Why does Zipline(QuickJS) need a single threaded q...

# squarelibraries

[Aditya Kurkure]

Why does Zipline(QuickJS) need a single threaded queue? Even a Dispatcher with limited parallelsim fails 😕.

[jessewilson]

Our native JS engine, QuickJS, is not concurrent

[Aditya Kurkure]

But wouldn't limited parallelism (set to 1) ensure that it is accessed by one thread at a time?

[glureau]

one thread at a time != always the same thread

[Aditya Kurkure]

but it would still ensure that ensure that it is not accessed concurrently. Is the restriction to access the instance from the same thread always or no concurrency?

[jessewilson]

That could work. There’s potentially memory-model challenge where we need to flush cache lines between thread hops

[jessewilson]

(I don’t know how much of a problem this is in practice)

[Aditya Kurkure]

Tried with limited parellism set to one but it causes a stack overflow error on android and on iOS it crashes with a bad access exception.

[jessewilson]

I think that might be a different issue. I’ve had problems with JS stack sizes and I’ve mitigated by configuring larger stack sizes on the non-main thread. But I think we aught to make this much easier.

[jessewilson]

https://github.com/cashapp/redwood/blob/trunk/redwood-treehouse-host/src/iosMain/kotlin/app/cash/redwood/treehouse/IosTreehouseDispatchers.kt

[jessewilson]

In particular we should move some of this to zipline from Redwood