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48 lines
1.3 KiB
C++
48 lines
1.3 KiB
C++
// future example
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// adapted from http://www.cplusplus.com/reference/future/future/
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#include <iostream> // std::cout
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#include <future> // std::async, std::future
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#include <chrono> // std::chrono::milliseconds
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// a non-optimized way of checking for prime numbers.
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bool is_prime (long int x) {
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for (long int i=2; i<x; ++i) {
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if (x%i == 0) return false;
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}
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return true;
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}
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void explicitly_waiting() {
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int p = 817504243;
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// call function asynchronously:
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std::future<bool> fut = std::async(std::launch::async, is_prime, p);
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// do something while waiting for function to set future:
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std::cout << "checking, please wait" << std::flush;
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std::chrono::milliseconds span(500);
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while (fut.wait_for(span) == std::future_status::timeout) {
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std::cout << '.' << std::flush;
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}
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std::cout << std::endl;
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bool x = fut.get(); // retrieve return value
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std::cout << p << " " << (x?"is":"is not") << " prime." << std::endl;
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}
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void implicitly_waiting() {
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long int p2 = 685102597328182763;
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std::future<bool> fut = std::async(std::launch::async, is_prime, p2);
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std::cout << "just getting the result, doing an implicit wait():" << std::endl;
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bool x = fut.get();
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std::cout << p2 << " " << (x?"is":"is not") << " prime." << std::endl;
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}
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int main () {
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explicitly_waiting();
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implicitly_waiting();
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return 0;
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}
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