C++11 并发指南六(atomic 类型详解三 std::atomic (续))

2023-01-25 11:02:48

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。

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