c – 当shared_ptr的实例仍在范围内时,共享指针的对象被删除

我有一个STL映射,其中包含在多个线程中操作的对象的共享指针.正在删除shared_ptr所拥有的对象,而智能指针仍然存在于容器和/或其他功能的范围内.所有shared_ptr实例都按值传递(因此滥用引用不会出现问题).我在源 here的印象中,只要shared_ptr的实例存在(从现有的shared_ptr复制),它所拥有的对象就不会被释放.

这基本上就是我在做的事情：

/* Remove Event response in Thread A */
std::map<std::string,std::shared_ptr<object>>::iterator it = objects.find(id);
if(it != objects.end())
{
    std::shared_ptr<object> ob = it->second;
    objects.erase(it);

    //Do cleanup work with ob
}

/* Add Event response in Thread B */
std::map<std::string,std::shared_ptr<object>>::iterator it = objects.find(id);
if(it == objects.end())
{
    std::shared_ptr<object> ob(new object(id));
    objects[id] = ob;

    //Do setup work with ob
}

/* Duty Cycle Event response in Thread C (very frequent) */
//Take snapshot of objects so Remove Event does not invalidate iterators of duty cycle
std::map<std::string,std::shared_ptr<object>> temp_objects = objects; 
for(std::map<std::string,std::shared_ptr<object>>::const_iterator it = temp_objects.begin(); it != temp_objects.end(); ++it)
{
    std::shared_ptr<object> ob = it->second;
    //Access violation can (but doesn't always) occur when dereferencing ob (ob is empty)
}

我究竟做错了什么？我是否滥用共享指针或对其运作方式做出不正确的假设？