Properly stopping a Thallium server

Stopping a server is done by calling the engine::finalize() function. By passing the engine object into the closure of a lambda, as a reference, we can make this very easy. For example:

#include <iostream>
#include <thallium.hpp>

namespace tl = thallium;

int main(int argc, char** argv) {

    tl::engine myEngine("tcp://127.0.0.1:1234", THALLIUM_SERVER_MODE);

    std::function<void(const tl::request&, int, int)> sum =
        [&myEngine](const tl::request& req, int x, int y) {
            std::cout << "Computing " << x << "+" << y << std::endl;
            req.respond(x+y);
            myEngine.finalize();
        };

    myEngine.define("sum", sum);

    return 0;
}

In this version of the server, the server will shut down after the first RPC is received. Note that the engine is captured by reference. Thallium engines are indeed non-copyable.