/*
* Copyright (C) Internet Systems Consortium, Inc. ("ISC")
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* See the COPYRIGHT file distributed with this work for additional
* information regarding copyright ownership.
*/
#ifndef ISC_REFCOUNT_H
#define ISC_REFCOUNT_H 1
#include <isc/assertions.h>
#include <isc/atomic.h>
#include <isc/error.h>
#include <isc/lang.h>
#include <isc/mutex.h>
#include <isc/platform.h>
#include <isc/types.h>
#if defined(ISC_PLATFORM_HAVESTDATOMIC)
#include <stdatomic.h>
#endif
/*! \file isc/refcount.h
* \brief Implements a locked reference counter.
*
* These functions may actually be
* implemented using macros, and implementations of these macros are below.
* The isc_refcount_t type should not be accessed directly, as its contents
* depend on the implementation.
*/
ISC_LANG_BEGINDECLS
/*
* Function prototypes
*/
/*
* isc_result_t
* isc_refcount_init(isc_refcount_t *ref, unsigned int n);
*
* Initialize the reference counter. There will be 'n' initial references.
*
* Requires:
* ref != NULL
*/
/*
* void
* isc_refcount_destroy(isc_refcount_t *ref);
*
* Destroys a reference counter.
*
* Requires:
* ref != NULL
* The number of references is 0.
*/
/*
* void
* isc_refcount_increment(isc_refcount_t *ref, unsigned int *targetp);
* isc_refcount_increment0(isc_refcount_t *ref, unsigned int *targetp);
*
* Increments the reference count, returning the new value in targetp if it's
* not NULL. The reference counter typically begins with the initial counter
* of 1, and will be destroyed once the counter reaches 0. Thus,
* isc_refcount_increment() additionally requires the previous counter be
* larger than 0 so that an error which violates the usage can be easily
* caught. isc_refcount_increment0() does not have this restriction.
*
* Requires:
* ref != NULL.
*/
/*
* void
* isc_refcount_decrement(isc_refcount_t *ref, unsigned int *targetp);
*
* Decrements the reference count, returning the new value in targetp if it's
* not NULL.
*
* Requires:
* ref != NULL.
*/
/*
* Sample implementations
*/
#ifdef ISC_PLATFORM_USETHREADS
#if (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE)) || defined(ISC_PLATFORM_HAVEXADD)
#define ISC_REFCOUNT_HAVEATOMIC 1
#if (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE))
#define ISC_REFCOUNT_HAVESTDATOMIC 1
#endif
typedef struct isc_refcount {
#if defined(ISC_REFCOUNT_HAVESTDATOMIC)
atomic_int_fast32_t refs;
#else
isc_int32_t refs;
#endif
} isc_refcount_t;
#if defined(ISC_REFCOUNT_HAVESTDATOMIC)
#define isc_refcount_current(rp) \
((unsigned int)(atomic_load_explicit(&(rp)->refs, \
memory_order_relaxed)))
#define isc_refcount_destroy(rp) ISC_REQUIRE(isc_refcount_current(rp) == 0)
#define isc_refcount_increment0(rp, tp) \
do { \
unsigned int *_tmp = (unsigned int *)(tp); \
isc_int32_t prev; \
prev = atomic_fetch_add_explicit \
(&(rp)->refs, 1, memory_order_relaxed); \
if (_tmp != NULL) \
*_tmp = prev + 1; \
} while (0)
#define isc_refcount_increment(rp, tp) \
do { \
unsigned int *_tmp = (unsigned int *)(tp); \
isc_int32_t prev; \
prev = atomic_fetch_add_explicit \
(&(rp)->refs, 1, memory_order_relaxed); \
ISC_REQUIRE(prev > 0); \
if (_tmp != NULL) \
*_tmp = prev + 1; \
} while (0)
#define isc_refcount_decrement(rp, tp) \
do { \
unsigned int *_tmp = (unsigned int *)(tp); \
isc_int32_t prev; \
prev = atomic_fetch_sub_explicit \
(&(rp)->refs, 1, memory_order_relaxed); \
ISC_REQUIRE(prev > 0); \
if (_tmp != NULL) \
*_tmp = prev - 1; \
} while (0)
#else /* ISC_REFCOUNT_HAVESTDATOMIC */
#define isc_refcount_current(rp) \
((unsigned int)(isc_atomic_xadd(&(rp)->refs, 0)))
#define isc_refcount_destroy(rp) ISC_REQUIRE(isc_refcount_current(rp) == 0)
#define isc_refcount_increment0(rp, tp) \
do { \
unsigned int *_tmp = (unsigned int *)(tp); \
isc_int32_t prev; \
prev = isc_atomic_xadd(&(rp)->refs, 1); \
if (_tmp != NULL) \
*_tmp = prev + 1; \
} while (0)
#define isc_refcount_increment(rp, tp) \
do { \
unsigned int *_tmp = (unsigned int *)(tp); \
isc_int32_t prev; \
prev = isc_atomic_xadd(&(rp)->refs, 1); \
ISC_REQUIRE(prev > 0); \
if (_tmp != NULL) \
*_tmp = prev + 1; \
} while (0)
#define isc_refcount_decrement(rp, tp) \
do { \
unsigned int *_tmp = (unsigned int *)(tp); \
isc_int32_t prev; \
prev = isc_atomic_xadd(&(rp)->refs, -1); \
ISC_REQUIRE(prev > 0); \
if (_tmp != NULL) \
*_tmp = prev - 1; \
} while (0)
#endif /* ISC_REFCOUNT_HAVESTDATOMIC */
#else /* ISC_PLATFORM_HAVEXADD */
typedef struct isc_refcount {
int refs;
isc_mutex_t lock;
} isc_refcount_t;
/*% Destroys a reference counter. */
#define isc_refcount_destroy(rp) \
do { \
isc_result_t _result; \
ISC_REQUIRE((rp)->refs == 0); \
_result = isc_mutex_destroy(&(rp)->lock); \
ISC_ERROR_RUNTIMECHECK(_result == ISC_R_SUCCESS); \
} while (0)
#define isc_refcount_current(rp) ((unsigned int)((rp)->refs))
/*%
* Increments the reference count, returning the new value in
* 'tp' if it's not NULL.
