enable_shared_from_this returns bad_weak_ptr 错误

Question

我在我的项目中使用了 boost 库。在我编写 rest http 客户端代码时出现此错误。

libc++abi.dylib: 以 std::__1::bad_weak_ptr 类型的未捕获异常终止：bad_weak_ptr

template <typename M>
 21 class Http: public std::enable_shared_from_this<Http<M>>
 22 {
 23     M* message_;
 24     bool isSubscribe_;
 25     boost::asio::io_context io_;
 26     boost::asio::ip::tcp::resolver resolver_;
 27     boost::beast::tcp_stream stream_;
 28     boost::beast::flat_buffer buffer_;
 29     boost::beast::http::request<boost::beast::http::empty_body> req_;
 30     boost::beast::http::response<boost::beast::http::string_body> res_;
 31     std::function<void(M*)> callback_;
 32 
 33     void SetUpRestHeader() {
 34         req_.method(boost::beast::http::verb::get);
 35         req_.target(message_ -> header_ -> target_);
 36         req_.set(boost::beast::http::field::host, message_ -> header_ -> host_);
 37         req_.set(boost::beast::http::field::user_agent, BOOST_BEAST_VERSION_STRING);
 38 
 39         resolver_.async_resolve(message_ -> header_ -> host_
 40                 , message_ -> header_ -> port_
 41                 , boost::beast::bind_front_handler(
 42                     &Http::OnResolve
 43                     , this -> shared_from_this()));
 44     }
 45 

.......

128     explicit Http()
129         :io_{}
130         , resolver_(io_)
131         , stream_(io_)
132     {
133         message_ = new M;
134     }
135 
136     M RequestRestMessage()
137     {
138         auto ptr = this -> shared_from_this();
139         isSubscribe_ = false;
140         SetUpRestHeader();
141     }
142   };

151 int main()
152 {
153     Http<binance::ServerTime> http;
154     http.RequestRestMessage();
155 }

即使我没有在构造函数中调用 shared_from_this，也会发生错误。请分享你的智慧。谢谢！

Answer 1

如果你看一下 std::enable_shared_from_this: Examples 你会看到这个：

 // Bad: shared_from_this is called without having std::shared_ptr owning the caller 
try {
  Good not_so_good;
  std::shared_ptr<Good> gp1 = not_so_good.getptr();
} catch(std::bad_weak_ptr& e) {
  // undefined behavior (until C++17) and std::bad_weak_ptr thrown (since C++17)
  std::cout << e.what() << '\n';    
}

您的 Http<binance::ServerTime> http; 使用 automatic storage duration 创建了一个对象，因此它（并且不能）由 shared_ptr 拥有。您的 http.RequestRestMessage() 然后调用 this -> shared_from_this，这就是您收到该错误的原因。

std::enable_shared_from_this::shared_from_this

It is permitted to call shared_from_this only on a previously shared object, i.e. on an object managed by std::shared_ptr (in particular, shared_from_this cannot be called during construction of *this).

Otherwise the behavior is undefined (until C++17) std::bad_weak_ptr is thrown (by the shared_ptr constructor from a default-constructed weak_this) (since C++17).

enable_shared_from_this returns bad_weak_ptr 错误

enable_shared_from_this returns bad_weak_ptr error

c++

boost

shared-ptr

enable-shared-from-this