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

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C++

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Libreria di Utilità

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Espressioni regolari (C++11)

Operazioni atomicche (C++11)

Multithreading (C++11)

 

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^=

 

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Elemento definito nell'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).

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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.

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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.

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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.

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.

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Eccezioni

noexcept specification:  

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noexcept

  (dal C++11)

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.

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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;
}

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

Vedi anche

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)

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)