Namespace
Varianti

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

 
 
Atomic operazioni di biblioteca
Tipi
Original:
Types
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atomic(C++11)
atomic_is_lock_free(C++11)
Funzioni
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)
Bandiere Atomic
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)
Inizializzazione
Original:
Initialization
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atomic_init(C++11)
ATOMIC_VAR_INIT(C++11)
ATOMIC_FLAG_INIT(C++11)
Memoria di ordinazione
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) (dal 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) (dal 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) (dal 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) (dal C++11)
Confronta atomico il valore puntato da obj con il valore puntato da expected, e se quelli sono uguali, sostituisce la precedente con desired (esegue lettura-modifica-scrittura). In caso contrario, carica il valore reale puntato da obj in *expected (esegue l'operazione di carico).
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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I modelli di memoria per la lettura-modifica-scrittura e le operazioni di carico sono succ e fail rispettivamente. I (1-2) versioni utilizzano std::memory_order_seq_cst di default.
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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Le forme deboli ((1) e (3)) delle funzioni possono fallire spurio, che è, agire come se *obj != *expected anche se sono uguali. Quando un confronto e di scambio è in un ciclo, la versione debole produrrà migliori prestazioni su alcune piattaforme. Quando un debole confronto e scambio richiederebbe un ciclo e uno forte non, il forte è preferibile.
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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Queste funzioni sono definiti in termini di funzioni membro di 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)

Indice

[modifica] Parametri

obj -
puntatore all'oggetto atomica per testare e modificare
Original:
pointer to the atomic object to test and modify
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expected -
puntatore al valore atteso per essere trovato in oggetto atomico
Original:
pointer to the value expected to be found in the atomic object
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desired -
il valore da memorizzare nell'oggetto atomico se è come previsto
Original:
the value to store in the atomic object if it is as expected
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succ -
la memoria sycnhronization ordinamento per la lettura-modifica-scrittura, se il confronto ha esito positivo. Tutti i valori sono consentiti .
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 di ordinazione per l'operazione di caricamento, se il paragone non regge. Non può essere std::memory_order_release o std::memory_order_ack_rel e non può specificare più forte ordine di 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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[modifica] Valore di ritorno

Il risultato del confronto: se true *obj è stato pari a *exp, false altrimenti.
Original:
The result of the comparison: true if *obj was equal to *exp, false otherwise.
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[modifica] Eccezioni

noexcept specification:  
noexcept
  (dal C++11)

[modifica] Esempio

Questo esempio mostra come confronto e di scambio può essere utilizzato per implementare senza blocchi append a una lista concatenata
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));
}


[modifica] Vedi anche

confronta atomicamente il valore dell'oggetto atomica con non-atomica argomento ed esegue lo scambio atomico se il carico uguale o atomico in caso contrario
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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(membro pubblico of std::atomic funzione) [edit]
sostituisce atomicamente il valore dell'oggetto atomica con non-atomica argomento e restituisce il vecchio valore del atomica
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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(funzione di modello) [edit]
specializzata operazioni atomiche per std :: shared_ptr
Original:
specializes atomic operations for std::shared_ptr
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(funzione di modello)
C documentation for atomic_compare_exchange, atomic_compare_exchange_explicit