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refcount.h
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/* * 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 https://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 <inttypes.h> #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) #if defined (__cplusplus) #include <isc/stdatomic.h> #else #include <stdatomic.h> #endif #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) # define ISC_REFCOUNT_HAVEATOMIC 1 # define ISC_REFCOUNT_HAVESTDATOMIC 1 #else /* defined(ISC_PLATFORM_HAVESTDATOMIC) */ # if defined(ISC_PLATFORM_HAVEXADD) # define ISC_REFCOUNT_HAVEATOMIC 1 # endif /* defined(ISC_PLATFORM_HAVEXADD */ #endif /* !defined(ISC_REFCOUNT_HAVEATOMIC) */ #if defined(ISC_REFCOUNT_HAVEATOMIC) typedef struct isc_refcount { #if defined(ISC_REFCOUNT_HAVESTDATOMIC) atomic_int_fast32_t refs; #else 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_acquire))) #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); \ 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); \ 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); \ int32_t prev; \ prev = atomic_fetch_sub_explicit \ (&(rp)->refs, 1, memory_order_acq_rel); \ ISC_REQUIRE(prev > 0); \ if (_tmp != NULL) \ *_tmp = prev - 1; \ } while (0) #else /* defined(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); \ 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); \ 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); \ int32_t prev; \ prev = isc_atomic_xadd(&(rp)->refs, -1); \ ISC_REQUIRE(prev > 0); \ if (_tmp != NULL) \ *_tmp = prev - 1; \ } while (0) #endif /* defined(ISC_REFCOUNT_HAVESTDATOMIC) */ #else /* defined(ISC_REFCOUNT_HAVEATOMIC) */ 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) unsigned int isc_refcount_current(isc_refcount_t *rp); /*% * 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_REFCOUNT_ATOMIC) */ #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 */