2 * Copyright (c) 2013, 2014 Nicira, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at:
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
18 #define OVS_ATOMIC_H 1
22 * This library implements atomic operations with an API based on the one
23 * defined in C11. It includes multiple implementations for compilers and
24 * libraries with varying degrees of built-in support for C11, including a
25 * fallback implementation for systems that have pthreads but no other support
28 * This comment describes the common features of all the implementations.
34 * The following atomic types are supported as typedefs for atomic versions of
35 * the listed ordinary types:
37 * ordinary type atomic version
38 * ------------------- ----------------------
42 * signed char atomic_schar
43 * unsigned char atomic_uchar
46 * unsigned short atomic_ushort
49 * unsigned int atomic_uint
52 * unsigned long atomic_ulong
54 * long long atomic_llong
55 * unsigned long long atomic_ullong
57 * size_t atomic_size_t
58 * ptrdiff_t atomic_ptrdiff_t
60 * intmax_t atomic_intmax_t
61 * uintmax_t atomic_uintmax_t
63 * intptr_t atomic_intptr_t
64 * uintptr_t atomic_uintptr_t
66 * uint8_t atomic_uint8_t (*)
67 * uint16_t atomic_uint16_t (*)
68 * uint32_t atomic_uint32_t (*)
69 * int8_t atomic_int8_t (*)
70 * int16_t atomic_int16_t (*)
71 * int32_t atomic_int32_t (*)
73 * (*) Not specified by C11.
75 * Atomic types may also be obtained via ATOMIC(TYPE), e.g. ATOMIC(void *).
76 * Only basic integer types and pointer types can be made atomic this way,
77 * e.g. atomic structs are not supported.
79 * The atomic version of a type doesn't necessarily have the same size or
80 * representation as the ordinary version; for example, atomic_int might be a
81 * typedef for a struct. The range of an atomic type does match the range of
82 * the corresponding ordinary type.
84 * C11 says that one may use the _Atomic keyword in place of the typedef name,
85 * e.g. "_Atomic int" instead of "atomic_int". This library doesn't support
92 * To initialize an atomic variable at its point of definition, use
95 * static atomic_int ai = ATOMIC_VAR_INIT(123);
97 * To initialize an atomic variable in code, use atomic_init():
99 * static atomic_int ai;
101 * atomic_init(&ai, 123);
107 * enum memory_order specifies the strictness of a memory barrier. It has the
110 * memory_order_relaxed:
112 * Compiler barrier only. Does not imply any CPU memory ordering.
114 * memory_order_acquire:
116 * Memory accesses after an acquire barrier cannot be moved before the
117 * barrier. Memory accesses before an acquire barrier *can* be moved
120 * memory_order_release:
122 * Memory accesses before a release barrier cannot be moved after the
123 * barrier. Memory accesses after a release barrier *can* be moved
126 * memory_order_acq_rel:
128 * Memory accesses cannot be moved across an acquire-release barrier in
131 * memory_order_seq_cst:
133 * Prevents movement of memory accesses like an acquire-release barrier,
134 * but whereas acquire-release synchronizes cooperating threads,
135 * sequential-consistency synchronizes the whole system.
137 * memory_order_consume:
139 * A slight relaxation of memory_order_acquire.
141 * The following functions insert explicit barriers. Most of the other atomic
142 * functions also include barriers.
144 * void atomic_thread_fence(memory_order order);
146 * Inserts a barrier of the specified type.
148 * For memory_order_relaxed, this is a no-op.
150 * void atomic_signal_fence(memory_order order);
152 * Inserts a barrier of the specified type, but only with respect to
153 * signal handlers in the same thread as the barrier. This is
154 * basically a compiler optimization barrier, except for
155 * memory_order_relaxed, which is a no-op.
161 * In this section, A is an atomic type and C is the corresponding non-atomic
164 * The "store" primitives match C11:
166 * void atomic_store(A *object, C value);
167 * void atomic_store_explicit(A *object, C value, memory_order);
169 * Atomically stores 'value' into '*object', respecting the given
170 * memory order (or memory_order_seq_cst for atomic_store()).
172 * The following primitives differ from the C11 ones (and have different names)
173 * because there does not appear to be a way to implement the standard
174 * primitives in standard C:
176 * void atomic_read(A *src, C *dst);
177 * void atomic_read_explicit(A *src, C *dst, memory_order);
179 * Atomically loads a value from 'src', writing the value read into
180 * '*dst', respecting the given memory order (or memory_order_seq_cst
181 * for atomic_read()).
183 * void atomic_add(A *rmw, C arg, C *orig);
184 * void atomic_sub(A *rmw, C arg, C *orig);
185 * void atomic_or(A *rmw, C arg, C *orig);
186 * void atomic_xor(A *rmw, C arg, C *orig);
187 * void atomic_and(A *rmw, C arg, C *orig);
188 * void atomic_add_explicit(A *rmw, C arg, C *orig, memory_order);
189 * void atomic_sub_explicit(A *rmw, C arg, C *orig, memory_order);
190 * void atomic_or_explicit(A *rmw, C arg, C *orig, memory_order);
191 * void atomic_xor_explicit(A *rmw, C arg, C *orig, memory_order);
192 * void atomic_and_explicit(A *rmw, C arg, C *orig, memory_order);
194 * Atomically applies the given operation, with 'arg' as the second
195 * operand, to '*rmw', and stores the original value of '*rmw' into
196 * '*orig', respecting the given memory order (or memory_order_seq_cst
197 * if none is specified).
