1 /*
2 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
3 *
4 * SPDX-License-Identifier: MPL-2.0
5 *
6 * This Source Code Form is subject to the terms of the Mozilla Public
7 * License, v. 2.0. If a copy of the MPL was not distributed with this
8 * file, you can obtain one at https://mozilla.org/MPL/2.0/.
9 *
10 * See the COPYRIGHT file distributed with this work for additional
11 * information regarding copyright ownership.
12 */
13
14 #pragma once
15
16 #include <inttypes.h>
17
18 #include <isc/assertions.h>
19 #include <isc/atomic.h>
20 #include <isc/error.h>
21 #include <isc/lang.h>
22 #include <isc/mutex.h>
23 #include <isc/platform.h>
24 #include <isc/types.h>
25
26 /*! \file isc/refcount.h
27 * \brief Implements a locked reference counter.
28 *
29 * These macros uses C11(-like) atomic functions to implement reference
30 * counting. The isc_refcount_t type must not be accessed directly.
31 */
32
33 ISC_LANG_BEGINDECLS
34
35 typedef atomic_uint_fast32_t isc_refcount_t;
36
37 /** \def isc_refcount_init(ref, n)
38 * \brief Initialize the reference counter.
39 * \param[in] ref pointer to reference counter.
40 * \param[in] n an initial number of references.
41 * \return nothing.
42 *
43 * \warning No memory barrier are being imposed here.
44 */
45 #define isc_refcount_init(target, value) atomic_init(target, value)
46
47 /** \def isc_refcount_current(ref)
48 * \brief Returns current number of references.
49 * \param[in] ref pointer to reference counter.
50 * \returns current value of reference counter.
51 *
52 * Undo implicit promotion to 64 bits in our Windows implementation of
53 * atomic_load_explicit() by casting to uint_fast32_t.
54 */
55
56 #define isc_refcount_current(target) (uint_fast32_t) atomic_load_acquire(target)
57
58 /** \def isc_refcount_destroy(ref)
59 * \brief a destructor that makes sure that all references were cleared.
60 * \param[in] ref pointer to reference counter.
61 * \returns nothing.
62 */
63 #define isc_refcount_destroy(target) \
64 ISC_REQUIRE(isc_refcount_current(target) == 0)
65
66 /** \def isc_refcount_increment0(ref)
67 * \brief increases reference counter by 1.
68 * \param[in] ref pointer to reference counter.
69 * \returns previous value of reference counter.
70 */
71 #if _MSC_VER
72 static inline uint_fast32_t
isc_refcount_increment0(isc_refcount_t * target)73 isc_refcount_increment0(isc_refcount_t *target) {
74 uint_fast32_t __v;
75 __v = (uint_fast32_t)atomic_fetch_add_relaxed(target, 1);
76 INSIST(__v < UINT32_MAX);
77 return (__v);
78 }
79 #else /* _MSC_VER */
80 #define isc_refcount_increment0(target) \
81 ({ \
82 /* cppcheck-suppress shadowVariable */ \
83 uint_fast32_t __v; \
84 __v = atomic_fetch_add_relaxed(target, 1); \
85 INSIST(__v < UINT32_MAX); \
86 __v; \
87 })
88 #endif /* _MSC_VER */
89
90 /** \def isc_refcount_increment(ref)
91 * \brief increases reference counter by 1.
92 * \param[in] ref pointer to reference counter.
93 * \returns previous value of reference counter.
94 */
95 #if _MSC_VER
96 static inline uint_fast32_t
isc_refcount_increment(isc_refcount_t * target)97 isc_refcount_increment(isc_refcount_t *target) {
98 uint_fast32_t __v;
99 __v = (uint_fast32_t)atomic_fetch_add_relaxed(target, 1);
100 INSIST(__v > 0 && __v < UINT32_MAX);
101 return (__v);
102 }
103 #else /* _MSC_VER */
104 #define isc_refcount_increment(target) \
105 ({ \
106 /* cppcheck-suppress shadowVariable */ \
107 uint_fast32_t __v; \
108 __v = atomic_fetch_add_relaxed(target, 1); \
109 INSIST(__v > 0 && __v < UINT32_MAX); \
110 __v; \
111 })
112 #endif /* _MSC_VER */
113
114 /** \def isc_refcount_decrement(ref)
115 * \brief decreases reference counter by 1.
116 * \param[in] ref pointer to reference counter.
117 * \returns previous value of reference counter.
118 */
119 #if _MSC_VER
120 static inline uint_fast32_t
isc_refcount_decrement(isc_refcount_t * target)121 isc_refcount_decrement(isc_refcount_t *target) {
122 uint_fast32_t __v;
123 __v = (uint_fast32_t)atomic_fetch_sub_acq_rel(target, 1);
124 INSIST(__v > 0);
125 return (__v);
126 }
127 #else /* _MSC_VER */
128 #define isc_refcount_decrement(target) \
129 ({ \
130 /* cppcheck-suppress shadowVariable */ \
131 uint_fast32_t __v; \
132 __v = atomic_fetch_sub_acq_rel(target, 1); \
133 INSIST(__v > 0); \
134 __v; \
135 })
136 #endif /* _MSC_VER */
137
138 #define isc_refcount_decrementz(target) \
139 do { \
140 uint_fast32_t _refs = isc_refcount_decrement(target); \
141 ISC_INSIST(_refs == 1); \
142 } while (0)
143
144 #define isc_refcount_decrement1(target) \
145 do { \
146 uint_fast32_t _refs = isc_refcount_decrement(target); \
147 ISC_INSIST(_refs > 1); \
148 } while (0)
149
150 #define isc_refcount_decrement0(target) \
151 do { \
152 uint_fast32_t _refs = isc_refcount_decrement(target); \
153 ISC_INSIST(_refs > 0); \
154 } while (0)
155
156 ISC_LANG_ENDDECLS
157