std::atomic_fetch_add, std::atomic_fetch_add_explicit

 

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アトミック操作ライブラリ

タイプ Original: Types The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

atomic (C++11)

atomic_is_lock_free (C++11)

機能します Original: Functions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

atomic_store atomic_store_explicit (C++11) (C++11)

atomic_load atomic_load_explicit (C++11) (C++11)

atomic_exchange atomic_exchange_explicit (C++11) (C++11)

atomic_compare_exchange_weak atomic_compare_exchange_weak_explicit atomic_compare_exchange_strong atomic_compare_exchange_strong_explicit (C++11) (C++11) (C++11) (C++11)

atomic_fetch_add atomic_fetch_add_explicit (C++11) (C++11)

atomic_fetch_sub atomic_fetch_sub_explicit (C++11) (C++11)

atomic_fetch_and atomic_fetch_and_explicit (C++11) (C++11)

atomic_fetch_or atomic_fetch_or_explicit (C++11) (C++11)

atomic_fetch_xor atomic_fetch_xor_explicit (C++11) (C++11)

アトミックのフラグ Original: Atomic flags The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

atomic_flag (C++11)

atomic_flag_test_and_set atomic_flag_test_and_set_explicit (C++11) (C++11)

atomic_flag_clear atomic_flag_clear_explicit (C++11) (C++11)

初期化 Original: Initialization The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

atomic_init (C++11)

ATOMIC_VAR_INIT (C++11)

ATOMIC_FLAG_INIT (C++11)

メモリは発注 Original: Memory ordering The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

memory_order (C++11)

kill_dependency (C++11)

atomic_thread_fence (C++11)

atomic_signal_fence (C++11)

 

Defined in header <atomic>
template< class Integral > Integral atomic_fetch_add( std::atomic<Integral>* obj, Integral arg );	(1)	(C + + 11以来)
template< class Integral > Integral atomic_fetch_add( volatile std::atomic<Integral>* obj, Integral arg );	(2)	(C + + 11以来)
template< class Integral > Integral atomic_fetch_add_explicit( std::atomic<Integral>* obj, Integral arg,                                     std::memory_order order );	(3)	(C + + 11以来)
template< class Integral > Integral atomic_fetch_add_explicit( volatile std::atomic<Integral>* obj, Integral arg,                                     std::memory_order order );	(4)	(C + + 11以来)
template< class T > T* atomic_fetch_add( std::atomic<T*>* obj, std::ptrdiff_t arg );	(5)	(C + + 11以来)
template< class T > T* atomic_fetch_add( volatile std::atomic<T*>* obj, std::ptrdiff_t arg );	(6)	(C + + 11以来)
template< class T > T* atomic_fetch_add_explicit( std::atomic<T*>* obj, std::ptrdiff_t arg,                               std::memory_order order );	(7)	(C + + 11以来)
template< class T > T* atomic_fetch_add_explicit( volatile std::atomic<T*>* obj, std::ptrdiff_t arg,                               std::memory_order order );	(8)	(C + + 11以来)

1-2) Atomically adds arg to the value pointed to by obj and returns the value obj held previously, as if by obj->fetch_add(arg)

3-4) Atomically adds arg to the value pointed to by obj and returns the value obj held previously, as if by obj->fetch_add(arg, order)

5-6) Atomically increments the pointer value, pointed to by obj, by arg, and returns the value obj held previously, as if by obj->fetch_add(arg)

7-8) Atomically increments the pointer value, pointed to by obj, by arg, and returns the value obj held previously, as if by obj->fetch_add(arg, order)

パラメータ

obj	-	変更するアトミックオブジェクトへのポインタ Original: pointer to the atomic object to modify The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
arg	-	原子オブジェクトに格納された値に追加する値 Original: the value to add to the value stored in the atomic object The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
order	-	メモリsycnhronizationは、この操作の順序：すべての値が許可されています. Original: the memory sycnhronization ordering for this operation: all values are permitted. The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

値を返します

原子オブジェクトによって以前に開催された値がobjが指す

Original:

The value held previously by the atomic object pointed to by obj

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例外

noexcept specification:  

noexcept

  (C + + 11以来)

可能な実装

First version
template< class T > typename std::enable_if<std::is_integral<T>::value && !std::is_same<T, bool>::value, T>::type atomic_fetch_add( std::atomic<T>* obj, T arg ); { return obj->fetch_add(arg); }
Second version
template< class T > T* atomic_fetch_add( std::atomic<T*>* obj, std::ptrdiff_t arg) { return obj->fetch_add(arg); }

例

Single-writer/multiple-reader lock can be made with fetch_add. Note that this simplistic implementation is not lockout-free

#include <string>
#include <thread>
#include <vector>
#include <iostream>
#include <atomic>
#include <chrono>
 
// meaning of cnt:
// 10: there are no active readers or writers.
// 1...9: there are 9...1 readers active, The writer is blocked
// 0: temporary value between fetch_sub and fetch_add in reader lock
// -1: there is a writer active. The readers are blocked.
const int N = 10; // nine concurrent readers are allowed
std::atomic<int> cnt = ATOMIC_VAR_INIT(N);
 
std::vector<int> data;
 
void reader(int id)
{
    for(;;)
    {
        // lock
        while(std::atomic_fetch_sub(&cnt, 1) <= 0)
            std::atomic_fetch_add(&cnt, 1);
        // read
        if(!data.empty())
            std::cout << (  "reader " + std::to_string(id)
                          + " sees " + std::to_string(*data.rbegin()) + '\n');
        if(data.size() == 100)
            break;
        // unlock
        std::atomic_fetch_add(&cnt, 1);
        // pause
        std::this_thread::sleep_for(std::chrono::milliseconds(1));
    }
}
 
void writer()
{
    for(int n = 0; n < 100; ++n)
    {
        // lock
        while(std::atomic_fetch_sub(&cnt, N+1) != N)
            std::atomic_fetch_add(&cnt, N+1);
        // write
        data.push_back(n);
        std::cout << "writer pushed back " << n << '\n';
        // unlock
        std::atomic_fetch_add(&cnt, N+1);
        // pause
        std::this_thread::sleep_for(std::chrono::milliseconds(1));
    }
}
 
int main()
{
    std::vector<std::thread> v;
    for (int n = 0; n < N; ++n) {
        v.emplace_back(reader, n);
    }
    v.emplace_back(writer);
    for (auto& t : v) {
        t.join();
    }
}

Output:

writer pushed back 0
reader 8 sees 0
reader 3 sees 0
reader 1 sees 0
<...>
reader 2 sees 99
reader 6 sees 99
reader 1 sees 99

も参照してください

fetch_add (C++11)	アトミックアトミックオブジェクトに格納された値に引数を追加し、以前に保持している値を取得します Original: atomically adds the argument to the value stored in the atomic object and obtains the value held previously The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (パブリックメンバ関数of std::atomic)
atomic_fetch_sub atomic_fetch_sub_explicit (C++11) (C++11)	原子オブジェクトから非アトミック値を減算し、アトミックの前の値を取得します Original: subtracts a non-atomic value from an atomic object and obtains the previous value of the atomic The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (関数テンプレート)
C documentation for atomic_fetch_add, atomic_fetch_add_explicit