Namespace
Varianti

std::atomic_flag_test_and_set, std::atomic_flag_test_and_set_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>
bool atomic_flag_test_and_set( volatile std::atomic_flag* p );
(1) (dal C++11)
bool atomic_flag_test_and_set( std::atomic_flag* p );
(2) (dal C++11)
bool atomic_flag_test_and_set_explicit( volatile std::atomic_flag* p,
                                        std::memory_order order );
(3) (dal C++11)
bool atomic_flag_test_and_set_explicit( std::atomic_flag* p,
                                        std::memory_order order );
(4) (dal C++11)
Atomico cambia lo stato di un std::atomic_flag puntato da p per impostare (true) e restituisce il valore di essa deteneva prima.
Original:
Atomically changes the state of a std::atomic_flag pointed to by p to set (true) and returns the value it held before.
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Indice

[modifica] Parametri

p -
puntatore a std::atomic_flag per accedere
Original:
pointer to std::atomic_flag to access
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order -
la sincronizzazione fine memoria per questa operazione
Original:
the memory synchronization order for this operation
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[modifica] Valore di ritorno

Il valore precedentemente detenuta dalla bandiera a cui punta p
Original:
The value previously held by the flag pointed to by p
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[modifica] Eccezioni

noexcept specification:  
noexcept
  (dal C++11)

[modifica] Possibile implementazione

First version
bool atomic_flag_test_and_set(volatile std::atomic_flag* p)
{
    return p->test_and_set();
}
Second version
bool atomic_flag_test_and_set(std::atomic_flag* p)
{
    return p->test_and_set();
}
Third version
bool atomic_flag_test_and_set_explicit(volatile std::atomic_flag* p, 
                                       std::memory_order order)
{
    return p->test_and_set(order);
}
Fourth version
bool atomic_flag_test_and_set_explicit(std::atomic_flag* p, 
                                       std::memory_order order) 
{
    return p->test_and_set(order);
}

[modifica] Esempio

Un mutex spinlock può essere implementato in spazio utente utilizzando un atomic_flag
Original:
A spinlock mutex can be implemented in userspace using an atomic_flag
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#include <thread>
#include <vector>
#include <iostream>
#include <atomic>
 
std::atomic_flag lock = ATOMIC_FLAG_INIT;
 
void f(int n)
{
    for(int cnt = 0; cnt < 100; ++cnt) {
        while(std::atomic_flag_test_and_set_explicit(&lock, std::memory_order_acquire))
             ; // spin until the lock is acquired
        std::cout << "Output from thread " << n << '\n';
        std::atomic_flag_clear_explicit(&lock, std::memory_order_release);
    }
}
int main()
{
    std::vector<std::thread> v;
    for (int n = 0; n < 10; ++n) {
        v.emplace_back(f, n);
    }
    for (auto& t : v) {
        t.join();
    }
}

Output:

Output from thread 2
Output from thread 6
Output from thread 7
...<exactly 1000 lines>...

[modifica] Vedi anche

il blocco privo di tipo booleano atomica
Original:
the lock-free boolean atomic type
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(classe) [edit]
imposta atomicamente il valore della bandiera false
Original:
atomically sets the value of the flag to false
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(funzione) [edit]
definisce i limiti di memoria di ordinazione per il data operazione atomica
Original:
defines memory ordering constraints for the given atomic operation
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(typedef) [edit]
C documentation for atomic_flag_test_and_set, atomic_flag_test_and_set_explicit