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std::async

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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) (seit 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) (seit C++11)
Die Template-Funktion async führt die Funktion f asynchron (möglicherweise in einem separaten Thread) und gibt einen std::future, die schließlich halten wird das Ergebnis dieser Funktion Anruf .
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)
Bewirkt das gleiche wie async(std::launch::async | std::launch::deferred, f, args...). Mit anderen Worten kann f in einem neuen Thread gestartet werden, oder sie kann synchron betrieben werden, wenn die resultierende std::future für einen Wert abgefragt wird .
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)
Ruft eine Funktion f mit Argumenten args nach einem bestimmten Start-Politik policy:
Original:
Calls a function f with arguments args according to a specific launch policy policy:
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  • Wenn die async Flag gesetzt ist (dh policy & std::launch::async != 0), dann async startet einen neuen Thread der Ausführung wie von std::thread(f, args...), außer dass, wenn die Funktion f einen Wert zurückgibt oder eine Ausnahme auslöst, wird es in der gemeinsamen Staat zugänglich aufbewahrt durch die std::future, dass async zum Aufrufer zurückkehrt .
    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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  • Wenn die latenten Flag gesetzt ist (dh policy & std::launch::deferred != 0), dann async Konvertiten args... die gleiche Weise wie std::thread Konstruktor, aber nicht laichen einen neuen Thread. Stattdessen wird lazy evaluation durchgeführt: Der erste Anruf wird zu einer nicht-Zeitüberschreitung warten Funktion auf dem std::future, dass async an den Aufrufer zurückgegeben verursachen f(args...) in den aktuellen Thread ausgeführt werden. Alle weiteren Zugriffen auf den gleichen std::future wird das Ergebnis sofort zurück .
    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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  • Wenn sowohl die std::launch::async und std::launch::deferred Flaggen in policy gesetzt sind, ist es an der Umsetzung, ob asynchrone Ausführung oder faul Auswertung durchführen .
    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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Inhaltsverzeichnis

[Bearbeiten] Parameter

f -
Funktion oder Objekt zu nennen
Original:
function or function object to call
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args... -
Parameter, die an f passieren
Original:
parameters to pass to f
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policy -
Bitmaskenwert, wo einzelne Bits steuern die zulässigen Methoden der Ausführung
Bit
Erklärung
Original:
Explanation
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std::launch::async
ermöglichen asynchrone Auswertung
Original:
enable asynchronous evaluation
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std::launch::deferred
ermöglichen lazy evaluation
Original:
enable lazy evaluation
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bitmask value, where individual bits control the allowed methods of execution
Bit
Erklärung
Original:
Explanation
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std::launch::async
ermöglichen asynchrone Auswertung
Original:
enable asynchronous evaluation
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std::launch::deferred
ermöglichen lazy evaluation
Original:
enable lazy evaluation
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[Bearbeiten] Rückgabewert

std::future bezogen auf den Rückgabewert der Funktion .
Original:
std::future referring to the return value of the function.
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[Bearbeiten] Ausnahmen

Wirft std::system_error mit Fehlerbedingung std::errc::resource_unavailable_try_again wenn der Start Politik ist std::launch::async und die Umsetzung ist nicht in der Lage, einen neuen Thread starten .
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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[Bearbeiten] Notes

Die Implementierung kann das Verhalten des ersten Überlastung std::async indem zusätzliche (Implementierung definiert) Bits in der Standard-Start-Politik erweitern .
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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[Bearbeiten] Beispiel

#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';
}

Output:

The sum is 10000