AsyncWorkers prevent Node.js from exiting

[toyobayashi]

lovell/sharp#3522

https://github.com/lovell/sharp/pull/3522/files#diff-f1d20c9f37b79bd0729e7379d212de61e425488d7ceb987ed964326f874d7c43R44-R66

[RReverser]

Oh nice, I thought I'd eventually implement this myself but cool that you already did 😅

I think it's still better at some point to implement as much as possible upstream in Emscripten though - in particular, there is no reason not to add the refcounter to emscripten_keepalive_runtime_{push,pop} which you already used.

[toyobayashi]

Agree with you. But I'm not familiar with how to contribute emscripten codebase, and it may be not easy to pull some dependencies due to the network environment limitation in China mainland. Could you help take this to emscripten?

In addition, is there a better way than using setInterval?

[RReverser]

and it may be not easy to pull some dependencies

I don't think it uses any special dependencies outside of what emsdk has (Python and Node.js + some modules). Not sure if any of those modules are blocked in China, but worth a try. But yeah, I can try and can help myself too.

In addition, is there a better way than using setInterval?

Oh... you're using setInterval? Where? That definitely shouldn't be necessary.

[toyobayashi]

emnapi/packages/runtime/src/Context.ts

Lines 80 to 99 in adbc3d0

	class NodejsWaitingRequestCounter {
	private timer: any = undefined
	private count: number = 0
	public increase (): void {
	if (this.count === 0) {
	this.timer = setInterval(() => {}, 1e8)
	}
	this.count++
	}
	public decrease (): void {
	if (this.count === 0) return
	if (this.count === 1) {
	clearInterval(this.timer)
	this.timer = undefined
	}
	this.count--
	}
	}

I didn't think of any other way at the time. All the emnapi async worker threads should be unreffed, but there must be a strong ref to prevent nodejs from exiting the event loop.

[RReverser]

Yeah I was thinking on it before for the mentioned contribution, and I thought I'd go with MessageChannel instead. MessagePort is probably the most lightweight way to .ref()/.unref() something without ever accidentally triggering the handler or having to subscribe to the timer.

That is, just do refHandle = new MessageChannel().port1 and use that for all .ref()/.unref() operations.

[toyobayashi]

Thanks, learned from you again