cc: Implement states for Task for stricter control.

cc/raster/task.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // 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 {
+class Task;
+
+// States to manage life cycle of a task. Task gets created with NEW state and
+// concludes either in FINISHED or CANCELLED state. So possible life cycle
+// paths for task are -
+//   NEW -> SCHEDULED -> RUNNING -> FINISHED
+//   NEW -> SCHEDULED -> CANCELED
+class CC_EXPORT TaskState {
+ public:
+  bool IsScheduled() const;
+  bool IsRunning() const;
+  bool IsFinished() const;
+  bool IsCanceled() const;
+
+  // Functions to change the state of task. These functions should be called
+  // only from TaskGraphWorkQueue where the life cycle of a task is decided or
+  // from tests. These functions are not thread-safe. Caller is responsible for
+  // thread safety.
+  void Reset();  // Sets state to NEW.
+  void DidSchedule();
+  void DidStart();
+  void DidFinish();
+  void DidCancel();
+
+ private:
+  friend class Task;
+
+  // Let only Task class create the TaskState.
+  TaskState();
+  ~TaskState();
+
+  enum { NEW, SCHEDULED, RUNNING, FINISHED, CANCELED } value_;

[ericrk, 2016/04/21 18:24:25]

please use an "enum class" for extra safety.

[prashant.n, 2016/04/22 03:57:56]

I thought using simple enum as it is private.

I'll add class.

+};
 
 // 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;
 
+  TaskState& state() { return state_; }
+
   // 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_;
+ private:
+  TaskState state_;
 };
 
 // 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.
@@ skipping 33 matching lines @@
   void Swap(TaskGraph* other);
   void Reset();
 
   Node::Vector nodes;
   Edge::Vector edges;
 };
 
 }  // namespace cc
 
 #endif  // CC_RASTER_TASK_H_