服务与未完成的完成处理程序
我写了一个异步boost :: asio TCP应用程序，它使用声明为std::vector<std::thread> mIOServicePool 。 这些线程异步读取和写入TCP数据到服务器。 以下代码取自GUI的开始按钮事件处理程序。
// launch multiple asio service threads to
// handle the protocol instances - effectively
// thread pooling the ioservice
//mpIOService->reset();
for (auto i=0; i<3; i++) {
mIOServicePool.emplace_back(
std::thread([this]() { mpIOService->run(); }));
}
该代码是基于Qt的GUI应用程序的一部分，其中mIOServicePool作为GUI主窗口类的成员存储。
这在我启动应用程序并保持运行时正常工作，但是，在尝试重新启动与后端服务器的连接时，事情开始出错。 这个问题很可能与未完成的处理程序有关，当我重置与io_service::work关联的io_service::work时（当按下GUI停止按钮时），我认为它会被刷新。 当我尝试在读取内存asio :: socket的流缓冲区时，通过访问冲突尝试启动TCP通信（至少在Windows上）时，问题就会显现出来。 从下面的堆栈跟踪中可以看到，它正在处理与读取套接字关联的完成处理程序。
app739.exe!boost::asio::basic_streambuf<std::allocator<char> >::commit(unsigned __int64 n) Line 226 C++
app739.exe!boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const & __ptr64>,boost::_bi::list2<boost::_bi::value<VCDUProtocol * __ptr64>,boost::arg<1> > > >::operator()(const boost::system::error_code & ec, unsigned __int64 bytes_transferred, int start) Line 624 C++
app739.exe!boost::asio::detail::binder2<boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const & __ptr64>,boost::_bi::list2<boost::_bi::value<VCDUProtocol * __ptr64>,boost::arg<1> > > >,boost::system::error_code,unsigned __int64>::operator()() Line 129 C++
app739.exe!boost::asio::asio_handler_invoke<boost::asio::detail::binder2<boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const & __ptr64>,boost::_bi::list2<boost::_bi::value<VCDUProtocol * __ptr64>,boost::arg<1> > > >,boost::system::error_code,unsigned __int64> >(boost::asio::detail::binder2<boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const &>,boost::_bi::list2<boost::_bi::value<VCDUProtocol *>,boost::arg<1> > > >,boost::system::error_code,unsigned __int64> & function, ...) Line 70 C++
app739.exe!boost_asio_handler_invoke_helpers::invoke<boost::asio::detail::binder2<boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const & __ptr64>,boost::_bi::list2<boost::_bi::value<VCDUProtocol * __ptr64>,boost::arg<1> > > >,boost::system::error_code,unsigned __int64>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const & __ptr64>,boost::_bi::list2<boost::_bi::value<VCDUProtocol * __ptr64>,boost::arg<1> > > >(boost::asio::detail::binder2<boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const &>,boost::_bi::list2<boost::_bi::value<VCDUProtocol *>,boost::arg<1> > > >,boost::system::error_code,unsigned __int64> & function, boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const &>,boost::_bi::list2<boost::_bi::value<VCDUProtocol *>,boost::arg<1> > > & context) Line 39 C++
app739.exe!boost::asio::detail::asio_handler_invoke<boost::asio::detail::binder2<boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const & __ptr64>,boost::_bi::list2<boost::_bi::value<VCDUProtocol * __ptr64>,boost::arg<1> > > >,boost::system::error_code,unsigned __int64>,boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const & __ptr64>,boost::_bi::list2<boost::_bi::value<VCDUProtocol * __ptr64>,boost::arg<1> > > >(boost::asio::detail::binder2<boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const &>,boost::_bi::list2<boost::_bi::value<VCDUProtocol *>,boost::arg<1> > > >,boost::system::error_code,unsigned __int64> & function, boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const &>,boost::_bi::list2<boost::_bi::value<VCDUProtocol *>,boost::arg<1> > > > * this_handler) Line 685 C++
