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C++ 并发专题 - C++线程同步的几种方法

article 2025/1/22 17:43:57

一：概述

线程同步是多线程编程中的一个重要概念，它用于控制多个线程之间对共享资源的访问，避免竞态条件（race condition）和数据不一致的问题。线程同步确保在多线程环境中，多个线程访问共享数据时能够按照某种预定的顺序或规则进行，以保证程序的正确性和稳定性。

二：线程同步方法

1. 信号量


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

std::vector<int> myVec{};

std::counting_semaphore<1> prepareSignal(0);

void prepareWork() {

    myVec.insert(myVec.end(), {0, 1, 0, 3});
    std::cout << "Sender: Data prepared."  << '\n';
    prepareSignal.release();
}

void completeWork() {

    std::cout << "Waiter: Waiting for data." << '\n';
    prepareSignal.acquire();
    myVec[2] = 2;
    std::cout << "Waiter: Complete the work." << '\n';
    for (auto i: myVec) std::cout << i << " ";
    std::cout << '\n';
    
}

int main() {

    std::cout << '\n';

    std::thread t1(prepareWork);
    std::thread t2(completeWork);

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

    std::cout << '\n';
  
}

2. 条件变量



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

std::mutex mut;
std::condition_variable condVar;

std::vector<int> myVec{};

void prepareWork() {                                       

    {
        std::lock_guard<std::mutex> lck(mut);
        myVec.insert(myVec.end(), {0, 1, 0, 3});           
    }
    std::cout << "Sender: Data prepared."  << '\n';
    condVar.notify_one();
}

void completeWork() {                                       

    std::cout << "Waiter: Waiting for data." << '\n';
    std::unique_lock<std::mutex> lck(mut);
    condVar.wait(lck, [] { return not myVec.empty(); });
    myVec[2] = 2;                                           
    std::cout << "Waiter: Complete the work." << '\n';
    for (auto i: myVec) std::cout << i << " ";
    std::cout << '\n';
    
}

int main() {

    std::cout << '\n';

    std::thread t1(prepareWork);
    std::thread t2(completeWork);

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

    std::cout << '\n';
  
}

3. Atomic


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

std::vector<int> myVec{};

std::atomic<bool> atomicBool{false};

void prepareWork() {

    myVec.insert(myVec.end(), {0, 1, 0, 3});
    std::cout << "Sender: Data prepared."  << '\n';
    atomicBool.store(true);
    atomicBool.notify_one();

}

void completeWork() {

    std::cout << "Waiter: Waiting for data." << '\n';
    atomicBool.wait(false);                                
    myVec[2] = 2;
    std::cout << "Waiter: Complete the work." << '\n';
    for (auto i: myVec) std::cout << i << " ";
    std::cout << '\n';
    
}

int main() {

    std::cout << '\n';

    std::thread t1(prepareWork);
    std::thread t2(completeWork);

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

    std::cout << '\n';
  
}

4. Promise - Feature

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

std::vector<int> myVec{};

void prepareWork(std::promise<void> prom) {

    myVec.insert(myVec.end(), {0, 1, 0, 3});
    std::cout << "Sender: Data prepared."  << '\n';
    prom.set_value();                                    

}

void completeWork(std::future<void> fut){

    std::cout << "Waiter: Waiting for data." << '\n';
    fut.wait();                                           
    myVec[2] = 2;
    std::cout << "Waiter: Complete the work." << '\n';
    for (auto i: myVec) std::cout << i << " ";
    std::cout << '\n';
    
}

int main() {

    std::cout << '\n';

    std::promise<void> sendNotification;
    auto waitForNotification = sendNotification.get_future();

    std::thread t1(prepareWork, std::move(sendNotification));
    std::thread t2(completeWork, std::move(waitForNotification));

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

    std::cout << '\n';
  
}

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