upb/mem/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

/* upb_Arena is a specific allocator implementation that uses arena allocation.
 * The user provides an allocator that will be used to allocate the underlying
 * arena blocks.  Arenas by nature do not require the individual allocations
 * to be freed.  However the Arena does allow users to register cleanup
 * functions that will run when the arena is destroyed.
 *
 * A upb_Arena is *not* thread-safe.
 *
 * You could write a thread-safe arena allocator that satisfies the
 * upb_alloc interface, but it would not be as efficient for the
 * single-threaded case. */

#ifndef UPB_MEM_ARENA_H_
#define UPB_MEM_ARENA_H_

#include <stddef.h>
#include <stdint.h>

#include "upb/mem/alloc.h"
#include "upb/mem/internal/arena.h"

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

typedef struct upb_Arena upb_Arena;

#ifdef __cplusplus
extern "C" {
#endif

// Creates an arena from the given initial block (if any -- n may be 0).
// Additional blocks will be allocated from |alloc|.  If |alloc| is NULL, this
// is a fixed-size arena and cannot grow.
UPB_API upb_Arena* upb_Arena_Init(void* mem, size_t n, upb_alloc* alloc);

UPB_API void upb_Arena_Free(upb_Arena* a);
UPB_API bool upb_Arena_Fuse(upb_Arena* a, upb_Arena* b);

bool upb_Arena_IncRefFor(upb_Arena* a, const void* owner);
void upb_Arena_DecRefFor(upb_Arena* a, const void* owner);

size_t upb_Arena_SpaceAllocated(upb_Arena* a, size_t* fused_count);
uint32_t upb_Arena_DebugRefCount(upb_Arena* a);

UPB_API_INLINE upb_Arena* upb_Arena_New(void) {
  return upb_Arena_Init(NULL, 0, &upb_alloc_global);
}

UPB_API_INLINE void* upb_Arena_Malloc(struct upb_Arena* a, size_t size);

UPB_API_INLINE void* upb_Arena_Realloc(upb_Arena* a, void* ptr, size_t oldsize,
                                       size_t size);

// Sets the maximum block size for all arenas. This is a global configuration
// setting that will affect all existing and future arenas. If
// upb_Arena_Malloc() is called with a size larger than this, we will exceed
// this size and allocate a larger block.
//
// This API is meant for experimentation only. It will likely be removed in
// the future.
void upb_Arena_SetMaxBlockSize(size_t max);

// Shrinks the last alloc from arena.
// REQUIRES: (ptr, oldsize) was the last malloc/realloc from this arena.
// We could also add a upb_Arena_TryShrinkLast() which is simply a no-op if
// this was not the last alloc.
UPB_API_INLINE void upb_Arena_ShrinkLast(upb_Arena* a, void* ptr,
                                         size_t oldsize, size_t size);

#ifdef UPB_TRACING_ENABLED
void upb_Arena_SetTraceHandler(void (*initArenaTraceHandler)(const upb_Arena*,
                                                             size_t size),
                               void (*fuseArenaTraceHandler)(const upb_Arena*,
                                                             const upb_Arena*),
                               void (*freeArenaTraceHandler)(const upb_Arena*));
#endif

#ifdef __cplusplus
} /* extern "C" */
#endif

#include "upb/port/undef.inc"

#endif /* UPB_MEM_ARENA_H_ */