app739.exe!boost_asio_handler_invoke_helpers::invoke<boost::asio::detail::binder2<boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const & __ptr64>,boost::_bi::list2<boost::_bi::value<VCDUProtocol * __ptr64>,boost::arg<1> > > >,boost::system::error_code,unsigned __int64>,boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const & __ptr64>,boost::_bi::list2<boost::_bi::value<VCDUProtocol * __ptr64>,boost::arg<1> > > > >(boost::asio::detail::binder2<boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const &>,boost::_bi::list2<boost::_bi::value<VCDUProtocol *>,boost::arg<1> > > >,boost::system::error_code,unsigned __int64> & function, boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const &>,boost::_bi::list2<boost::_bi::value<VCDUProtocol *>,boost::arg<1> > > > & context) Line 39 C++
app739.exe!boost::asio::detail::win_iocp_socket_recv_op<boost::asio::mutable_buffers_1,boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp,boost::asio::stream_socket_service<boost::asio::ip::tcp> >,std::allocator<char>,boost::_bi::bind_t<void,boost::_mfi::mf1<void,VCDUProtocol,boost::system::error_code const & __ptr64>,boost::_bi::list2<boost::_bi::value<VCDUProtocol * __ptr64>,boost::arg<1> > > > >::do_complete(boost::asio::detail::win_iocp_io_service * owner, boost::asio::detail::win_iocp_operation * base, const boost::system::error_code & result_ec, unsigned __int64 bytes_transferred) Line 97 C++
app739.exe!boost::asio::detail::win_iocp_operation::complete(boost::asio::detail::win_iocp_io_service & owner, const boost::system::error_code & ec, unsigned __int64 bytes_transferred) Line 47 C++
app739.exe!boost::asio::detail::win_iocp_io_service::do_one(bool block, boost::system::error_code & ec) Line 406 C++
app739.exe!boost::asio::detail::win_iocp_io_service::run(boost::system::error_code & ec) Line 164 C++
app739.exe!boost::asio::io_service::run() Line 59 C++
app739.exe!MainWindow::on_pushButtonStart_clicked::__l13::<lambda>() Line 943 C++
这个答案表明问题可能与io_service.reset() 。 访问冲突时的堆栈跟踪显示该线程正在处理一个asio完成处理程序。 我认为通过阅读其他帖子，解决这个问题的关键是要正确地将io_service.stop()和io_service.reset()排序到boost::asio::io_service对象，在停止之前重置套接字也很重要io_service或重置哨兵工作对象。
下面的代码显示了我如何尝试停止io_service线程，同时调试代码，我发现所有线程都完成了它们的连接，所以我不明白为什么有完成处理程序出现。
void
MainWindow::stopSys()
{
// make sure that we have no more work keeping services alive
mpWork.reset();
// check to see if the protocol threads were started
if (mVCDUProtocol) {
// terminate protocol thread by setting the shared mShutdown atomic flag
mVCDUProtocol->shutdown();
// Once each thread sees the shutdown flag, it will cleanly
// terminate so we can call join here to wait for the entire
// pool to finish
std::for_each(mIOServicePool.begin(), mIOServicePool.end(),
[](std::thread& rNext) {
rNext.join();
});
mIOServicePool.clear();
}
}
我的代码如下所示非常简单。 它启动了一个异步解析 - 这是在一个lambda处理程序中处理的。 从那里，它调用start_async_ops(endPointIter)以执行一个异步connect()并从该拉姆达，代码调用VCDUProtocol::do_read()其执行boost::asio::async_read_until()以等待来自所述数据服务器。
void
VCDUProtocol::prosimAsyncIOThreadFn()
{
static auto& gLogger = gpLogger->getLoggerRef(
gUseSysLog ? Logger::LogDest::SysLog :
Logger::LogDest::EventLog);
try {
// convert the host-name/port to a usable endpoint
tcp::resolver resolver(*mpIOService);
tcp::resolver::query query(mProtocolConfig.getProsimHostName(),
std::to_string(mProtocolConfig.getProsimPortNum()));
const auto endPointIter = std::find_if(
resolver.resolve(query), tcp::resolver::iterator(),
[](const tcp::endpoint& next) {
return next.protocol() == tcp::v4();
});
if (endPointIter != tcp::resolver::iterator()) {
mpSocket = std::make_unique<tcp::socket>(*mpIOService);
mpSocketTimer = std::make_unique<deadline_timer>(*mpIOService);
start_async_ops(endPointIter);
}
} catch (std::exception& rEx) {
LOG_ERROR(gLogger, gChannel) << boost::format(
"%1%: %2%")
% __FUNCTION__
% rEx.what();
}
}
void
VCDUProtocol::start_async_ops(tcp::resolver::iterator endpoint_iter)
{
// Start the connect actor.
