From a4650a50a0b35e9e4342d6600b6eb24fd94bb8e5 Mon Sep 17 00:00:00 2001
From: Dan Stoza <stoza@google.com>
Date: Tue, 12 May 2015 12:56:16 -0700
Subject: 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 | 42 +++++++++++++++-------------------------
 1 file changed, 16 insertions(+), 26 deletions(-)

(limited to 'libs/gui/BufferQueueConsumer.cpp')

diff --git a/libs/gui/BufferQueueConsumer.cpp b/libs/gui/BufferQueueConsumer.cpp
index 336ddb667d..4174676c76 100644
--- a/libs/gui/BufferQueueConsumer.cpp
+++ b/libs/gui/BufferQueueConsumer.cpp
@@ -36,7 +36,7 @@ BufferQueueConsumer::BufferQueueConsumer(const sp<BufferQueueCore>& core) :
 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 @@ status_t BufferQueueConsumer::acquireBuffer(BufferItem* outBuffer,
         // 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 @@ status_t BufferQueueConsumer::acquireBuffer(BufferItem* outBuffer,
             //
             // 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 @@ status_t BufferQueueConsumer::acquireBuffer(BufferItem* outBuffer,
             }
             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 @@ sp<NativeHandle> BufferQueueConsumer::getSidebandStream() const {
     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);
 }
-- 
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