Using boost::asio::io_service::post()

Question

First i asked this Running a function on the main thread from a boost thread and passing parameters to that function

so now i am trying this:

The following is a console c++ project where i perfectly simulated my big project

TestServicePost.cpp

#include "stdafx.h"
#include "SomeClass.h"


int _tmain(int argc, _TCHAR* argv[])
{
    SomeClass* s = new SomeClass();
    while(true)
    {
        s->update();
    }
    return 0;
}

SomeClass.h

#include <boost/thread.hpp>
#include <boost/asio.hpp>
#include <queue>

class ServiceNote
{
public:
    std::string getType()
    {
        std::stringstream typeSS;
        typeSS << "LamasaTech.MultiWall.PostNote." << (NoteType.compare("Normal") == 0 ? "Node" : "Header") << "." << Shape << "." << Colour;
        return typeSS.str();
    }
    int Action; 
    int CNoteId;    
    std::string Colour; 
    int NoteId; 
    std::string NoteType;   
    int SessionId;  
    std::string Shape;  
    std::string Style;  
    std::string Text;   
    int X;  
    int Y;  
};

class SomeClass
{
public:
    SomeClass();
    ~SomeClass();
    void update();

private:
    std::queue<ServiceNote> pendingNotes;
    void addToQueue(ServiceNote sn);
    void pollService(boost::asio::io_service* svc);
    int getMessage(boost::asio::io_service* svc, std::string sessionId, int messageId);
    boost::thread servicePoller;
};

SomeClass.cpp

#include "stdafx.h"
#include "SomeClass.h"
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>
#include <boost/asio/signal_set.hpp>

#define POLL_SERVICE = 0;
#define POLLING_WAIT_TIME 1000
#define SAVE_SESSION_EVERY 1800000

SomeClass::SomeClass()
{
    boost::asio::io_service io_servicePoller;
    io_servicePoller.run();
    servicePoller = boost::thread(boost::bind(&SomeClass::pollService, this, &io_servicePoller));
    /*boost::asio::io_service io_sessionSaver;
    boost::asio::signal_set signalsSaver(io_sessionSaver, SIGINT, SIGTERM);
    signalsSaver.async_wait( boost::bind(&boost::asio::io_service::stop, &io_sessionSaver));
    sessionSaver = boost::thread(&SomeClass::saveSessionEvery, io_sessionSaver);*/
}

SomeClass::~SomeClass()
{
}

void SomeClass::update()
{   
    while(!pendingNotes.empty())
    {
        ServiceNote sn = pendingNotes.front();

        pendingNotes.pop();
    }
}

void SomeClass::addToQueue(ServiceNote sn)
{
    pendingNotes.push(sn);
}

void SomeClass::pollService(boost::asio::io_service* svc)
{
    int messageId = 1;
    while(true)
    {
        if(boost::this_thread::interruption_enabled() && boost::this_thread::interruption_requested())
            return;
        int currentId = messageId;
        messageId = getMessage(svc, "49", messageId);
        if(currentId == messageId)
            boost::this_thread::sleep(boost::posix_time::milliseconds(POLLING_WAIT_TIME));
    }
}

int SomeClass::getMessage(boost::asio::io_service* svc, std::string sessionId, int messageId)
{
    try
    {
        boost::asio::io_service io_service;

        // Get a list of endpoints corresponding to the server name.
        boost::asio::ip::tcp::resolver resolver(io_service);
        boost::asio::ip::tcp::resolver::query query("mw.rombus.com", "http");
        boost::asio::ip::tcp::resolver::iterator endpoint_iterator = resolver.resolve(query);

        // Try each endpoint until we successfully establish a connection.
        boost::asio::ip::tcp::socket socket(io_service);
        boost::asio::connect(socket, endpoint_iterator);

