aw: Do not cancel fallback tick on pipeline stall

This can cause a live lock if pipeline is stalled waiting for the
fallback tick. However we cannot skip invalidate to avoid drawing a bad
frame.

BUG=420702

Review URL: https://codereview.chromium.org/630953003

Cr-Commit-Position: refs/heads/master@{#298369}

2 files changed, 31 insertions, 12 deletions

diff --git a/android_webview/browser/browser_view_renderer.cc b/android_webview/browser/browser_view_renderer.cc
index 505919d..50fe66c 100644
--- a/android_webview/browser/browser_view_renderer.cc
+++ b/android_webview/browser/browser_view_renderer.cc
@@ -119,6 +119,7 @@ BrowserViewRenderer::BrowserViewRenderer(
       clear_view_(false),
       compositor_needs_continuous_invalidate_(false),
       block_invalidates_(false),
+      fallback_tick_pending_(false),
       width_(0),
       height_(0) {
   CHECK(web_contents_);
@@ -265,8 +266,7 @@ bool BrowserViewRenderer::OnDrawHardware(jobject java_canvas) {
     TRACE_EVENT_INSTANT0("android_webview",
                          "EarlyOut_PreviousFrameUnconsumed",
                          TRACE_EVENT_SCOPE_THREAD);
-    // TODO(boliu): Rename this method. We didn't actually composite here.
-    DidComposite();
+    SkippedCompositeInDraw();
     return client_->RequestDrawGL(java_canvas, false);
   }
 
@@ -316,7 +316,7 @@ void BrowserViewRenderer::UpdateParentDrawConstraints() {
       !parent_draw_constraints_.Equals(
         shared_renderer_state_->ParentDrawConstraints())) {
     shared_renderer_state_->SetForceInvalidateOnNextDrawGL(false);
-    EnsureContinuousInvalidation(true);
+    EnsureContinuousInvalidation(true, false);
   }
 }
 
@@ -398,7 +398,7 @@ void BrowserViewRenderer::ClearView() {
 
   clear_view_ = true;
   // Always invalidate ignoring the compositor to actually clear the webview.
-  EnsureContinuousInvalidation(true);
+  EnsureContinuousInvalidation(true, false);
 }
 
 void BrowserViewRenderer::SetIsPaused(bool paused) {
@@ -408,7 +408,7 @@ void BrowserViewRenderer::SetIsPaused(bool paused) {
                        "paused",
                        paused);
   is_paused_ = paused;
-  EnsureContinuousInvalidation(false);
+  EnsureContinuousInvalidation(false, false);
 }
 
 void BrowserViewRenderer::SetViewVisibility(bool view_visible) {
@@ -427,7 +427,7 @@ void BrowserViewRenderer::SetWindowVisibility(bool window_visible) {
                        "window_visible",
                        window_visible);
   window_visible_ = window_visible;
-  EnsureContinuousInvalidation(false);
+  EnsureContinuousInvalidation(false, false);
 }
 
 void BrowserViewRenderer::OnSizeChanged(int width, int height) {
@@ -512,7 +512,7 @@ void BrowserViewRenderer::SetContinuousInvalidate(bool invalidate) {
                        invalidate);
   compositor_needs_continuous_invalidate_ = invalidate;
 
-  EnsureContinuousInvalidation(false);
+  EnsureContinuousInvalidation(false, false);
 }
 
 void BrowserViewRenderer::SetDipScale(float dip_scale) {
@@ -678,7 +678,9 @@ void BrowserViewRenderer::DidOverscroll(gfx::Vector2dF accumulated_overscroll,
   client_->DidOverscroll(rounded_overscroll_delta);
 }
 
