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std::atomic::compare_exchange_weak, std::atomic::compare_exchange_strong

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< cpp‎ | atomic‎ | atomic

 
 
Atomique opérations de la bibliothèque
Types
Original:
Types
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atomic (C++11)
atomic_is_lock_free (C++11)
Fonctions
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)
Drapeaux atomiques
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)
Initialisation
Original:
Initialization
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atomic_init (C++11)
ATOMIC_VAR_INIT (C++11)
ATOMIC_FLAG_INIT (C++11)
Mémoire de la commande
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Memory ordering
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memory_order (C++11)
kill_dependency (C++11)
atomic_thread_fence (C++11)
atomic_signal_fence (C++11)
 
std::atomic
Les fonctions membres
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Member functions
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atomic::atomic
atomic::operator=
atomic::is_lock_free
atomic::store
atomic::load
atomic::operator T
atomic::exchange
atomic::compare_exchange
Fonctions membres spécialisés
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Specialized member functions
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atomic::fetch_add
atomic::fetch_sub
atomic::fetch_and
atomic::fetch_or
atomic::fetch_xor
atomic::operator++
atomic::operator++(int)
atomic::operator--
atomic::operator--(int)
atomic::operator+=
atomic::operator-=
atomic::operator&=
atomic::operator|=
atomic::operator^=
 
Defined in header <atomic>
bool compare_exchange_weak( T& expected, T desired,

                            std::memory_order success,
                            std::memory_order failure );

bool compare_exchange_weak( T& expected, T desired,
                            std::memory_order success,

                            std::memory_order failure ) volatile;
(1) (depuis C++11)
bool compare_exchange_weak( T& expected, T desired,

                            std::memory_order order =
                                std::memory_order_seq_cst );

bool compare_exchange_weak( T& expected, T desired,
                            std::memory_order order =

                                std::memory_order_seq_cst ) volatile;
(2) (depuis C++11)
bool compare_exchange_strong( T& expected, T desired,

                              std::memory_order success,
                              std::memory_order failure );

bool compare_exchange_strong( T& expected, T desired,
                              std::memory_order success,

                              std::memory_order failure ) volatile;
(3) (depuis C++11)
bool compare_exchange_strong( T& expected, T desired,

                              std::memory_order order =
                                  std::memory_order_seq_cst );

bool compare_exchange_strong( T& expected, T desired,
                              std::memory_order order =

                                  std::memory_order_seq_cst ) volatile;
(4) (depuis C++11)
Compare atomiquement la valeur stockée dans *this avec la valeur pointée par expected, et si ceux-ci sont égaux, remplace l'ancien desired (effectue lecture-modification-écriture). Sinon, charge la valeur réelle stockée dans *this en *expected (effectue une opération de charge) .
Original:
Atomically compares the value stored in *this 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 stored in *this into *expected (performs load operation).
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Les modèles de la mémoire pour la lecture-modification-écriture et les opérations de chargement et sont success failure respectivement. Dans l'(2) ​​et (4) versions order est utilisé à la fois pour lire-modifier-écrire et charger des opérations, sauf que std::memory_order_release et std::memory_order_relaxed sont utilisés pour l'opération de chargement si order == std::memory_order_acq_rel, ou order == std::memory_order_release respectivement .
Original:
The memory models for the read-modify-write and load operations are success and failure respectively. In the (2) and (4) versions order is used for both read-modify-write and load operations, except that std::memory_order_release and std::memory_order_relaxed are used for the load operation if order == std::memory_order_acq_rel, or order == std::memory_order_release respectively.
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Les formes faibles (1-2) des fonctions sont autorisés à ne pas faussement, qui est, comme si *this != *expected même si elles sont égales. Quand une comparaison et d'échange est dans une boucle, la version faible donnera de meilleures performances sur certaines plates-formes. Quand un faible compare-and-échange, il faudrait une boucle et une forte ne serait pas, le fort est préférable .
Original:
The weak forms (1-2) of the functions are allowed to fail spuriously, that is, act as if *this != *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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Sommaire

[modifier] Paramètres

expected -
pointeur à la valeur prévue pour être trouvé dans l'objet atomique
Original:
pointer to the value expected to be found in the atomic object
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desired -
la valeur à stocker dans l'objet atomique si elle est conforme aux attentes
Original:
the value to store in the atomic object if it is as expected
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success -
la synchronisation de la mémoire de commande de lecture-modification-écriture, si la comparaison aboutit. Toutes les valeurs sont permises .
Original:
the memory synchronization ordering for the read-modify-write operation if the comparison succeeds. All values are permitted.
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failure -
la synchronisation de mémoire de commande pour l'opération de chargement si la comparaison échoue. Ne peut pas être std::memory_order_release ou std::memory_order_ack_rel et ne pouvez pas spécifier plus forte que success ordre
Original:
the memory synchronization 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 success
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order -
la synchronisation de mémoire de commande pour les deux opérations
Original:
the memory synchronization ordering for both operations
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[modifier] Retourne la valeur

true si la valeur sous-jacente atomique a été changé, false autrement .
Original:
true if the underlying atomic value was changed, false otherwise.
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[modifier] Exceptions

noexcept specification:  
noexcept
   (depuis C++11)

[modifier] Exemple

Montre comment compare_exchange_strong soit des changements de la valeur de la variable atomique ou la variable de référence .
Original:
Demonstrates how compare_exchange_strong either changes the value of the atomic variable or the variable used for comparison.
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#include <atomic>
#include <iostream>
 
std::atomic<int>  ai;
 
int  tst_val= 4;
int  new_val= 5;
bool exchanged= false;
 
void valsout()
{
    std::cout << "ai= " << ai
	      << "  tst_val= " << tst_val
	      << "  new_val= " << new_val
	      << "  exchanged= " << std::boolalpha << exchanged
	      << "\n";
}
 
int main()
{
    ai= 3;
    valsout();
 
    // tst_val != ai   ==>  tst_val is modified
    exchanged= ai.compare_exchange_strong( tst_val, new_val );
    valsout();
 
    // tst_val == ai   ==>  ai is modified
    exchanged= ai.compare_exchange_strong( tst_val, new_val );
    valsout();
 
    return 0;
}

Résultat :

ai= 3  tst_val= 4  new_val= 5  exchanged= false
ai= 3  tst_val= 3  new_val= 5  exchanged= false
ai= 5  tst_val= 3  new_val= 5  exchanged= true

[modifier] Voir aussi

compare atomiquement la valeur de l'objet atomique non atomique avec l'argument, et réalise un échange atomique égal ou si la charge atomique sinon
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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(fonction générique) [edit]