C++11 併發指南六(atomic 類型詳解三 std::atomic (續))

C++11 併發指南六( <atomic> 類型詳解二 std::atomic ) 介紹了基本的原子類型 std::atomic 的用法，本節我會給你們介紹C++11 標準庫中的 std::atomic 針對整形(integral)和指針類型的特化版本作了哪些改進。

總地來講，C++11 標準庫中的 std::atomic 針對整形(integral)和指針類型的特化版本新增了一些算術運算和邏輯運算操做。具體以下：

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);

 下面咱們來簡單介紹以上的 std::atomic 特化版本的成員函數。

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;

將原子對象的封裝值加 val，並返回原子對象的舊值（適用於整形和指針類型的 std::atomic 特化版本），整個過程是原子的。sync 參數指定內存序：

Memory Order 值	Memory Order 類型
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，若是第二個參數不指定（取默認參數 memory_order_seq_cst），則 fetch_add 至關與 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;

將原子對象的封裝值減 val，並返回原子對象的舊值（適用於整形和指針類型的 std::atomic 特化版本），整個過程是原子的。sync 參數指定內存序：

Memory Order 值	Memory Order 類型
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，若是第二個參數不指定（取默認參數 memory_order_seq_cst），則 fetch_sub 至關與 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;

 

將原子對象的封裝值按位與 val，並返回原子對象的舊值（只適用於整型的 std::atomic 特化版本），整個過程是原子的。sync 參數指定內存序：

Memory Order 值	Memory Order 類型
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，若是第二個參數不指定（取默認參數 memory_order_seq_cst），則 fetch_add 至關與 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;

 

將原子對象的封裝值按位或 val，並返回原子對象的舊值（只適用於整型的 std::atomic 特化版本），整個過程是原子的。sync 參數指定內存序：

Memory Order 值	Memory Order 類型
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，若是第二個參數不指定（取默認參數 memory_order_seq_cst），則 fetch_or 至關與 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;

將原子對象的封裝值按位異或 val，並返回原子對象的舊值（只適用於整型的 std::atomic 特化版本），整個過程是原子的。sync 參數指定內存序：

Memory Order 值	Memory Order 類型
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，若是第二個參數不指定（取默認參數 memory_order_seq_cst），則 fetch_xor 至關與 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;

自增運算符重載， 第一種形式 (1) 返回自增後的值（即前綴++），第二種形式(2) 返回自增前的值（即後綴++），適用於整形和指針類型的 std::atomic 特化版本。

operator--

自減運算符重載， 第一種形式 (1) 返回自減後的值（即前綴--），第二種形式(2) 返回自減前的值（即後綴--），適用於整形和指針類型的 std::atomic 特化版本。

atomic::operator (comp. assign.)

複合賦值運算符重載，主要包含如下形式：

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;

以上各個 operator 都會有對應的 fetch_* 操做，詳細見下表：

操做符	成員函數		支持類型
	複合賦值	等價於	整型	指針類型	其餘類型
+	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，本節先介紹這裏，下一節我會介紹 C++11 中 C 風格的原子操做 API。