C++11 并发指南六( <atomic> 类型详解二 std::atomic ) 介绍了基本的原子类型 std::atomic 的用法，本节我会给大家介绍C++11 标准库中的 std::atomic 针对整形(integral)和指针类型的特化版本做了哪些改进。
总地来说，C++11 标准库中的 std::atomic 针对整形(integral)和指针类型的特化版本新增了一些算术运算和逻辑运算操作。具体如下：
integral fetch_add(integral, memory_order = memory_order_seq_cst) volatile;
integral fetch_add(integral, memory_order = memory_order_seq_cst);
integral fetch_sub(integral, memory_order = memory_order_seq_cst) volatile;
integral fetch_sub(integral, memory_order = memory_order_seq_cst);
integral fetch_and(integral, memory_order = memory_order_seq_cst) volatile;
integral fetch_and(integral, memory_order = memory_order_seq_cst);
integral fetch_or(integral, memory_order = memory_order_seq_cst) volatile;
integral fetch_or(integral, memory_order = memory_order_seq_cst);
integral fetch_xor(integral, memory_order = memory_order_seq_cst) volatile;
integral fetch_xor(integral, memory_order = memory_order_seq_cst);
integral operator++(int) volatile;
integral operator++(int);
integral operator--(int) volatile;
integral operator--(int);
integral operator++() volatile;
integral operator++();
integral operator--() volatile;
integral operator--();
integral operator+=(integral) volatile;
integral operator+=(integral);
integral operator-=(integral) volatile;
integral operator-=(integral);
integral operator&=(integral) volatile;
integral operator&=(integral);
integral operator|=(integral) volatile;
integral operator|=(integral);
integral operator^=(integral) volatile;
integral operator^=(integral);
下面我们来简单介绍以上的 std::atomic 特化版本的成员函数。
- fetch_add
| if T is integral (1) |
T fetch_add (T val, memory_order sync = memory_order_seq_cst) volatile noexcept;
T fetch_add (T val, memory_order sync = memory_order_seq_cst) noexcept;
|
| if T is pointer (2) |
T fetch_add (ptrdiff_t val, memory_order sync = memory_order_seq_cst) volatile noexcept;
T fetch_add (ptrdiff_t val, memory_order sync = memory_order_seq_cst) noexcept;
|
- 将原子对象的封装值加 val，并返回原子对象的旧值（适用于整形和指针类型的 std::atomic 特化版本），整个过程是原子的。sync 参数指定内存序：
| Memory Order 值 |
Memory Order 类型 |
| memory_order_relaxed |
Relaxed |
| memory_order_consume |
Consume |
| memory_order_acquire |
Acquire |
| memory_order_release |
Release |
| memory_order_acq_rel |
Acquire/Release |
| memory_order_seq_cst |
Sequentially consistent |
- 另外，如果第二个参数不指定（取默认参数 memory_order_seq_cst），则 fetch_add 相当与 std::atomic::operator+=。
- fetch_sub
| if T is integral (1) |
T fetch_sub (T val, memory_order sync = memory_order_seq_cst) volatile noexcept;
T fetch_sub (T val, memory_order sync = memory_order_seq_cst) noexcept;
|
| if T is pointer (2) |
T fetch_sub (ptrdiff_t val, memory_order sync = memory_order_seq_cst) volatile noexcept;
T fetch_sub (ptrdiff_t val, memory_order sync = memory_order_seq_cst) noexcept;
|
- 将原子对象的封装值减 val，并返回原子对象的旧值（适用于整形和指针类型的 std::atomic 特化版本），整个过程是原子的。sync 参数指定内存序：
| Memory Order 值 |
Memory Order 类型 |
| memory_order_relaxed |
Relaxed |
| memory_order_consume |
Consume |
| memory_order_acquire |
Acquire |
| memory_order_release |
Release |
| memory_order_acq_rel |
Acquire/Release |
| memory_order_seq_cst |
Sequentially consistent |
- 另外，如果第二个参数不指定（取默认参数 memory_order_seq_cst），则 fetch_sub 相当与 std::atomic::operator-=。
- fetch_and
