Namespace
Varianti

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

Da cppreference.com.
< cpp‎ | atomic‎ | atomic

 
 
Atomic operazioni di biblioteca
Tipi
Original:
Types
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
atomic(C++11)
atomic_is_lock_free(C++11)
Funzioni
Original:
Functions
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
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
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
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
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
atomic_init(C++11)
ATOMIC_VAR_INIT(C++11)
ATOMIC_FLAG_INIT(C++11)
Memoria di ordinazione
Original:
Memory ordering
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
memory_order(C++11)
kill_dependency(C++11)
atomic_thread_fence(C++11)
atomic_signal_fence(C++11)
 
std::atomic
Membri funzioni
Original:
Member functions
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
atomic::atomic
atomic::operator=
atomic::is_lock_free
atomic::store
atomic::load
atomic::operator T
atomic::exchange
atomic::compare_exchange
Funzioni membro specializzati
Original:
Specialized member functions
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
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) (dal 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) (dal 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) (dal 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) (dal C++11)
Atomicamente confronta il valore memorizzato in *this con il valore puntato da expected, e se questi sono uguali, sostituisce il primo con desired (esegui lettura-modifica-scrittura). In caso contrario, carica il valore reale memorizzato in *this in *expected (esegue l'operazione di carico).
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).
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
I modelli di memoria per la lettura-modifica-scrittura e le operazioni di carico sono success e failure rispettivamente. Nella (2) e (4) versioni order viene utilizzato sia per lettura-modifica-scrittura e caricare operazioni, tranne che std::memory_order_release std::memory_order_relaxed e sono utilizzati per l'operazione di carico se order == std::memory_order_acq_rel, o order == std::memory_order_release rispettivamente.
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.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
Le forme deboli (1-2) delle funzioni possono fallire spurio, che è, agire come se *this != *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 (1-2) 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.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

Indice

[modifica] Parametri

expected -
puntatore al valore atteso per essere trovato in oggetto atomico
Original:
pointer to the value expected to be found in the atomic object
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
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
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
success -
la sincronizzazione memoria ordinamento per la lettura-modifica-scrittura, se il confronto ha esito positivo. Tutti i valori sono consentiti .
Original:
the memory synchronization ordering for the read-modify-write operation if the comparison succeeds. All values are permitted.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
failure -
la sincronizzazione della 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 success
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
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
order -
la sincronizzazione memoria ordinamento per entrambe le operazioni
Original:
the memory synchronization ordering for both operations
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

[modifica] Valore di ritorno

true se il valore sottostante atomico è stato modificato, false altrimenti.
Original:
true if the underlying atomic value was changed, false otherwise.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

[modifica] Eccezioni

noexcept specification:  
noexcept
  (dal C++11)

[modifica] Esempio

Viene illustrato come compare_exchange_strong né cambia il valore della variabile atomico o la variabile utilizzata per il confronto .
Original:
Demonstrates how compare_exchange_strong either changes the value of the atomic variable or the variable used for comparison.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

#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;
}

Output:

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

[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
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

(funzione di modello) [edit]