*/
#define isc_refcount_increment0(rp, tp) \
do { \
isc_result_t _result; \
unsigned int *_tmp = (unsigned int *)(tp); \
_result = isc_mutex_lock(&(rp)->lock); \
ISC_ERROR_RUNTIMECHECK(_result == ISC_R_SUCCESS); \
++((rp)->refs); \
if (_tmp != NULL) \
*_tmp = ((rp)->refs); \
_result = isc_mutex_unlock(&(rp)->lock); \
ISC_ERROR_RUNTIMECHECK(_result == ISC_R_SUCCESS); \
} while (0)
#define isc_refcount_increment(rp, tp) \
do { \
isc_result_t _result; \
unsigned int *_tmp = (unsigned int *)(tp); \
_result = isc_mutex_lock(&(rp)->lock); \
ISC_ERROR_RUNTIMECHECK(_result == ISC_R_SUCCESS); \
ISC_REQUIRE((rp)->refs > 0); \
++((rp)->refs); \
if (_tmp != NULL) \
*_tmp = ((rp)->refs); \
_result = isc_mutex_unlock(&(rp)->lock); \
ISC_ERROR_RUNTIMECHECK(_result == ISC_R_SUCCESS); \
} while (0)
/*%
* Decrements the reference count, returning the new value in 'tp'
* if it's not NULL.
*/
#define isc_refcount_decrement(rp, tp) \
do { \
isc_result_t _result; \
unsigned int *_tmp = (unsigned int *)(tp); \
_result = isc_mutex_lock(&(rp)->lock); \
ISC_ERROR_RUNTIMECHECK(_result == ISC_R_SUCCESS); \
ISC_REQUIRE((rp)->refs > 0); \
--((rp)->refs); \
if (_tmp != NULL) \
*_tmp = ((rp)->refs); \
_result = isc_mutex_unlock(&(rp)->lock); \
ISC_ERROR_RUNTIMECHECK(_result == ISC_R_SUCCESS); \
} while (0)
#endif /* (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE)) || defined(ISC_PLATFORM_HAVEXADD) */
#else /* ISC_PLATFORM_USETHREADS */
typedef struct isc_refcount {
int refs;
} isc_refcount_t;
#define isc_refcount_destroy(rp) ISC_REQUIRE((rp)->refs == 0)
#define isc_refcount_current(rp) ((unsigned int)((rp)->refs))
#define isc_refcount_increment0(rp, tp) \
do { \
unsigned int *_tmp = (unsigned int *)(tp); \
int _n = ++(rp)->refs; \
if (_tmp != NULL) \
*_tmp = _n; \
} while (0)
#define isc_refcount_increment(rp, tp) \
do { \
unsigned int *_tmp = (unsigned int *)(tp); \
int _n; \
ISC_REQUIRE((rp)->refs > 0); \
_n = ++(rp)->refs; \
if (_tmp != NULL) \
*_tmp = _n; \
} while (0)
#define isc_refcount_decrement(rp, tp) \
do { \
unsigned int *_tmp = (unsigned int *)(tp); \
int _n; \
ISC_REQUIRE((rp)->refs > 0); \
_n = --(rp)->refs; \
if (_tmp != NULL) \
*_tmp = _n; \
} while (0)
#endif /* ISC_PLATFORM_USETHREADS */
isc_result_t
isc_refcount_init(isc_refcount_t *ref, unsigned int n);
ISC_LANG_ENDDECLS
#endif /* ISC_REFCOUNT_H */