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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';}