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std::atomic_flag_test_and_set, std::atomic_flag_test_and_set_explicit

De cppreference.com
< cpp‎ | atomic

 
 
Operaciones de biblioteca Atómica
Tipos
Original:
Types
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(C++11)
Funciones
Original:
Functions
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Banderas atómicas
Original:
Atomic flags
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atomic_flag_test_and_setatomic_flag_test_and_set_explicit
(C++11)(C++11)
Inicialización
Original:
Initialization
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Memoria pedido
Original:
Memory ordering
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Definido en la cabecera <atomic>
bool atomic_flag_test_and_set( volatile std::atomic_flag* p );
(1) (desde C++11)
bool atomic_flag_test_and_set( std::atomic_flag* p );
(2) (desde C++11)
bool atomic_flag_test_and_set_explicit( volatile std::atomic_flag* p,
                                        std::memory_order order );
(3) (desde C++11)
bool atomic_flag_test_and_set_explicit( std::atomic_flag* p,
                                        std::memory_order order );
(4) (desde C++11)
Atómicamente cambia el estado de un std::atomic_flag apuntado por p establecer (true) y devuelve el valor que se celebrará antes .
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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Contenido

[editar] Parámetros

p -
puntero a std::atomic_flag acceder
Original:
pointer to std::atomic_flag to access
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order -
el orden de sincronización de la memoria para esta operación
Original:
the memory synchronization order for this operation
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[editar] Valor de retorno

El valor anteriormente en manos de la bandera a la que apunta p
Original:
The value previously held by the flag pointed to by p
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[editar] Excepciones

noexcept specification:  
noexcept
  (desde C++11)

[editar] Posible implementación

Primera versión
bool atomic_flag_test_and_set(volatile std::atomic_flag* p)
{
    return p->test_and_set();
}
Segunda versión
bool atomic_flag_test_and_set(std::atomic_flag* p)
{
    return p->test_and_set();
}
Tercera versión
bool atomic_flag_test_and_set_explicit(volatile std::atomic_flag* p, 
                                       std::memory_order order)
{
    return p->test_and_set(order);
}
Cuarta versión
bool atomic_flag_test_and_set_explicit(std::atomic_flag* p, 
                                       std::memory_order order) 
{
    return p->test_and_set(order);
}

[editar] Ejemplo

Un mutex spinlock puede ser implementado en el espacio de usuario utilizando 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();
    }
}

Salida:

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

[editar] Ver también

el bloqueo libre de tipo atómico booleano
Original:
the lock-free boolean atomic type
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(clase) [editar]
atómicamente establece el valor de la bandera de false
Original:
atomically sets the value of the flag to false
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(función) [editar]
define las limitaciones de memoria de pedido para la operación dada atómica
Original:
defines memory ordering constraints for the given atomic operation
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(typedef) [editar]
C documentation for atomic_flag_test_and_set, atomic_flag_test_and_set_explicit