std::atomic_fetch_add, std::atomic_fetch_add_explicit

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Atomare Operationen Bibliothek

Types 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)

Funktionen 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)

Atomic Fahnen 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)

Initialisierung 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)

Speicher Bestellung 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)

 

<tbody> </tbody>

definiert in Header <atomic>
template< class Integral > Integral atomic_fetch_add( std::atomic<Integral>* obj, Integral arg );	(1)	(seit C++11)
template< class Integral > Integral atomic_fetch_add( volatile std::atomic<Integral>* obj, Integral arg );	(2)	(seit C++11)
template< class Integral > Integral atomic_fetch_add_explicit( std::atomic<Integral>* obj, Integral arg, std::memory_order order );	(3)	(seit C++11)
template< class Integral > Integral atomic_fetch_add_explicit( volatile std::atomic<Integral>* obj, Integral arg, std::memory_order order );	(4)	(seit C++11)
template< class T > T* atomic_fetch_add( std::atomic<T*>* obj, std::ptrdiff_t arg );	(5)	(seit C++11)
template< class T > T* atomic_fetch_add( volatile std::atomic<T*>* obj, std::ptrdiff_t arg );	(6)	(seit C++11)
template< class T > T* atomic_fetch_add_explicit( std::atomic<T*>* obj, std::ptrdiff_t arg, std::memory_order order );	(7)	(seit C++11)
template< class T > T* atomic_fetch_add_explicit( volatile std::atomic<T*>* obj, std::ptrdiff_t arg, std::memory_order order );	(8)	(seit C++11)

1-2) Atomically adds arg to the value pointed to by obj and returns the value obj held previously, as if by obj->fetch_add(arg)

3-4) Atomically adds arg to the value pointed to by obj and returns the value obj held previously, as if by obj->fetch_add(arg, order)

5-6) Atomically increments the pointer value, pointed to by obj, by arg, and returns the value obj held previously, as if by obj->fetch_add(arg)

7-8) Atomically increments the pointer value, pointed to by obj, by arg, and returns the value obj held previously, as if by obj->fetch_add(arg, order)

Parameter

obj	-	Zeiger auf den atomaren Objekts zu ändern Original: pointer to the atomic object to modify The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
arg	-	der Wert, der dem Wert in der atomaren Objekt gespeichert hinzuzufügen Original: the value to add to the value stored 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.
order	-	der Speicher sycnhronization Bestellung für diesen Vorgang: Alle Werte sind zulässig . Original: the memory sycnhronization ordering for this operation: 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.

Rückgabewert

Die zuvor von der atomaren Objekt gehalten, auf die obj

Original:

The value held previously by the atomic object pointed to by obj

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You can help to correct and verify the translation. Click here for instructions.

Ausnahmen

noexcept specification:  

<tbody> </tbody>

noexcept

  (seit C++11)

Mögliche Implementierung

First version
template< class T > typename std::enable_if<std::is_integral<T>::value && !std::is_same<T, bool>::value, T>::type atomic_fetch_add( std::atomic<T>* obj, T arg ); { return obj->fetch_add(arg); }
Second version
template< class T > T* atomic_fetch_add( std::atomic<T*>* obj, std::ptrdiff_t arg) { return obj->fetch_add(arg); }

Beispiel

Single-writer/multiple-reader lock can be made with fetch_add. Note that this simplistic implementation is not lockout-free

#include <string>
#include <thread>
#include <vector>
#include <iostream>
#include <atomic>
#include <chrono>
 
// meaning of cnt:
// 10: there are no active readers or writers.
// 1...9: there are 9...1 readers active, The writer is blocked
// 0: temporary value between fetch_sub and fetch_add in reader lock
// -1: there is a writer active. The readers are blocked.
const int N = 10; // nine concurrent readers are allowed
std::atomic<int> cnt = ATOMIC_VAR_INIT(N);

std::vector<int> data;

void reader(int id)
{
    for(;;)
    {
        // lock
        while(std::atomic_fetch_sub(&cnt, 1) <= 0)
            std::atomic_fetch_add(&cnt, 1);
        // read
        if(!data.empty())
            std::cout << (  "reader " + std::to_string(id)
                          + " sees " + std::to_string(*data.rbegin()) + '\n');
        if(data.size() == 100)
            break;
        // unlock
        std::atomic_fetch_add(&cnt, 1);
        // pause
        std::this_thread::sleep_for(std::chrono::milliseconds(1));
    }
}

void writer()
{
    for(int n = 0; n < 100; ++n)
    {
        // lock
        while(std::atomic_fetch_sub(&cnt, N+1) != N)
            std::atomic_fetch_add(&cnt, N+1);
        // write
        data.push_back(n);
        std::cout << "writer pushed back " << n << '\n';
        // unlock
        std::atomic_fetch_add(&cnt, N+1);
        // pause
        std::this_thread::sleep_for(std::chrono::milliseconds(1));
    }
}
 
int main()
{
    std::vector<std::thread> v;
    for (int n = 0; n < N; ++n) {
        v.emplace_back(reader, n);
    }
    v.emplace_back(writer);
    for (auto& t : v) {
        t.join();
    }
}

Output:

writer pushed back 0
reader 8 sees 0
reader 3 sees 0
reader 1 sees 0
<...>
reader 2 sees 99
reader 6 sees 99
reader 1 sees 99

Siehe auch

fetch_add (C++11)	atomar fügt das Argument zu dem Wert in dem atomaren Objekt gespeichert und erhält den Wert gehalten zuvor Original: atomically adds the argument to the value stored in the atomic object and obtains the value held previously The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (öffentliche Elementfunktion of std::atomic)
atomic_fetch_sub atomic_fetch_sub_explicit (C++11) (C++11)	subtrahiert eine nicht-elementare Wert aus einer atomaren Objekt und erhält den vorherigen Wert des atomaren Original: subtracts a non-atomic value from an atomic object and obtains the previous 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. (Funktions-Template)
C documentation for atomic_fetch_add, atomic_fetch_add_explicit