base/memory/nonscannable_memory.h

// Copyright (c) 2021 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_MEMORY_NONSCANNABLE_MEMORY_H_
#define BASE_MEMORY_NONSCANNABLE_MEMORY_H_

#include <cstdint>

#include <atomic>
#include <memory>

#include "base/allocator/buildflags.h"
#include "base/base_export.h"

#if BUILDFLAG(USE_PARTITION_ALLOC_AS_MALLOC)
#include "base/allocator/partition_allocator/partition_alloc.h"
#endif

// This file contains allocation/deallocation functions for memory that doesn't
// need to be scanned by PCScan. Such memory should only contain "data" objects,
// i.e. objects that don't have pointers/references to other objects. An example
// would be strings or socket/IPC/file buffers. Use with caution.
namespace base {

#if BUILDFLAG(USE_PARTITION_ALLOC_AS_MALLOC)
template <typename>
class NoDestructor;

namespace internal {

// Represents allocator that contains memory for data-like objects (that don't
// contain pointers) and therefore doesn't require scanning.
class BASE_EXPORT NonScannableAllocator final {
 public:
  static NonScannableAllocator& Instance();

  NonScannableAllocator(const NonScannableAllocator&) = delete;
  NonScannableAllocator& operator=(const NonScannableAllocator&) = delete;

  void* Alloc(size_t size);
  static void Free(void*);

  // Returns PartitionRoot corresponding to the allocator, or nullptr if the
  // allocator is not enabled.
  ThreadSafePartitionRoot* root() {
    if (!allocator_.get())
      return nullptr;
    return allocator_->root();
  }

  void EnablePCScan();

 private:
  template <typename>
  friend class base::NoDestructor;

  NonScannableAllocator();
  ~NonScannableAllocator();

  std::unique_ptr<base::PartitionAllocator> allocator_;
  std::atomic_bool pcscan_enabled_{false};
};

}  // namespace internal
#endif  // BUILDFLAG(USE_PARTITION_ALLOC_AS_MALLOC)

// Allocate/free non-scannable memory.
BASE_EXPORT void* AllocNonScannable(size_t size);
BASE_EXPORT void FreeNonScannable(void* ptr);

// Deleters to be used with std::unique_ptr.
struct NonScannableDeleter {
  void operator()(void* ptr) const { FreeNonScannable(ptr); }
};

}  // namespace base

#endif  // BASE_MEMORY_NONSCANNABLE_MEMORY_H_