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

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
- atomic::operator-= atomic::fetch_sub
& atomic::operator&= atomic::fetch_and
| atomic::operator|= atomic::fetch_or
^ atomic::operator^= atomic::fetch_xor

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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