Pepper takes ownership of a mailbox before passing it to the texture layer.

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 77aa684d64747cef8b723d01b931a554c8e97832..c59161ee49de62e2a277b363aea0b684b28745f9 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -594,7 +594,11 @@ class GLES2DecoderImpl : public GLES2Decoder, public ErrorStateClient {
                   const std::vector<int32_t>& attribs) override;
   void Destroy(bool have_context) override;
   void SetSurface(const scoped_refptr<gfx::GLSurface>& surface) override;
+  void ReleaseSurface() override;
   void ProduceFrontBuffer(const Mailbox& mailbox) override;
+  void TakeFrontBuffer(const Mailbox& mailbox) override;
+  void ReturnFrontBuffer(const Mailbox& mailbox,
+                         bool is_lost) override;
   bool ResizeOffscreenFrameBuffer(const gfx::Size& size) override;
   void UpdateParentTextureInfo();
   bool MakeCurrent() override;
@@ -2044,6 +2048,33 @@ class GLES2DecoderImpl : public GLES2Decoder, public ErrorStateClient {
   scoped_refptr<TextureRef>
       offscreen_saved_color_texture_info_;
 
+  // When a client requests ownership of the swapped front buffer, all
+  // information is saved in this structure, and |in_use| is set to true. When a
+  // client releases ownership, |in_use| is set to false.
+  //
+  // An instance of this struct, with |in_use| = false may be reused instead of
+  // making a new BackTexture.
+  struct SavedBackTexture {
+    std::unique_ptr<BackTexture> back_texture;
+    scoped_refptr<TextureRef> texture_ref;
+    bool in_use;
+  };
+  std::vector<SavedBackTexture> saved_back_textures_;
+
+  // If there's a SavedBackTexture that's not in use, takes that. Otherwise,
+  // generates a new back texture.
+  void CreateBackTexture();
+  size_t create_back_texture_count_for_test_ = 0;
+
+  // Releases all saved BackTextures that are not in use by a client.
+  void ReleaseNotInUseBackTextures();
+
+  // Releases all saved BackTextures.
+  void ReleaseAllBackTextures();
+
+  size_t GetSavedBackTextureCountForTest() override;
+  size_t GetCreatedBackTextureCountForTest() override;
+
   // The copy that is used as the destination for multi-sample resolves.
   std::unique_ptr<BackFramebuffer> offscreen_resolved_frame_buffer_;
   std::unique_ptr<BackTexture> offscreen_resolved_color_texture_;
@@ -4146,6 +4177,7 @@ void GLES2DecoderImpl::Destroy(bool have_context) {
     offscreen_saved_color_texture_->Invalidate();
     offscreen_saved_color_texture_info_ = NULL;
   }
+  ReleaseAllBackTextures();
   if (have_context) {
     if (copy_texture_CHROMIUM_.get()) {
       copy_texture_CHROMIUM_->Destroy();
@@ -4284,7 +4316,19 @@ void GLES2DecoderImpl::SetSurface(
   RestoreCurrentFramebufferBindings();
 }
 
+void GLES2DecoderImpl::ReleaseSurface() {
+  if (!context_.get())
+    return;
+  if (WasContextLost()) {
+    DLOG(ERROR) << "  GLES2DecoderImpl: Trying to release lost context.";
+    return;
+  }
+  context_->ReleaseCurrent(surface_.get());
+  surface_ = nullptr;
+}
+
 void GLES2DecoderImpl::ProduceFrontBuffer(const Mailbox& mailbox) {
+  NOTREACHED();

[ccameron, 2016/04/22 18:25:55]

Should this be "TODO: delete me" as well?

   if (!offscreen_saved_color_texture_.get()) {
     LOG(ERROR) << "Called ProduceFrontBuffer on a non-offscreen context";
     return;
@@ -4301,6 +4345,109 @@ void GLES2DecoderImpl::ProduceFrontBuffer(const Mailbox& mailbox) {
       mailbox, offscreen_saved_color_texture_info_->texture());
 }
 
