Espaços nominais
Variantes
Acções

std::atomic_fetch_add, std::atomic_fetch_add_explicit

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< cpp‎ | atomic

 
 
Biblioteca operações atômica
Tipos
Original:
Types
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atomic(C++11)
atomic_is_lock_free(C++11)
Funções
Original:
Functions
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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)
Bandeiras atômicas
Original:
Atomic flags
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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)
Inicialização
Original:
Initialization
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atomic_init(C++11)
ATOMIC_VAR_INIT(C++11)
ATOMIC_FLAG_INIT(C++11)
Memória de encomenda
Original:
Memory ordering
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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) (a partir do C++ 11)
template< class Integral >
Integral atomic_fetch_add( volatile std::atomic<Integral>* obj, Integral arg );
(2) (a partir do C++ 11)
template< class Integral >

Integral atomic_fetch_add_explicit( std::atomic<Integral>* obj, Integral arg,

                                    std::memory_order order );
(3) (a partir do C++ 11)
template< class Integral >

Integral atomic_fetch_add_explicit( volatile std::atomic<Integral>* obj, Integral arg,

                                    std::memory_order order );
(4) (a partir do C++ 11)
template< class T >
T* atomic_fetch_add( std::atomic<T*>* obj, std::ptrdiff_t arg );
(5) (a partir do C++ 11)
template< class T >
T* atomic_fetch_add( volatile std::atomic<T*>* obj, std::ptrdiff_t arg );
(6) (a partir do C++ 11)
template< class T >

T* atomic_fetch_add_explicit( std::atomic<T*>* obj, std::ptrdiff_t arg,

                              std::memory_order order );
(7) (a partir do C++ 11)
template< class T >

T* atomic_fetch_add_explicit( volatile std::atomic<T*>* obj, std::ptrdiff_t arg,

                              std::memory_order order );
(8) (a partir do C++ 11)

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)

Índice

[editar] Parâmetros

obj -
ponteiro para o objeto atômico modificar
Original:
pointer to the atomic object to modify
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arg -
o valor a adicionar ao valor armazenado no objeto atómica
Original:
the value to add to the value stored in the atomic object
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order -
o sycnhronization memória de ordenação para esta operação: todos os valores são permitidos .
Original:
the memory sycnhronization ordering for this operation: all values are permitted.
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[editar] Valor de retorno

O valor realizado anteriormente pelo objeto atômico apontado por obj
Original:
The value held previously by the atomic object pointed to by obj
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[editar] Exceções

noexcept specification:  
noexcept
  (a partir do C++ 11)

[editar] Possível implementação

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);
}

[editar] Exemplo

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

[editar] Veja também

(C++11)
atomicamente acrescenta o argumento para o valor armazenado no objeto atômico e obtém o valor retido anteriormente
Original:
atomically adds the argument to the value stored in the atomic object and obtains the value held previously
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(of std::atomic função pública membro) [edit]
subtrai um valor não atômica de um objeto atômico e obtém o valor anterior do nuclear
Original:
subtracts a non-atomic value from an atomic object and obtains the previous value of the atomic
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(modelo de função) [edit]
C documentation for atomic_fetch_add, atomic_fetch_add_explicit