As someone who’s gone down the rust “native pointers vs pin vs …” rabbit hole many times now, I really recommend just using a Vec for the data and storing indexes into the vec when you need a pointer.
Pin adds a huge amount of weird incidental complexity to your code base - since you need to pin-project your struct fields (but which ones?). You can’t just take an &self or &mut self in functions if your value is pinned, and pin is just generally confusing, hard to use and hard to reason about.
The article ended up with Vec<Box<T>> - but that’s a huge code smell in my book. It’s much less performant than Vec<T> because every object needs to be individually allocated & deallocated. So you have orders of magitude more calls to malloc & free, more memory fragmentation and way more cache misses while accessing your data. The impact this has on performance is insane.
Vec & indexes is a lovely middle ground. In my experience it’s often (remarkably) slightly more performant than using raw pointers. You don’t have to worry about vec reallocations (since the indexes don’t change). And it’s 100% safe rust. It feels weird at first - indexes are just pointers with more steps. But I find rust’s language affordances just work better if you write your code like that. Code is simple, safe, ergonomic and obvious.
Dunno about 'safe' -- or at least not in the more general sense that you seem to intend, rather than the more limited sense of rust's safe/unsafe distinction. If you store an index into a Vec<T> as a usize, rather than a &T, very little is stopping you from invalidating that pseudo-pointer without knowing it. (Or from using it as an index into the wrong vector, etc...)
These problems are manageable and I'm not saying 'never do this' -- I've done it myself on occasion. It's just that there are more pitfalls than you're indicating here, and it is actually a meaningful tradeoff of bug potential for ease-of-use.
I mean safe in the narrow way that rust intends. It’s memory safe, but as you imply, we’re leaving the door to open to logic bugs if you misuse those array indices.
But honestly, I think danger from that is wildly overstated. The author isn’t talking about implementing an ECS or b-tree here. They’re just populating an array from a file when the program launches, then freeing the whole thing when the program terminates. It’s really not rocket science.
The other big advantage of this approach is that you don’t have to deal with unsafe rust. So, no unsafe {} blocks. No wrangling with rust’s frankly awful syntax for following raw pointers. No stressing about whether or not a future version of rust will change some subtle invariant you’re accidentally depending on, or worrying about if you need to use MaybeInit or something like that. I think the chance of making a mistake while interacting with unsafe code is far higher than the chance of misusing an array index. And the impact is usually worse.
The author details running into exactly that problem while coding - since they assumed memory allocated by vec would be pinned (it isn’t). And the program they ended up with still doesn’t use pin, even though they depend on the memory being pinned. That’s cause for far more concern than a simple array index.
As someone who went down this path many years ago, I think the GTK numbers in the article are a bit misleading. You wouldn't create 1000 buttons to do a flamegraph properly in GTK.
In Sysprof, it uses a single widget for the flamegraph which means in less than 150 mb resident I can browse recordings in the GB size range. It really comes down to how much data gets symbolized at load time as the captures themselves are mmap'able. In nominal cases, Sysprof even calculates those and appends them after the capture phase stops so they can be mmap'd too.
That just leaves the augmented n-ary tree key'd by instruction pointer converted to string key, which naturally deduplicates/compresses.
The biggest chunk of memory consumed is GPU shaders.
Damn I hate it when you write a whole project and someone comes along and says "this already exists" and you realise how much time you wasted (yeah even if some of it counts towards learning I'd still rather not needlessly repeat other people's work).
Anyway, pprof has a fantastic interactive Flamegraph viewer that lets you narrow down to specific functions. It's really very good, I would use that.
It uses the Firefox profiler to view its recorded profiles. You can (don't have to, just can) even share them, I was looking at this profile just yesterday: https://share.firefox.dev/3PxfriB for my day job, for example.
Yep. Personally I love the Firefox profiler for interacting with perf - since it can show you flame graphs and let you explore a perf trace by dominators and whatnot.
But I applaud the effort to make small, native apps. I agree with the author - not everything should live in the browser.
I think they were saying "fast and native" because web things usually aren't fast. In this case it is though, so I don't see why it would be a problem for it to be web based.
or w/e and when it completes (can be one-time run or long-running / interactive) now I have a great native experience exploring the profile.
