Motown in-proc streaming framework used to implement media services.

services/media/framework/allocator.cc

+// 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.
+
+#include <cstdlib>
+
+#include "base/logging.h"
+#include "services/media/framework/allocator.h"
+
+namespace mojo {
+namespace media {
+
+namespace {
+
+class DefaultAllocator : public Allocator {
+ public:
+  constexpr DefaultAllocator() {}

[jeffbrown, 2016/02/02 05:35:45]

constexpr isn't appropriate here

[johngro, 2016/02/02 17:21:37]

constexpr is required here to satisfy style.  Later on, he has a static global
instance of the default allocator class (to hand out during calls to
Allocator::GetDefault()).  Style's opinion on global statics of class type
currently says...

"""
Variables of class type with static storage duration are forbidden: they cause
hard-to-find bugs due to indeterminate order of construction and destruction.
However, such variables are allowed if they are constexpr: they have no dynamic
initialization or destruction.
"""

Declaring the instance of the class as constexpr requires that the class have a
constexpr constructor, hence the constexpr keyword here.

[dalesat, 2016/02/02 21:46:38]

Acknowledged.

+
+  // Allocator implementation.
+  void* AllocatePayloadBuffer(uint64_t size) override;
+
+  void ReleasePayloadBuffer(uint64_t size, void* buffer) override;
+};
+
+void* DefaultAllocator::AllocatePayloadBuffer(uint64_t size) {
+  DCHECK(size > 0);

[jeffbrown, 2016/02/02 05:35:45]

Why can't the size be zero?  malloc allows this, though I suppose it's silly.

[dalesat, 2016/02/02 21:46:38]

I'd be OK with it, but I'd want to return nullptr.

+  return std::malloc(static_cast<size_t>(size));
+}
+
+void DefaultAllocator::ReleasePayloadBuffer(uint64_t size, void* buffer) {
+  DCHECK(size > 0);
+  DCHECK(buffer);
+  std::free(buffer);
+}
+
+static constexpr DefaultAllocator default_allocator;

[jeffbrown, 2016/02/02 05:35:46]

I don't think you want constexpr here since this isn't a constant expression.

If you mean to say that the value won't change after initialization then put
const on the end, say if it were a pointer.

eg. static DefaultAllocator* const default_allocator

That said, static initializers are banned in our tree.  You'll need someone to
call a function to set this up during startup.

[johngro, 2016/02/02 17:21:37]

See comment above.  This is mandated by style, and the reason is to prevent the
need to have a ctor style initializer.

[dalesat, 2016/02/02 21:46:38]

Acknowledged.

+
+} // namespace
+
+// static
+Allocator* Allocator::GetDefault() {
+  return const_cast<DefaultAllocator*>(&default_allocator);
+}
+
+} // namespace media
+} // namespace mojo