Boost.Asio segfault, no idea why

问题:

This is a SSCCE from my Boost.Asio project based on the examples. It took me about an hour to track the bug down to this:

#include <boost/bind.hpp>
#include <boost/asio.hpp>
#include <boost/shared_ptr.hpp>

class Connection  {
public:
    Connection(boost::asio::io_service& io_service) : socket(io_service) {}

private:
    boost::asio::ip::tcp::socket socket;
};

class Server {
public:
    Server() : signal_monitor(io_service) {
        signal_monitor.add(SIGINT);
        signal_monitor.add(SIGTERM);

        signal_monitor.async_wait(
            boost::bind(&Server::handle_signal_caught, this)
        );
    }

    void run() {
        // comment out the next line and there's no segfault
        connection.reset(new Connection(io_service));

        io_service.run();
    }

private:
    void handle_signal_caught() {
        io_service.stop();
    }

    boost::shared_ptr<Connection> connection;
    boost::asio::io_service io_service;
    boost::asio::signal_set signal_monitor;
};

int main(int argc, char **argv) {
    Server server;
    server.run();

    return 0;
}

When I send a signal (ctrl+C) the program segfaults instead of shutting down nicely. I've spent the last half hour looking at this, but I simply do not see why this would segfault, can any of you guys spot the issue?

回答1:

I think I found out the issue. Note the declaration order of the members of Server:

boost::shared_ptr<Connection> connection;
boost::asio::io_service io_service;
boost::asio::signal_set signal_monitor;

Destruction order is done in the opposite order of declaration. This means that first signal_monitor, then io_service and finally connection get destroyed. But connection contains a boost::asio::ip::tcp::socket containing a reference to io_service, which got destroyed.

And indeed, this is pretty much what happening, and causes a segfault too:

int main(int argc, char **argv) {
    auto io_service = new boost::asio::io_service();
    auto socket = new boost::asio::ip::tcp::socket(*io_service);

    delete io_service;
    delete socket;

    return 0;
}

Declaring connection after io_service solves the issue.

_Damn