使用 boost 的 SSL asio 代码，async_write_some 挂起

Question

我有一些使用 Boost 的 SSL ASIO 库的多线程代码。代码是多线程的，但是每个 SSL 连接都有一个互斥锁，并且对async_*函数的调用是通过持有互斥锁完成的。

我有时会看到我的代码停止运行。有一个卡住的线程。线程卡在bio_write. 堆栈跟踪如下所示：

#0  0x00000000010a974f in bio_write ()   

#1  0x00000000010a3529 in BIO_write ()

#2  0x000000000105fe72 in ssl3_write_pending ()

#3  0x0000000001060b02 in ssl3_write_bytes ()

#4  0x0000000000cce43a in boost::asio::ssl::detail::engine::do_write
(this=0x1e618a0, data=0x234c7b0, length=189) at
/usr/include/boost/asio/ssl/detail/impl/engine.ipp:294

#5  0x0000000000cce109 in boost::asio::ssl::detail::engine::perform(this=0x1e618a0, op=(int
(boost::asio::ssl::detail::engine::*)(boost::asio::ssl::detail::engine *
const, void *, std::size_t)) 0xcce3fc<boost::asio::ssl::detail::engine::do_write(void*, unsigned long)>,
data=0x234c7b0, length=189, ec=..., bytes_transferred=0x7fff8ad74d48) at
/usr/include/boost/asio/ssl/detail/impl/engine.ipp:219

#6  0x0000000000ccdd23 in boost::asio::ssl::detail::engine::write
(this=0x1e618a0, data=..., ec=..., bytes_transferred=@0x7fff8ad74d48: 0) at
/usr/include/boost/asio/ssl/detail/impl/engine.ipp:137

#7  0x0000000000dac504 in boost::asio::ssl::detail::write_op<boost::asio::mutable_buffers_1>::operator()
(this=0x7fff8ad74d20, eng=..., ec=..., bytes_transferred=@0x7fff8ad74d48: 0)
at /usr/include/boost/asio/ssl/detail/write_op.hpp:51

#8  0x0000000000da9d8a in boost::asio::ssl::detail::io_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
boost::asio::stream_socket_service<boost::asio::ip::tcp> >,
boost::asio::ssl::detail::write_op<boost::asio::mutable_buffers_1>,
boost::asio::detail::write_op<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
boost::asio::stream_socket_service<boost::asio::ip::tcp> > >,
boost::asio::mutable_buffers_1, boost::asio::detail::transfer_all_t,
boost::_bi::bind_t<void, boost::_mfi::mf2<void, Peer,
boost::system::error_code const&, unsigned long>,
boost::_bi::list3<boost::_bi::value<boost::shared_ptr<Peer> >, boost::arg<1>
(*)(), boost::arg<2> (*)()> > > >::operator() (this=0x7fff8ad74d10, ec=..., 
bytes_transferred=0, start=1) at /usr/include/boost/asio/ssl/detail/io.hpp:136

#9  0x0000000000da7f42 in boost::asio::ssl::detail::async_io<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
boost::asio::stream_socket_service<boost::asio::ip::tcp> >,
boost::asio::ssl::detail::write_op<boost::asio::mutable_buffers_1>,
boost::asio::detail::write_op<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
boost::asio::stream_socket_service<boost::asio::ip::tcp> > >,
boost::asio::mutable_buffers_1, boost::asio::detail::transfer_all_t,
boost::_bi::bind_t<void, boost::_mfi::mf2<void, Peer,
boost::system::error_code const&, unsigned long>,
boost::_bi::list3<boost::_bi::value<boost::shared_ptr<Peer> >, boost::arg<1> (*)(),
boost::arg<2> (*)()> > > > (next_layer=..., core=..., op=...,
handler=...) at /usr/include/boost/asio/ssl/detail/io.hpp:322

#10 0x0000000000da634d in
boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
boost::asio::stream_socket_service<boost::asio::ip::tcp> >
>::async_write_some<boost::asio::mutable_buffers_1,
boost::asio::detail::write_op<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
boost::asio::stream_socket_service<boost::asio::ip::tcp> > >,
boost::asio::mutable_buffers_1, boost::asio::detail::transfer_all_t,
boost::_bi::bind_t<void, boost::_mfi::mf2<void, Peer,
boost::system::error_code const&, unsigned long>,
boost::_bi::list3<boost::_bi::value<boost::shared_ptr<Peer> >, boost::arg<1>
(*)(), boost::arg<2> (*)()> > > > (this=0x1e61880, buffers=..., handler=...)
at /usr/include/boost/asio/ssl/stream.hpp:502

#11 0x0000000000da3032 in
boost::asio::detail::write_op<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
boost::asio::stream_socket_service<boost::asio::ip::tcp> > >,
boost::asio::mutable_buffers_1, boost::asio::detail::transfer_all_t,
boost::_bi::bind_t<void, boost::_mfi::mf2<void, Peer,
boost::system::error_code const&, unsigned long>,
boost::_bi::list3<boost::_bi::value<boost::shared_ptr<Peer> >, boost::arg<1>
(*)(), boost::arg<2> (*)()> > >::operator() (this=0x7fff8ad74f00, ec=...,   
bytes_transferred=0, start=1) at /usr/include/boost/asio/impl/write.hpp:250 

#12 0x0000000000d9ffbb in
boost::asio::async_write<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
boost::asio::stream_socket_service<boost::asio::ip::tcp> > >,
boost::asio::mutable_buffers_1, boost::_bi::bind_t<void,
boost::_mfi::mf2<void, Peer, boost::system::error_code const&, unsigned
long>, boost::_bi::list3<boost::_bi::value<boost::shared_ptr<Peer> >,  
boost::arg<1> (*)(), boost::arg<2> (*)()> > > (s=..., buffers=...,     
handler=...) at /usr/include/boost/asio/impl/write.hpp:585

有任何想法吗？

Answer 1

这是多线程问题的结果。

对于大多数 Boost.Asio 对象，在一个对象上挂起多个异步操作是安全的；只是指定对象上的并发调用是不安全的。尽管如此，它通常不会在某些类型上出现问题，例如ip::tcp::socket. 然而，ssl::stream强调的是：

应用程序还必须确保所有异步操作都在同一个隐式或显式链中执行。

在您的情况下，解决方案是wrap()通过相同的链对每个组合操作的完成处理程序进行处理。这将导致在链中调用所有中间操作。有关线程安全性和链的细微差别细节的更多详细信息，请考虑阅读此答案。