Fix latency calculation when multiple rendered buffers are in flight.

content/common/gpu/image_transport_surface.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/common/gpu/image_transport_surface.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 184 matching lines @@
   base::TimeTicks swap_time = base::TimeTicks::Now();
   for (auto& latency : latency_info_) {
     latency.AddLatencyNumberWithTimestamp(
         ui::INPUT_EVENT_GPU_SWAP_BUFFER_COMPONENT, 0, 0, swap_time, 1);
   }
 
   // We use WeakPtr here to avoid manual management of life time of an instance
   // of this class. Callback will not be called once the instance of this class
   // is destroyed. However, this also means that the callback can be run on
   // the calling thread only.
+  std::vector<ui::LatencyInfo> latency_info;
+  latency_info.swap(latency_info_);
   return gfx::GLSurfaceAdapter::SwapBuffersAsync(
       base::Bind(&PassThroughImageTransportSurface::SwapBuffersCallBack,
-          weak_ptr_factory_.GetWeakPtr()));
+                 weak_ptr_factory_.GetWeakPtr(), latency_info));
 }
 
 bool PassThroughImageTransportSurface::PostSubBuffer(
     int x, int y, int width, int height) {
   SendVSyncUpdateIfAvailable();
 
   base::TimeTicks swap_time = base::TimeTicks::Now();
   for (auto& latency : latency_info_) {
     latency.AddLatencyNumberWithTimestamp(
         ui::INPUT_EVENT_GPU_SWAP_BUFFER_COMPONENT, 0, 0, swap_time, 1);
   }
 
   // We use WeakPtr here to avoid manual management of life time of an instance
   // of this class. Callback will not be called once the instance of this class
   // is destroyed. However, this also means that the callback can be run on
   // the calling thread only.
-  return gfx::GLSurfaceAdapter::PostSubBufferAsync(x, y, width, height,
+  std::vector<ui::LatencyInfo> latency_info;
+  latency_info.swap(latency_info_);

[brianderson, 2015/05/14 19:06:12]

Although this swap avoids one copy, I think there are still two copies after
this: once on Bind and again on SwapBuffersCallback. It would be nice to avoid
those copies since we're trying to keep the overhead of LatencyInfo low.

Since std::move isn't allowed, could we instead do:
std::vector<ui::LatencyInfo>* latency_info_ptr = new
std::vector<ui::LatencyInfo>;
latency_info_ptr->swap(latency_info_);

...Bind(..., Owned(latency_info_ptr));


Or scoped_ptr<vector<...>> and Passed(latency_info)?

[alexst (slow to review), 2015/05/14 19:32:41]

Sounds good, done.

+  return gfx::GLSurfaceAdapter::PostSubBufferAsync(
+      x, y, width, height,
       base::Bind(&PassThroughImageTransportSurface::SwapBuffersCallBack,
-          weak_ptr_factory_.GetWeakPtr()));
+                 weak_ptr_factory_.GetWeakPtr(), latency_info));
 }
 
-void PassThroughImageTransportSurface::SwapBuffersCallBack() {
+void PassThroughImageTransportSurface::SwapBuffersCallBack(
+    std::vector<ui::LatencyInfo> latency_info) {
   base::TimeTicks swap_ack_time = base::TimeTicks::Now();
-  for (auto& latency : latency_info_) {
+  for (auto& latency : latency_info) {
     latency.AddLatencyNumberWithTimestamp(
         ui::INPUT_EVENT_LATENCY_TERMINATED_FRAME_SWAP_COMPONENT, 0, 0,
         swap_ack_time, 1);
   }
 
-  helper_->stub()->SendSwapBuffersCompleted(latency_info_);
-  latency_info_.clear();
+  helper_->stub()->SendSwapBuffersCompleted(latency_info);
 }
 
 bool PassThroughImageTransportSurface::OnMakeCurrent(gfx::GLContext* context) {
   if (!did_set_swap_interval_) {
     ImageTransportHelper::SetSwapInterval(context);
     did_set_swap_interval_ = true;
   }
   return true;
 }
 
@@ skipping 22 matching lines @@
 void PassThroughImageTransportSurface::SendVSyncUpdateIfAvailable() {
   gfx::VSyncProvider* vsync_provider = GetVSyncProvider();
   if (vsync_provider) {
     vsync_provider->GetVSyncParameters(
         base::Bind(&GpuCommandBufferStub::SendUpdateVSyncParameters,
                    helper_->stub()->AsWeakPtr()));
   }
 }
 
 }  // namespace content