do_connect(endpoint_iter);
// Start the deadline actor. You will note that we're not setting any
// particular deadline here. Instead, the connect and input actors will
// update the deadline prior to each asynchronous operation.
mpSocketTimer->async_wait(boost::bind(
&VCDUProtocol::check_deadline, this, _1));
}
void
VCDUProtocol::do_connect(
tcp::resolver::iterator endpoint_iter)
{
if (endpoint_iter != tcp::resolver::iterator()) {
// Set a deadline for the connect operation to complete.
mpSocketTimer->expires_from_now(boost::posix_time::seconds(5));
boost::asio::async_connect(*mpSocket, endpoint_iter,
[this](boost::system::error_code ec, tcp::resolver::iterator) {
if (!mShutdownFlag && !ec) {
// successfully connected here - cancel the
// connect timer and kick off async write ops
mpSocketTimer->cancel();
// kick off the prosim read operation
do_read();
}
});
} else {
// No more endpoints. Close the socket.
shutdown();
}
}
void
VCDUProtocol::do_read()
{
// Start or continue an asynchronous line reads. This will read at least
// up to a carriage return or line feed
async_read_until(*mpSocket, *mTLS->mSocketStreamBuf, "rn",
boost::bind(&VCDUProtocol::handle_read, this, _1));
}
这是异步读取完成处理程序 - 这是需要取消的地方，我在某处读取简单地关闭套接字是不够的，因为完成处理程序不会被调用。 我应该打电话给取消;
/**
* Asynchronous read callback.
*
* @param ec [in] Boost ASIO library error code.
*/
void
VCDUProtocol::handle_read(const boost::system::error_code& ec)
{
static auto& gLogger = gpLogger->getLoggerRef(
gUseSysLog ? Logger::LogDest::SysLog :
Logger::LogDest::EventLog);
if (!mShutdownFlag) {
if (!ec) {
// Extract the newline-delimited message from the buffer.
std::string line;
std::istream is(mTLS->mSocketStreamBuf.get());
while (std::getline(is, line)) {
// Critical Section
std::lock_guard<std::mutex> lock (gMutexGuard);
// handle partial line reads
if (is.eof()) {
mTLS->mPartialLine = std::move(line);
continue;
} else if (!mTLS->mPartialLine.empty()) {
line = std::move(mTLS->mPartialLine) + line;
}
. . .
// update GUI
mpListener->handlePageUpdate(
mProtocolConfig.getCduID(),
mTLS->mVCDUPage, bRefreshCDU);
}
// not really required
line.clear();
}
// keep reading
do_read();
} else {
LOG_ERROR(gLogger, gChannel) << boost::format(
"CDU_%1%: handle_read - error[%2%]")
% mProtocolConfig.getCduID()
% ec.message();
shutdown();
}
}
}
用未完成的完成处理程序重新启动tcp boost asio io_service
AFAICT，这是不可能的。
该文档明确指出必须在run()可以再次调用之前调用reset() 。
我认为唯一可行的选择是基于例如poll_one()创建自己的事件循环，从而防止首先停止服务。
这是异步读取完成处理程序 - 这是需要取消的地方，我在某处读取简单地关闭套接字是不够的，因为完成处理程序不会被调用。
这不是真的。 取消套接字将取消在飞行中的操作，它们将导致完成处理程序以ec == operation_aborted进行调用。 关闭套接字可能会导致不同的错误代码，如bad_socket 。