BufferQueues: Always respect setMaxDequeuedBufferCount

For some reason, this wouldn't be respected if no buffers had been
queued. This could lead to surprising behavior of a (with unlimited
buffers, essentially unbounded) buffers being dequeued for new BQs.

This is flag gated to capture potential issues, since I'm worried about
chesterton's fence.

Bug: 399328309
Flag: com.android.graphics.libgui.flags.bq_always_use_max_dequeued_buffer_count
Test: new tests

Change-Id: I756eb4f621f6eec1a5bb43a490305018ec69c477

Author: Jim Shargo

libs/gui/BufferQueueProducer.cpp

@@ -364,8 +364,10 @@ status_t BufferQueueProducer::waitForFreeSlotThenRelock(FreeSlotCaller caller,
         // Producers are not allowed to dequeue more than
         // mMaxDequeuedBufferCount buffers.
         // This check is only done if a buffer has already been queued
-        if (mCore->mBufferHasBeenQueued &&
-                dequeuedCount >= mCore->mMaxDequeuedBufferCount) {
+        using namespace com::android::graphics::libgui::flags;
+        bool flagGatedBufferHasBeenQueued =
+                bq_always_use_max_dequeued_buffer_count() || mCore->mBufferHasBeenQueued;
+        if (flagGatedBufferHasBeenQueued && dequeuedCount >= mCore->mMaxDequeuedBufferCount) {
             // Supress error logs when timeout is non-negative.
             if (mDequeueTimeout < 0) {
                 BQ_LOGE("%s: attempting to exceed the max dequeued buffer "

libs/gui/libgui_flags.aconfig

@@ -153,3 +153,14 @@ flag {
   }
   is_fixed_read_only: true
 } # allocate_buffer_priority
+
+flag {
+  name: "bq_always_use_max_dequeued_buffer_count"
+  namespace: "core_graphics"
+  description: "BufferQueueProducer::dequeue's respects setMaxDequeuedBufferCount even before a buffer is dequeued."
+  bug: "399328309"
+  metadata {
+    purpose: PURPOSE_BUGFIX
+  }
+  is_fixed_read_only: true
+} # bq_always_use_max_dequeued_buffer_count

libs/gui/tests/Surface_test.cpp

@@ -2246,6 +2246,52 @@ TEST_F(SurfaceTest, BatchIllegalOperations) {
     ASSERT_EQ(NO_ERROR, surface->disconnect(NATIVE_WINDOW_API_CPU));
 }
 
+TEST_F(SurfaceTest, setMaxDequeuedBufferCount_setMaxAcquiredBufferCount_allocations) {
+    //
+    // Set up the consumer and producer--nothing fancy.
+    //
+    auto [consumer, surface] =
+            BufferItemConsumer::create(GRALLOC_USAGE_SW_READ_OFTEN | GRALLOC_USAGE_HW_RENDER);
+    sp<SurfaceListener> surfaceListener = sp<StubSurfaceListener>::make();
+    surface->connect(NATIVE_WINDOW_API_CPU, surfaceListener);
+    sp<GraphicBuffer> buffer;
+    sp<Fence> fence;
+
+    //
+    // These values are independent. The consumer can dequeue 3 and the consumer can acquire 3 at
+    // the same time.
+    //
+    ASSERT_EQ(OK, consumer->setMaxAcquiredBufferCount(3));
+    ASSERT_EQ(OK, surface->setMaxDequeuedBufferCount(3));
+
+    //
+    // Take all three buffers out of the queue--a fourth can't be retrieved. Then queue them.
+    //
+    std::vector<Surface::BatchBuffer> dequeuedBuffers(3);
+    EXPECT_EQ(OK, surface->dequeueBuffers(&dequeuedBuffers));
+    if (::com::android::graphics::libgui::flags::bq_always_use_max_dequeued_buffer_count()) {
+        EXPECT_EQ(INVALID_OPERATION, surface->dequeueBuffer(&buffer, &fence));
+    }
+
+    for (auto& batchBuffer : dequeuedBuffers) {
+        EXPECT_EQ(OK,
+                  surface->queueBuffer(GraphicBuffer::from(batchBuffer.buffer),
+                                       sp<Fence>::make(batchBuffer.fenceFd)));
+    }
+    dequeuedBuffers.assign(3, {});
+
+    //
+    // Acquire all three, then we should be able to dequeue 3 more.
+    //
+    std::vector<BufferItem> acquiredBuffers(3);
+    for (auto& bufferItem : acquiredBuffers) {
+        EXPECT_EQ(OK, consumer->acquireBuffer(&bufferItem, 0));
+    }
+
+    EXPECT_EQ(OK, surface->dequeueBuffers(&dequeuedBuffers));
+    EXPECT_EQ(INVALID_OPERATION, surface->dequeueBuffer(&buffer, &fence));
+}
+
 #if COM_ANDROID_GRAPHICS_LIBGUI_FLAGS(WB_PLATFORM_API_IMPROVEMENTS)
 
 TEST_F(SurfaceTest, PlatformBufferMethods) {