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 (*)
72 * uint64_t atomic_uint64_t (*)
73 * int64_t atomic_int64_t (*)
75 * (*) Not specified by C11.
77 * Atomic types may also be obtained via ATOMIC(TYPE), e.g. ATOMIC(void *).
78 * Only basic integer types and pointer types can be made atomic this way,
79 * e.g. atomic structs are not supported.
81 * The atomic version of a type doesn't necessarily have the same size or
82 * representation as the ordinary version; for example, atomic_int might be a
83 * typedef for a struct. The range of an atomic type does match the range of
84 * the corresponding ordinary type.
86 * C11 says that one may use the _Atomic keyword in place of the typedef name,
87 * e.g. "_Atomic int" instead of "atomic_int". This library doesn't support
94 * To initialize an atomic variable at its point of definition, use
97 * static atomic_int ai = ATOMIC_VAR_INIT(123);
99 * To initialize an atomic variable in code, use atomic_init():
101 * static atomic_int ai;
103 * atomic_init(&ai, 123);
105 * C11 does not hav an destruction function for atomic types, but some
106 * implementations of the OVS atomics do need them. Thus, the following
107 * function is provided for destroying non-static atomic objects (A is any
110 * void atomic_destroy(A *object);
118 * enum memory_order specifies the strictness of a memory barrier. It has the
121 * memory_order_relaxed:
123 * Compiler barrier only. Does not imply any CPU memory ordering.
125 * memory_order_acquire:
127 * Memory accesses after an acquire barrier cannot be moved before the
128 * barrier. Memory accesses before an acquire barrier *can* be moved
131 * memory_order_release:
133 * Memory accesses before a release barrier cannot be moved after the
134 * barrier. Memory accesses after a release barrier *can* be moved
137 * memory_order_acq_rel:
139 * Memory accesses cannot be moved across an acquire-release barrier in
142 * memory_order_seq_cst:
144 * Prevents movement of memory accesses like an acquire-release barrier,
145 * but whereas acquire-release synchronizes cooperating threads,
146 * sequential-consistency synchronizes the whole system.
148 * memory_order_consume:
150 * A slight relaxation of memory_order_acquire.
152 * The following functions insert explicit barriers. Most of the other atomic
153 * functions also include barriers.
155 * void atomic_thread_fence(memory_order order);
157 * Inserts a barrier of the specified type.
159 * For memory_order_relaxed, this is a no-op.
161 * void atomic_signal_fence(memory_order order);
163 * Inserts a barrier of the specified type, but only with respect to
164 * signal handlers in the same thread as the barrier. This is
165 * basically a compiler optimization barrier, except for
166 * memory_order_relaxed, which is a no-op.
172 * In this section, A is an atomic type and C is the corresponding non-atomic
175 * The "store" primitives match C11:
177 * void atomic_store(A *object, C value);
178 * void atomic_store_explicit(A *object, C value, memory_order);
180 * Atomically stores 'value' into '*object', respecting the given
181 * memory order (or memory_order_seq_cst for atomic_store()).
183 * The following primitives differ from the C11 ones (and have different names)
184 * because there does not appear to be a way to implement the standard
185 * primitives in standard C:
187 * void atomic_read(A *src, C *dst);
188 * void atomic_read_explicit(A *src, C *dst, memory_order);
190 * Atomically loads a value from 'src', writing the value read into
191 * '*dst', respecting the given memory order (or memory_order_seq_cst
192 * for atomic_read()).
194 * void atomic_add(A *rmw, C arg, C *orig);
195 * void atomic_sub(A *rmw, C arg, C *orig);
196 * void atomic_or(A *rmw, C arg, C *orig);
197 * void atomic_xor(A *rmw, C arg, C *orig);
198 * void atomic_and(A *rmw, C arg, C *orig);
199 * void atomic_add_explicit(A *rmw, C arg, C *orig, memory_order);
200 * void atomic_sub_explicit(A *rmw, C arg, C *orig, memory_order);
201 * void atomic_or_explicit(A *rmw, C arg, C *orig, memory_order);
202 * void atomic_xor_explicit(A *rmw, C arg, C *orig, memory_order);
203 * void atomic_and_explicit(A *rmw, C arg, C *orig, memory_order);
205 * Atomically applies the given operation, with 'arg' as the second
206 * operand, to '*rmw', and stores the original value of '*rmw' into
207 * '*orig', respecting the given memory order (or memory_order_seq_cst
208 * if none is specified).
210 * The results are similar to those that would be obtained with +=, -=,
211 * |=, ^=, or |= on non-atomic types.
217 * atomic_flag is a typedef for a type with two states, set and clear, that
218 * provides atomic test-and-set functionality.
224 * ATOMIC_FLAG_INIT is an initializer for atomic_flag. The initial state is
227 * C11 does not have an initialization or destruction function for atomic_flag,
228 * because implementations should not need one (one may simply
229 * atomic_flag_clear() an uninitialized atomic_flag), but some implementations
230 * of the OVS atomics do need them. Thus, the following two functions are
231 * provided for initializing and destroying non-static atomic_flags:
233 * void atomic_flag_init(volatile atomic_flag *object);
235 * Initializes 'object'. The initial state is "clear".
