如何一個接一個地并行運行兩個執行緒？

在 C 中，我如何撰寫兩個并行執行緒，它們將一個接一個地作業。例如，在下面的代碼中，它需要順序列印 0 t 100。在下面的代碼中，數字正在列印，但都不是順序的。我需要像 1 一樣列印,2,3,4,5,6.....99。如果有人知道，請嘗試添加示例代碼。

    #pragma once
#include <mutex>
#include <iostream>
#include <vector>
#include <thread>
#include <condition_variable>
using namespace std;
class CuncurrentThread
{
public:
    mutex mtx;
    condition_variable cv;
    static bool ready;
    static bool processed;
    void procThread1()
    {
        for (int i = 0; i < 100; i  = 2)
        {
            unique_lock<mutex> lk(mtx);
            cv.notify_one();
            if(lk.owns_lock())
                cv.wait(lk);
            cout << "procThread1 : " << i << "\n";
            lk.unlock();
            cv.notify_one();
        }
    };
    void procThread2()
    {
        for (int i = 1; i < 100; i  = 2)
        {
            unique_lock<mutex> lk(mtx);
            cv.notify_one();
            if (lk.owns_lock())
                cv.wait(lk);
            cout << "procThread2 : " << i << "\n";
            lk.unlock();
            cv.notify_one();
        }
    };
    static void ThreadDriver(CuncurrentThread* thr)
    {
        vector<thread> threads;
        threads.push_back(thread(&CuncurrentThread::procThread1, thr));
        threads.push_back(thread(&CuncurrentThread::procThread2, thr));

        for (auto& thread : threads) 
            thread.join();

    };
};
bool CuncurrentThread::ready = false;
int main()
{
    CuncurrentThread tr;
    CuncurrentThread::ThreadDriver(&tr);
    
}

uj5u.com熱心網友回復：

假設您有一個使用這樣的兩個執行緒的有效用例，這里有一個示例。我更喜歡使用 std::async 而不是 std::thread 它具有更好的抽象和與主執行緒的資訊交換。該示例是為 2 個執行緒撰寫的，但可以輕松更改為更多執行緒。

現場演示：https ://onlinegdb.com/eQex9o_nMz

#include <future>
#include <condition_variable>
#include <iostream>

// Setup a helper class that sets up
// the three things needed to correctly
// use a condition variable
// 1) a mutex
// 2) a variable
// 3) a condition_variable (which is more of a signal then a variable)
//
// also give this class some functions
// so the the code becomes more self-explaining

class thread_switcher_t
{
public:
    void thread1_wait_for_turn()
    {
        std::unique_lock<std::mutex> lock{ m_mtx };
        m_cv.wait(lock, [&] {return (thread_number==0); });
    }

    void thread2_wait_for_turn()
    {
        std::unique_lock<std::mutex> lock{ m_mtx };
        m_cv.wait(lock, [&] {return (thread_number==1); });
    }

    void next_thread()
    {
        std::unique_lock<std::mutex> lock{ m_mtx };
        thread_number = (thread_number   1) % 2;
        m_cv.notify_all();
    }

private:
    std::size_t thread_number{ 0 };
    std::mutex m_mtx;
    std::condition_variable m_cv;
};


int main()
{
    thread_switcher_t switcher;
    
    auto future1 = std::async(std::launch::async, [&]
    {
        for(std::size_t n = 0; n <= 100; n =2)
        {
            switcher.thread1_wait_for_turn();
            std::cout << "thread 1 : " << n << "\n";
            switcher.next_thread();
        }
    });

    auto future2 = std::async(std::launch::async, [&]
    {
        for (std::size_t n = 1; n <= 100; n  = 2)
        {
            switcher.thread2_wait_for_turn();
            std::cout << "thread 2 : " << n << "\n";
            switcher.next_thread();
        }
    });

    future1.get();
    future2.get();

    return 0;
}

uj5u.com熱心網友回復：

您可以使用ready變數作為條件變數的條件。

#include <mutex>
#include <iostream>
#include <vector>
#include <thread>
#include <condition_variable>
using namespace std;

class CuncurrentThread
{
public:
    mutex mtx;
    condition_variable cv;
    static bool ready;
    //static bool processed;
    void procThread1()
    {
        for (int i = 0; i < 100; i  = 2)
        {
            unique_lock<mutex> lk(mtx);
            // cv.notify_one();
            // if(lk.owns_lock())

            // wait until this condition is true i.e. until ready is false
            cv.wait(lk, [&]() { return !ready; });
            cout << "procThread1 : " << i << "\n";

            // set ready to true and notify waiting thread
            ready = true;
            lk.unlock();
            cv.notify_one();
        }
    };
    void procThread2()
    {
        for (int i = 1; i < 100; i  = 2)
        {
            unique_lock<mutex> lk(mtx);
            // cv.notify_one();
            // if (lk.owns_lock())

            // wait until this condition is true i.e. until ready is true
            cv.wait(lk, [&]() { return ready; });
            cout << "procThread2 : " << i << "\n";

            // set ready to false and notify waiting thread
            ready = false;
            lk.unlock();
            cv.notify_one();
        }
    };
    static void ThreadDriver(CuncurrentThread* thr)
    {
        vector<thread> threads;
        threads.push_back(thread(&CuncurrentThread::procThread1, thr));
        threads.push_back(thread(&CuncurrentThread::procThread2, thr));

        for (auto& thread : threads) 
            thread.join();

    };
};
bool CuncurrentThread::ready = false;
int main()
{
    CuncurrentThread tr;
    CuncurrentThread::ThreadDriver(&tr);
}

我測驗的鏈接：https ://godbolt.org/z/4jEns16oq

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