cc: Start commit early and block on tree activation

cc/trees/thread_proxy.cc

 // Copyright 2011 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 "cc/trees/thread_proxy.h"
 
 #include <string>
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
@@ skipping 415 matching lines @@
 }
 
 void ThreadProxy::OnHasPendingTreeStateChanged(bool has_pending_tree) {
   DCHECK(IsImplThread());
   TRACE_EVENT1("cc", "ThreadProxy::OnHasPendingTreeStateChanged",
                "has_pending_tree", has_pending_tree);
   scheduler_on_impl_thread_->SetHasTrees(
       has_pending_tree,
       layer_tree_host_impl_->active_tree() ?
           !layer_tree_host_impl_->active_tree()->root_layer() : true);
+
+  if (!has_pending_tree && !deferred_start_commit_on_impl_thread_.is_null()) {
+    Proxy::ImplThreadTaskRunner()->PostTask(
+        FROM_HERE,
+        deferred_start_commit_on_impl_thread_);
+    deferred_start_commit_on_impl_thread_.Reset();
+  }
 }
 
 void ThreadProxy::SetNeedsCommitOnImplThread() {
   DCHECK(IsImplThread());
   TRACE_EVENT0("cc", "ThreadProxy::SetNeedsCommitOnImplThread");
   scheduler_on_impl_thread_->SetNeedsCommit();
 }
 
 void ThreadProxy::PostAnimationEventsToMainThreadOnImplThread(
     scoped_ptr<AnimationEventsVector> events,
@@ skipping 427 matching lines @@
   DCHECK(scheduler_on_impl_thread_);
   DCHECK(scheduler_on_impl_thread_->CommitPending());
 
   if (!layer_tree_host_impl_) {
     TRACE_EVENT0("cc", "EarlyOut_NoLayerTree");
     completion->Signal();
 
     return;
   }
 
+  // We defer forced commits while there is a pending tree here.

[Sami, 2013/08/13 15:56:02]

Could this be done in the state machine instead? Seems like it has all the
necessary bits of information already.

[brianderson, 2013/09/07 01:18:54]

Hmm, I'll give that a try. I did it this way because I knew for sure that we
haven't affected state on the impl-thread at this point yet. Doing it in the
scheduler would allow us to defer the commit even later into the process.

+  if (layer_tree_host_impl_->pending_tree()) {
+    TRACE_EVENT0("cc", "EarlyOut_DeferringDueToPendingTree");
+    DCHECK(deferred_start_commit_on_impl_thread_.is_null());
+    deferred_start_commit_on_impl_thread_ =
+        base::Bind(&ThreadProxy::StartCommitOnImplThread,
+                   impl_thread_weak_ptr_,
+                   completion,
+                   raw_queue,
+                   offscreen_context_provider);
+    return;
+  }
+
   scoped_ptr<ResourceUpdateQueue> queue(raw_queue);
 
   if (offscreen_context_provider.get())
     offscreen_context_provider->BindToCurrentThread();
   layer_tree_host_impl_->resource_provider()->
       set_offscreen_context_provider(offscreen_context_provider);
 
   if (layer_tree_host_->contents_texture_manager()) {
     if (layer_tree_host_->contents_texture_manager()->
             LinkedEvictedBackingsExist()) {
@@ skipping 650 matching lines @@
     DCHECK(layer_tree_host_impl_->settings().impl_side_painting);
     completion_event_for_commit_held_on_tree_activation_->Signal();
     completion_event_for_commit_held_on_tree_activation_ = NULL;
   }
 
   commit_to_activate_duration_history_.InsertSample(
       base::TimeTicks::HighResNow() - commit_complete_time_);
 }
 
 }  // namespace cc