Add skeleton circular queue file.

base/containers/vector_buffer.h

+// Copyright 2017 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 BASE_CONTAINERS_VECTOR_BUFFERS_H_
+#define BASE_CONTAINERS_VECTOR_BUFFERS_H_
+
+#include <stdlib.h>
+#include <string.h>
+
+#include <type_traits>
+#include <utility>
+
+#include "base/logging.h"
+#include "base/macros.h"
+
+namespace base {
+namespace internal {
+
+// Internal implementation detail of base/containers.
+//
+// Implements a vector-like buffer that holds a certain capacity of T. Unlike
+// std::vector, VectorBuffer never constructs or destructs its arguments, and
+// can't change sizes. But it does implement templates to assist in efficient
+// moving and destruction of those items manually.
+//
+// In particular, te destructor function does not iterate over the items if
+// there is no destructor. Moves should be implemented as a memcpy/memmove for
+// trivially copyable objects (POD) otherwise, it should be a std::move if
+// possible, and as a last resort it falls back to a copy. This behavior is
+// similar to std::vector.
+//
+// No special consideration is done for noexcept move constructors since
+// we compile without exceptions.
+//
+// The current API does not support moving overlapping ranges.
+template <typename T>
+class VectorBuffer {
+ public:
+  VectorBuffer() {}
+  VectorBuffer(size_t count)
+      : buffer_(reinterpret_cast<T*>(malloc(sizeof(T) * count))),
+        capacity_(count) {}
+  VectorBuffer(VectorBuffer&& other) noexcept
+      : buffer_(other.buffer_), capacity_(other.capacity_) {
+    other.buffer_ = nullptr;
+    other.capacity_ = 0;
+  }
+
+  ~VectorBuffer() { free(buffer_); }
+
+  VectorBuffer& operator=(VectorBuffer&& other) {
+    free(buffer_);
+    buffer_ = other.buffer_;
+    capacity_ = other.capacity_;
+
+    other.buffer_ = nullptr;
+    other.capacity_ = 0;
+    return *this;
+  }
+
+  size_t capacity() const { return capacity_; }
+
+  T& operator[](size_t i) { return buffer_[i]; }
+  const T& operator[](size_t i) const { return buffer_[i]; }
+  T* begin() { return buffer_; }
+  T* end() { return &buffer_[capacity_]; }
+
+  // DestructRange ------------------------------------------------------------
+
+  // Trivially destructible objects need not have their destructors called.
+  template <typename T2 = T,
+            typename std::enable_if<std::is_trivially_destructible<T2>::value,
+                                    int>::type = 0>
+  void DestructRange(T* begin, T* end) {}
+
+  // Non-trivially destructible objects must have their destructors called
+  // individually.
+  template <typename T2 = T,
+            typename std::enable_if<!std::is_trivially_destructible<T2>::value,
+                                    int>::type = 0>
+  void DestructRange(T* begin, T* end) {
+    while (begin != end) {
+      begin->~T();
+      begin++;
+    }
+  }
+
+  // MoveRange ----------------------------------------------------------------
+  //
+  // The destructor will be called (as necessary) for all moved types. The
+  // ranges must not overlap.
+
+  // Trivially copyable types can use memcpy. trivially copyable implies
+  // that there is a trivial destructor as we don't have to call it.
+  template <typename T2 = T,
+            typename std::enable_if<base::is_trivially_copyable<T2>::value,
+                                    int>::type = 0>
+  static void MoveRange(T* from_begin, T* from_end, T* to) {
+    DCHECK(!RangesOverlap(from_begin, from_end, to));
+    memcpy(to, from_begin, (from_end - from_begin) * sizeof(T));
+  }
+
+  // Not trivially copyable, but movable: call the move constructor and
+  // destruct the original.
+  template <typename T2 = T,
+            typename std::enable_if<std::is_move_constructible<T2>::value &&
+                                        !base::is_trivially_copyable<T2>::value,
+                                    int>::type = 0>
+  static void MoveRange(T* from_begin, T* from_end, T* to) {
+    DCHECK(!RangesOverlap(from_begin, from_end, to));
+    while (from_begin != from_end) {
+      new (to) T(std::move(*from_begin));
+      from_begin->~T();
+      from_begin++;
+      to++;
+    }
+  }
+
+  // Not movable, not trivially copyable: call the copy constructor and
+  // destruct the original.
+  template <typename T2 = T,
+            typename std::enable_if<!std::is_move_constructible<T2>::value &&
+                                        !base::is_trivially_copyable<T2>::value,
+                                    int>::type = 0>
+  static void MoveRange(T* from_begin, T* from_end, T* to) {
+    DCHECK(!RangesOverlap(from_begin, from_end, to));
+    while (from_begin != from_end) {
+      new (to) T(*from_begin);
+      from_begin->~T();
+      from_begin++;
+      to++;
+    }
+  }
+
+ private:
+  static bool RangesOverlap(const T* from_begin,
+                            const T* from_end,
+                            const T* to) {
+    return !(to >= from_end || to + (from_end - from_begin) <= from_begin);
+  }
+
+  T* buffer_ = nullptr;
+  size_t capacity_ = 0;
+
+  DISALLOW_COPY_AND_ASSIGN(VectorBuffer);
+};
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_CONTAINERS_VECTOR_BUFFERS_H_