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) // 避免自转账时的死锁
        return;
    // 无死锁地锁定两个互斥量
    std::lock(from.m, to.m);
    // 确保两个已锁定的互斥量在作用域结束时被解锁
    std::lock_guard lock1{from.m, std::adopt_lock};
    std::lock_guard lock2{to.m, std::adopt_lock};
// 等效方法：
//  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';
}