64
-                    " (%" PRId64 ") now=%" PRId64,
+                    " (%" PRId64 ") now=%" PRId64 " frame=%" PRIu64
+                    " consumer=%" PRIu64,
                     desiredPresent, expectedPresent,
                     desiredPresent - expectedPresent,
-                    systemTime(CLOCK_MONOTONIC));
+                    systemTime(CLOCK_MONOTONIC),
+                    front->mFrameNumber, maxFrameNumber);
             return PRESENT_LATER;
         }
 
@@ -553,14 +551,6 @@
     return mCore->mSidebandStream;
 }
 
-void BufferQueueConsumer::setShadowQueueSize(size_t size) {
-    ATRACE_CALL();
-    BQ_LOGV("setShadowQueueSize: %zu", size);
-    Mutex::Autolock lock(mCore->mMutex);
-    mCore->mConsumerHasShadowQueue = true;
-    mCore->mConsumerShadowQueueSize = size;
-}
-
 void BufferQueueConsumer::dump(String8& result, const char* prefix) const {
     mCore->dump(result, prefix);
 }