我们有一个与服务器通信的C ++应用程序。它向它发送两条消息，服务器用另一条消息响应每个消息。我们使用的是Boost，但是当我们尝试关闭套接字时，Boost Socket（整个应用程序）会阻塞。
这是我们正在做的一般想法：
由于我们发送了两条消息，因此我们将其循环执行（显然只有两次迭代）。
我们确切知道错误的出处，因为如果删除该行，它将正常工作。它位于第5步。不幸的是，这是很重要的一步。我们找不到错误的解决方法。
代码如下：
bool ReallyImportantService::sendMessages( int messageNum ) {
// ...some error-checking here...
bool successCode = false;
for( int i = 0; i < 2; ++i ) {
successCode = false;
unique_ptr<boost::asio::ip::tcp::socket> theSocket = connect();
if( theSocket == nullptr ) {
theLogger->error( "Could not create socket, could not send input messageNum to service" );
return successCode;
}
string message = encodeMessage( messageNum );
// send the message
boost::system::error_code error;
size_t bytesSent = boost::asio::write(*theSocket,
boost::asio::buffer(message),
boost::asio::transfer_all(), error);
// inspect the result
if( !messageNumSendSuccessful(message.length(), bytesSent) ) {
return successCode;
}
// Get the response message
string response;
boost::system::error_code e;
boost::asio::streambuf buffer;
// this is step #5 above, the line that kills it. But it responds with no errors
boost::asio::read_until(*theSocket, buffer, "\0", e);
if( e.value() == boost::system::errc::success ) {
istream str(&buffer);
getline(str, response);
// validate response
successCode = messageAckIsValid( response, messageNum );
}
else {
theLogger->error( "Got erroneous response from server when sending messageNum" );
}
// close it all up
boost::system::error_code eShut;
theSocket->shutdown(boost::asio::socket_base::shutdown_type::shutdown_both, eShut);
// We never get an error code here, all clean
try {
boost::system::error_code ec;
// This is where it all goes belly-up. It doesn't throw an exception, doesn't return an
// error-code. Stepping through, we can see the call stack shows a Segmentation fault,
// but we don't know what could be causing this.
theSocket->close( ec );
}
catch(boost::system::system_error& se) {
theLogger->error( "sendMessages() barfed on close! " + string(se.what()) );
}
catch( ... ) {
theLogger->error( "sendMessages() barfed on close! " );
}
}
return successCode;
}
string ReallyImportantService::encodeMessage( int messageNum ) {
// Encode the message
stringstream ss;
ss << "^FINE=";
ss << to_string(messageNum) << "\n";
string message = ss.str();
theLogger->info( message );
return message;
}
unique_ptr<boost::asio::ip::tcp::socket> ReallyImportantService::connect() {
// Addresses from configuration
string address( server_ip );
string port( server_port );
// Resolve the IP address
boost::asio::io_service ioService;
boost::asio::ip::tcp::resolver resolver(ioService);
boost::asio::ip::tcp::resolver::query query(address, port);
boost::asio::ip::tcp::resolver::iterator ep_iterator = resolver.resolve(query);
// create the socket
unique_ptr<boost::asio::ip::tcp::socket> theSocket = make_unique<boost::asio::ip::tcp::socket>(ioService);
// not sure if this is necessary, but couldn't hurt; we do reuse the IP address the second time around
boost::system::error_code ec;
theSocket->set_option(boost::asio::socket_base::reuse_address(true), ec);
// Connect
try {
boost::asio::connect(*theSocket, ep_iterator);
} catch(const boost::system::system_error &e){
theSocket = nullptr;
theLogger->error( "Exception while attempting to create socket: " + string(e.what()) );
} catch(const exception &e){
theSocket = nullptr;
theLogger->error( "Exception while attempting to create socket: " + string(e.what()) );
}
return theSocket;
}
这是发生错误时我们得到的调用堆栈：
(Suspended : Signal : SIGSEGV:Segmentation fault)
pthread_mutex_lock() at 0x7ffff7bc8c30
boost::asio::detail::posix_mutex::lock() at posix_mutex.hpp:52 0x969072
boost::asio::detail::scoped_lock<boost::asio::detail::posix_mutex>::scoped_lock() at scoped_lock.hpp:36 0x980b66
boost::asio::detail::epoll_reactor::free_descriptor_state() at epoll_reactor.ipp:517 0x96c6fa
boost::asio::detail::epoll_reactor::deregister_descriptor() at epoll_reactor.ipp:338 0x96bccc
boost::asio::detail::reactive_socket_service_base::close() at reactive_socket_service_base.ipp:103 0xb920aa
boost::asio::stream_socket_service<boost::asio::ip::tcp>::close() at stream_socket_service.hpp:151 0xb975e0
boost::asio::basic_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> >::close() at basic_socket.hpp:339 0xb94f0d
ReallyImportantService::sendMessages() at ReallyImportantService.cc:116 0xb8ce19
<...more frames...>
我们创建了一个最小的实现，只是：
它运行完美。我们将其循环放置，可以进行数十次迭代而不会出现任何问题。
我们正在使用Eclipse CDT和gcc进行编译。
有什么想法吗？
答案 0 :(得分：1)
您违反了基本规则。
io_service的寿命必须超过在其上创建的所有对象。
您的connect()函数创建一个io_service，在其上创建一个套接字并返回该套接字（包装在unique_ptr中）。然后io_service被销毁。
从那时起，所有赌注都消失了，因为套接字将使用与刚销毁的io_service关联的套接字服务对象。现在，此套接字服务只是其中包含未定义值的内存。您很不幸，程序在段错误之前就已经实现了。
通常，每个应用程序需要一个io_service。所有需要它的对象都应带有对它的引用。
您的连接功能将变为：
bool connect(boost::asio::ip::tcp& theSocket) {
// Addresses from configuration
string address( server_ip );
string port( server_port );
// Resolve the IP address
boost::asio::ip::tcp::resolver resolver(theSocket.get_io_service());
boost::asio::ip::tcp::resolver::query query(address, port);
boost::asio::ip::tcp::resolver::iterator ep_iterator = resolver.resolve(query);
// not sure if this is necessary, but couldn't hurt; we do reuse the IP address the second time around
boost::system::error_code ec;
theSocket.set_option(boost::asio::socket_base::reuse_address(true), ec);
// Connect
try {
boost::asio::connect(theSocket, ep_iterator);
} catch(const boost::system::system_error &e){
theSocket = nullptr;
theLogger->error( "Exception while attempting to create socket: " + string(e.what()) );
return false;
} catch(const exception &e){
theSocket = nullptr;
theLogger->error( "Exception while attempting to create socket: " + string(e.what()) );
return false;
}
return true;
}
bool sendMessages(boost::asio::io_service& ios, int messageNum)
{
boost::asio::ip::tcp::socket theSocket(ios);
auto ok = connect(theSocket);
// ... carry on ...
}
尽可能地保留对套接字等的引用。将它们包装在unique_ptr中是一种令人困惑的间接层。
从c ++ 11和最新版本的boost开始，asio套接字是可移动的。您可以按值返回它们，而不必像我那样传递引用。
我注意到您在代码中混合了异常和非异常错误处理。您可能希望坚持使用另一种方法（在我看来，基于异常的错误处理比较干净，但这不是通用视图）。