本文深入探讨了FRR路由套件中ATOMIC模块的实现细节，该模块利用GCC特性提供原子操作支持。文章详细解释了不同GCC版本下原子操作的具体实现方式，包括宏定义、内存顺序标记以及特定GCC函数的使用，为后续项目提供了有价值的参考。
FRR的ATOMIC 利用GCC的实现，后续项目可以参考
/*
* Copyright (c) 2015-16 David Lamparter, for NetDEF, Inc.
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#ifndef _FRRATOMIC_H
#define _FRRATOMIC_H
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#ifndef FRR_AUTOCONF_ATOMIC
#error autoconf checks for atomic functions were not properly run
#endif
/* ISO C11 */
#ifdef HAVE_STDATOMIC_H
#include <stdatomic.h>
/* These are available in gcc, but not in stdatomic */
#define atomic_add_fetch_explicit __atomic_add_fetch
#define atomic_sub_fetch_explicit __atomic_sub_fetch
#define atomic_and_fetch_explicit __atomic_and_fetch
#define atomic_or_fetch_explicit __atomic_or_fetch
/* gcc 4.7 and newer */
#elif defined(HAVE___ATOMIC)
#define _Atomic volatile
#define memory_order_relaxed __ATOMIC_RELAXED
#define memory_order_consume __ATOMIC_CONSUME
#define memory_order_acquire __ATOMIC_ACQUIRE
#define memory_order_release __ATOMIC_RELEASE
#define memory_order_acq_rel __ATOMIC_ACQ_REL
#define memory_order_seq_cst __ATOMIC_SEQ_CST
#define atomic_load_explicit __atomic_load_n
#define atomic_store_explicit __atomic_store_n
#define atomic_exchange_explicit __atomic_exchange_n
#define atomic_fetch_add_explicit __atomic_fetch_add
#define atomic_fetch_sub_explicit __atomic_fetch_sub
#define atomic_fetch_and_explicit __atomic_fetch_and
#define atomic_fetch_or_explicit __atomic_fetch_or
#define atomic_add_fetch_explicit __atomic_add_fetch
#define atomic_sub_fetch_explicit __atomic_sub_fetch
#define atomic_and_fetch_explicit __atomic_and_fetch
#define atomic_or_fetch_explicit __atomic_or_fetch
#define atomic_compare_exchange_weak_explicit(atom, expect, desire, mem1, \
mem2) \
__atomic_compare_exchange_n(atom, expect, desire, 1, mem1, mem2)
/* gcc 4.1 and newer,
* clang 3.3 (possibly older)
*
* __sync_swap isn't in gcc's documentation, but clang has it
*
* note __sync_synchronize()
*/
#elif defined(HAVE___SYNC)
#define _Atomic volatile
#define memory_order_relaxed 0
#define memory_order_consume 0
#define memory_order_acquire 0
#define memory_order_release 0
#define memory_order_acq_rel 0
#define memory_order_seq_cst 0
#define atomic_load_explicit(ptr, mem) \
({ \
__sync_synchronize(); \
typeof(*ptr) rval = __sync_fetch_and_add((ptr), 0); \
__sync_synchronize(); \
rval; \
})
#define atomic_store_explicit(ptr, val, mem) \
({ \
__sync_synchronize(); \
*(ptr) = (val); \
__sync_synchronize(); \
(void)0; \
})
#ifdef HAVE___SYNC_SWAP
#define atomic_exchange_explicit(ptr, val, mem) \
({ \
__sync_synchronize(); \
typeof(*ptr) rval = __sync_swap((ptr, val), 0); \
__sync_synchronize(); \
rval; \
})
#else /* !HAVE___SYNC_SWAP */
#define atomic_exchange_explicit(ptr, val, mem) \
({ \
typeof(ptr) _ptr = (ptr); \
typeof(val) _val = (val); \
__sync_synchronize(); \
typeof(*ptr) old1, old2 = __sync_fetch_and_add(_ptr, 0); \
do { \
old1 = old2; \
old2 = __sync_val_compare_and_swap(_ptr, old1, _val); \
} while (old1 != old2); \
__sync_synchronize(); \
old2; \
})
#endif /* !HAVE___SYNC_SWAP */
#define atomic_fetch_add_explicit(ptr, val, mem) \
({ \
__sync_synchronize(); \
typeof(*ptr) rval = __sync_fetch_and_add((ptr), (val)); \
__sync_synchronize(); \
rval; \
})
#define atomic_fetch_sub_explicit(ptr, val, mem) \
({ \
__sync_synchronize(); \
typeof(*ptr) rval = __sync_fetch_and_sub((ptr), (val)); \
__sync_synchronize(); \
rval; \
})
#define atomic_compare_exchange_weak_explicit(atom, expect, desire, mem1, \
mem2) \
({ \
typeof(atom) _atom = (atom); \
typeof(expect) _expect = (expect); \
typeof(desire) _desire = (desire); \
__sync_synchronize(); \
typeof(*atom) rval = \
__sync_val_compare_and_swap(_atom, *_expect, _desire); \
__sync_synchronize(); \
bool ret = (rval == *_expect); \
*_expect = rval; \
ret; \
})
#define atomic_fetch_and_explicit(ptr, val, mem) \
({ \
__sync_synchronize(); \
typeof(*ptr) rval = __sync_fetch_and_and(ptr, val); \
__sync_synchronize(); \
rval; \
})
#define atomic_fetch_or_explicit(ptr, val, mem) \
({ \
__sync_synchronize(); \
typeof(*ptr) rval = __sync_fetch_and_or(ptr, val); \
__sync_synchronize(); \
rval; \
})
#define atomic_add_fetch_explicit(ptr, val, mem) \
({ \
__sync_synchronize(); \
typeof(*ptr) rval = __sync_add_and_fetch((ptr), (val)); \
__sync_synchronize(); \
rval; \
})
#define atomic_sub_fetch_explicit(ptr, val, mem) \
({ \
__sync_synchronize(); \
typeof(*ptr) rval = __sync_sub_and_fetch((ptr), (val)); \
__sync_synchronize(); \
rval; \
})
#define atomic_and_fetch_explicit(ptr, val, mem) \
({ \
__sync_synchronize(); \
typeof(*ptr) rval = __sync_and_and_fetch(ptr, val); \
__sync_synchronize(); \
rval; \
})
#define atomic_or_fetch_explicit(ptr, val, mem) \
({ \
__sync_synchronize(); \
typeof(*ptr) rval = __sync_or_and_fetch(ptr, val); \
__sync_synchronize(); \
rval; \
})
#else /* !HAVE___ATOMIC && !HAVE_STDATOMIC_H */
#error no atomic functions...
#endif
#endif /* _FRRATOMIC_H */
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