Risk for memory leaks with subscriptions on page reload

[NordlingDev]

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Sometimes during development it's necessary to fully reload the page. I created this little subscription procedure to see whether there is a risk for memory leaks. And yes, there is. Check the code below:

let count = 0;

export const testSubscription = publicProcedure.subscription(async () => {
  return observable<string>(() => {
    count ++;
    console.log(count);

    return () => {
      count --;
    };
  });
});

Whenever this procedure is being subscribed to, count will increment or decrement to keep track of amount of active subscriptions. However, if you do a page reload, there is no cleanup process being made and count keeps increasing.

[NordlingDev]

I fixed this with a simple workaround inside the app itself (React app) by having a beforeunload listener on the window to unmount the app before the page actually reloads. See below:

import { StrictMode, useEffect } from "react";
import * as ReactDOM from "react-dom/client";

import { Root } from "./app";

const root = ReactDOM.createRoot(document.getElementById("root") as HTMLElement);

window.addEventListener("beforeunload", () => {
  root.unmount();
});

root.render(
  <StrictMode>
    <Root />
  </StrictMode>,
);

Now, I'm not sure if this is the prettiest way to do it and neither am I sure it covers all potential cases. So is this is something worth investigating?

[jsonnull]

Hey, so I looked into this and I don't think there's an actual leak happening here.

When we create new subscriptions for a given window, we'll actually overwrite existing subscriptions for that window when the new ones are created. In some ways the behavior is the same as tRPC over browser+server, but the key difference is that a tRPC server can catch broken websocket connections and perform cleanup. I think electron-trpc can do this as well, but we don't currently.

[NordlingDev]

@jsonnull Yeah there is no leak actually happening. I was just saying there is a risk for it if devs aren't aware that no cleanup is being made to subscriptions when "connections" are lost (due to page reload in this case).

[jsonnull]

Marking this as completed as of #165, which is out in 0.6.0.