cc: Allow the main thread to cancel commits

cc/trees/thread_proxy.cc

Index: cc/trees/thread_proxy.cc
diff --git a/cc/trees/thread_proxy.cc b/cc/trees/thread_proxy.cc
index 3ea5f8813507c674afcfefb7eed7f1254264fb39..8cd2a48b6630898ab93192cf6c1c88e409f5efaa 100644
--- a/cc/trees/thread_proxy.cc
+++ b/cc/trees/thread_proxy.cc
@@ -90,6 +90,7 @@ ThreadProxy::ThreadProxy(
       using_synchronous_renderer_compositor_(
           layer_tree_host->settings().using_synchronous_renderer_compositor),
       inside_draw_(false),
+      can_cancel_commit_(false),
       defer_commits_(false),
       renew_tree_priority_on_impl_thread_pending_(false),
       draw_duration_history_(kDurationHistorySize),
@@ -128,10 +129,15 @@ bool ThreadProxy::CompositeAndReadback(void* pixels, gfx::Rect rect) {
                    &begin_frame_sent_to_main_thread_completion));
     begin_frame_sent_to_main_thread_completion.Wait();
   }
+
   in_composite_and_readback_ = true;
   BeginFrameOnMainThread(scoped_ptr<BeginFrameAndCommitState>());
   in_composite_and_readback_ = false;
 
+  // Composite and readback requires a second commit to undo any changes
+  // that it made.
+  can_cancel_commit_ = false;
+
   // Perform a synchronous readback.
   ReadbackRequest request;
   request.rect = rect;
@@ -301,6 +307,17 @@ void ThreadProxy::OnOutputSurfaceInitializeAttempted(
   }
 }
 
+void ThreadProxy::SendCommitRequestToImplThreadIfNeeded() {
+  DCHECK(IsMainThread());
+  if (commit_request_sent_to_impl_thread_)
+    return;
+  commit_request_sent_to_impl_thread_ = true;
+  Proxy::ImplThreadTaskRunner()->PostTask(
+      FROM_HERE,
+      base::Bind(&ThreadProxy::SetNeedsCommitOnImplThread,
+                 impl_thread_weak_ptr_));
+}
+
 const RendererCapabilities& ThreadProxy::GetRendererCapabilities() const {
   DCHECK(IsMainThread());
   DCHECK(!layer_tree_host_->output_surface_lost());
@@ -314,30 +331,26 @@ void ThreadProxy::SetNeedsAnimate() {
 
   TRACE_EVENT0("cc", "ThreadProxy::SetNeedsAnimate");
   animate_requested_ = true;
+  can_cancel_commit_ = false;
+  SendCommitRequestToImplThreadIfNeeded();
+}
 
-  if (commit_request_sent_to_impl_thread_)
-    return;
-  commit_request_sent_to_impl_thread_ = true;
-  Proxy::ImplThreadTaskRunner()->PostTask(
-      FROM_HERE,
-      base::Bind(&ThreadProxy::SetNeedsCommitOnImplThread,
-                 impl_thread_weak_ptr_));
+void ThreadProxy::SetNeedsUpdateLayers() {
+  DCHECK(IsMainThread());
+  SendCommitRequestToImplThreadIfNeeded();
 }
 
 void ThreadProxy::SetNeedsCommit() {
   DCHECK(IsMainThread());
+  // Unconditionally set here to handle SetNeedsCommit calls during a commit.
+  can_cancel_commit_ = false;
+
   if (commit_requested_)
     return;
   TRACE_EVENT0("cc", "ThreadProxy::SetNeedsCommit");
   commit_requested_ = true;
 
-  if (commit_request_sent_to_impl_thread_)
-    return;
-  commit_request_sent_to_impl_thread_ = true;
-  Proxy::ImplThreadTaskRunner()->PostTask(
-      FROM_HERE,
-      base::Bind(&ThreadProxy::SetNeedsCommitOnImplThread,
-                 impl_thread_weak_ptr_));
+  SendCommitRequestToImplThreadIfNeeded();
 }
 
 void ThreadProxy::DidLoseOutputSurfaceOnImplThread() {
@@ -688,10 +701,12 @@ void ThreadProxy::BeginFrameOnMainThread(
     commit_request_sent_to_impl_thread_ = false;
 
