protobuf/upb/mem/internal/arena.h

// Protocol Buffers - Google's data interchange format
// Copyright 2023 Google LLC.  All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd

#ifndef UPB_MEM_INTERNAL_ARENA_H_
#define UPB_MEM_INTERNAL_ARENA_H_

#include "upb/mem/arena.h"

// Must be last.
#include "upb/port/def.inc"

typedef struct _upb_MemBlock _upb_MemBlock;

// LINT.IfChange(struct_definition)
struct upb_Arena {
  _upb_ArenaHead head;

  // upb_alloc* together with a low bit which signals if there is an initial
  // block.
  uintptr_t block_alloc;

  // When multiple arenas are fused together, each arena points to a parent
  // arena (root points to itself). The root tracks how many live arenas
  // reference it.

  // The low bit is tagged:
  //   0: pointer to parent
  //   1: count, left shifted by one
  UPB_ATOMIC(uintptr_t) parent_or_count;

  // All nodes that are fused together are in a singly-linked list.
  UPB_ATOMIC(upb_Arena*) next;  // NULL at end of list.

  // The last element of the linked list.  This is present only as an
  // optimization, so that we do not have to iterate over all members for every
  // fuse.  Only significant for an arena root.  In other cases it is ignored.
  UPB_ATOMIC(upb_Arena*) tail;  // == self when no other list members.

  // Linked list of blocks to free/cleanup.  Atomic only for the benefit of
  // upb_Arena_SpaceAllocated().
  UPB_ATOMIC(_upb_MemBlock*) blocks;
};
// LINT.ThenChange(//depot/google3/third_party/upb/bits/typescript/arena.ts)

#include "upb/port/undef.inc"

#endif /* UPB_MEM_INTERNAL_ARENA_H_ */