Index: cc/scheduler/scheduler_state_machine.cc |
diff --git a/cc/scheduler/scheduler_state_machine.cc b/cc/scheduler/scheduler_state_machine.cc |
index 2fbeca2d8a992d87cd118a09a78eeb5db8b61d3b..fae4b72b3288fe5c0758f7fee539e73c70acf3d5 100644 |
--- a/cc/scheduler/scheduler_state_machine.cc |
+++ b/cc/scheduler/scheduler_state_machine.cc |
@@ -402,6 +402,19 @@ bool SchedulerStateMachine::CouldSendBeginMainFrame() const { |
return true; |
} |
+bool SchedulerStateMachine::SendingBeginMainFrameMightCauseDeadlock() const { |
+ // NPAPI is the only case where the UI thread makes synchronous calls to the |
+ // Renderer main thread. During that synchronous call, we may not get a |
+ // SwapAck for the UI thread, which may prevent BeginMainFrame's from |
+ // completing if there's enough back pressure. If the BeginMainFrame can't |
+ // make progress, the Renderer can't service the UI thread's synchronous call |
+ // and we have deadlock. |
+ // This returns true if there's too much backpressure to finish a commit |
+ // if we were to initiate a BeginMainFrame. |
+ return has_pending_tree_ && active_tree_needs_first_draw_ && |
+ pending_swaps_ >= max_pending_swaps_; |
+} |
+ |
bool SchedulerStateMachine::ShouldSendBeginMainFrame() const { |
if (!CouldSendBeginMainFrame()) |
return false; |
@@ -411,6 +424,9 @@ bool SchedulerStateMachine::ShouldSendBeginMainFrame() const { |
return false; |
// Only send BeginMainFrame when there isn't another commit pending already. |
+ // Other parts of the state machine indirectly defer the BeginMainFrame |
+ // by transitioning to WAITING commit states rather than going |
+ // immediately to IDLE. |
if (commit_state_ != COMMIT_STATE_IDLE) |
return false; |
@@ -432,6 +448,9 @@ bool SchedulerStateMachine::ShouldSendBeginMainFrame() const { |
// We need a new commit for the forced redraw. This honors the |
// single commit per interval because the result will be swapped to screen. |
+ // TODO(brianderson): Remove this or move it below the |
+ // SendingBeginMainFrameMightCauseDeadlock check since we want to avoid |
+ // ever returning true from this method if we might cause deadlock. |
if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_COMMIT) |
return true; |
@@ -439,14 +458,22 @@ bool SchedulerStateMachine::ShouldSendBeginMainFrame() const { |
if (!HasInitializedOutputSurface()) |
return false; |
- // SwapAck throttle the BeginMainFrames unless we just swapped. |
- // TODO(brianderson): Remove this restriction to improve throughput. |
- bool just_swapped_in_deadline = |
- begin_impl_frame_state_ == BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE && |
- did_perform_swap_in_last_draw_; |
- if (pending_swaps_ >= max_pending_swaps_ && !just_swapped_in_deadline) |
+ // Make sure the BeginMainFrame can finish eventually if we start it. |
+ if (SendingBeginMainFrameMightCauseDeadlock()) |
return false; |
+ if (!settings_.main_frame_while_swap_throttled_enabled) { |
+ // SwapAck throttle the BeginMainFrames unless we just swapped to |
+ // potentially improve impl-thread latency over main-thread throughput. |
+ // TODO(brianderson): Remove this restriction to improve throughput or |
+ // make it conditional on impl_latency_takes_priority_. |
+ bool just_swapped_in_deadline = |
+ begin_impl_frame_state_ == BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE && |
+ did_perform_swap_in_last_draw_; |
+ if (pending_swaps_ >= max_pending_swaps_ && !just_swapped_in_deadline) |
+ return false; |
+ } |
+ |
if (skip_begin_main_frame_to_reduce_latency_) |
return false; |
@@ -463,11 +490,14 @@ bool SchedulerStateMachine::ShouldCommit() const { |
return false; |
} |
- // Prioritize drawing the previous commit before finishing the next commit. |
- if (active_tree_needs_first_draw_) |
- return false; |
+ // If impl-side-painting, commit to the pending tree as soon as we can. |
+ if (settings_.impl_side_painting) |
+ return true; |
- return true; |
+ // If we only have an active tree, it is incorrect to replace it |
+ // before we've drawn it when we aren't impl-side-painting. |
+ DCHECK(!settings_.impl_side_painting); |
+ return !active_tree_needs_first_draw_; |
} |
bool SchedulerStateMachine::ShouldPrepareTiles() const { |