stdthread(7) concurrent unique_lock flexibility

1. It can be called at any position after the declaration, which can reduce the scope of the lock and provide a higher degree of concurrency

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

int v = 1;

void critical_section(int change_v) {
    
    
    static std::mutex mtx;
    std::unique_lock<std::mutex> lock(mtx);
    // 执行竞争操作
    v = change_v;
    std::cout << v << std::endl;
    // 将锁进行释放
    lock.unlock();

    // 在此期间，任何人都可以抢夺 v 的持有权

    // 开始另一组竞争操作，再次加锁
    lock.lock();
    v += 1;
    std::cout << v << std::endl;
}

int main() {
    
    
    std::thread t1(critical_section, 2), t2(critical_section, 3);
    t1.join();
    t2.join();
    return 0;
}