future

---

1. Asynchronous File Reading

#include <future>
#include <fstream>
#include <iostream>

int main() {
    std::ifstream file("input.txt");
    std::future<std::string> file_contents = std::async(
        [] (std::ifstream& file) {
            return std::string((std::istreambuf_iterator<char>(file)),
                std::istreambuf_iterator<char>());
        },
        std::ref(file));

    // Do other work while file is being read asynchronously.

    std::cout << file_contents.get() << std::endl;
    return 0;
}

2. Parallel Matrix Multiplication

#include <future>
#include <vector>
#include <numeric>

std::vector<std::vector<int>> multiply(const std::vector<std::vector<int>>& a, const std::vector<std::vector<int>>& b) {
    const int num_threads = std::thread::hardware_concurrency();
    const int row_count = a.size();
    const int col_count = b[0].size();
    std::vector<std::vector<int>> result(row_count, std::vector<int>(col_count));

    std::vector<std::future<void>> tasks;
    for (int i = 0; i < row_count; ++i) {
        for (int j = 0; j < col_count; ++j) {
            tasks.emplace_back(std::async(std::launch::async, [&](int i, int j) {
                result[i][j] = std::inner_product(a[i].begin(), a[i].end(), b[j].begin(), 0);
            }, i, j));
        }
    }

    for (auto& task : tasks) {
        task.get();
    }

    return result;
}

3. Concurrency Limiter

#include <future>
#include <queue>
#include <functional>
#include <thread>

template<typename F, typename... Args>
void concurrent(int max_concurrency, F&& func, Args&&... args) {
    std::queue<std::packaged_task<void()>> tasks;
    std::condition_variable cv;
    std::mutex m;

    std::thread producer([&]{
        int running = 0;
        while (true) {
            std::unique_lock<std::mutex> lock(m);
            cv.wait(lock, [&]{ return tasks.empty() || running < max_concurrency; });
            if (tasks.empty()) {
                break;
            }
            std::packaged_task<void()> task = std::move(tasks.front());
            tasks.pop();
            ++running;
            lock.unlock();
            task();
            lock.lock();
            --running;
            cv.notify_one();
        }
    });

    std::thread consumer([&]{
        std::packaged_task<void()> task;
        while (true) {
            {
                std::unique_lock<std::mutex> lock(m);
                cv.wait(lock, [&]{ return !tasks.empty(); });
                if (tasks.empty()) {
                    break;
                }
                task = std::move(tasks.front());
                tasks.pop();
            }
            task();
        }
    });

    for (int i = 0; i < 1000; ++i) {
        tasks.emplace(std::bind(std::forward<F>(func), args...));
        cv.notify_one();
    }

    cv.notify_all();
    producer.join();
    consumer.join();
}

4. Asynchronous Error Handling

#include <future>
#include <exception>
#include <iostream>

int main() {
    std::future<int> result = std::async([] { return 1 / 0; });

    try {
        std::cout << result.get() << std::endl;
    }
    catch (const std::exception& e) {
        std::cout << "Error: " << e.what() << std::endl;
    }
    return 0;
}

5. Asynchronous Retry

#include <future>
#include <chrono>
#include <iostream>

int main() {
    int num_retries = 3;
    std::chrono::duration<int, std::milli> timeout(100);

    std::future<bool> result = std::async([&num_retries, &timeout] {
        bool success = false;
        for (int i = 0; i < num_retries; ++i) {
            // Try to perform the operation.
            if (/* ... */) {
                success = true;
                break;
            }
            std::this_thread::sleep_for(timeout);
        }
        return success;
    });

    std::cout << "Operation " << (result.get() ? "succeeded" : "failed") << std::endl;
    return 0;
}

6. Asynchronous Result Aggregation

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

int main() {
    std::vector<std::future<int>> results;

    for (int i = 0; i < 10; ++i) {
        results.emplace_back(std::async([] { return std::rand() % 100; }));
    }

    int total = 0;
    for (auto& result : results) {
        total += result.get();
    }

    std::cout << "Total: " << total << std::endl;
    return 0;
}

7. Asynchronous UI Updates

#include <future>
#include <thread>
#include <QtWidgets/QApplication>
#include <QtWidgets/QLabel>

int main(int argc, char* argv[]) {
    QApplication app(argc, argv);

    QLabel label("Loading...");
    label.show();

    std::future<void> result = std::async([](&label) {
        // Perform a long-running operation.
        std::this_thread::sleep_for(std::chrono::seconds(5));

        // Update the UI from the main thread.
        std::invoke(QApplication::invokeLater, [&label] { label.setText("Loaded!"); });
    }, &label);

    return app.exec();
}

8. Asynchronous Networking

#include <future>
#include <iostream>
#include <asio/io_context.hpp>
#include <asio/ip/tcp.hpp>

int main() {
    asio::io_context io_context;

    asio::ip::tcp::socket socket(io_context);
    asio::ip::tcp::endpoint endpoint(asio::ip::address::from_string("127.0.0.1"), 8080);

    std::future<void> result = std::async([&socket, &endpoint] {
        socket.connect(endpoint);
        // Send and receive data.
        socket.close();
    });

    io_context.run();
    result.get();

    return 0;
}

9. Asynchronous Image Processing

#include <future>
#include <opencv2/opencv.hpp>

int main() {
    cv::Mat image = cv::imread("image.png");

    std::future<cv::Mat> gray_image = std::async([](const cv::Mat& image) {
        cv::Mat gray_image;
        cv::cvtColor(image, gray_image, cv::COLOR_BGR2GRAY);
        return gray_image;
    }, image);

    std::future<cv::Mat> blurred_image = std::async([](const cv::Mat& image) {
        cv::Mat blurred_image;
        cv::GaussianBlur(image, blurred_image, cv::Size(5, 5), 0);
        return blurred_image;
    }, image);

    cv::imshow("Original Image", image);
    cv::imshow("Gray Image", gray_image.get());
    cv::imshow("Blurred Image", blurred_image.get());
    cv::waitKey(0);
    return 0;
}

10. Asynchronous Data Extraction

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

int main() {
    std::vector<int> numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

    std::future<int> min_value = std::async([](const std::vector<int>& numbers) {
        return *std::min_element(numbers.begin(), numbers.end());
    }, numbers);

    std::future<int> max_value = std::async([](const std::vector<int>& numbers) {
        return *std::max_element(numbers.begin(), numbers.end());
    }, numbers);

    std::cout << "Min value: " << min_value.get() << std::endl;
    std::cout << "Max value: " << max_value.get() << std::endl;
    return 0;
}

11. Asynchronous Function Chaining

#include <future>
#include <iostream>

int add(int a, int b) { return a +