        // Form the request. We specify the "Connection: close" header so that the
        // server will close the socket after transmitting the response. This will
        // allow us to treat all data up until the EOF as the content.
        boost::asio::streambuf request;
        std::ostream request_stream(&request);
        request_stream << "GET " "/Service.svc/message/" << sessionId << "/" << messageId << " HTTP/1.0\r\n";
        request_stream << "Host: " << "mw.rombus.com" << "\r\n";
        request_stream << "Accept: */*\r\n";
        request_stream << "Connection: close\r\n\r\n";

        // Send the request.
        boost::asio::write(socket, request);

        // Read the response status line. The response streambuf will automatically
        // grow to accommodate the entire line. The growth may be limited by passing
        // a maximum size to the streambuf constructor.
        boost::asio::streambuf response;
        boost::asio::read_until(socket, response, "\r\n");

        // Check that response is OK.
        std::istream response_stream(&response);
        std::string http_version;
        response_stream >> http_version;
        unsigned int status_code;
        response_stream >> status_code;
        std::string status_message;
        std::getline(response_stream, status_message);
        if (!response_stream || http_version.substr(0, 5) != "HTTP/")
        {
            //std::cout << "Invalid response\n";
            return messageId;
        }
        if (status_code != 200)
        {
            //std::cout << "Response returned with status code " << status_code << "\n";
            return messageId;
        }

        // Read the response headers, which are terminated by a blank line.
        boost::asio::read_until(socket, response, "\r\n\r\n");

        // Process the response headers.
        std::string header;
        std::string fullHeader = "";
        while (std::getline(response_stream, header) && header != "\r")
            fullHeader.append(header).append("\n");

        // Write whatever content we already have to output.
        std::string fullResponse = "";
        if (response.size() > 0)
        {
            std::stringstream ss;
            ss << &response;
            fullResponse = ss.str();
            try
            {
                boost::property_tree::ptree pt;
                boost::property_tree::read_json(ss, pt);
                ServiceNote sn;
                sn.Action =  pt.get<int>("Action");
                sn.CNoteId =  pt.get<int>("CNoteId");
                sn.Colour =  pt.get<std::string>("Colour");
                sn.NoteId =  pt.get<int>("NoteId");
                sn.NoteType =  pt.get<std::string>("NoteType");
                sn.SessionId =  pt.get<int>("SessionId");
                sn.Shape =  pt.get<std::string>("Shape");
                sn.Style =  pt.get<std::string>("Style");
                sn.Text =  pt.get<std::string>("Text");
                sn.X =  pt.get<int>("X");
                sn.Y =  pt.get<int>("Y");
                svc->post(boost::bind(&SomeClass::addToQueue, this, sn));
                //pendingNotes.push(sn);
            }
            catch (std::exception const& e)
            {
                std::string test = e.what();
                //std::cerr << e.what() << std::endl;
            }
            messageId++;
        }

        // Read until EOF, writing data to output as we go.
        std::string fullSth = "";
        boost::system::error_code error;
        while (boost::asio::read(socket, response,
                boost::asio::transfer_at_least(1), error))
        {
            std::ostringstream ss;
            ss << &response;
            fullSth = ss.str();
        }
        if (error != boost::asio::error::eof)
            throw boost::system::system_error(error);
    }
    catch (std::exception& e)
    {
        std::string test = e.what();
        std::cout << "Exception: " << e.what() << "\n";
    }
    return messageId;
}

but i get Unhandled exception at 0x771215de in TestServicePost.exe: 0xC0000005: Access violation writing location 0xcccccce4., right after this line executes:

svc->post(boost::bind(&SomeClass::addToQueue, this, sn));

I couldn't define io_service as a class member so i can use it in the destructor ~SomeClass(), would appreciate help on that too

If io_service.post is not the best solution for me please recommend something, as you can see i have a constructor, destructor and an update method who is called every tick, i tried using this and the queue alone but it wasn't thread safe, is there an easy thread safe FIFO to use ?

Answer 1

In SomeClass constructor you actually do the following:

1. Define a local io_service instance.
2. Call its run() member-function, which returns immediately, because io_service has no work.
3. Pass an address of the local object to another thread.

This certainly won't work.

Note that io_service::run() is a kind of "message loop", so it should block the calling thread. Don't call it in object constructor.