cc: Make eviction queue building consistent with raster.

cc/resources/tile_manager.cc

Index: cc/resources/tile_manager.cc
diff --git a/cc/resources/tile_manager.cc b/cc/resources/tile_manager.cc
index 81ae8b5c9ee656486454580dacd4e726a8c1a9c7..f0c8895a70f3141f790ff224864a58289df83bf1 100644
--- a/cc/resources/tile_manager.cc
+++ b/cc/resources/tile_manager.cc
@@ -240,7 +240,6 @@ TileManager::TileManager(
           task_runner_.get(),
           base::Bind(&TileManager::CheckIfMoreTilesNeedToBePrepared,
                      base::Unretained(this))),
-      eviction_priority_queue_is_up_to_date_(false),
       did_notify_ready_to_activate_(false),
       did_notify_ready_to_draw_(false) {
   tile_task_runner_->SetClient(this);
@@ -374,15 +373,12 @@ void TileManager::PrepareTiles(
     did_notify_ready_to_draw_ = false;
   } else {
     if (global_state_.hard_memory_limit_in_bytes == 0) {
-      // TODO(vmpstr): Add a function to unconditionally create an eviction
-      // queue and guard the rest of the calls sites with this flag, instead of
-      // clearing here and building, which is a bit awkward.
-      eviction_priority_queue_is_up_to_date_ = false;
       resource_pool_->CheckBusyResources(false);
       MemoryUsage memory_limit(0, 0);
       MemoryUsage memory_usage(resource_pool_->acquired_memory_usage_bytes(),
                                resource_pool_->acquired_resource_count());
       FreeTileResourcesUntilUsageIsWithinLimit(memory_limit, &memory_usage);
+      eviction_priority_queue_.reset();
     }
 
     did_notify_ready_to_activate_ = false;
@@ -493,17 +489,12 @@ void TileManager::BasicStateAsValueInto(base::debug::TracedValue* state) const {
 }
 
 void TileManager::RebuildEvictionQueueIfNeeded() {
-  TRACE_EVENT1("cc",
-               "TileManager::RebuildEvictionQueueIfNeeded",
-               "eviction_priority_queue_is_up_to_date",
-               eviction_priority_queue_is_up_to_date_);
-  if (eviction_priority_queue_is_up_to_date_)
+  TRACE_EVENT0("cc", "TileManager::RebuildEvictionQueueIfNeeded");
+  if (eviction_priority_queue_)
     return;
 
-  eviction_priority_queue_.Reset();
-  client_->BuildEvictionQueue(&eviction_priority_queue_,
-                              global_state_.tree_priority);
-  eviction_priority_queue_is_up_to_date_ = true;
+  eviction_priority_queue_ =
+      client_->BuildEvictionQueue(global_state_.tree_priority);
 }
 
 bool TileManager::FreeTileResourcesUntilUsageIsWithinLimit(
@@ -511,13 +502,13 @@ bool TileManager::FreeTileResourcesUntilUsageIsWithinLimit(
     MemoryUsage* usage) {
   while (usage->Exceeds(limit)) {
     RebuildEvictionQueueIfNeeded();
-    if (eviction_priority_queue_.IsEmpty())
+    if (eviction_priority_queue_->IsEmpty())
       return false;
 
-    Tile* tile = eviction_priority_queue_.Top();
+    Tile* tile = eviction_priority_queue_->Top();
     *usage -= MemoryUsage::FromTile(tile);
     FreeResourcesForTileAndNotifyClientIfTileWasReadyToDraw(tile);
-    eviction_priority_queue_.Pop();
+    eviction_priority_queue_->Pop();
   }
   return true;
 }
@@ -528,16 +519,16 @@ bool TileManager::FreeTileResourcesWithLowerPriorityUntilUsageIsWithinLimit(
     MemoryUsage* usage) {
   while (usage->Exceeds(limit)) {
     RebuildEvictionQueueIfNeeded();
-    if (eviction_priority_queue_.IsEmpty())
+    if (eviction_priority_queue_->IsEmpty())
       return false;
 
-    Tile* tile = eviction_priority_queue_.Top();
+    Tile* tile = eviction_priority_queue_->Top();
     if (!other_priority.IsHigherPriorityThan(tile->combined_priority()))
       return false;
 
     *usage -= MemoryUsage::FromTile(tile);
     FreeResourcesForTileAndNotifyClientIfTileWasReadyToDraw(tile);
-    eviction_priority_queue_.Pop();
+    eviction_priority_queue_->Pop();
   }
   return true;
 }
@@ -584,7 +575,7 @@ void TileManager::AssignGpuMemoryToTiles(
   MemoryUsage memory_usage(resource_pool_->acquired_memory_usage_bytes(),
                            resource_pool_->acquired_resource_count());
 
-  eviction_priority_queue_is_up_to_date_ = false;
+  DCHECK(!eviction_priority_queue_);
   for (; !raster_priority_queue->IsEmpty(); raster_priority_queue->Pop()) {
     Tile* tile = raster_priority_queue->Top();
     TilePriority priority = tile->combined_priority();
@@ -649,6 +640,8 @@ void TileManager::AssignGpuMemoryToTiles(
   // as possible to stay within the memory limit.
   FreeTileResourcesUntilUsageIsWithinLimit(hard_memory_limit, &memory_usage);
 
+  eviction_priority_queue_.reset();

[danakj, 2015/01/22 23:12:23]

Can you explain this? There's a DCHECK above that it's null. What in between
will make a queue?

[vmpstr, 2015/01/22 23:45:03]

Since creating an eviction queue might be expensive, we only create it if we
need it in FreeTileResources* function call. Since that eviction queue becomes
stale at the end of this call, I reset it so in the future we know to create a
new one (and that's what the DCHECK is checking). I've added a comment similar
to this. Please see if it's more clear.

I could also basically replace each call of
"eviction_priority_queue_is_up_to_date_" to eviction_priority_queue_.reset() if
that's cleaner. I kind of decided to do it after, instead of before the loop but
it shouldn't matter in practice.

+
   UMA_HISTOGRAM_BOOLEAN("TileManager.ExceededMemoryBudget",
                         !had_enough_memory_to_schedule_tiles_needed_now);
   did_oom_on_last_assign_ = !had_enough_memory_to_schedule_tiles_needed_now;