BLI_linear_allocator.hh

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/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */

 
#pragma once
 
#include "BLI_cpp_type.hh"
#include "BLI_string_ref.hh"
#include "BLI_utility_mixins.hh"
#include "BLI_vector.hh"
 
namespace blender {

// #define BLI_DEBUG_LINEAR_ALLOCATOR_SIZE

template<typename Allocator = GuardedAllocator> class LinearAllocator : NonCopyable, NonMovable {
 private:
  BLI_NO_UNIQUE_ADDRESS Allocator allocator_;
  Vector<void *, 2> owned_buffers_;
 
  uintptr_t current_begin_;
  uintptr_t current_end_;
 
  /* Buffers larger than that are not packed together with smaller allocations to avoid wasting
   * memory. */
  constexpr static int64_t large_buffer_threshold = 4096;
 
 public:
#ifdef BLI_DEBUG_LINEAR_ALLOCATOR_SIZE
  int64_t user_requested_size_ = 0;
  int64_t owned_allocation_size_ = 0;
#endif
 
  LinearAllocator()
  {
    current_begin_ = 0;
    current_end_ = 0;
  }
 
  ~LinearAllocator()
  {
    for (void *ptr : owned_buffers_) {
      allocator_.deallocate(ptr);
    }
  }

  void *allocate(const int64_t size, const int64_t alignment)
  {
    BLI_assert(size >= 0);
    BLI_assert(alignment >= 1);
    BLI_assert(is_power_of_2(alignment));
 
    const uintptr_t alignment_mask = alignment - 1;
    const uintptr_t potential_allocation_begin = (current_begin_ + alignment_mask) &
                                                 ~alignment_mask;
    const uintptr_t potential_allocation_end = potential_allocation_begin + size;
 
    if (potential_allocation_end <= current_end_) {
#ifdef BLI_DEBUG_LINEAR_ALLOCATOR_SIZE
      user_requested_size_ += size;
#endif
      current_begin_ = potential_allocation_end;
      return reinterpret_cast<void *>(potential_allocation_begin);
    }
    if (size <= large_buffer_threshold) {
      this->allocate_new_buffer(size + alignment, alignment);
      return this->allocate(size, alignment);
    }
#ifdef BLI_DEBUG_LINEAR_ALLOCATOR_SIZE
    user_requested_size_ += size;
#endif
    return this->allocator_large_buffer(size, alignment);
  };

  template<typename T> T *allocate()
  {
    return static_cast<T *>(this->allocate(sizeof(T), alignof(T)));
  }

  void *allocate(const CPPType &type)
  {
    return this->allocate(type.size, type.alignment);
  }

  template<typename T> MutableSpan<T> allocate_array(int64_t size)
  {
    T *array = static_cast<T *>(this->allocate(sizeof(T) * size, alignof(T)));
    return MutableSpan<T>(array, size);
  }

  void *allocate_array(const CPPType &type, const int64_t size)
  {
    return this->allocate(type.size * size, type.alignment);
  }

  template<typename T, typename... Args> destruct_ptr<T> construct(Args &&...args)
  {
    void *buffer = this->allocate(sizeof(T), alignof(T));
    T *value = new (buffer) T(std::forward<Args>(args)...);
    return destruct_ptr<T>(value);
  }

  template<typename T, typename... Args>
  MutableSpan<T> construct_array(int64_t size, Args &&...args)
  {
    MutableSpan<T> array = this->allocate_array<T>(size);
    for (const int64_t i : IndexRange(size)) {
      new (&array[i]) T(std::forward<Args>(args)...);
    }
    return array;
  }

  template<typename T> MutableSpan<T> construct_array_copy(Span<T> src)
  {
    if (src.is_empty()) {
      return {};
    }
    MutableSpan<T> dst = this->allocate_array<T>(src.size());
    uninitialized_copy_n(src.data(), src.size(), dst.data());
    return dst;
  }

  StringRefNull copy_string(StringRef str)
  {
    const int64_t alloc_size = str.size() + 1;
    char *buffer = static_cast<char *>(this->allocate(alloc_size, 1));
    str.copy_unsafe(buffer);
    return StringRefNull(static_cast<const char *>(buffer));
  }
 