+void GLES2DecoderImpl::TakeFrontBuffer(const Mailbox& mailbox) {
+  if (!offscreen_saved_color_texture_.get()) {
+    LOG(ERROR) << "Called TakeFrontBuffer on a non-offscreen context";
+    return;
+  }
+
+  if (!offscreen_saved_color_texture_info_.get()) {
+    GLuint service_id = offscreen_saved_color_texture_->id();
+    offscreen_saved_color_texture_info_ = TextureRef::Create(
+        texture_manager(), 0, service_id);
+    texture_manager()->SetTarget(offscreen_saved_color_texture_info_.get(),
+                                 GL_TEXTURE_2D);
+    UpdateParentTextureInfo();
+  }
+
+  mailbox_manager()->ProduceTexture(
+      mailbox, offscreen_saved_color_texture_info_->texture());
+
+  // Save the BackTexture and TextureRef.
+  SavedBackTexture save;
+  save.back_texture.swap(offscreen_saved_color_texture_);
+  save.texture_ref = offscreen_saved_color_texture_info_;
+  offscreen_saved_color_texture_info_ = nullptr;
+  save.in_use = true;
+  saved_back_textures_.push_back(std::move(save));
+
+  CreateBackTexture();
+}
+
+void GLES2DecoderImpl::ReturnFrontBuffer(const Mailbox& mailbox,
+                                         bool is_lost) {
+  for (auto it = saved_back_textures_.begin(); it != saved_back_textures_.end();
+       ++it) {
+    Texture* texture = mailbox_manager()->ConsumeTexture(mailbox);

[ccameron, 2016/04/22 18:25:55]

Pull the ConsumeTexture above the loop?

[erikchen, 2016/04/25 20:58:23]

Done.

+    if (texture != it->texture_ref->texture())
+      continue;
+
+    if (is_lost || it->back_texture->size() != offscreen_size_) {
+      it->back_texture->Invalidate();
+      saved_back_textures_.erase(it);
+      return;
+    }
+
+    it->in_use = false;

[ccameron, 2016/04/22 18:25:55]

Are there circumstances where we would be concerned about the growth of
non-in_use saved_back_textures_?

[erikchen, 2016/04/25 20:58:23]

If this becomes a problem, we can deal with it. I'd like to avoid premature
optimization.

[This is the same thing we do for WebGL].

+    return;
+  }
+
+  NOTREACHED();
+}
+
+void GLES2DecoderImpl::CreateBackTexture() {
+  for (auto it = saved_back_textures_.begin(); it != saved_back_textures_.end();
+       ++it) {
+    if (it->in_use)
+      continue;
+
+    if (it->back_texture->size() != offscreen_size_)
+      continue;
+    offscreen_saved_color_texture_ = std::move(it->back_texture);
+    offscreen_saved_color_texture_info_ = it->texture_ref;
+    saved_back_textures_.erase(it);
+    return;
+  }
+
+  ++create_back_texture_count_for_test_;
+  offscreen_saved_color_texture_.reset(
+      new BackTexture(memory_tracker(), &state_));
+  offscreen_saved_color_texture_->Create();
+  offscreen_saved_color_texture_->AllocateStorage(
+      offscreen_size_, offscreen_saved_color_format_, false);
+  offscreen_saved_frame_buffer_->AttachRenderTexture(
+      offscreen_saved_color_texture_.get());
+}
+
+void GLES2DecoderImpl::ReleaseNotInUseBackTextures() {
+  for (auto& saved_back_texture : saved_back_textures_) {
+    if (!saved_back_texture.in_use)
+      saved_back_texture.back_texture->Invalidate();
+  }
+
+  std::remove_if(saved_back_textures_.begin(), saved_back_textures_.end(),
+                 [](const SavedBackTexture& saved_back_texture) {
+                   return !saved_back_texture.in_use;
+                 });
+}
+
+void GLES2DecoderImpl::ReleaseAllBackTextures() {
+  for (auto& saved_back_texture : saved_back_textures_) {
+    // The texture will be destroyed by texture_ref's destructor.
+    DCHECK(saved_back_texture.texture_ref);
+    saved_back_texture.back_texture->Invalidate();
+  }
+  saved_back_textures_.clear();
+}
+
+size_t GLES2DecoderImpl::GetSavedBackTextureCountForTest() {
+  return saved_back_textures_.size();
+}
+
+size_t GLES2DecoderImpl::GetCreatedBackTextureCountForTest() {
+  return create_back_texture_count_for_test_;
+}
+
 bool GLES2DecoderImpl::ResizeOffscreenFrameBuffer(const gfx::Size& size) {
   bool is_offscreen = !!offscreen_target_frame_buffer_.get();
   if (!is_offscreen) {
@@ -12843,6 +12990,10 @@ void GLES2DecoderImpl::DoSwapBuffers() {
         glFinish();
       }
 
+      // The size has changed, so none of the cached BackTextures are useful
+      // anymore.
+      ReleaseNotInUseBackTextures();
+
       // Allocate the offscreen saved color texture.
       DCHECK(offscreen_saved_color_format_);
       offscreen_saved_color_texture_->AllocateStorage(