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std::future - cppreference.com

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Definido no cabeçalho

<future>

template< class T > class future;

 (1) (desde C++11)

template< class T > class future<T&>;

 (2) (desde C++11)

template<> class future<void>;

 (3) (desde C++11)

O std::future modelo de classe fornece um mecanismo para acessar o resultado de operações assíncronas:

Original:

The class template std::future provides a mechanism to access the result of asynchronous operations:

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  • Uma operação assíncrona (criado através std::async, std::packaged_task, ou std::promise) pode fornecer um objeto std::future para o criador do que a operação assíncrona.

    Original:

    An asynchronous operation (created via std::async, std::packaged_task, or std::promise) can provide a std::future object to the creator of that asynchronous operation.

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  • O criador da operação assíncrona pode então usar uma variedade de métodos para consulta, aguarde, ou extrair um valor da std::future. Estes métodos podem bloquear se a operação assíncrona ainda não forneceu um valor.

    Original:

    The creator of the asynchronous operation can then use a variety of methods to query, wait for, or extract a value from the std::future. These methods may block if the asynchronous operation has not yet provided a value.

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  • Quando a operação assíncrona está pronto para enviar um resultado para o criador, ele pode fazer isso modificando o estado compartilhado' (por exemplo std::promise::set_value) que está ligado a std::future do criador.

    Original:

    When the asynchronous operation is ready to send a result to the creator, it can do so by modifying shared state (e.g. std::promise::set_value) that is linked to the creator's std::future.

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Note que as referências std::future compartilhada estado que não é compartilhado com todos os objetos assíncronos outras retorno (ao contrário de std::shared_future).

Original:

Note that std::future references shared state that is not shared with any other asynchronous return objects (as opposed to std::shared_future).

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Funções de membro

constrói o objeto futuro

Original:

constructs the future object

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(função pública membro) [edit]

destrói o objeto futuro

Original:

destructs the future object

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(função pública membro) [edit]

move o objeto futuro

Original:

moves the future object

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(função pública membro) [edit]

devolve uma

shared_future

referindo-se ao resultado, associado à *this

Original:

returns a

shared_future

referring to the result associated to *this

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(função pública membro) [edit]

Obtendo o resultado

Original:

Getting the result

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devolve o resultado

Original:

returns the result

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(função pública membro) [edit]

Estado

Original:

State

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Verifica se o futuro tem estado compartilhado com uma promessa

Original:

checks if the future has shared state with a promise

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(função pública membro) [edit]

aguarda o resultado de se tornarem disponíveis

Original:

waits for the result to become available

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(função pública membro) [edit]
waits for the result, returns if it is not available for the specified timeout duration
(função pública membro) [edit]

aguarda o resultado, retorna se ele não está disponível até que ponto de tempo especificado, foi atingido

Original:

waits for the result, returns if it is not available until specified time point has been reached

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(função pública membro) [edit]

Exemplo

#include <iostream>
#include <future>
#include <thread>

int main()
{
    // future from a packaged_task
    std::packaged_task<int()> task([](){ return 7; }); // wrap the function
    std::future<int> f1 = task.get_future();  // get a future
    std::thread(std::move(task)).detach(); // launch on a thread

    // future from an async()
    std::future<int> f2 = std::async(std::launch::async, [](){ return 8; });

    // future from a promise
    std::promise<int> p;
    std::future<int> f3 = p.get_future();
    std::thread( [](std::promise<int>& p){ p.set_value(9); }, 
                 std::ref(p) ).detach();

    std::cout << "Waiting...";
    f1.wait();
    f2.wait();
    f3.wait();
    std::cout << "Done!\nResults are: "
              << f1.get() << ' ' << f2.get() << ' ' << f3.get() << '\n';
}

Saída: 

Waiting...Done!
Results are: 7 8 9

Veja também

executa uma função de forma assíncrona (potencialmente em um novo segmento) e retorna uma std::future que vai segurar o resultado

Original:

runs a function asynchronously (potentially in a new thread) and returns a std::future that will hold the result

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(modelo de função) [edit]

espera por um valor (possivelmente relacionado por outros futuros) que é definido de forma assíncrona

Original:

waits for a value (possibly referenced by other futures) that is set asynchronously

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(modelo de classe) [edit]