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std::async

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Bibliothèque de support fil
Threads
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Threads
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thread (C++11)
this_thread espace de noms
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this_thread namespace
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yield (C++11)
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L'exclusion mutuelle
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Mutual exclusion
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mutex (C++11)
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Gestion du verrouillage générique
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Generic lock management
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defer_lock_t
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Futures
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Futures
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promise (C++11)
future (C++11)
shared_future (C++11)
packaged_task (C++11)
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Defined in header <future>
template< class Function, class... Args>

std::future<typename std::result_of<Function(Args...)>::type>

    async( Function&& f, Args&&... args );
(1) (depuis C++11)
template< class Function, class... Args >

std::future<typename std::result_of<Function(Args...)>::type>

    async( std::launch policy, Function&& f, Args&&... args );
(2) (depuis C++11)
Le async fonction de modèle exécute la fonction f asynchrone (potentiellement dans un thread séparé) et renvoie une std::future qui finira par contenir le résultat de cet appel de fonction .
Original:
The template function async runs the function f asynchronously (potentially in a separate thread) and returns a std::future that will eventually hold the result of that function call.
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1)
Se comporte comme async(std::launch::async | std::launch::deferred, f, args...). En d'autres termes, f peut être démarré dans un nouveau thread ou il peut être exécuté de façon synchrone lorsque le std::future résultant est interrogé pour une valeur .
Original:
Behaves the same as async(std::launch::async | std::launch::deferred, f, args...). In other words, f may be started in a new thread or it may be run synchronously when the resulting std::future is queried for a value.
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2)
Appelle une fonction avec des arguments f args selon une politique de lancement spécifique policy:
Original:
Calls a function f with arguments args according to a specific launch policy policy:
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  • Si le' async drapeau est positionné (c.-à-policy & std::launch::async != 0), puis async génère un nouveau thread d'exécution comme par std::thread(f, args...), sauf que si la fonction renvoie une valeur f ou lève une exception, elle est stockée dans l'état partagé accessible à travers le std::future que async retourne à 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' différé est activé (c'est à dire policy & std::launch::deferred != 0), puis convertis async args... la même manière que par le constructeur std::thread, mais ne lance pas un nouveau thread d'exécution. Au lieu de cela,' évaluation paresseuse est réalisée: le premier appel à un non-chronométré attendre fonction sur le std::future que async renvoyé à l'appelant fera f(args...) être exécuté dans le thread courant. Tous les accès supplémentaires à la même std::future retournera le résultat immédiatement .
    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 à la fois le std::launch::async et std::launch::deferred sont mis en policy, c'est à la mise en œuvre s'il faut effectuer l'exécution asynchrone ou l'évaluation 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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Sommaire

[modifier] Paramètres

f -
objet fonction ou la fonction à appeler
Original:
function or function object to call
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args... -
paramètres à passer au f
Original:
parameters to pass to f
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policy -
valeur masque, où chaque bit de contrôler les méthodes autorisées d'exécution
Bit
Explication
Original:
Explanation
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std::launch::async
permettre l'évaluation asynchrone
Original:
enable asynchronous evaluation
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std::launch::deferred
permettre l'évaluation paresseuse
Original:
enable lazy evaluation
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Original:
bitmask value, where individual bits control the allowed methods of execution
Bit
Explication
Original:
Explanation
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std::launch::async
permettre l'évaluation asynchrone
Original:
enable asynchronous evaluation
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std::launch::deferred
permettre l'évaluation paresseuse
Original:
enable lazy evaluation
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[modifier] Retourne la valeur

std::future se référant à la valeur de retour de la fonction .
Original:
std::future referring to the return value of the function.
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[modifier] Exceptions

Lance std::system_error avec std::errc::resource_unavailable_try_again condition d'erreur si la politique de lancement est std::launch::async et la mise en œuvre est incapable de démarrer un nouveau thread .
Original:
Throws std::system_error with error condition std::errc::resource_unavailable_try_again if the launch policy is std::launch::async and the implementation is unable to start a new thread.
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[modifier] Notes

La mise en œuvre peut étendre le comportement de la première surcharge de std::async en permettant à d'autres (définie par l'implémentation) bits dans la politique de lancement par défaut .
Original:
The implementation may extend the behavior of the first overload of std::async by enabling additional (implementation-defined) bits in the default launch policy.
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[modifier] 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';
}

Résultat :

The sum is 10000