std::async

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• Si le' async drapeau est positionn (c.--policy & std::launch::async != 0), puis async gnre un nouveau thread d'excution comme par std::thread(f, args...), sauf que si la fonction renvoie une valeur f ou lve une exception, elle est stocke dans l'tat partag accessible travers le std::future que async retourne l'appelant .

  Original:

  If the async flag is set (i.e. policy & std::launch::async != 0), then async spawns a new thread of execution as if by std::thread(f, args...), except that if the function f returns a value or throws an exception, it is stored in the shared state accessible through the std::future that async returns to the caller.

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• Si le drapeau' diffr est activ (c'est dire policy & std::launch::deferred != 0), puis convertis async args... la mme manire que par le constructeur std::thread, mais ne lance pas un nouveau thread d'excution. Au lieu de cela,' valuation paresseuse est ralise: le premier appel un non-chronomtr attendre fonction sur le std::future que async renvoy l'appelant fera f(args...) tre excut dans le thread courant. Tous les accs supplmentaires la mme std::future retournera le rsultat immdiatement .

  Original:

  If the deferred flag is set (i.e. policy & std::launch::deferred != 0), then async converts args... the same way as by std::thread constructor, but does not spawn a new thread of execution. Instead, lazy evaluation is performed: the first call to a non-timed wait function on the std::future that async returned to the caller will cause f(args...) to be executed in the current thread. All further accesses to the same std::future will return the result immediately.

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• Si drapeaux la fois le std::launch::async et std::launch::deferred sont mis en policy, c'est la mise en uvre s'il faut effectuer l'excution asynchrone ou l'valuation paresseuse .

  Original:

  If both the std::launch::async and std::launch::deferred flags are set in policy, it is up to the implementation whether to perform asynchronous execution or lazy evaluation.

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Paramtres

Retourne la valeur

Exceptions

Notes

Exemple

#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <future>

template <typename RAIter>
int parallel_sum(RAIter beg, RAIter end)
{
    typename RAIter::difference_type len = end-beg;
    if(len < 1000)
        return std::accumulate(beg, end, 0);

    RAIter mid = beg + len/2;
    auto handle = std::async(std::launch::async,
                              parallel_sum<RAIter>, mid, end);
    int sum = parallel_sum(beg, mid);
    return sum + handle.get();
}

int main()
{
    std::vector<int> v(10000, 1);
    std::cout << "The sum is " << parallel_sum(v.begin(), v.end()) << '\n';
}

The sum is 10000