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* Copyright 2014 Google Inc. All Rights Reserved.
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include "nb/allocator.h"
namespace nb {
// FixedNoFreeAllocator is an allocator that allocates memory but cannot reuse
// previously allocated memory. Specifying that the allocator will not reuse
// previously allocated memory allows for a simple and fast implementation
// of Allocate(), namely that it can continually increment an internal "next
// memory address" pointer. The allocator does not own the memory it is
// managing. This is so that logic to deal with how to allocate and free
// the memory range can remain separate from the allocator managing it.
// An example usage of this class is to act as a "fallback" allocator to a more
// complicated allocator that can reuse old memory. When the reuse allocator
// runs out of memory to recycle, it can fall back to this fallback allocator.
// This makes sense if there's a finite area of memory dedicated to graphics
// memory and we would like to wrap it in an allocator.
class FixedNoFreeAllocator : public Allocator {
FixedNoFreeAllocator(void* memory_start, std::size_t memory_size);
void* Allocate(std::size_t size) { return Allocate(&size, 1, true); }
void* Allocate(std::size_t size, std::size_t alignment) {
return Allocate(&size, alignment, true);
void* AllocateForAlignment(std::size_t* size, std::size_t alignment) {
return Allocate(size, alignment, false);
void Free(void* memory);
std::size_t GetCapacity() const;
std::size_t GetAllocated() const;
void PrintAllocations() const;
void* Allocate(std::size_t* size, std::size_t alignment, bool align_pointer);
// The start of our memory range, as passed in to the constructor.
void* const memory_start_;
// Equal to the first value of memory outside of the allocator's memory range.
const void* memory_end_;
// The memory location that will be passed out upon the next allocation.
void* next_memory_;
} // namespace nb