-void BrowserViewRenderer::EnsureContinuousInvalidation(bool force_invalidate) {
+void BrowserViewRenderer::EnsureContinuousInvalidation(
+    bool force_invalidate,
+    bool skip_reschedule_tick) {
   // This method should be called again when any of these conditions change.
   bool need_invalidate =
       compositor_needs_continuous_invalidate_ || force_invalidate;
@@ -701,18 +703,23 @@ void BrowserViewRenderer::EnsureContinuousInvalidation(bool force_invalidate) {
     return;
 
   block_invalidates_ = compositor_needs_continuous_invalidate_;
+  if (skip_reschedule_tick && fallback_tick_pending_)
+    return;
 
   // Unretained here is safe because the callbacks are cancelled when
   // they are destroyed.
   post_fallback_tick_.Reset(base::Bind(&BrowserViewRenderer::PostFallbackTick,
                                        base::Unretained(this)));
   fallback_tick_fired_.Cancel();
+  fallback_tick_pending_ = false;
 
   // No need to reschedule fallback tick if compositor does not need to be
   // ticked. This can happen if this is reached because force_invalidate is
   // true.
-  if (compositor_needs_continuous_invalidate_)
+  if (compositor_needs_continuous_invalidate_) {
+    fallback_tick_pending_ = true;
     ui_task_runner_->PostTask(FROM_HERE, post_fallback_tick_.callback());
+  }
 }
 
 void BrowserViewRenderer::PostFallbackTick() {
@@ -739,6 +746,7 @@ void BrowserViewRenderer::FallbackTickFired() {
   // This should only be called if OnDraw or DrawGL did not come in time, which
   // means block_invalidates_ must still be true.
   DCHECK(block_invalidates_);
+  fallback_tick_pending_ = false;
   if (compositor_needs_continuous_invalidate_ && compositor_) {
     ForceFakeCompositeSW();
   } else {
@@ -768,7 +776,13 @@ void BrowserViewRenderer::DidComposite() {
   block_invalidates_ = false;
   post_fallback_tick_.Cancel();
   fallback_tick_fired_.Cancel();
-  EnsureContinuousInvalidation(false);
+  fallback_tick_pending_ = false;
+  EnsureContinuousInvalidation(false, false);
+}
+
+void BrowserViewRenderer::SkippedCompositeInDraw() {
+  block_invalidates_ = false;
+  EnsureContinuousInvalidation(false, true);
 }
 
 std::string BrowserViewRenderer::ToString(AwDrawGLInfo* draw_info) const {
diff --git a/android_webview/browser/browser_view_renderer.h b/android_webview/browser/browser_view_renderer.h
index 717225e..31d952e 100644
--- a/android_webview/browser/browser_view_renderer.h
+++ b/android_webview/browser/browser_view_renderer.h
@@ -149,11 +149,15 @@ class BrowserViewRenderer : public content::SynchronousCompositorClient,
   void SetTotalRootLayerScrollOffset(gfx::Vector2dF new_value_dip);
   // Checks the continuous invalidate and block invalidate state, and schedule
   // invalidates appropriately. If |force_invalidate| is true, then send a view
-  // invalidate regardless of compositor expectation.
-  void EnsureContinuousInvalidation(bool force_invalidate);
+  // invalidate regardless of compositor expectation. If |skip_reschedule_tick|
+  // is true and if there is already a pending fallback tick, don't reschedule
+  // them.
+  void EnsureContinuousInvalidation(bool force_invalidate,
+                                    bool skip_reschedule_tick);
   bool OnDrawSoftware(jobject java_canvas);
   bool CompositeSW(SkCanvas* canvas);
   void DidComposite();
+  void SkippedCompositeInDraw();
   scoped_ptr<base::Value> RootLayerStateAsValue(
       const gfx::Vector2dF& total_scroll_offset_dip,
       const gfx::SizeF& scrollable_size_dip);
@@ -219,6 +223,7 @@ class BrowserViewRenderer : public content::SynchronousCompositorClient,
 
   base::CancelableClosure post_fallback_tick_;
   base::CancelableClosure fallback_tick_fired_;
+  bool fallback_tick_pending_;
 
   int width_;
   int height_;