  MutableSpan<void *> allocate_elements_and_pointer_array(int64_t element_amount,
                                                          int64_t element_size,
                                                          int64_t element_alignment)
  {
    void *pointer_buffer = this->allocate(element_amount * sizeof(void *), alignof(void *));
    void *elements_buffer = this->allocate(element_amount * element_size, element_alignment);
 
    MutableSpan<void *> pointers(static_cast<void **>(pointer_buffer), element_amount);
    void *next_element_buffer = elements_buffer;
    for (int64_t i : IndexRange(element_amount)) {
      pointers[i] = next_element_buffer;
      next_element_buffer = POINTER_OFFSET(next_element_buffer, element_size);
    }
 
    return pointers;
  }
 
  template<typename T, typename... Args>
  Span<T *> construct_elements_and_pointer_array(int64_t n, Args &&...args)
  {
    MutableSpan<void *> void_pointers = this->allocate_elements_and_pointer_array(
        n, sizeof(T), alignof(T));
    MutableSpan<T *> pointers = void_pointers.cast<T *>();
 
    for (int64_t i : IndexRange(n)) {
      new (static_cast<void *>(pointers[i])) T(std::forward<Args>(args)...);
    }
 
    return pointers;
  }

  void provide_buffer(void *buffer, const int64_t size)
  {
    BLI_assert(owned_buffers_.is_empty());
    current_begin_ = uintptr_t(buffer);
    current_end_ = current_begin_ + size;
  }
 
  template<size_t Size, size_t Alignment>
  void provide_buffer(AlignedBuffer<Size, Alignment> &aligned_buffer)
  {
    this->provide_buffer(aligned_buffer.ptr(), Size);
  }

  void free_end_of_previous_allocation(const int64_t original_allocation_size,
                                       const void *free_after)
  {
    /* If the original allocation size was large, it might have been separately allocated. In this
     * case, we can't free the end of it anymore. */
    if (original_allocation_size <= large_buffer_threshold) {
      const int64_t new_begin = uintptr_t(free_after);
      BLI_assert(new_begin <= current_begin_);
#ifndef NDEBUG
      /* This condition is not really necessary but it helps finding the cases where memory was
       * freed. */
      const int64_t freed_bytes_num = current_begin_ - new_begin;
      if (freed_bytes_num > 0) {
        current_begin_ = new_begin;
      }
#else
      current_begin_ = new_begin;
#endif
    }
  }

  void transfer_ownership_from(LinearAllocator<> &other)
  {
    owned_buffers_.extend(other.owned_buffers_);
#ifdef BLI_DEBUG_LINEAR_ALLOCATOR_SIZE
    user_requested_size_ += other.user_requested_size_;
    owned_allocation_size_ += other.owned_allocation_size_;
#endif
    other.owned_buffers_.clear();
    std::destroy_at(&other);
    new (&other) LinearAllocator<>();
  }
 
 private:
  void allocate_new_buffer(int64_t min_allocation_size, int64_t min_alignment)
  {
    /* Possibly allocate more bytes than necessary for the current allocation. This way more small
     * allocations can be packed together. Large buffers are allocated exactly to avoid wasting too
     * much memory. */
    int64_t size_in_bytes = min_allocation_size;
    if (size_in_bytes <= large_buffer_threshold) {
      /* Gradually grow buffer size with each allocation, up to a maximum. */
      const int grow_size = 1 << std::min<int>(owned_buffers_.size() + 6, 20);
      size_in_bytes = std::min(large_buffer_threshold,
                               std::max<int64_t>(size_in_bytes, grow_size));
    }
 
    void *buffer = this->allocated_owned(size_in_bytes, min_alignment);
    current_begin_ = uintptr_t(buffer);
    current_end_ = current_begin_ + size_in_bytes;
  }
 
  void *allocator_large_buffer(const int64_t size, const int64_t alignment)
  {
    return this->allocated_owned(size, alignment);
  }
 
  void *allocated_owned(const int64_t size, const int64_t alignment)
  {
    void *buffer = allocator_.allocate(size, alignment, __func__);
    owned_buffers_.append(buffer);
#ifdef BLI_DEBUG_LINEAR_ALLOCATOR_SIZE
    owned_allocation_size_ += size;
#endif
    return buffer;
  }
};
 
}  // namespace blender