std::atomic_fetch_sub, std::atomic_fetch_sub_explicit
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<metanoindex/>
<tbody> </tbody>| Elemento definito nell'header <atomic>
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template< class Integral > Integral atomic_fetch_sub( std::atomic<Integral>* obj, Integral arg ); |
(1) | (dal C++11) |
template< class Integral > Integral atomic_fetch_sub( volatile std::atomic<Integral>* obj, Integral arg ); |
(2) | (dal C++11) |
template< class Integral > Integral atomic_fetch_sub_explicit( std::atomic<Integral>* obj, Integral arg, std::memory_order order ); |
(3) | (dal C++11) |
template< class Integral > Integral atomic_fetch_sub_explicit( volatile std::atomic<Integral>* obj, Integral arg, std::memory_order order); |
(4) | (dal C++11) |
template< class T > T* atomic_fetch_sub( std::atomic<T*>* obj, std::ptrdiff_t arg ); |
(5) | (dal C++11) |
template< class T > T* atomic_fetch_sub( volatile std::atomic<T*>* obj, std::ptrdiff_t arg ); |
(6) | (dal C++11) |
template< class T > T* atomic_fetch_sub_explicit( std::atomic<T*>* obj, std::ptrdiff_t arg, std::memory_order order ); |
(7) | (dal C++11) |
template< class T > T* atomic_fetch_sub_explicit( volatile std::atomic<T*>* obj, std::ptrdiff_t arg, std::memory_order order ); |
(8) | (dal 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)
Parametri
| obj | - | puntatore all'oggetto atomica da modificare
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 | - | il valore da sottrarre dal valore memorizzato nell'oggetto atomica
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 | - | sycnhronization la memoria di ordinazione per questa operazione: tutti i valori sono consentiti .
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. |
Valore di ritorno
Il valore contenuto in precedenza dall'oggetto atomico puntato da
objOriginal:
The value held previously by the atomic object pointed to by
objThe text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
You can help to correct and verify the translation. Click here for instructions.
Eccezioni
Possibile implementazione
| 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);
}
|
Esempio
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
Vedi anche
(C++11) |
sottrae atomicamente l'argomento dal valore memorizzato nell'oggetto atomica e ottiene il valore contenuto in precedenza 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. (metodo pubblico) |
(C++11) (C++11) |
aggiunge un non-atomico valore a un oggetto atomico e ottiene il valore precedente della atomico 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. (funzione di modello) |
C documentation for atomic_fetch_sub, atomic_fetch_sub_explicit
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