commit 35b4e3839a2eb405bd172351042f81d842183715
author Jorim Jaggi <jjaggi@google.com> Thu Mar 28 00:44:03 2019 +0100
committer Jorim Jaggi <jjaggi@google.com> Tue Apr 02 22:40:12 2019 +0200
tree 39ee0e9f82836355b195abfcc7c8b66a88868af7
parent 6ae550323264bacc45da2d8fca90534d02815308

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

libs/gui/BufferQueueProducer.cpp

diff --git a/libs/gui/BufferQueueProducer.cpp b/libs/gui/BufferQueueProducer.cpp
index c17a525..b353ffe 100644
--- a/libs/gui/BufferQueueProducer.cpp
+++ b/libs/gui/BufferQueueProducer.cpp
@@ -59,7 +59,8 @@
     mNextCallbackTicket(0),
     mCurrentCallbackTicket(0),
     mCallbackCondition(),
-    mDequeueTimeout(-1) {}
+    mDequeueTimeout(-1),
+    mDequeueWaitingForAllocation(false) {}
 
 BufferQueueProducer::~BufferQueueProducer() {}
 
@@ -383,6 +384,15 @@
     { // 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 @@
             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
     }
 }