Is it possible shared an event loop (libuv) between uWebSockets and my backend ?

[theo-issarni-wmx]

Hi,

I am trying to build an asynchronus http server with uWebSockets that would allow me to query my backend before responding to the http call.
I have a code base based on libuv (wrapped with https://github.com/skypjack/uvw) that allow me to communicate with my backend and I am trying to integrate it with the http server.
I am trying use the same event loop for both the http server and the backend communication but I am having some issues.

int main() {
  std::shared_ptr<uvw::loop> loop = uvw::loop::get_default();
  uv_loop_t* uvLoop = loop->raw();

  uWS::Loop::get(uvLoop);
  uWS::App app;
  app
    .listen(3630,
            [](auto* listen_socket) {
              if (listen_socket) {
                fmt::print("Listening on port {}\n", 3630);
              }
            })
    .get("/health", [&](auto* res, auto* /*req*/) { 
      // Want to be able to interact with our backend before responding/ending the call
      res->end("OK");
    });

  std::shared_ptr<uvw::timer_handle> timer = loop->resource<uvw::timer_handle>();
  timer->on<uvw::timer_event>([&loop](const auto&, uvw::timer_handle& handle) { loop->stop(); });
  timer->start(uvw::timer_handle::time{100000}, uvw::timer_handle::time{0});

  loop->run(); // Does not seems to "run" the http server
  // app.run(); // Does not seems to "run" the uv_loop
  app.close();
}

Is it possible to run both the http server and the backend communication on the same event loop ? Or should I run them on separate event loops and find a way to communicate between them ?
Any advice on how to achieve this would be greatly appreciated.

[uNetworkingAB]

Yes that's how it's intended to be used. Sharing event loop is exactly how you do it proper Den tis 14 jan. 2025 12:28Théo Issarni ***@***.***> skrev:

…

Hi, I am trying to build an asynchronus http server with uWebSockets that would allow me to query my backend before responding to the http call. I have a code base based on libuv (wrapped with https://github.com/skypjack/uvw) that allow me to communicate with my backend and I am trying to integrate it with the http server. I am trying use the same event loop for both the http server and the backend communication but I am having some issues. int main() { std::shared_ptr<uvw::loop> loop = uvw::loop::get_default(); uv_loop_t* uvLoop = loop->raw(); uWS::Loop::get(uvLoop); uWS::App app; app .listen(3630, [](auto* listen_socket) { if (listen_socket) { fmt::print("Listening on port {}\n", 3630); } }) .get("/health", [&](auto* res, auto* /*req*/) { // Want to be able to interact with our backend before responding/ending the call res->end("OK"); }); std::shared_ptr<uvw::timer_handle> timer = loop->resource<uvw::timer_handle>(); timer->on<uvw::timer_event>([&loop](const auto&, uvw::timer_handle& handle) { loop->stop(); }); timer->start(uvw::timer_handle::time{100000}, uvw::timer_handle::time{0}); loop->run(); // Does not seems to "run" the http server // app.run(); // Does not seems to "run" the uv_loop app.close(); } Is it possible to run both the http server and the backend communication on the same event loop ? Or should I run them on separate event loops and find a way to communicate between them ? Any advice on how to achieve this would be greatly appreciated. — Reply to this email directly, view it on GitHub <#1833>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/A2NMOMPYJ3AWCUU2KCHQQOD2KTYHJAVCNFSM6AAAAABVEVRHOOVHI2DSMVQWIX3LMV43ERDJONRXK43TNFXW4OZXHAZDEOBZGU> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[theo-issarni-wmx]

Thanks for your quick reply and your confirmation.

As said above I have some issues using the same event loop with uWebSockets and my backend.
I am providing uWebSockets with the event loop as follow: uWS::Loop::get(uvLoop);
but running the event loop with : loop->run(); // aka uv_run(uvLoop, UV_RUN_DEFAULT) does not seems to run the http server, running the uWS::App does not seems to run the event loop neither.

I think I am missing something, do you have any idea what I am doing wrong ?

[theo-issarni-wmx]

I figured my problem. I was compiling my POC with the WITH_LIBUV=1 flag and linking with the uWesbSockets lib instead of compiling the uWesbSockets lib with the WITH_LIBUV=1 and linking it to my binary.
So the loop used by the uWebSockets lib was not the libuv loop, but the default one.

If someone read my discution and want to combine an uWebSockets server with an existing libuv loop, here is an example :

int main() {
  uWS::Loop::get(uvw::loop::get_default()->raw());
  auto app = std::make_unique<uWS::App>();

  app->get("/health", [&](auto* res, auto* req) {
    fmt::print("Url {}, Method {}\n", req->getUrl(), req->getMethod());

    res->onData([res](std::string_view data, bool isLast) {
      auto delay = 1000;
      fmt::print("Data : {} need {} ms before response\n", data, delay);

      // We are using a timer to simulate async process
      std::shared_ptr<uvw::timer_handle> responseTimer = uvw::loop::get_default()->resource<uvw::timer_handle>();
      responseTimer->on<uvw::timer_event>([res, data](const auto&, uvw::timer_handle& handle) {
        res->end(fmt::format("Response : {}\n", data));
        handle.stop();
        handle.close();
      });

      responseTimer->start(uvw::timer_handle::time{delay}, uvw::timer_handle::time{0});
    });

    // On onAborted alow us to not respond to the request, we can do async things, and when we are ready we can
    // respond to the request, we only need to keep the response object
    res->onAborted([]() { fmt::print("onAborted\n"); });
  });

  app->listen(3630, [](auto* listen_socket) {
    if (listen_socket) {
      fmt::print("Listening on port {}\n", 3630);
    }
  });

  uvw::loop::get_default()->run();
}

[uNetworkingAB]

Good, but if you use AddressSanitizer or Valgrind you can catch all these issues and more.