Reland - Refactor signaling in RWP

cc/raster/task_graph_work_queue.cc

Index: cc/raster/task_graph_work_queue.cc
diff --git a/cc/raster/task_graph_work_queue.cc b/cc/raster/task_graph_work_queue.cc
index 29474023c6539a17ab44c9cc8b0b0d67645dd635..da85c774ad2a827ad0a8db75e26eafea93434ac1 100644
--- a/cc/raster/task_graph_work_queue.cc
+++ b/cc/raster/task_graph_work_queue.cc
@@ -97,9 +97,12 @@ void TaskGraphWorkQueue::ScheduleTasks(NamespaceToken token, TaskGraph* graph) {
       continue;
 
     // Skip if already running.
-    if (std::find(task_namespace.running_tasks.begin(),
-                  task_namespace.running_tasks.end(),
-                  node.task) != task_namespace.running_tasks.end())
+    const auto& running_tasks_for_category =
+        task_namespace.running_tasks.find(node.category);
+    if (running_tasks_for_category != task_namespace.running_tasks.cend() &&
+        std::find(running_tasks_for_category->second.cbegin(),
+                  running_tasks_for_category->second.cend(),
+                  node.task) != running_tasks_for_category->second.cend())
       continue;
 
     task_namespace.ready_to_run_tasks[node.category].push_back(PrioritizedTask(
@@ -127,9 +130,12 @@ void TaskGraphWorkQueue::ScheduleTasks(NamespaceToken token, TaskGraph* graph) {
       continue;
 
     // Skip if already running.
-    if (std::find(task_namespace.running_tasks.begin(),
-                  task_namespace.running_tasks.end(),
-                  node.task) != task_namespace.running_tasks.end())
+    const auto& running_tasks_for_category =
+        task_namespace.running_tasks.find(node.category);
+    if (running_tasks_for_category != task_namespace.running_tasks.cend() &&
+        std::find(running_tasks_for_category->second.cbegin(),
+                  running_tasks_for_category->second.cend(),
+                  node.task) != running_tasks_for_category->second.cend())
       continue;
 
     DCHECK(std::find(task_namespace.completed_tasks.begin(),
@@ -195,7 +201,7 @@ TaskGraphWorkQueue::PrioritizedTask TaskGraphWorkQueue::GetNextTaskToRun(
   }
 
   // Add task to |running_tasks|.
-  task_namespace->running_tasks.push_back(task.task);
+  task_namespace->running_tasks[category].push_back(task.task);
 
   return task;
 }
@@ -203,13 +209,19 @@ TaskGraphWorkQueue::PrioritizedTask TaskGraphWorkQueue::GetNextTaskToRun(
 void TaskGraphWorkQueue::CompleteTask(const PrioritizedTask& completed_task) {
   TaskNamespace* task_namespace = completed_task.task_namespace;
   scoped_refptr<Task> task(completed_task.task);
+  uint16_t category = completed_task.category;
 
   // Remove task from |running_tasks|.
-  auto it = std::find(task_namespace->running_tasks.begin(),
-                      task_namespace->running_tasks.end(), task);
-  DCHECK(it != task_namespace->running_tasks.end());
-  std::swap(*it, task_namespace->running_tasks.back());
-  task_namespace->running_tasks.pop_back();
+  auto& running_tasks_for_category = task_namespace->running_tasks[category];
+  auto it = std::find(running_tasks_for_category.begin(),
+                      running_tasks_for_category.end(), task);
+  DCHECK(it != running_tasks_for_category.end());
+  std::swap(*it, running_tasks_for_category.back());
+  running_tasks_for_category.pop_back();
+
+  // If |running_tasks_for_category| is empty, remove it from |running_tasks|.

[reveman, 2016/02/10 20:49:32]

Is this necessary? Doesn't it cause some heap allocations that it would be
better to avoid?

[ericrk, 2016/02/10 22:30:04]

I guess it's a trade-off - we either do this here or do more iteration later to
ensure all categories are emtpy.. Switching this, as I guess the heap allocation
is worse than the quick read-only scan of the list.

+  if (running_tasks_for_category.size() == 0)
+    task_namespace->running_tasks.erase(category);
 
   // Now iterate over all dependents to decrement dependencies and check if they
   // are ready to run.