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feat(core) support AbortSignal in Deno.listen #11569

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feat(core) support AbortSignal in Deno.listen #11569

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c9df4e1
feat(core) support AbortSignal in Deno.listen
benjamingr Aug 3, 2021
3873c43
signal ref
benjamingr Aug 3, 2021
82b9986
types
benjamingr Aug 3, 2021
b193404
async fn
benjamingr Aug 3, 2021
ba494b1
run deno format
benjamingr Aug 3, 2021
23c0253
no reason for this test to be different from all the other ones
benjamingr Aug 3, 2021
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21 changes: 21 additions & 0 deletions cli/tests/unit/net_test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -598,3 +598,24 @@ unitTest(
listener.close();
},
);

unitTest(
{ perms: { net: true } },
async function netTcpListenCloseSignal(): void {
const ac = new AbortController();
const listener = Deno.listen({
hostname: "127.0.0.1",
port: 3500,
signal: ac.signal,
});
const p = listener.accept();
ac.abort();
await assertThrowsAsync(
async (): Promise<void> => {
await p;
},
Deno.errors.BadResource,
"Listener has been closed",
);
},
);
11 changes: 10 additions & 1 deletion extensions/net/01_net.js
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Original file line number Diff line number Diff line change
Expand Up @@ -207,7 +207,16 @@
...options,
});

return new Listener(res.rid, res.localAddr);
const listener = new Listener(res.rid, res.localAddr);
if (options?.signal) {
// TODO(benjamingr) there is memory leak potential here if the signal outlives the
// server significantly it can retain it. Ideally Deno would have internal weak
// event listener like Node does *or* it would have an event for the server closing.
options?.signal?.addEventListener("abort", () => listener.close(), {
once: true,
});
}
Comment on lines +211 to +218
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Suggested change
if (options?.signal) {
// TODO(benjamingr) there is memory leak potential here if the signal outlives the
// server significantly it can retain it. Ideally Deno would have internal weak
// event listener like Node does *or* it would have an event for the server closing.
options?.signal?.addEventListener("abort", () => listener.close(), {
once: true,
});
}
if (options?.signal) {
const weak = new WeakRef(listener);
options?.signal.addEventListener("abort", () => weak.deref()?.close(), {
once: true,
});
}

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That won't help - it still leaks the listener :) Happy to elaborate if that is unclear

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it's true that function captures everything
if v8 is failing to optimize that without any invocations, we can move event callback creation outside scope

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@evanwashere even if the capture was only of the listener this is still a memory leak since the listener itself is captured.

Weak event listeners need to be baked into the event target implementation itself for this to not leak (here is an example how I did it in Node.js nodejs/node#36607 and I am happy to point to whatwg discussions).

That said - another (not bad) alternative is to expose a way to know when the listener is closed (and remove the handler then) but I didn't want to propose a change of the API of Deno.listen just for that :]

(This leak is small and not very problematic to be fair)

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listener is wrapped in weakref, so capture won't matter and problem will be fixed

{
  const listener = {...};
  if (signal) signal.add('event', createListenerAbortCallback(new WeakRef(listener)));
}

function createListenerAbortCallback(weakref) {
  return () => weakref.deref()?.close();
}

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yes, the fact it needs a separate fix is why I added a TODO for it :) The actual leak here is contrived, edge-casey and not that bad.

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Bit of a drive-by comment but can't this be fixed with a WeakMap?

const weakrefs = new WeakMap();

function listen({ hostname, ...options }) {
  // ...
  if (signal) {
    weakrefs.set(signal, new WeakRef(listener));
    signal.addEventListener("abort", handleAbort);
  }
  // ...
}

function handleAbort(e) {
  weakrefs.get(e.target)?.deref()?.close();
}

(Use of primordials omitted for brevity.)

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@bnoordhuis that would still leak the handleAbort function reference.

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That's not a problem though, is it? The solutions outlined earlier leak because they create new closures every time, whereas the handleAbort() closure is created only once (and at the top-level so it's going to stay around forever anyway.)

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@bnoordhuis is the handleAbort reference still going to be in the listeners array?

The "interesting" case here is a long-lived signal (imagine a signal owned by a controller that gets aborted on SIGINT for graceful shutdown) that gets registered often (imagine in this case you start a server on every request and do something).

Since this is Deno.listen it's not very likely - but that's the case we guarded against in Node

return listener;
}

async function connect(options) {
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10 changes: 9 additions & 1 deletion extensions/net/02_tls.js
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,7 @@
hostname = "0.0.0.0",
transport = "tcp",
alpnProtocols,
signal,
}) {
const res = opListenTls({
port,
Expand All @@ -61,7 +62,14 @@
transport,
alpnProtocols,
});
return new TLSListener(res.rid, res.localAddr);
const listener = new TLSListener(res.rid, res.localAddr);
if (signal) {
// TODO(benjamingr) there is memory leak potential here. See comment in 01_net.js
signal.addEventListener("abort", () => listener.close(), {
once: true,
});
}
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return listener;
}

async function startTls(
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2 changes: 2 additions & 0 deletions extensions/net/lib.deno_net.d.ts
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Expand Up @@ -51,6 +51,8 @@ declare namespace Deno {
/** A literal IP address or host name that can be resolved to an IP address.
* If not specified, defaults to `0.0.0.0`. */
hostname?: string;
// Allows closing the server by aborting the associated AbortController
signal?: AbortSignal;
}

/** Listen announces on the local transport address.
Expand Down