reference-crdts
sdk
reference-crdts | sdk | |
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5 | 307 | |
110 | 9,809 | |
- | 0.6% | |
6.6 | 10.0 | |
5 months ago | about 13 hours ago | |
TypeScript | Dart | |
- | BSD 3-clause "New" or "Revised" License |
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reference-crdts
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CRDTs make multiplayer text editing part of Zed's DNA
> The goog version seems to work well but I have had nothing but frustration with ms word. Bad merges and weird states are typical, particularly from the fat client.
Argh not getting this stuff right is really frustrating. I've been working on collaborative editing for over a decade now, and I still can't implement any of these algorithms correctly without the help of a fuzz testing. But fuzz testing done right finds all of these problems! There's no excuse!
Fuzzers work so well here because all of these algorithms have a clear correctness criteria: After syncing, state should always converge to the same result. So its pretty easy to write code which does this in a loop:
1. Generates some random changes on some fake "peers"
2. Picks 2 peers at random and sync their changes, using your new fancy synchronization algorithm
3. Assert that the state has converged between the peers
I've been working on this stuff for over a decade. I've implemented dozens of these algorithms. And every single time I write a fuzzy boi to check my work I find convergence bugs. Playing whack-a-mole with a fuzzer is a rite of passage for implementing systems like this.
When your fuzzer runs all night, you should never have lingering convergence bugs like you're describing with Word.
As an example, here's a simple fuzzer for a reference list CRDT implementation: https://github.com/josephg/reference-crdts/blob/9f4f9c3a97b4...
The code is so small it almost fits on my laptop screen.
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WebAssembly 2.0 Working Draft
> In this case, the bottleneck at 9 million LoC is not CPU cycles but memory usage. That's where I am considering pushing down into WebAssembly
How often does this come up in practice? I can't think of many files I've opened which were 9 million lines long. And you say "LoC" (lines of code). Are you doing syntax highlighting on 9 million lines of source code in javascript? Thats impressive!
> I guess my point is why do you need balanced trees? Is this a CRDT specific thing? Can you implement CRDT with just an array of lines / gap buffer?
Of course! Its just going to be slower. I made a simple reference implementation of Yjs, Automerge and Sync9's list types in javascript here[1]. This code is not optimized, and it takes 30 seconds to process an editing trace that diamond types (in native rust) takes 0.01 seconds to process. We could speed that up - yjs does the same thing in 1 second. But I don't think javascript will ever run as fast as optimized rust code.
The b-tree in diamond types is used for merging. If you're merging 2 branches, we need to map insert locations from the incoming branch into positions in the target (merged) branch. As items are inserted, the mapping changes dynamically. The benchmark I've been using for this is how long it takes to replay (and re-merge) all the changes in the most edited file in the nodejs git repository. That file has just shy of 1M single character insert / delete operations. If you're curious, the causal graph of changes looks like this[2].
Currently it takes 250ms to re-merge the entire causal graph. This is much slower than I'd like, but we can cache the merged positions in about 4kb on disk or something so we only need to do it once. I also want to replace the b-tree with a skip list. I think that'll make the code faster and smaller.
A gap buffer in javascript might work ok... if you're keen, I'd love to see that benchmark. The code to port is here: [3]
> Undo support -> In which case, you only have to stack / remember the set of commands and not have to store the state on every change. I'm not sure if this overlaps with the data structure choice, other than implementation details.
Yeah, I basically never store a snapshot of the state. Not on every change. Not really at all. Everything involves sending around patches. But you can't just roll back the changes when you undo.
Eg: I type "aaa" at position 0 (the start of the document). You type "bbb" at the start of the document. The document is now "bbbaaa". I hit undo. What should happen? Surely, we delete the "aaa" - now at position 3.
Translating from position 0 to position 3 is essentially the same algorithm we need to run in order to merge.
> I was just looking into TypedArrays.
I tried optimizing a physics library a few years ago by putting everything in typedarrays and it was weirdly slower than using raw javascript arrays. I have no idea why - but maybe thats fixed now.
TypedArrays are useful, but they're no panacea. You could probably write a custom b-tree on top of a typedarray in javascript if you really want to - assuming your data also fits into typedarrays. But at that point you may as well just use wasm. It'll be way faster and more ergonomic.
[1] https://github.com/josephg/reference-crdts
[2] https://home.seph.codes/public/node_graph.svg
[3] https://github.com/josephg/diamond-types/tree/master/src/lis...
sdk
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- Lançamento do App Edudu
- Dart: Improve JavaScript Interop
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Top Paying Programming Technologies 2024
50. Dart - $55,862
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What are your thoughts about gerrit?
Gerrit is optimized for in-house work lead by engineers who would rather be using Subversion. ("Subversion merge isn't worth using so I don't see why we need it.") It tends to be hostile to community contribution: outsiders get a second-class experience, so if community participation is your goal it's a bad choice.
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Understanding Flutter Architecture Part 1 - Introduction
First off, Flutter uses Dart for its codebase. This means that the Dart programming language is used to develop the UIs, logic, and functionalities of applications and software built with Flutter.
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The Road to Enhanced Flutter Development Part 1
The methods and other important information are documented in detail here. I have been exploring it and received some advice from Norbert 🙌.
- Flutter 3 on Devuan 4: 始め方
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Flutter 3 on Devuan 4: Getting started
Programming Language: Dart
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Flutter: Unleashing the Power of Cross-Platform App Development!
Official Dart website: dart.dev Dart Language Tour: dart.dev/guides/language/language-tour Dart API Reference: api.dart.dev
What are some alternatives?
wai - A language binding generator for `wai` (a precursor to WebAssembly interface types)
obs-websocket - Remote-control of OBS Studio through WebSocket
multi-memory - Multiple per-module memories for Wasm
asdf - Extendable version manager with support for Ruby, Node.js, Elixir, Erlang & more
diamond-types - The world's fastest CRDT. WIP.
flutterfire - 🔥 A collection of Firebase plugins for Flutter apps.
uwm-masters-thesis - My thesis for my Master's in Computer Science degree from the University of Wisconsin - Milwaukee.
starter_architecture_flutter_firebase - Time Tracking app with Flutter & Firebase
wit-bindgen - A language binding generator for WebAssembly interface types
buildozer - Generic Python packager for Android and iOS
yjs - Shared data types for building collaborative software
TypeScript - TypeScript is a superset of JavaScript that compiles to clean JavaScript output.