【C++】マルチスレッド入門！10のサンプルコードで徹底解説

#include <iostream>
#include <thread>

void helloFunction() {
    std::cout << "Hello from thread!" << std::endl;
}

int main() {
    std::thread t(helloFunction);
    t.join();
    return 0;
}

#include <iostream>
#include <thread>
#include <vector>

void worker(int id) {
    std::cout << "Worker " << id << " is running" << std::endl;
}

int main() {
    std::vector<std::thread> threads;
    for (int i = 0; i < 5; ++i) {
        threads.push_back(std::thread(worker, i));
    }

    for (auto& t : threads) {
        t.join();
    }
    return 0;
}

#include <iostream>
#include <mutex>
#include <thread>

int sharedData = 0;
std::mutex mtx;

void incrementSharedData() {
    mtx.lock();
    ++sharedData;
    std::cout << "Data incremented to " << sharedData << std::endl;
    mtx.unlock();
}

int main() {
    std::thread t1(incrementSharedData);
    std::thread t2(incrementSharedData);

    t1.join();
    t2.join();
    return 0;
}

#include <iostream>
#include <mutex>
#include <condition_variable>
#include <thread>

std::mutex mtx;
std::condition_variable cv;
bool ready = false;

void worker() {
    std::unique_lock<std::mutex> lock(mtx);
    while (!ready) {
        cv.wait(lock);
    }
    std::cout << "Worker thread is processing data" << std::endl;
}

int main() {
    std::thread t(worker);

    {
        std::lock_guard<std::mutex> lock(mtx);
        ready = true;
    }
    cv.notify_one();

    t.join();
    return 0;
}

#include <iostream>
#include <vector>
#include <thread>
#include <queue>
#include <mutex>
#include <condition_variable>

class ThreadPool {
private:
    std::vector<std::thread> workers;
    std::queue<std::function<void()>> tasks;
    std::mutex queueMutex;
    std::condition_variable condition;
    bool stop;

public:
    ThreadPool(size_t threads) : stop(false) {
        for(size_t i = 0; i < threads; ++i)
            workers.emplace_back([this] {
                while(true) {
                    std::function<void()> task;
                    {
                        std::unique_lock<std::mutex> lock(this->queueMutex);
                        this->condition.wait(lock, [this]{ return this->stop || !this->tasks.empty(); });
                        if(this->stop && this->tasks.empty())
                            return;
                        task = std::move(this->tasks.front());
                        this->tasks.pop();
                    }
                    task();
                }
            });
    }

    template<class F, class... Args>
    auto enqueue(F&& f, Args&&... args) 
        -> std::future<typename std::result_of<F(Args...)>::type> {
        using return_type = typename std::result_of<F(Args...)>::type;
        auto task = std::make_shared< std::packaged_task<return_type()> >(
            std::bind(std::forward<F>(f), std::forward<Args>(args)...)
        );
        std::future<return_type> res = task->get_future();
        {
            std::unique_lock<std::mutex> lock(queueMutex);
            if(stop)
                throw std::runtime_error("enqueue on stopped ThreadPool");
            tasks.emplace([task](){ (*task)(); });
        }
        condition.notify_one();
        return res;
    }

    ~ThreadPool() {
        {
            std::unique_lock<std::mutex> lock(queueMutex);
            stop = true;
        }
        condition.notify_all();
        for(std::thread &worker: workers)
            worker.join();
    }
};

int main() {
    ThreadPool pool(4);
    pool.enqueue([] {
        std::cout << "Hello from thread!" << std::endl;
    });
    return 0;
}

#include <iostream>
#include <future>

int main() {
    std::future<void> ftr = std::async([]{
        std::cout << "Hello from async task!" << std::endl;
    });
    ftr.wait();
    return 0;
}

#include <iostream>
#include <thread>
#include <stdexcept>

void threadFunction() {
    try {
        // 何かの処理を行う
        throw std::runtime_error("Error in thread");
    } catch (const std::exception& e) {
        std::cerr << "Exception caught in thread: " << e.what() << std::endl;
        // 適切なエラー処理を行う
    }
}

int main() {
    std::thread t(threadFunction);
    t.join();
    return 0;
}

#include <iostream>
#include <thread>
#include <chrono>

void heavyTask() {
    // 時間のかかる処理を模擬
    std::this_thread::sleep_for(std::chrono::seconds(1));
}

int main() {
    auto start = std::chrono::high_resolution_clock::now();

    std::thread t1(heavyTask);
    std::thread t2(heavyTask);

    t1.join();
    t2.join();

    auto end = std::chrono::high_resolution_clock::now();
    std::chrono::duration<double, std::milli> elapsed = end - start;
    std::cout << "Elapsed time: " << elapsed.count() << " ms\n";

    return 0;
}

#include <iostream>
#include <atomic>
#include <thread>

std::atomic<int> count(0);

void increment() {
    for (int i = 0; i < 100; ++i) {
        count++;
    }
}

int main() {
    std::thread t1(increment);
    std::thread t2(increment);

    t1.join();
    t2.join();

    std::cout << "Count: " << count << std::endl;
    return 0;
}

#include <iostream>
#include <atomic>
#include <thread>

std::atomic<bool> ready(false);
std::atomic<int> data(0);

void producer() {
    data.store(100, std::memory_order_relaxed);
    ready.store(true, std::memory_order_release);
}

void consumer() {
    while (!ready.load(std::memory_order_acquire)) {
        // busy-wait
    }
    std::cout << "Consumed data: " << data.load(std::memory_order_relaxed) << std::endl;
}

int main() {
    std::thread producerThread(producer);
    std::thread consumerThread(consumer);

    producerThread.join();
    consumerThread.join();
    return 0;
}

#include <iostream>
#include <mutex>
#include <thread>

class SafeCounter {
private:
    int value;
    std::mutex mtx;

public:
    SafeCounter() : value(0) {}

    void increment() {
        std::lock_guard<std::mutex> lock(mtx);
        ++value;
    }

    int getValue() {
        std::lock_guard<std::mutex> lock(mtx);
        return value;
    }
};

int main() {
    SafeCounter counter;

    std::thread t1([&counter] { for (int i = 0; i < 100; ++i) counter.increment(); });
    std::thread t2([&counter] { for (int i = 0; i < 100; ++i) counter.increment(); });

    t1.join();
    t2.join();

    std::cout << "Final value: " << counter.getValue() << std::endl;
    return 0;
}