std:: defer_lock, std:: try_to_lock, std:: adopt_lock, std:: defer_lock_t, std:: try_to_lock_t, std:: adopt_lock_t

#include <iostream>
#include <mutex>
#include <thread>
struct bank_account
{
    explicit bank_account(int balance) : balance{balance} {}
    int balance;
    std::mutex m;
};
void transfer(bank_account& from, bank_account& to, int amount)
{
    if (&from == &to) // 자기 자신에게 이체하는 경우 데드락 방지
        return;
    // 데드락 없이 두 뮤텍스 모두 잠금
    std::lock(from.m, to.m);
    // 이미 잠긴 두 뮤텍스가 스코프 종료 시 해제되도록 보장
    std::lock_guard lock1{from.m, std::adopt_lock};
    std::lock_guard lock2{to.m, std::adopt_lock};
// 동등한 접근 방식:
//  std::unique_lock<std::mutex> lock1{from.m, std::defer_lock};
//  std::unique_lock<std::mutex> lock2{to.m, std::defer_lock};
//  std::lock(lock1, lock2);
    from.balance -= amount;
    to.balance += amount;
}
int main()
{
    bank_account my_account{100};
    bank_account your_account{50};
    std::thread t1{transfer, std::ref(my_account), std::ref(your_account), 10};
    std::thread t2{transfer, std::ref(your_account), std::ref(my_account), 5};
    t1.join();
    t2.join();
    std::cout << "my_account.balance = " << my_account.balance << "\n"
                 "your_account.balance = " << your_account.balance << '\n';
}