How to pass io_service object to a new thread using boost::bind?

Question

I have a class called overlay_server which has a public method

void member_list_server(boost::asio::io_service &io_service){

Now I want to run this in a new thread. So I create a new thread, and use bind in its constructor.

Before I was creating an io_service inside the void member_list_server function. But Now I am trying create an io_service object in main and pass it to this thread where i get the error?

  int main(){

    boost::asio::io_service io_service_;

    overlay_server overlay_server_(8002);
    boost::thread thread_(
        boost::bind(&overlay_server::member_list_server, overlay_server_, io_service_)
        );

Why do I get the error

error C2248: 'boost::noncopyable_::noncopyable::noncopyable' : cannot access private member declared in class 'boost::noncopyable_::noncopyable'
I will create instances of other classes also, which need io_service. What is the best way, should I create one io_service object in main and pass it to all threads?

or create a separate one inside all the threads I create in future?

You've got something noncopyable, and bind intends to make a copy of it. According to boost::bind's docs, you can use boost::ref or boost::cref to get around this, however be aware of the typical dangers of dangling references. — huskerchad
Besides, after you bind boost:ref(io_service), note that io_service must outlive the thread, otherwise it will have a dangling reference. So io_service can't be local as in your example. — Igor R.
Why not just make io_service a class member that can be accessed by all threads? That is what I do. — Bob Bryan

Moshe Rubin Moshe Rubin · Accepted Answer · 2013-05-30T09:52:23

The problem is that you are passing the boost::asio::io_service object by value, rather than by reference. This implies that the boost::asio::io_service default copy constructor should be invoked, something that is not allowed for io_service.

One option is to pass a pointer to the boost::asio::io_service object. Following is some code of mine that does just that:

void Model::TcpPortListener (boost::asio::io_service &io_service, 
                             boost::asio::ip::tcp::acceptor &a, 
                             boost::asio::ip::tcp::endpoint &lep, 
                             SocketObject *readSocketObject)
{
    boost::asio::ip::tcp::acceptor *b = &a;
    boost::asio::io_service *s = &io_service;
    . . .
    boost::asio::ip::tcp::socket *sock (new boost::asio::ip::tcp::socket (io_service));

    a.async_accept (*sock, boost::bind (&Model::HandleRemoteAccept, this, s, b, sock, lep, boost::asio::placeholders::error));
}

void Model::HandleRemoteAccept (boost::asio::io_service *io_service, 
                                boost::asio::ip::tcp::acceptor *a, 
                                boost::asio::ip::tcp::socket *sock, 
                                boost::asio::ip::tcp::endpoint &lep, 
                                const boost::system::error_code& error)
{
    . . .
    // Continue listening
    TcpPortListener (*io_service, *a, lep, 0);
}

The points to observe are:

In Model::TcpPortListener(), 's' is assigned the address of io_service
In the same function, 's' is passed as the third argument to boost::bind(). Since it is an address rather than an object, there's no invocation of the default copy constructor.
In Model::HandleRemoteAccept(), io_service is dereferenced and passed to the TcpPortListener() function.

The point raised by others about dangling references is an important one and should be well accounted for by you.

How to pass io_service object to a new thread using boost::bind?

1 Answers