Espaços nominais
Variantes
Acções

std::atomic_compare_exchange_weak, std::atomic_compare_exchange_strong, std::atomic_compare_exchange_weak_explicit, std::atomic_compare_exchange_strong_explicit

Da cppreference.com
< 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 T >

bool atomic_compare_exchange_weak( std::atomic<T>* obj,
                                   T* expected, T desired );
template< class T >
bool atomic_compare_exchange_weak( volatile std::atomic<T>* obj,

                                   T* expected, T desired );
(1) (a partir do C++ 11)
template< class T >

bool atomic_compare_exchange_strong( std::atomic<T>* obj,
                                     T* expected, T desired );
template< class T >
bool atomic_compare_exchange_strong( volatile std::atomic<T>* obj,

                                     T* expected, T desired );
(2) (a partir do C++ 11)
template< class T >

bool atomic_compare_exchange_weak_explicit( std::atomic<T>* obj,
                                            T* expected, T desired,
                                            std::memory_order succ,
                                            std::memory_order fail );
template< class T >
bool atomic_compare_exchange_weak_explicit( volatile std::atomic<T>* obj,
                                            T* expected, T desired,
                                            std::memory_order succ,

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

bool atomic_compare_exchange_strong_explicit( std::atomic<T>* obj,
                                              T* expected, T desired,
                                              std::memory_order succ,
                                              std::memory_order fail );
template< class T >
bool atomic_compare_exchange_strong_explicit( volatile std::atomic<T>* obj,
                                              T* expected, T desired,
                                              std::memory_order succ,

                                              std::memory_order fail );
(4) (a partir do C++ 11)
Atomicamente compara o valor apontado por obj com o valor apontado por expected, e se estas forem iguais, substitui o ex-desired (executa ler-modificar-escrever a operação). Caso contrário, carrega o valor real apontado por obj em *expected (executa a operação de carga).
Original:
Atomically compares the value pointed to by obj with the value pointed to by expected, and if those are equal, replaces the former with desired (performs read-modify-write operation). Otherwise, loads the actual value pointed to by obj into *expected (performs load operation).
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Os modelos de memória para a leitura-modificação-gravação e operações de carga são succ e fail respectivamente. As versões (1-2) usar std::memory_order_seq_cst por padrão.
Original:
The memory models for the read-modify-write and load operations are succ and fail respectively. The (1-2) versions use std::memory_order_seq_cst by default.
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As formas fracas ((1) e (3)) das funções podem falhar spuriously, isto é, actuar como se *obj != *expected mesmo se eles forem iguais. Quando uma comparação e troca-se em um loop, a versão fraca trará melhor desempenho em algumas plataformas. Quando um fraco comparar-e-troca exigiria um laço e um forte não, o forte é preferível.
Original:
The weak forms ((1) and (3)) of the functions are allowed to fail spuriously, that is, act as if *obj != *expected even if they are equal. When a compare-and-exchange is in a loop, the weak version will yield better performance on some platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the strong one is preferable.
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Essas funções são definidas em termos de funções de membro de std::atomic:
Original:
These functions are defined in terms of member functions of std::atomic:
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1) obj->compare_exchange_weak(exp, desr)
2) obj->compare_exchange_strong(exp, desr)
3) obj->compare_exchange_weak(exp, desr, succ, fail)
4) obj->compare_exchange_strong(exp, desr, succ, fail)

Índice

[editar] Parâmetros

obj -
ponteiro para o objeto atômico para testar e modificar
Original:
pointer to the atomic object to test and modify
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expected -
ponteiro para o valor esperado para ser encontrado no objeto atómica
Original:
pointer to the value expected to be found in the atomic object
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desired -
o valor para armazenar no objeto atômico se for como o esperado
Original:
the value to store in the atomic object if it is as expected
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succ -
o sycnhronization memória de ordenação para a leitura-modificação-gravação operação, se a comparação for bem-sucedido. Todos os valores são permitidos .
Original:
the memory sycnhronization ordering for the read-modify-write operation if the comparison succeeds. All values are permitted.
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fail -
o sycnhronization memória de ordenação para a operação de carga se a comparação falhar. Não pode ser std::memory_order_release ou std::memory_order_ack_rel e não pode especificar mais forte do que succ ordenação
Original:
the memory sycnhronization ordering for the load operation if the comparison fails. Cannot be std::memory_order_release or std::memory_order_ack_rel and cannot specify stronger ordering than succ
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[editar] Valor de retorno

O resultado da comparação: true se *obj foi igual a *exp, false contrário.
Original:
The result of the comparison: true if *obj was equal to *exp, false otherwise.
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[editar] Exceções

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

[editar] Exemplo

Este exemplo mostra como comparar-e-troca pode ser usado para implementar sem bloqueio de acrescentar a uma lista vinculada isoladamente
Original:
This example shows how compare-and-exchange may be used to implement lock-free append to a singly linked list
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void append(list* s, node* n)
{
    node* head;
    do {
        head = s->head;
        n->next = head;
    } while(! std::atomic_compare_exchange_weak(s->head, head, n));
}


[editar] Veja também

atomicamente compara o valor do objeto atômico com não atômica argumento e realiza troca atômica se carga igual ou atômica se não
Original:
atomically compares the value of the atomic object with non-atomic argument and performs atomic exchange if equal or atomic load if not
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(of std::atomic função pública membro) [edit]
atomicamente substitui o valor do objeto atômico com não atômica argumento e retorna o valor antigo do atômica
Original:
atomically replaces the value of the atomic object with non-atomic argument and returns the old value of the atomic
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(modelo de função) [edit]
especializada operações atômicas para std :: shared_ptr
Original:
specializes atomic operations for std::shared_ptr
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(modelo de função)
C documentation for atomic_compare_exchange, atomic_compare_exchange_explicit