Reland - Refactor signaling in RWP

cc/raster/task_graph_work_queue.h

Index: cc/raster/task_graph_work_queue.h
diff --git a/cc/raster/task_graph_work_queue.h b/cc/raster/task_graph_work_queue.h
index 95d3c772c24f22ea478757e2d1a81d40ab231b9e..4089d152bd381ff5ee4eed224258339243a2de17 100644
--- a/cc/raster/task_graph_work_queue.h
+++ b/cc/raster/task_graph_work_queue.h
@@ -145,6 +145,22 @@ class CC_EXPORT TaskGraphWorkQueue {
     return ready_to_run_namespaces_;
   }
 
+  uint32_t NumRunningTasks() const {

[reveman, 2016/02/08 19:10:21]

Do we need both of these functions or is the one below sufficient?

[ericrk, 2016/02/10 18:44:49]

Not really - we can drop this one for now.

+    uint32_t count = 0;
+    for (const auto& running_task_count_entry : running_task_count_) {
+      count += running_task_count_entry.second;
+    }
+    return count;
+  }
+
+  uint32_t NumRunningTasksForCategory(uint16_t category) const {
+    auto found = running_task_count_.find(category);
+    if (found != running_task_count_.end()) {
+      return found->second;
+    }
+    return 0;
+  }
+
   // Helper function which ensures that graph dependencies were correctly
   // configured.
   static bool DependencyMismatch(const TaskGraph* graph);
@@ -167,6 +183,11 @@ class CC_EXPORT TaskGraphWorkQueue {
   // Map from category to a vector of ready to run namespaces for that category.
   std::map<uint16_t, TaskNamespace::Vector> ready_to_run_namespaces_;
 
+  // Helper variable tracking the number of running tasks in each category. We
+  // could calculate this from data in namespaces_, but it would be less
+  // efficient.
+  std::map<uint16_t, uint32_t> running_task_count_;

[reveman, 2016/02/08 19:10:21]

I'd prefer if we minimized state and looped over all namespaces to compute this.
We only have one namespace in the most common case. It also seems consistent
with TaskNamespace::ready_to_run_tasks to also have ::running_tasks be a map.
Wdyt?

[ericrk, 2016/02/10 18:44:49]

Sure, went back and forth on this - can make this change.

+
   // Provides a unique id to each NamespaceToken.
   int next_namespace_id_;
 };