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Comment by celeritascelery | Hacker News Reader

depends on the context. The rule of thumb I have seen is that anything under 100ms is perceived as instantaneous by a user. So for interactive editing those latencies are acceptable. Though is should be noted those latencies are only for 1 GB file, so they will get worse as the edited file gets larger. But if you are building something like a CRDT where you can have edits coming in from many sources then those will start to compound, and will destroy your responsiveness. Also if you are performing edits while doing something like scrolling you will start to drop frames. Jumprope and Xi-rope were specifically designed for the CRDT use case. As Raph points out, the latencies are what will really bite you. And latency is actually why I picked a gap buffer; the ropes have too high of latency with regex searches. If that was ever fixed I would be tempted to switch to ropes.

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An occasional 100ms pause while I'm editing a huge 1GB file wouldn't be a deal-breaker for me, as long as regular-sized files have <10ms latency. It's been a long time since I opened a text file that huge, and I think the editor I was using at the time chugged something awful.

VSCode is slightly laggy for me just editing a 10k line text file, so my standards are sadly not that high, even though I find typing latency really annoying.

I’ve always found that latency number to be suspect. In some contexts, it’s imperceivable. In others it is.

For example, dragging an item around a screen with your finger, 100ms is definitely noticeable. Typing seems to be less although I had a coworker claim he could. So it’s hard to say if we don’t notice it vs we’ve just become accustomed to interacting with text with 100ms of latency (or something about the task of typing is more latency insensitive).

I would be interested in seeing the the same data driven analysis for human factors as HCI is even less intuitive than computer algorithm performance.

Searching is not a particularly latency sensitive task as your next match is probably significantly within 1 gib where you’re paying 250ms at worst. But yeah, if regex searching is the task to optimize around, ropes in Rust won’t work well due to the lack of incremental search at this time.

I would definitely notice 100ms of latency when typing, considering that at my usual speed, the time between characters is around 70ms.

The problem is that your thought is at the level of sentences with your muscle memory being automatic and your visual system mainly scanning for errors. Your “what character do I type next” at speed is less likely to be driven via visual feedback and more by direct proprieception / tactile feedback. Also, it’s not like you have a fixed 100ms delay between each character -the display system is asynchronous and will effectively batch everything up. So that 100ms delay means 100ms after your most recently typed character, not an additive 100ms delay.

Again, I’m not saying you won’t notice it, but I know I’m a very fast typer and when I was working on Oculus AirLink we had a prototype virtual desktop thing and I know I personally didn’t really notice any lag despite our internal metrics saying ~100ms of latency (we’d artificially inject extra latency for studies). It may be people differences, but keep in mind that how you measure is also important and almost no one measures true key stroke to display latency nor do they run human factors studies to accurately characterize if there really is anyone who does notice it (even at Oculus - most studies are very poor quality often with limited sample size, skewed population, and very poor reproduction/analysis because the time allotted for these projects is just enough to try to get guidance on next steps)

I notice 100ms latency when flipping a mechanical light switch (found out while dialling in debounce on ESPHome).

What regex engines do people use for this task generally? Most regex engines I'm aware of don't support stream/incremental searching.

This comment by someone at GitHub mentioned that Atom used PCRE’s partial match functionality, but I have no idea about what is used most commonly.

https://news.ycombinator.com/item?id=15386155

I was just going from the linked issue where I thought I read that Go’s engine supports incremental search. Maybe I misread?

While I have you, how close is the Rust incremental search support? It sounded like regex-automata might make it possible but hard to easily get a sense of high level progress from a GitHub issue.

Go has this: https://pkg.go.dev/regexp#Regexp.MatchReader --- That just tells you whether an io.Reader contains a match anywhere or not. I don't think it tells you anything else, like the position of the match.

> While I have you, how close is the Rust incremental search support? It sounded like regex-automata might make it possible but hard to easily get a sense of high level progress from a GitHub issue.

I'm not working on it. The current status is that other people are working on trying to write it themselves on top of regex-automata in a way that works for their specific use case. That was my high level strategy: release a separately versioned library with the regex internals[1] exposed so that others can experiment and build on top of it.

The regex-automata crate exposes the low level DFA (and lazy DFA) transition function. So you can pretty much do some kind of stream searching out of the box today (certainly at least what Go provides): https://docs.rs/regex-automata/latest/regex_automata/#build-...

Bottom line here is that if you're looking to implement stream searching in Rust, then you should be able to go out and build something to do it today with regex-automata. But you aren't going to get a streamlined experience. (And whether you ever will or not remains unclear to me.)

[1]: https://blog.burntsushi.net/regex-internals/

> Go ... I don't think it tells you anything else, like the position of the match.

The regexp.Regexp.FindReaderIndex and .FindReaderSubmatchIndex methods tell you the position of the match.

Despite having studied Go's regex engine in depth, I have somehow missed those methods. To the point that when you responded, I assumed they were added recently. I checked to be sure, and indeed not. They've been there since Go 1.0.

Thanks for the correction!

> ropes in Rust won’t work well due to the lack of incremental search at this time

Unless you don't mind implementing a couple dozen lines yourself. The regex_automata crate allows you to directly access the DFA, so with iteration through the rope and a bit of state tracking you can already do this, just not as convenient (yet) as a single method call.

It’s not quite that simple, but folks are working on it.

https://github.com/rust-lang/regex/issues/425#issuecomment-1...

https://github.com/helix-editor/helix/pull/211#issuecomment-...

Note that the lazy DFA and its lower level APIs exists now and threads this needle.

Maybe not in the general case for arbitrary abstracted datastructures, but I have done it in a basic test to see if it's viable for my use-case, which is why I made that claim at all.

Our brains are very good at adjusting to latency, but only if it’s a constant.

Search is 100% a valid justification to use contiguous storage. It wasn't high in my list of considerations when I was starting out.

>The rule of thumb I have seen is that anything under 100ms is perceived as instantaneous by a user.

for typing characters into a text box this is not imperceptible. it should happen in a single frame.

And it gets more perceptible when moving the caret (more pixels to track and you're actively tracking).

Users can easily feel one frame of latency at 60hz given enough visual feedback (pixels in this case). It gets harder at 120hz and above. I have a toy editor with Ropey and WGPU, just added a 100ms wait on char insert and it's rubber banding when typing fast.

Instead of the rule of thumb you’ve seen how about the rule of thumb you’ve tried? Make two simple HTML forms: one with an input that instantaneously accepts input and another with 100 ms delay. You can definitely tell the difference.

You are not measuring what you want. You measure 0+~20ms vs 100+~20ms.

Ok, change the experiment to add 80ms artificial delay instead…

I'd say 100ms is perceptible in almost any context, at least if it's on top of the already existing latencies of the hardware & OS (e.g. some laptops already add 150ms latency to every keypress [0], so good luck)

[0] https://danluu.com/input-lag/

100ms is 6 frames of input latency at 60hz! Absolutely noticable.

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