All the normal bells and whistles are there and I can double click on something and see it inline in the source code with per-line (cumulative) timings.
It really isn't. It's probably the slowest profiler UI I've ever used (it loves to beachball…), it hardly has any hardware performance counters, and its actual profiling core (xctrace) is… just really buggy? After the fifth time where it told me “this function uses 5% CPU” and you optimize it away and absolutely nothing happened, because it was just another Instruments mirage. Or the time where it told me opening a file on iOS took 1000+ ms, but that was just because its end timestamps were pure fabrications.
Maybe it's better if you have toy examples, but for large applications, it's among the worst profilers I've ever seen along almost every axis. I'll give you that gprof is worse, though…
Something that’s been on my mind recently is that there’s a need of a high-performance flame graph library for the web. Unfortunately the most popular flame graph as a library / component, basically the react and d3 ones, work fine but the authors don’t actively maintain them anymore and their performance with large profiles is quite poor.
Most people that care about performance either hard-fork the Firefox profiler / speedscope flame graph component or create their own.
Would be nice to have a reusable, high performance flame graph for web platforms.
I recently went through trying to profile Rust code recently. I realized that the profiling toolchain is underdeveloped across the board - "perf", the recommended profiler, isn't cross-platform (and there aren't any profilers that I found that "just work"); visualizing traces from a multi-threaded app is not fun; there isn't an IDE plugin to highlight the problematic lines, etc.
For the prodfiler.com flamegraph viewer we ended up building it in Pixi.JS, which allowed us to have nice GPU acceleration and render massive flamegraphs quickly. Omitting to draw blocks of less than half a pixel width is also a good idea, as is the monospace font.
The article linked as “W3C specifications are bigger than POSIX.” is also worth reading.
The total word count of the W3C specification catalogue is 114 million words at the time of writing. If you added the combined word counts of the C11, C++17, UEFI, USB 3.2, and POSIX specifications, all 8,754 published RFCs, and the combined word counts of everything on Wikipedia’s list of longest novels, you would be 12 million words short of the W3C specifications.
Hello, I found that it's difficult to visualize the flamegraph out of the huge amount of data when I was profiling Rust Analyzer. Viewing the flamegraph in a browser (Firefox and Chrome) made it impossible to view. In fact, it was simply frozen. I made this visualizer to solve my problem. Maybe it would help someone else. I leave the link to my article about it, but you can find the link to the project right in the first paragraph.
Props to you for making a cool little project, but as somebody who's been involved in Linux graphics a bit: please just let Xlib die. It's an outdated API, even if you ignore the existence of Wayland. For something like fast visualizations, you should really go with something that does offscreen rendering and then blits the result. As long as you're just drawing a bunch of rectangles, even CPU software rendering may be the better solution, though obviously modern tools should use GPU rendering.
I see your journey and how you ended up with Xlib. But I think that's really more of an indictment of the sorry state of GUI in Rust.
I know that's not your job, I just couldn't let this use of Xlib stand uncommented because it's really bad for the larger ecosystem.
I think going for xlib is somewhat missing the forest for the trees. Does it take less memory? Yeah, but you lose out on any gpu assistance you might get for free otherwise.
This only really matters as you get to bigger resolutions tho, as you avoid redrawing.
Pin adds a huge amount of weird incidental complexity to your code base - since you need to pin-project your struct fields (but which ones?). You can’t just take an &self or &mut self in functions if your value is pinned, and pin is just generally confusing, hard to use and hard to reason about.
The article ended up with Vec<Box<T>> - but that’s a huge code smell in my book. It’s much less performant than Vec<T> because every object needs to be individually allocated & deallocated. So you have orders of magitude more calls to malloc & free, more memory fragmentation and way more cache misses while accessing your data. The impact this has on performance is insane.
Vec & indexes is a lovely middle ground. In my experience it’s often (remarkably) slightly more performant than using raw pointers. You don’t have to worry about vec reallocations (since the indexes don’t change). And it’s 100% safe rust. It feels weird at first - indexes are just pointers with more steps. But I find rust’s language affordances just work better if you write your code like that. Code is simple, safe, ergonomic and obvious.
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