cc: Simplify task and its derived classes.

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 <vector>
+
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "cc/base/cc_export.h"
+
+namespace cc {
+
+// A task with or without dependencies 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> {

[reveman, 2016/04/06 12:18:06]

dependencies should not be part of the task. it should be contained in the task
graph only.

[prashant.n, 2016/04/06 13:11:50]

Yes. I just checked, we are already keeping that information in edges. :).
Thanks for this point.

+ public:
+  typedef std::vector<scoped_refptr<Task>> Vector;
+
+  const Task::Vector& dependencies() const { return dependencies_; }
+
+  // Subclasses should implement these methods. ScheduleOnOriginThread() and
+  // CompleteOnOriginThread() must be called on origin thread and
+  // RunOnWorkerThread() may be called on any thread (origin or worker). The
+  // subclasses are responsible for locking and thread safety.
+  virtual void ScheduleOnOriginThread() = 0;
+  virtual void CompleteOnOriginThread() = 0;

[reveman, 2016/04/06 12:18:06]

Schedule/Complete should not be part of the task class. These need to be removed
from the task classes that you're trying to unify before we can do this.

[prashant.n, 2016/04/06 13:11:50]

Do you mean to say, having this only in dervied classes
RasterTaskImpl/ImageDecodeTaskImpl?

One way I can think of implementing this is Having functionality of schedule and
complete in ctor and dtor.

But as per below line
https://code.google.com/p/chromium/codesearch#chromium/src/cc/raster/tile_tas...

We would need to check how we can avoid
AcquireBufferForRaster/ReleaseBufferForRaster, when task is already scheduled.

Do let me know your opinion?

+  virtual void RunOnWorkerThread() = 0;
+
+  void WillSchedule();
+  void DidSchedule();
+  bool HasBeenScheduled() const;
+
+  void WillComplete();
+  void DidComplete();
+  bool HasCompleted() const;
+
+  void WillRun();
+  void DidRun();
+  bool HasFinishedRunning() const;
+
+ protected:
+  friend class base::RefCountedThreadSafe<Task>;
+
+  // For creating task without dependencies.
+  Task();
+  // For creating task with dependencies.
+  explicit Task(Task::Vector* dependencies);
+  virtual ~Task();
+
+  bool did_schedule_;
+  bool did_complete_;
+  bool will_run_;
+  bool did_run_;
+
+  Task::Vector dependencies_;
+};
+
+}  // namespace cc
+
+#endif  // CC_RASTER_TASK_H_