Motown: Remove LPCM optimizations, fix prepare, add flush, add ActiveMultistreamSink model/stage

services/media/framework/refs.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 SERVICES_MEDIA_FRAMEWORK_REFS_H_
+#define SERVICES_MEDIA_FRAMEWORK_REFS_H_
+
+#include <stdint.h>
+
+namespace mojo {
+namespace media {
+
+class Graph;
+class Stage;
+class Input;
+class Output;
+class Engine;
+class InputRef;
+class OutputRef;
+
+// Opaque Stage pointer used for graph building.
+class PartRef {
+ public:
+  PartRef() : stage_(nullptr) {}
+
+  size_t input_count() const;
+  InputRef input(size_t index) const;
+  InputRef input() const;
+  size_t output_count() const;
+  OutputRef output(size_t index) const;
+  OutputRef output() const;
+
+ private:
+  explicit PartRef(Stage* stage) : stage_(stage) {}
+
+  explicit operator bool() const { return stage_ != nullptr; }
+
+  bool valid() const { return stage_ != nullptr; }

[johngro, 2016/02/08 22:33:36]

why make valid() (and its operator bool form) private?  Also, to ensure
consistency, why not just make the operator call valid()?

[dalesat, 2016/02/09 00:34:11]

The operator should be public...did that.

I don't want to make them call each other in case one or the other is modified
somehow. This would be clearer with some docs...adding.

+
+  Stage* stage_;
+
+  friend Graph;
+  friend InputRef;
+  friend OutputRef;
+  friend Engine;
+};
+
+// Opaque Input pointer used for graph building.
+class InputRef {
+ public:
+  InputRef() : stage_(nullptr), index_(0) {}
+
+  InputRef& operator=(std::nullptr_t) {
+    stage_ = nullptr;
+    index_ = 0;
+    return *this;
+  }
+
+  explicit operator bool() const { return stage_ != nullptr; }

[johngro, 2016/02/08 22:33:36]

Note; everything here applies to OutputRef as well.

re: consistency point made above.  Why does the bool operator not do the same
thing as valid() (valid checks both the pointer and the validity of the stage
index)?  Also, why is the operator public but the valid method private? 
Finally, why inline the valid method for PartRef, but not for (Input|Output)Ref?

[dalesat, 2016/02/09 00:34:11]

The operator is essentially a null check while valid() is really for DCHECKs.
The expense of the index check isn't warranted for the operator.

I'm hiding valid() just to make the class simpler from the perspective of an
external user.

The valid() implementations require full class definitions, which aren't
available (for OutputRef here). OutputRef::valid() is only non-inline for
consistency.

+
+  PartRef part() const { return PartRef(stage_); }
+
+  bool connected() const;
+
+  const OutputRef& mate() const;
+
+ private:
+  InputRef(Stage* stage, size_t index);
+
+  Input& actual() const;
+
+  bool valid() const;
+
+  Stage* stage_;
+  size_t index_;
+
+  friend Graph;
+  friend PartRef;
+  friend OutputRef;
+  friend Output;
+  friend Engine;
+};
+
+// Opaque Output pointer used for graph building.
+class OutputRef {
+ public:
+  OutputRef() : stage_(nullptr), index_(0) {}
+
+  OutputRef& operator=(std::nullptr_t) {
+    stage_ = nullptr;
+    index_ = 0;
+    return *this;
+  }
+
+  explicit operator bool() const { return stage_ != nullptr; }
+
+  PartRef part() const { return PartRef(stage_); }
+
+  bool connected() const;
+
+  const InputRef& mate() const;
+
+ private:
+  OutputRef(Stage* stage, size_t index);
+
+  Output& actual() const;
+
+  bool valid() const;
+
+  Stage* stage_;
+  size_t index_;
+
+  friend Graph;
+  friend PartRef;
+  friend InputRef;
+  friend Input;
+  friend Engine;
+};
+
+}  // namespace media
+}  // namespace mojo
+
+#endif  // SERVICES_MEDIA_FRAMEWORK_REFS_H_