cc: Simplify Task and its derived classes.

cc/raster/task.h

+// Copyright 2016 The Chromium Authors. All rights reserved.

[reveman, 2016/04/19 05:02:16]

nit: maybe it makes more sense for this file to be named task_graph.h but either
is fine with me

[prashant.n, 2016/04/19 05:28:07]

I too was in dilemma which name to be chosen, but then thought having simple
name - task.h, so that we can have tile_task.h for derived category.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CC_RASTER_TASK_H_
+#define CC_RASTER_TASK_H_
+
+#include <stdint.h>
+
+#include <vector>
+
+#include "base/memory/ref_counted.h"
+#include "cc/base/cc_export.h"
+
+namespace cc {
+
+// A task which can be run by a TaskGraphRunner. To run a Task, it should be
+// inserted into a TaskGraph, which can then be scheduled on the
+// TaskGraphRunner.
+class CC_EXPORT Task : public base::RefCountedThreadSafe<Task> {
+ public:
+  typedef std::vector<scoped_refptr<Task>> Vector;
+
+  // Subclasses should implement this method. RunOnWorkerThread may be called
+  // on any thread, and subclasses are responsible for locking and thread
+  // safety.
+  virtual void RunOnWorkerThread() = 0;
+
+  void WillRun();
+  void DidRun();
+  bool HasFinishedRunning() const;
+
+ protected:
+  friend class base::RefCountedThreadSafe<Task>;
+
+  Task();
+  virtual ~Task();
+
+  bool will_run_;
+  bool did_run_;
+};
+
+// A task dependency graph describes the order in which to execute a set
+// of tasks. Dependencies are represented as edges. Each node is assigned
+// a category, a priority and a run count that matches the number of
+// dependencies. Priority range from 0 (most favorable scheduling) to UINT16_MAX
+// (least favorable). Categories range from 0 to UINT16_MAX. It is up to the
+// implementation and its consumer to determine the meaning (if any) of a
+// category. A TaskGraphRunner implementation may chose to prioritize certain
+// categories over others, regardless of the individual priorities of tasks.
+struct CC_EXPORT TaskGraph {
+  struct Node {
+    typedef std::vector<Node> Vector;
+
+    Node(Task* task,
+         uint16_t category,
+         uint16_t priority,
+         uint32_t dependencies)
+        : task(task),
+          category(category),
+          priority(priority),
+          dependencies(dependencies) {}
+
+    Task* task;
+    uint16_t category;
+    uint16_t priority;
+    uint32_t dependencies;
+  };
+
+  struct Edge {
+    typedef std::vector<Edge> Vector;
+
+    Edge(const Task* task, Task* dependent)
+        : task(task), dependent(dependent) {}
+
+    const Task* task;
+    Task* dependent;
+  };
+
+  TaskGraph();
+  TaskGraph(const TaskGraph& other);
+  ~TaskGraph();
+
+  void Swap(TaskGraph* other);
+  void Reset();
+
+  Node::Vector nodes;
+  Edge::Vector edges;
+};
+
+}  // namespace cc
+
+#endif  // CC_RASTER_TASK_H_