     TRACE_EVENT0("cc", "EarlyOut_NotVisible");
+    bool cancel_commit = false;
     Proxy::ImplThreadTaskRunner()->PostTask(
         FROM_HERE,
         base::Bind(&ThreadProxy::BeginFrameAbortedByMainThreadOnImplThread,
-                   impl_thread_weak_ptr_));
+                   impl_thread_weak_ptr_,
+                   cancel_commit));
     return;
   }
 
@@ -718,24 +733,44 @@ void ThreadProxy::BeginFrameOnMainThread(
   // UpdateLayers.
   commit_requested_ = false;
   commit_request_sent_to_impl_thread_ = false;
+  bool can_cancel_this_commit =
+      can_cancel_commit_ && !in_composite_and_readback_;
+  can_cancel_commit_ = true;
 
   scoped_ptr<ResourceUpdateQueue> queue =
       make_scoped_ptr(new ResourceUpdateQueue);
-  layer_tree_host_->UpdateLayers(
+  bool updated = layer_tree_host_->UpdateLayers(
       queue.get(),
-      begin_frame_state ?
-          begin_frame_state->memory_allocation_limit_bytes : 0u);
+      begin_frame_state ? begin_frame_state->memory_allocation_limit_bytes
+                        : 0u);
 
   // Once single buffered layers are committed, they cannot be modified until
   // they are drawn by the impl thread.
   textures_acquired_ = false;
 
   layer_tree_host_->WillCommit();
-  // Before applying scrolls and calling animate, we set animate_requested_ to
-  // false. If it is true now, it means SetNeedAnimate was called again, but
-  // during a state when commit_request_sent_to_impl_thread_ = true. We need to
-  // force that call to happen again now so that the commit request is sent to
-  // the impl thread.
+
+  if (!updated && can_cancel_this_commit) {
+    TRACE_EVENT0("cc", "EarlyOut_NoUpdates");
+    bool cancel_commit = true;
+    Proxy::ImplThreadTaskRunner()->PostTask(
+        FROM_HERE,
+        base::Bind(&ThreadProxy::BeginFrameAbortedByMainThreadOnImplThread,
+                   impl_thread_weak_ptr_,
+                   cancel_commit));
+
+    // Although the commit is internally aborted, this is because it has been
+    // detected to be a no-op.  From the perspective of an embedder, this commit
+    // went through, and input should no longer be throttled, etc.
+    layer_tree_host_->CommitComplete();

[enne (OOO), 2013/07/15 22:23:28]

After some thought, I also added this.  Since when input is sent to the main
thread, render_widget prevents more input from being sent until a commit
happens.  I think it's important that to the embedder it still appears that the
commit occurred here.

+    layer_tree_host_->DidBeginFrame();
+    return;
+  }
+
+  // Before calling animate, we set animate_requested_ to false. If it is true
+  // now, it means SetNeedAnimate was called again, but during a state when
+  // commit_request_sent_to_impl_thread_ = true. We need to force that call to
+  // happen again now so that the commit request is sent to the impl thread.
   if (animate_requested_) {
     // Forces SetNeedsAnimate to consider posting a commit task.
     animate_requested_ = false;
@@ -831,13 +866,17 @@ void ThreadProxy::StartCommitOnImplThread(
       scheduler_on_impl_thread_->AnticipatedDrawTime());
 }
 
-void ThreadProxy::BeginFrameAbortedByMainThreadOnImplThread() {
+void ThreadProxy::BeginFrameAbortedByMainThreadOnImplThread(
+    bool cancel_commit) {
   TRACE_EVENT0("cc", "ThreadProxy::BeginFrameAbortedByMainThreadOnImplThread");
   DCHECK(IsImplThread());
   DCHECK(scheduler_on_impl_thread_);
   DCHECK(scheduler_on_impl_thread_->CommitPending());
 
-  scheduler_on_impl_thread_->BeginFrameAbortedByMainThread();
+  // The scroll and scale set was applied by the main thread, so the active tree
+  // needs to be updated as if these sent values were applied and committed.
+  layer_tree_host_impl_->active_tree()->ApplySentScrollAndScaleDeltas();
+  scheduler_on_impl_thread_->BeginFrameAbortedByMainThread(cancel_commit);
 }
 
 void ThreadProxy::ScheduledActionCommit() {
@@ -1067,6 +1106,7 @@ void ThreadProxy::AcquireLayerTextures() {
   completion.Wait();
 
   textures_acquired_ = true;
+  can_cancel_commit_ = false;
 }
 
 void ThreadProxy::AcquireLayerTexturesForMainThreadOnImplThread(