FRR - 基础数据结构篇 - 数据同步atomlist.c
程序员文章站
2024-02-13 20:42:28
...
atomlist.c和atomlist.h文件中数据的解读离不开frratomic.h文件。
数据
/* atomic_atomptr_t may look a bit odd, it's for the sake of C++ compat */
typedef uintptr_t atomptr_t;
typedef atomic_uintptr_t atomic_atomptr_t; //可能有些冗余，为了C++兼容看到这里可能有些迷糊，uintptr_t 和 atomic_uintptr_t 又是什么类型呢？在linux平台的/usr/include/stdint.h头文件中有如下定义：
/* Types for `void *' pointers. */
#if __WORDSIZE == 64 //64位机器
# ifndef __intptr_t_defined
typedef long int intptr_t;
# define __intptr_t_defined
# endif
typedef unsigned long int uintptr_t;
#else //32位机器
# ifndef __intptr_t_defined
typedef int intptr_t;
# define __intptr_t_defined
# endif
typedef unsigned int uintptr_t;
#endif在64位的机器上，intptr_t和uintptr_t分别是long int、unsigned long int的别名；在32位的机器上，intptr_t和uintptr_t分别是int、unsigned int的别名。这两个数据类型别名也是为了“void *”指针。在C语言中，任何类型的指针都可以转换为void *类型，并且在将它转换回原来的类型时不会丢失信息。
此外，在frratomic.h中有以下定义
/* ISO C11 */
#ifdef __cplusplus
#include <stdint.h>
#include <atomic>
using std::atomic_int;
using std::memory_order;
using std::memory_order_relaxed; //并行编程:设定6中指令执行顺序
using std::memory_order_acquire;
using std::memory_order_release;
using std::memory_order_acq_rel;
using std::memory_order_consume;
using std::memory_order_seq_cst;
typedef std::atomic<bool> atomic_bool; //多线程，原子类型
typedef std::atomic<size_t> atomic_size_t;
typedef std::atomic<uint_fast32_t> atomic_uint_fast32_t;
typedef std::atomic<uintptr_t> atomic_uintptr_t;
#elif defined(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 _ATOMIC_WANT_TYPEDEFS
#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)
#define atomic_compare_exchange_strong_explicit(atom, expect, desire, mem1, \
mem2) \
__atomic_compare_exchange_n(atom, expect, desire, 0, 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 _ATOMIC_WANT_TYPEDEFS
#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_strong_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_compare_exchange_weak_explicit \
atomic_compare_exchange_strong_explicit
#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
#include <stdint.h>
#include <stdbool.h>
typedef _Atomic bool atomic_bool;
typedef _Atomic size_t atomic_size_t;
typedef _Atomic uint_fast32_t atomic_uint_fast32_t;
typedef _Atomic uintptr_t atomic_uintptr_t;
#endif其中memory_order等6种解释过并行编程。对于atomic_TYPE来说，如果定义C++，则用的是原子类型，否则就是volatile类型的别名。对于C++中的原子类型，具体可参考c++11 多线程（3）atomic 总结。
可以知道对于变量，用是原子变量或者volatile，对于变量的获取和修改会用__sync_synchronize()防止指令优化扰乱原本的顺序，即内存屏障。
上一篇： CCNP1-CCNA回顾+浮动静态路由