C++ Rest SDK 卡萨布兰卡 Sigtrap

Question

我正在使用 C++ Rest SDK ("Casablanca")从 Websocket-Servers 接收提要。目前，我使用 websocket_callback_client class 与同时运行的三个不同服务器建立了三个不同的连接。 .

程序运行了一段未定义的时间，然后突然收到SIGTRAP，Trace/Breakpoint trap。这是 GDB 的输出:

#0  0x00007ffff5abec37 in __GI_raise (sig=5) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x000000000047bb8e in pplx::details::_ExceptionHolder::~_ExceptionHolder() ()
#2  0x000000000044be29 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release() ()
#3  0x000000000047fa39 in pplx::details::_Task_impl<unsigned char>::~_Task_impl() ()
#4  0x000000000044be29 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release() ()
#5  0x00007ffff6feb09f in std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count (this=0x7fffc8021420, __in_chrg=<optimized out>) at /usr/include/c++/4.8/bits/shared_ptr_base.h:546
#6  0x00007ffff6fffa38 in std::__shared_ptr<pplx::details::_Task_impl<unsigned char>, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr (this=0x7fffc8021418, __in_chrg=<optimized out>) at /usr/include/c++/4.8/bits/shared_ptr_base.h:781
#7  0x00007ffff6fffa52 in std::shared_ptr<pplx::details::_Task_impl<unsigned char> >::~shared_ptr (this=0x7fffc8021418, __in_chrg=<optimized out>) at /usr/include/c++/4.8/bits/shared_ptr.h:93
#8  0x00007ffff710f766 in pplx::details::_PPLTaskHandle<unsigned char, pplx::task<unsigned char>::_InitialTaskHandle<void, void web::websockets::client::details::wspp_callback_client::shutdown_wspp_impl<websocketpp::config::asio_tls_client>(std::weak_ptr<void> const&, bool)::{lambda()#1}, pplx::details::_TypeSelectorNoAsync>, pplx::details::_TaskProcHandle>::~_PPLTaskHandle() (this=0x7fffc8021410, __in_chrg=<optimized out>)
    at /home/cpprestsdk/Release/include/pplx/pplxtasks.h:1631
#9  0x00007ffff716e6f2 in pplx::task<unsigned char>::_InitialTaskHandle<void, void web::websockets::client::details::wspp_callback_client::shutdown_wspp_impl<websocketpp::config::asio_tls_client>(std::weak_ptr<void> const&, bool)::{lambda()#1}, pplx::details::_TypeSelectorNoAsync>::~_InitialTaskHandle() (this=0x7fffc8021410, __in_chrg=<optimized out>) at /home/cpprestsdk/Release/include/pplx/pplxtasks.h:3710
#10 0x00007ffff716e722 in pplx::task<unsigned char>::_InitialTaskHandle<void, void web::websockets::client::details::wspp_callback_client::shutdown_wspp_impl<websocketpp::config::asio_tls_client>(std::weak_ptr<void> const&, bool)::{lambda()#1}, pplx::details::_TypeSelectorNoAsync>::~_InitialTaskHandle() (this=0x7fffc8021410, __in_chrg=<optimized out>) at /home/cpprestsdk/Release/include/pplx/pplxtasks.h:3710
#11 0x00007ffff71f9cdd in boost::_bi::list1<boost::_bi::value<void*> >::operator()<void (*)(void*), boost::_bi::list0> (this=0x7fffdc7d7d28, f=@0x7fffdc7d7d20: 0x479180 <pplx::details::_TaskProcHandle::_RunChoreBridge(void*)>, a=...)
    at /usr/local/include/boost/bind/bind.hpp:259
#12 0x00007ffff71f9c8f in boost::_bi::bind_t<void, void (*)(void*), boost::_bi::list1<boost::_bi::value<void*> > >::operator() (this=0x7fffdc7d7d20) at /usr/local/include/boost/bind/bind.hpp:1222
#13 0x00007ffff71f9c54 in boost::asio::asio_handler_invoke<boost::_bi::bind_t<void, void (*)(void*), boost::_bi::list1<boost::_bi::value<void*> > > > (function=...) at /usr/local/include/boost/asio/handler_invoke_hook.hpp:69
#14 0x00007ffff71f9bea in boost_asio_handler_invoke_helpers::invoke<boost::_bi::bind_t<void, void (*)(void*), boost::_bi::list1<boost::_bi::value<void*> > >, boost::_bi::bind_t<void, void (*)(void*), boost::_bi::list1<boost::_bi::value<void*> > > > (function=..., context=...) at /usr/local/include/boost/asio/detail/handler_invoke_helpers.hpp:37
#15 0x00007ffff71f9b2e in boost::asio::detail::completion_handler<boost::_bi::bind_t<void, void (*)(void*), boost::_bi::list1<boost::_bi::value<void*> > > >::do_complete (owner=0x7488d0, base=0x7fffc801ecd0)
    at /usr/local/include/boost/asio/detail/completion_handler.hpp:68
#16 0x00000000004c34c1 in boost::asio::detail::task_io_service::run(boost::system::error_code&) ()
#17 0x00007ffff709fb27 in boost::asio::io_service::run (this=0x7ffff759ab78 <crossplat::threadpool::shared_instance()::s_shared+24>) at /usr/local/include/boost/asio/impl/io_service.ipp:59
#18 0x00007ffff7185a81 in crossplat::threadpool::thread_start (arg=0x7ffff759ab60 <crossplat::threadpool::shared_instance()::s_shared>) at /home/cpprestsdk/Release/include/pplx/threadpool.h:133
#19 0x00007ffff566e184 in start_thread (arg=0x7fffdc7d8700) at pthread_create.c:312
#20 0x00007ffff5b8237d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111

