Server Side C++ http listener with open connection. What happens with thread, when when client is terminated?

Question

I am trying to implement server open http connection with events using Cpp Rest SDK. I just started to investigate CPP Rest. I used this example with implementation:

MyServer::MyServer(utility::string_t url) : mListener(url)
{
  mListener.support(methods::GET, bind(&MyServer::handleGet, this, placeholders::_1));
}


void MyServer::handleGet(http_request iRequest)
{
  ucout << iRequest.to_string() << endl;

  http_response wResponse;

  // Setting headers
  wResponse.set_status_code(status_codes::OK);
  wResponse.headers().add(header_names::access_control_allow_origin, U("*"));
  wResponse.headers().add(header_names::content_type, U("text/event-stream"));

  // Preparing buffer
  streams::producer_consumer_buffer<char> wBuffer;
  streams::basic_istream<uint8_t> wStream(wBuffer);
  wResponse.set_body(wStream);

  auto wReplyTask = iRequest.reply(wResponse);

  wBuffer.putn_nocopy("data: a\n",10).wait();
  wBuffer.putn_nocopy("data: b\n\n",12).wait();
  wBuffer.sync().wait();  // seems equivalent to 'flush'

  this_thread::sleep_for(chrono::milliseconds(2000));

  wBuffer.putn_nocopy("data: c\n", 10).wait();
  wBuffer.putn_nocopy("data: d\n\n", 12).wait();
  wBuffer.sync().wait();
  // wBuffer.close(std::ios_base::out).wait();    // closes the connection
  wReplyTask.wait();      // blocking!
}

I running in debugger, and I never see thread is terminated. When client is aborted connection, still thread is sitting here, as I can see in the VS threads window in the debugger and no breakpoint after wait is happens. I am concerning to terminate thread handleGet, when client aborts connection. How can I do it?

With connection from multiple clients and knowledge about limit of 40 thread in SDK, I am not sure, how properly terminate thread created by the library.

Answer 1

Solved it by checking wReplyTask.is_done(). Removed wait, and processed response in the loop. When client aborted connection, is_done() returns true. Full function:

void MyServer::handleGet(http_request iRequest)
{
    ucout << iRequest.to_string() << endl;
    http_response wResponse;
    auto context = iRequest._get_server_context();

    // Setting headers
    wResponse.set_status_code(status_codes::OK);
    wResponse.headers().add(header_names::access_control_allow_origin, U("*"));
    wResponse.headers().add(header_names::content_type, U("text/event-stream"));

    // Preparing buffer
    streams::producer_consumer_buffer<char> wBuffer;
    streams::basic_istream<uint8_t> wStream(wBuffer);
    wResponse.set_body(wStream);

    auto wReplyTask = iRequest.reply(wResponse);// .then([this](pplx::task<void> t) { handle_error(t);  });

    wBuffer.putn_nocopy("id: 35\n", 7).wait();
    wBuffer.putn_nocopy("data: a\n", 8).wait();
    wBuffer.putn_nocopy("data: b\n\n", 9).wait();
    wBuffer.sync().wait();  // seems equivalent to 'flush'

    while (true)
    {
        this_thread::sleep_for(chrono::milliseconds(2000));
        
        if (wReplyTask.is_done())
        {
            wBuffer.close(std::ios_base::out).wait();
            return;
        }


        string datac = "data: c\n";
        wBuffer.putn_nocopy(datac.c_str(), datac.size()).wait();
        wBuffer.putn_nocopy("data: d\n\n", 9).wait();
        wBuffer.sync().wait();
    }


    // wBuffer.close(std::ios_base::out).wait();    // closes the connection
     //wReplyTask.wait();      // blocking!


}