std::atomic_fetch_sub, std::atomic_fetch_sub_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_sub( std::atomic<Integral>* obj, Integral arg );	(1)	(seit C++11)
template< class Integral > Integral atomic_fetch_sub( volatile std::atomic<Integral>* obj, Integral arg );	(2)	(seit C++11)
template< class Integral > Integral atomic_fetch_sub_explicit( std::atomic<Integral>* obj, Integral arg, std::memory_order order );	(3)	(seit C++11)
template< class Integral > Integral atomic_fetch_sub_explicit( volatile std::atomic<Integral>* obj, Integral arg, std::memory_order order);	(4)	(seit C++11)
template< class T > T* atomic_fetch_sub( std::atomic<T*>* obj, std::ptrdiff_t arg );	(5)	(seit C++11)
template< class T > T* atomic_fetch_sub( volatile std::atomic<T*>* obj, std::ptrdiff_t arg );	(6)	(seit C++11)
template< class T > T* atomic_fetch_sub_explicit( std::atomic<T*>* obj, std::ptrdiff_t arg, std::memory_order order );	(7)	(seit C++11)
template< class T > T* atomic_fetch_sub_explicit( volatile std::atomic<T*>* obj, std::ptrdiff_t arg, std::memory_order order );	(8)	(seit C++11)

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

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

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

7-8) Atomically decrements the pointer value, pointed to by obj, by arg, and returns the value obj held previously, as if by obj->fetch_sub(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 von dem Wert im atomaren Objekt gespeichert subtrahieren Original: the value to subtract from 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_sub( std::atomic<T>* obj, T arg ); { return obj->fetch_sub(arg); }
Second version
template< class T > T* atomic_fetch_sub( std::atomic<T*>* obj, std::ptrdiff_t arg) { return obj->fetch_sub(arg); }

Beispiel

Multiple threads may use fetch_sub to concurrently process an indexed container

#include <string>
#include <thread>
#include <vector>
#include <iostream>
#include <atomic>
#include <numeric>

const int N = 10000;
std::atomic<int> cnt;
std::vector<int> data(N);

void reader(int id) 
{
    for(;;) {
        int idx = atomic_fetch_sub_explicit(&cnt, 1, std::memory_order_relaxed);
        if (idx >= 0) {
            std::cout << "reader " << std::to_string(id) << " processed item "
                      << std::to_string(data[idx]) << '\n';
        } else {
            std::cout << "reader " << std::to_string(id) << " done\n";
            break;
        }
    }
}

int main()
{
    std::iota(data.begin(), data.end(), 1);
    cnt = data.size() - 1;

    std::vector<std::thread> v;
    for (int n = 0; n < 10; ++n) {
        v.emplace_back(reader, n);
    }
    for (auto& t : v) {
        t.join();
    }
}

Output:

reader 2 processed item 10000
reader 6 processed item 9994
reader 4 processed item 9996
reader 6 processed item 9992
<....>
reader 0 done
reader 5 done
reader 3 done
reader 9 done

Siehe auch

fetch_sub (C++11)	atomar zieht das Argument aus dem Wert in der atomaren Objekt gespeichert und erhält den Wert zuvor gehaltenen Original: atomically subtracts the argument from 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_add atomic_fetch_add_explicit (C++11) (C++11)	fügt eine nicht-elementare Wert einem atomaren Objekt und erhält den vorherigen Wert des atomaren Original: adds a non-atomic value to 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_sub, atomic_fetch_sub_explicit