Modify ScreenCaptureFrameQueue into a template

webrtc/modules/desktop_capture/screen_capture_queue.h

Index: webrtc/modules/desktop_capture/screen_capture_queue.h
diff --git a/webrtc/modules/desktop_capture/screen_capture_queue.h b/webrtc/modules/desktop_capture/screen_capture_queue.h
new file mode 100644
index 0000000000000000000000000000000000000000..d108ec0574e50e44635d7d32b4dfe10925f193a0
--- /dev/null
+++ b/webrtc/modules/desktop_capture/screen_capture_queue.h
@@ -0,0 +1,81 @@
+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_CAPTURE_QUEUE_H_
+#define WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_CAPTURE_QUEUE_H_
+
+#include <memory>
+
+#include "webrtc/base/constructormagic.h"
+
+namespace webrtc {
+
+// Represents a queue of reusable resources. Provides access to the 'current'

[Sergey Ulanov, 2016/04/20 21:22:34]

we use it for a queue of frames, so it should be clear from the comment

[Hzj_jie, 2016/04/20 23:56:15]

Done.

+// instance - the instance that the caller is working with at the moment, and to
+// the 'previous' instance - the predecessor of the current instance swapped by
+// MoveToNext() call, if any.
+//
+// The caller is expected to (re)allocate content if current() returns nullptr.
+// The caller can mark all frames in the queue for reallocation (when, say,
+// frame dimensions change). The queue records which instance need updating
+// which the caller can query.
+//
+// Content consumer is expected to never hold more than kQueueLength instances
+// created by this function and it should release the earliest one before trying
+// to capture a new frame (i.e. before MoveToNext() is called).
+//
+// This class is not thread-safe.
+template <typename T>

[Sergey Ulanov, 2016/04/20 21:22:34]

s/T/FrameType/

[Hzj_jie, 2016/04/21 18:44:54]

Done.

+class ScreenCaptureQueue {

[Sergey Ulanov, 2016/04/20 21:22:34]

Do we need to rename this class? In the DX capturer it will still be used to
store queue of frames.

[Hzj_jie, 2016/04/20 23:56:15]

I thought this is the main point we need this change, i.e. we are moving from a
frame queue into a common queue, so MoveToNextFrame needs to be changed into
MoveToNext. Is my understanding correctly?

[Sergey Ulanov, 2016/04/21 17:16:17]

We need this change to allow types other than DesktopFrame to be stored in the
queue. The Surface class that you adding for the new capturer is used to
represent a frame. So this is still a queue of frames.

[Hzj_jie, 2016/04/21 18:44:54]

Done.

+ public:
+  ScreenCaptureQueue() : current_(0) {}
+  virtual ~ScreenCaptureQueue() = default;
+
+  // Marks all instances obsolete and resets the previous instance pointer.
+  void Reset() {
+    for (int i = 0; i < kQueueLength; i++) {
+      frames_[i].reset();
+    }
+    current_ = 0;
+  }
+
+  // Moves to the next instance in the queue, moving the 'current' instance to
+  // become the 'previous' one.
+  void MoveToNext() {
+    current_ = (current_ + 1) % kQueueLength;
+  }
+
+  // Replaces the current instance with a new one allocated by the caller. The
+  // existing instance (if any) is destroyed. Takes ownership of |instance|.
+  void ReplaceCurrent(std::unique_ptr<T>&& instance) {
+    frames_[current_].reset(instance.release());
+  }
+
+  T* current() const {
+    return frames_[current_].get();
+  }
+
+  T* previous() const {
+    return frames_[(current_ + kQueueLength - 1) % kQueueLength].get();
+  }
+
+ private:
+  // Index of the current frame.
+  int current_;
+
+  static const int kQueueLength = 2;
+  std::unique_ptr<T> frames_[kQueueLength];
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(ScreenCaptureQueue);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_CAPTURE_QUEUE_H_