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

De cppreference.com
< cpp‎ | atomic

 
 
Operaciones de biblioteca Atómica
Tipos
Original:
Types
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atomic(C++11)
atomic_is_lock_free(C++11)
Funciones
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)
Banderas atómicas
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)
Inicialización
Original:
Initialization
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atomic_init(C++11)
ATOMIC_VAR_INIT(C++11)
ATOMIC_FLAG_INIT(C++11)
Memoria pedido
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) (desde 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) (desde 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) (desde 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) (desde C++11)
Atómicamente compara el valor apuntado por obj con el valor apuntado por expected, y si estos son iguales, sustituye a la anterior con desired (realiza lectura-modificación-escritura de la operación). De lo contrario, se carga el valor actual al que apunta obj en *expected (realiza la operación 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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Los modelos de memoria para la lectura-modificación-escritura y las operaciones de carga son succ y fail respectivamente. Las versiones (1-2) std::memory_order_seq_cst utilizar por defecto .
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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Las formas débiles ((1) y (3)) de las funciones pueden fallar falsamente, es decir, actuar como si *obj != *expected incluso si son iguales. Cuando una comparación y el intercambio se encuentra en un bucle, la versión débil dará un mejor rendimiento en algunas plataformas. Cuando un débil comparación y el intercambio requeriría un lazo y una más fuerte no lo haría, el fuerte es preferible .
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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Estas funciones se definen en términos de funciones miembro 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)

Contenido

[editar] Parámetros

obj -
puntero al objeto atómico para probar y modificar
Original:
pointer to the atomic object to test and modify
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expected -
puntero al valor que se espera encontrar en el objeto atómico
Original:
pointer to the value expected to be found in the atomic object
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desired -
el valor a almacenar en el objeto atómico si es como se esperaba
Original:
the value to store in the atomic object if it is as expected
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succ -
sycnhronization la memoria de pedido para la lectura-modificación-escritura de la operación si la comparación tiene éxito. Todos los valores están 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 -
sycnhronization la memoria de pedido para la operación de carga si la comparación falla. No puede ser std::memory_order_release o std::memory_order_ack_rel y no se puede especificar más fuerte que el ordenamiento succ
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

El resultado de la comparación: true si *obj era igual a *exp, false lo contrario .
Original:
The result of the comparison: true if *obj was equal to *exp, false otherwise.
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[editar] Excepciones

noexcept specification:  
noexcept
  (desde C++11)

[editar] Ejemplo

Este ejemplo muestra como comparación y de intercambio puede ser usado para implementar sin bloqueo anexar a una lista ligada sencilla
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] Ver también

atómicamente compara el valor del objeto atómica con no atómica argumento y realiza intercambio atómico si carga igual o atómica si no
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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(miembro público of std::atomic función) [edit]
atómicamente reemplaza el valor del objeto atómico con no atómico argumento y devuelve el valor antiguo de la atómica
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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(función de plantilla) [edit]
se especializa operaciones atómicas para std :: shared_ptr
Original:
specializes atomic operations for std::shared_ptr
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(función de plantilla)
C documentation for atomic_compare_exchange, atomic_compare_exchange_explicit