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

 

C++

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Libreria di Utilità

Stringhe

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Algoritmi

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Libreria matematca

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Localizzazione

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)

 

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

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:  

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

compare_exchange_weak compare_exchange_strong	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. (metodo pubblico)
atomic_exchange atomic_exchange_explicit (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 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)
std::atomic_compare_exchange_weak(std::shared_ptr) std::atomic_compare_exchange_strong(std::shared_ptr)	specializzata operazioni atomiche per std :: shared_ptr Original: specializes atomic operations for std::shared_ptr 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)
C documentation for atomic_compare_exchange, atomic_compare_exchange_explicit