arena.h

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// 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, although some functions related to its
 * managing its lifetime are, and are documented as such.
 *
 * 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;
 
typedef void upb_AllocCleanupFunc(upb_alloc* alloc);
 
#ifdef __cplusplus
extern "C" {
#endif
 
// Creates an arena from the given initial block (if any -- mem may be NULL). If
// an initial block is specified, the arena's lifetime cannot be extended by
// |upb_Arena_IncRefFor| or |upb_Arena_Fuse|. Additional blocks will be
// allocated from |alloc|. If |alloc| is NULL, this is a fixed-size arena and
// cannot grow. If an initial block is specified, |n| is its length; if there is
// no initial block, |n| is a hint of the size that should be allocated for the
// first block of the arena, such that `upb_Arena_Malloc(hint)` will not require
// another call to |alloc|.
UPB_API upb_Arena* upb_Arena_Init(void* mem, size_t n, upb_alloc* alloc);
 
UPB_API void upb_Arena_Free(upb_Arena* a);
// Sets the cleanup function for the upb_alloc used by the arena. Only one
// cleanup function can be set, which will be called after all blocks are
// freed.
UPB_API void upb_Arena_SetAllocCleanup(upb_Arena* a,
                                       upb_AllocCleanupFunc* func);
 
// Fuses the lifetime of two arenas, such that no arenas that have been
// transitively fused together will be freed until all of them have reached a
// zero refcount. This operation is safe to use concurrently from multiple
// threads.
UPB_API bool upb_Arena_Fuse(const upb_Arena* a, const upb_Arena* b);
 
// This operation is safe to use concurrently from multiple threads.
UPB_API bool upb_Arena_IsFused(const upb_Arena* a, const upb_Arena* b);
 
// Returns the upb_alloc used by the arena.
UPB_API upb_alloc* upb_Arena_GetUpbAlloc(upb_Arena* a);
 
// This operation is safe to use concurrently from multiple threads.
bool upb_Arena_IncRefFor(const upb_Arena* a, const void* owner);
// This operation is safe to use concurrently from multiple threads.
void upb_Arena_DecRefFor(const upb_Arena* a, const void* owner);
 
// This operation is safe to use concurrently from multiple threads.
uintptr_t upb_Arena_SpaceAllocated(const upb_Arena* a, size_t* fused_count);
// This operation is safe to use concurrently from multiple threads.
uint32_t upb_Arena_DebugRefCount(const upb_Arena* a);
 
UPB_API_INLINE upb_Arena* upb_Arena_New(void) {
  return upb_Arena_Init(NULL, 0, upb_alloc_global());
}
 
UPB_API_INLINE upb_Arena* upb_Arena_NewSized(size_t size_hint) {
  return upb_Arena_Init(NULL, size_hint, 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);
 
static const size_t UPB_PRIVATE(kUpbDefaultMaxBlockSize) =
    UPB_DEFAULT_MAX_BLOCK_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.
// This operation is safe to use concurrently from multiple threads.
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);
 
// Attempts to extend the given alloc from arena, in place. Is generally
// only likely to succeed for the most recent allocation from this arena. If it
// succeeds, returns true and `ptr`'s allocation is now `size` rather than
// `oldsize`. Returns false if the allocation cannot be extended; `ptr`'s
// allocation is unmodified. See also upb_Arena_Realloc.
// REQUIRES: `size > oldsize`; to shrink, use `upb_Arena_Realloc` or
// `upb_Arena_ShrinkLast`.
UPB_API_INLINE bool upb_Arena_TryExtend(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_ */