在第 18 行，来源 /pplx/threadpool.h:133给出。 这是围绕这些行的源代码:

  123     static void* thread_start(void *arg)
  124     {
  125 #if (defined(ANDROID) || defined(__ANDROID__))
  126         // Calling get_jvm_env() here forces the thread to be attached.
  127         get_jvm_env();
  128         pthread_cleanup_push(detach_from_java, nullptr);
  129 #endif
  130         threadpool* _this = reinterpret_cast<threadpool*>(arg);
  131         try
  132         {
  133             _this->m_service.run();
  134         }
  135         catch (const _cancel_thread&)
  136         {
  137             // thread was cancelled
  138         }
  139         catch (...)
  140         {
  141             // Something bad happened
  142 #if (defined(ANDROID) || defined(__ANDROID__))
  143             // Reach into the depths of the 'droid!
  144             // NOTE: Uses internals of the bionic library
  145             // Written against android ndk r9d, 7/26/2014
  146             __pthread_cleanup_pop(&__cleanup, true);
  147             throw;
  148 #endif
  149         }
  150 #if (defined(ANDROID) || defined(__ANDROID__))
  151         pthread_cleanup_pop(true);
  152 #endif
  153         return arg;
  154     }

需要说明的是，m_service 是一个 boost::asio::io_service。 在我看来，第 133 行抛出异常，它在第 139 行被捕获，然后重新抛出。在这一点上，我必须亲自捕获它，因为如果我不这样做并且 pplx 对象因未捕获的异常而被销毁，它将引发 SIGTRAP。

这是我的研究进展情况。问题是我不知道这是在哪里发生的。我用 try {} catch(...){} 包围了通过 websocket_callback_client 发送或接收数据的每个位置，它仍在发生。

也许以前使用过这个库的人可以帮助我。

Answer 1

根据我的经验，发生这种情况是由于一个单独的问题。
当调用 websocket_callback_client 的关闭处理程序时，大多数人会尝试删除 websocket_callback_client。这在内部调用了关闭函数。
发生这种情况时，websocket_callback_client 将等待关闭完成。如果另一个线程意识到连接已死并尝试清理，您将从 2 个不同位置删除同一个对象，这将导致重大问题。
Howto reconnect to a server which does not answer to close()对 cpprestsdk 调用关闭时发生的情况进行了相当彻底的审查。

希望这有帮助:)

编辑: 事实证明(我在链接问题中给出的答复有这个)，如果您尝试从关闭处理程序中关闭或删除 websocket_callback_client，它本身将调用关闭处理程序，这将锁定线程。
我发现最适合我的解决方案是在关闭处理程序中设置一个标志并在主线程或至少在备用线程中处理清理。