std::shared_ptr 删除器运行时，弱指针是否保证已过期？

Question

如果我有一个带有自定义删除器的 std::shared_ptr<Foo>，是否可以保证所有关联的弱指针都被删除器视为已过期？（如果您能引用标准中的相关章节，我将不胜感激。）

换句话说，下面的断言是否保证不会触发？

std::weak_ptr<Foo> weak;
std::shared_ptr<Foo> strong{
  new Foo,
  [&weak] (Foo* f) {
    assert(weak.expired());
    delete f;
  },
};

weak = strong;
strong.reset();

Answer 1

标准没有任何保证。对于 shared_ptr 的析构函数，规范只说：

If *this is empty or shares ownership with another shared_ptr instance (use_count() > 1), there are no side effects.

Otherwise, if *this owns an object p and a deleter d, d(p) is called.

Otherwise, *this owns a pointer p, and delete p is called.

[Note: Since the destruction of *this decreases the number of instances that share ownership with *this by one, after *this has been destroyed all shared_ptr instances that shared ownership with *this will report a use_count() that is one less than its previous value. —end note ]

而 reset 的定义是将 shared_ptr 交换为临时对象，然后将其销毁。

所以规范只保证 use_count 的状态在析构函数完成后将为零 。未指定在该过程中将其设置为 0 的确切时间。

Answer 2

C++14 标准中显然没有任何内容可以保证这一点。我现在已经为涵盖该问题的标准打开了 defect report。

std::shared_ptr 删除器运行时，弱指针是否保证已过期？

Are weak pointers guaranteed to have expired by the time the std::shared_ptr deleter runs?

c++

shared-ptr

c++11

c++14