Varianti

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

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    <metanoindex/>

     
    C++
     
    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)
     
    <tbody> </tbody>
    Elemento definito nell'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)

    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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    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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    Eccezioni

    noexcept specification:  
    <tbody> </tbody>
    noexcept
      (dal C++11)

    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));
}


    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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    (metodo pubblico) [modifica]
    (C++11)
    (C++11)
    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) [modifica]
    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