199 * The results are similar to those that would be obtained with +=, -=,
200 * |=, ^=, or |= on non-atomic types.
206 * atomic_flag is a typedef for a type with two states, set and clear, that
207 * provides atomic test-and-set functionality.
213 * ATOMIC_FLAG_INIT is an initializer for atomic_flag. The initial state is
216 * An atomic_flag may also be initialized at runtime with atomic_flag_clear().
222 * The following functions are available.
224 * bool atomic_flag_test_and_set(atomic_flag *object)
225 * bool atomic_flag_test_and_set_explicit(atomic_flag *object,
228 * Atomically sets '*object', respsecting the given memory order (or
229 * memory_order_seq_cst for atomic_flag_test_and_set()). Returns the
230 * previous value of the flag (false for clear, true for set).
232 * void atomic_flag_clear(atomic_flag *object);
233 * void atomic_flag_clear_explicit(atomic_flag *object, memory_order);
235 * Atomically clears '*object', respecting the given memory order (or
236 * memory_order_seq_cst for atomic_flag_clear()).
244 #include "compiler.h"
247 #define IN_OVS_ATOMIC_H
249 /* sparse doesn't understand some GCC extensions we use. */
250 #include "ovs-atomic-pthreads.h"
251 #elif HAVE_STDATOMIC_H
252 #include "ovs-atomic-c11.h"
253 #elif __has_extension(c_atomic)
254 #include "ovs-atomic-clang.h"
255 #elif __GNUC__ >= 4 && __GNUC_MINOR__ >= 7
256 #include "ovs-atomic-gcc4.7+.h"
257 #elif HAVE_GCC4_ATOMICS
258 #include "ovs-atomic-gcc4+.h"
260 #include "ovs-atomic-pthreads.h"
262 #undef IN_OVS_ATOMIC_H
264 #ifndef OMIT_STANDARD_ATOMIC_TYPES
265 typedef ATOMIC(bool) atomic_bool;
267 typedef ATOMIC(char) atomic_char;
268 typedef ATOMIC(signed char) atomic_schar;
269 typedef ATOMIC(unsigned char) atomic_uchar;
271 typedef ATOMIC(short) atomic_short;
272 typedef ATOMIC(unsigned short) atomic_ushort;
274 typedef ATOMIC(int) atomic_int;
275 typedef ATOMIC(unsigned int) atomic_uint;
277 typedef ATOMIC(long) atomic_long;
278 typedef ATOMIC(unsigned long) atomic_ulong;
280 typedef ATOMIC(long long) atomic_llong;
281 typedef ATOMIC(unsigned long long) atomic_ullong;
283 typedef ATOMIC(size_t) atomic_size_t;
284 typedef ATOMIC(ptrdiff_t) atomic_ptrdiff_t;
286 typedef ATOMIC(intmax_t) atomic_intmax_t;
287 typedef ATOMIC(uintmax_t) atomic_uintmax_t;
289 typedef ATOMIC(intptr_t) atomic_intptr_t;
290 typedef ATOMIC(uintptr_t) atomic_uintptr_t;
291 #endif /* !OMIT_STANDARD_ATOMIC_TYPES */
293 /* Nonstandard atomic types. */
294 typedef ATOMIC(uint8_t) atomic_uint8_t;
295 typedef ATOMIC(uint16_t) atomic_uint16_t;
296 typedef ATOMIC(uint32_t) atomic_uint32_t;
298 typedef ATOMIC(int8_t) atomic_int8_t;
299 typedef ATOMIC(int16_t) atomic_int16_t;
300 typedef ATOMIC(int32_t) atomic_int32_t;
302 /* Reference count. */
303 struct ovs_refcount {
307 /* Initializes 'refcount'. The reference count is initially 1. */
309 ovs_refcount_init(struct ovs_refcount *refcount)
311 atomic_init(&refcount->count, 1);
314 /* Increments 'refcount'. */
316 ovs_refcount_ref(struct ovs_refcount *refcount)
318 unsigned int old_refcount;
320 atomic_add(&refcount->count, 1, &old_refcount);
321 ovs_assert(old_refcount > 0);
324 /* Decrements 'refcount' and returns the previous reference count. Often used
327 * if (ovs_refcount_unref(&object->ref_cnt) == 1) {
328 * // ...uninitialize object...
332 static inline unsigned int
333 ovs_refcount_unref(struct ovs_refcount *refcount)
335 unsigned int old_refcount;
337 atomic_sub(&refcount->count, 1, &old_refcount);
338 ovs_assert(old_refcount > 0);
342 /* Reads and returns 'ref_count_''s current reference count.
345 static inline unsigned int
346 ovs_refcount_read(const struct ovs_refcount *refcount_)
348 struct ovs_refcount *refcount
349 = CONST_CAST(struct ovs_refcount *, refcount_);
352 atomic_read(&refcount->count, &count);
356 #endif /* ovs-atomic.h */