237 * void atomic_flag_destroy(volatile atomic_flag *object);
245 * The following functions are available.
247 * bool atomic_flag_test_and_set(atomic_flag *object)
248 * bool atomic_flag_test_and_set_explicit(atomic_flag *object,
251 * Atomically sets '*object', respsecting the given memory order (or
252 * memory_order_seq_cst for atomic_flag_test_and_set()). Returns the
253 * previous value of the flag (false for clear, true for set).
255 * void atomic_flag_clear(atomic_flag *object);
256 * void atomic_flag_clear_explicit(atomic_flag *object, memory_order);
258 * Atomically clears '*object', respecting the given memory order (or
259 * memory_order_seq_cst for atomic_flag_clear()).
267 #include "compiler.h"
270 #define IN_OVS_ATOMIC_H
272 /* sparse doesn't understand some GCC extensions we use. */
273 #include "ovs-atomic-pthreads.h"
274 #elif HAVE_STDATOMIC_H
275 #include "ovs-atomic-c11.h"
276 #elif __has_extension(c_atomic)
277 #include "ovs-atomic-clang.h"
278 #elif __GNUC__ >= 4 && __GNUC_MINOR__ >= 7
279 #include "ovs-atomic-gcc4.7+.h"
280 #elif HAVE_GCC4_ATOMICS
281 #include "ovs-atomic-gcc4+.h"
283 #include "ovs-atomic-pthreads.h"
285 #undef IN_OVS_ATOMIC_H
287 #ifndef OMIT_STANDARD_ATOMIC_TYPES
288 typedef ATOMIC(bool) atomic_bool;
290 typedef ATOMIC(char) atomic_char;
291 typedef ATOMIC(signed char) atomic_schar;
292 typedef ATOMIC(unsigned char) atomic_uchar;
294 typedef ATOMIC(short) atomic_short;
295 typedef ATOMIC(unsigned short) atomic_ushort;
297 typedef ATOMIC(int) atomic_int;
298 typedef ATOMIC(unsigned int) atomic_uint;
300 typedef ATOMIC(long) atomic_long;
301 typedef ATOMIC(unsigned long) atomic_ulong;
303 typedef ATOMIC(long long) atomic_llong;
304 typedef ATOMIC(unsigned long long) atomic_ullong;
306 typedef ATOMIC(size_t) atomic_size_t;
307 typedef ATOMIC(ptrdiff_t) atomic_ptrdiff_t;
309 typedef ATOMIC(intmax_t) atomic_intmax_t;
310 typedef ATOMIC(uintmax_t) atomic_uintmax_t;
312 typedef ATOMIC(intptr_t) atomic_intptr_t;
313 typedef ATOMIC(uintptr_t) atomic_uintptr_t;
314 #endif /* !OMIT_STANDARD_ATOMIC_TYPES */
316 /* Nonstandard atomic types. */
317 typedef ATOMIC(uint8_t) atomic_uint8_t;
318 typedef ATOMIC(uint16_t) atomic_uint16_t;
319 typedef ATOMIC(uint32_t) atomic_uint32_t;
320 typedef ATOMIC(uint64_t) atomic_uint64_t;
322 typedef ATOMIC(int8_t) atomic_int8_t;
323 typedef ATOMIC(int16_t) atomic_int16_t;
324 typedef ATOMIC(int32_t) atomic_int32_t;
325 typedef ATOMIC(int64_t) atomic_int64_t;
327 /* Reference count. */
328 struct ovs_refcount {
332 /* Initializes 'refcount'. The reference count is initially 1. */
334 ovs_refcount_init(struct ovs_refcount *refcount)
336 atomic_init(&refcount->count, 1);
339 /* Destroys 'refcount'. */
341 ovs_refcount_destroy(struct ovs_refcount *refcount)
343 atomic_destroy(&refcount->count);
346 /* Increments 'refcount'. */
348 ovs_refcount_ref(struct ovs_refcount *refcount)
350 unsigned int old_refcount;
352 atomic_add(&refcount->count, 1, &old_refcount);
353 ovs_assert(old_refcount > 0);
356 /* Decrements 'refcount' and returns the previous reference count. Often used
359 * if (ovs_refcount_unref(&object->ref_cnt) == 1) {
360 * // ...uninitialize object...
364 static inline unsigned int
365 ovs_refcount_unref(struct ovs_refcount *refcount)
367 unsigned int old_refcount;
369 atomic_sub(&refcount->count, 1, &old_refcount);
370 ovs_assert(old_refcount > 0);
374 /* Reads and returns 'ref_count_''s current reference count.
377 static inline unsigned int
378 ovs_refcount_read(const struct ovs_refcount *refcount_)
380 struct ovs_refcount *refcount
381 = CONST_CAST(struct ovs_refcount *, refcount_);
384 atomic_read(&refcount->count, &count);
388 #endif /* ovs-atomic.h */