Wait for buffer allocation

In dequeueBuffer, if we don't have a free slot but are in the
process of allocating, we wait for that to complete instead of
kicking off our own allocation, as it's likely that the allocation
from allocateBuffers is able to finish earlier than if we'd kick
off our own allocation.

Test: Swipe up, see less initial buffer dequeue delay
Fixes: 111517695
Change-Id: I735d68e87fc7e2ff5b7ec3595f0ced5a94ebbf9c

1 files changed, 17 insertions, 1 deletions

diff --git a/libs/gui/BufferQueueProducer.cpp b/libs/gui/BufferQueueProducer.cpp
index c17a525cb2..b353ffef92 100644
--- a/libs/gui/BufferQueueProducer.cpp
+++ b/libs/gui/BufferQueueProducer.cpp
@@ -59,7 +59,8 @@ BufferQueueProducer::BufferQueueProducer(const sp<BufferQueueCore>& core,
     mNextCallbackTicket(0),
     mCurrentCallbackTicket(0),
     mCallbackCondition(),
-    mDequeueTimeout(-1) {}
+    mDequeueTimeout(-1),
+    mDequeueWaitingForAllocation(false) {}
 
 BufferQueueProducer::~BufferQueueProducer() {}
 
@@ -383,6 +384,15 @@ status_t BufferQueueProducer::dequeueBuffer(int* outSlot, sp<android::Fence>* ou
     { // Autolock scope
         std::unique_lock<std::mutex> lock(mCore->mMutex);
 
+        // If we don't have a free buffer, but we are currently allocating, we wait until allocation
+        // is finished such that we don't allocate in parallel.
+        if (mCore->mFreeBuffers.empty() && mCore->mIsAllocating) {
+            mDequeueWaitingForAllocation = true;
+            mCore->waitWhileAllocatingLocked(lock);
+            mDequeueWaitingForAllocation = false;
+            mDequeueWaitingForAllocationCondition.notify_all();
+        }
+
         if (format == 0) {
             format = mCore->mDefaultBufferFormat;
         }
@@ -1421,6 +1431,12 @@ void BufferQueueProducer::allocateBuffers(uint32_t width, uint32_t height,
             mCore->mIsAllocating = false;
             mCore->mIsAllocatingCondition.notify_all();
             VALIDATE_CONSISTENCY();
+
+            // If dequeue is waiting for to allocate a buffer, release the lock until it's not
+            // waiting anymore so it can use the buffer we just allocated.
+            while (mDequeueWaitingForAllocation) {
+                mDequeueWaitingForAllocationCondition.wait(lock);
+            }
         } // Autolock scope
     }
 }