T fetch_and (T val, memory_order sync = memory_order_seq_cst) volatile noexcept;
T fetch_and (T val, memory_order sync = memory_order_seq_cst) noexcept;
- 将原子对象的封装值按位与 val，并返回原子对象的旧值（只适用于整型的 std::atomic 特化版本），整个过程是原子的。sync 参数指定内存序：
| Memory Order 值 |
Memory Order 类型 |
| memory_order_relaxed |
Relaxed |
| memory_order_consume |
Consume |
| memory_order_acquire |
Acquire |
| memory_order_release |
Release |
| memory_order_acq_rel |
Acquire/Release |
| memory_order_seq_cst |
Sequentially consistent |
- 另外，如果第二个参数不指定（取默认参数 memory_order_seq_cst），则 fetch_add 相当与 std::atomic::operator&=。
- fetch_or
T fetch_or (T val, memory_order sync = memory_order_seq_cst) volatile noexcept;
T fetch_or (T val, memory_order sync = memory_order_seq_cst) noexcept;
- 将原子对象的封装值按位或 val，并返回原子对象的旧值（只适用于整型的 std::atomic 特化版本），整个过程是原子的。sync 参数指定内存序：
| Memory Order 值 |
Memory Order 类型 |
| memory_order_relaxed |
Relaxed |
| memory_order_consume |
Consume |
| memory_order_acquire |
Acquire |
| memory_order_release |
Release |
| memory_order_acq_rel |
Acquire/Release |
| memory_order_seq_cst |
Sequentially consistent |
- 另外，如果第二个参数不指定（取默认参数 memory_order_seq_cst），则 fetch_or 相当与 std::atomic::operator|=。
- fetch_xor
T fetch_xor (T val, memory_order sync = memory_order_seq_cst) volatile noexcept;
T fetch_xor (T val, memory_order sync = memory_order_seq_cst) noexcept;
- 将原子对象的封装值按位异或 val，并返回原子对象的旧值（只适用于整型的 std::atomic 特化版本），整个过程是原子的。sync 参数指定内存序：
| Memory Order 值 |
Memory Order 类型 |
| memory_order_relaxed |
Relaxed |
| memory_order_consume |
Consume |
| memory_order_acquire |
Acquire |
| memory_order_release |
Release |
| memory_order_acq_rel |
Acquire/Release |
| memory_order_seq_cst |
Sequentially consistent |
- 另外，如果第二个参数不指定（取默认参数 memory_order_seq_cst），则 fetch_xor 相当与 std::atomic::operator^=。
- operator++
| pre-increment (1) |
T operator++() volatile noexcept;
T operator++() noexcept;
|
| post-increment (2) |
T operator++ (int) volatile noexcept;
T operator++ (int) noexcept;
|
- 自增运算符重载， 第一种形式 (1) 返回自增后的值（即前缀++），第二种形式(2) 返回自增前的值（即后缀++），适用于整形和指针类型的 std::atomic 特化版本。
- operator--
- 自减运算符重载， 第一种形式 (1) 返回自减后的值（即前缀--），第二种形式(2) 返回自减前的值（即后缀--），适用于整形和指针类型的 std::atomic 特化版本。
- atomic::operator (comp. assign.)
- 复合赋值运算符重载，主要包含以下形式：
| if T is integral (1) |
T operator+= (T val) volatile noexcept;
T operator+= (T val) noexcept;
T operator-= (T val) volatile noexcept;
T operator-= (T val) noexcept;
T operator&= (T val) volatile noexcept;
T operator&= (T val) noexcept;
T operator|= (T val) volatile noexcept;
T operator|= (T val) noexcept;
T operator^= (T val) volatile noexcept;
T operator^= (T val) noexcept;
|
| if T is pointer (2) |
T operator+= (ptrdiff_t val) volatile noexcept;
T operator+= (ptrdiff_t val) noexcept;
T operator-= (ptrdiff_t val) volatile noexcept;
T operator-= (ptrdiff_t val) noexcept;
|
以上各个 operator 都会有对应的 fetch_* 操作，详细见下表：
| 操作符 |
成员函数 |
支持类型 |
| 复合赋值 |
等价于 |
整型 |
指针类型 |
其他类型 |
+ |
atomic::operator+= |
atomic::fetch_add |
是 |
是 |
否 |
- |
atomic::operator-= |
atomic::fetch_sub |
是 |
是 |
否 |
& |
atomic::operator&= |
atomic::fetch_and |
是 |
否 |
否 |
| |
atomic::operator|= |
atomic::fetch_or |
是 |
否 |
否 |
^ |
atomic::operator^= |
atomic::fetch_xor |
是 |
否 |
否 |
好了，本节先介绍这里，下一节我会介绍 C++11 中 C 风格的原子操作 API。
