在 lambda 中锁定 std::shared_ptr 的复制操作

对于此示例代码：

#include <iostream>
#include <thread>
#include <mutex>
#include <memory>
struct A
{
int _i;
A(int i):_i(i)
{
std::cout<<"A() "<<_i<<std::endl;
}
~A()
{
std::cout<<"~A() "<<_i<<std::endl;
}
void Print()
{
std::cout<<"Print() "<<_i<<std::endl;
}
};
struct B
{
std::shared_ptr<A> Asp;
std::mutex AspMutex;
void SetA()
{
static int i = 0;
std::unique_lock<std::mutex> lock(AspMutex);
Asp = std::make_shared<A>(i);
}
void AccessA1()
{
std::shared_ptr<A> aspCopy;
{
std::unique_lock<std::mutex> lock(AspMutex);
aspCopy = Asp;
}
(*aspCopy).Print();
}
void AccessA2()
{
auto aspCopy = [&]()
{
std::unique_lock<std::mutex> lock(AspMutex);
return Asp;
}();
(*aspCopy).Print();
}
void AccessA3()
{
(*[&]()
{
std::unique_lock<std::mutex> lock(AspMutex);
return Asp;
}()
).Print();
}
};
int main()
{
B b;
b.SetA();
std::thread t([&]{b.SetA();});
b.AccessA1();
b.AccessA2();
b.AccessA3();
t.join();
}

我很好奇 c++17(或更高版本(标准是否会保证A::Access1和A::Access2方法是线程安全的(std::shared_ptr的副本将受到lock的保护(。