triple-buffer
hn-search
triple-buffer | hn-search | |
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4 | 1,627 | |
79 | 524 | |
- | 0.2% | |
6.3 | 2.9 | |
2 months ago | 6 months ago | |
Rust | TypeScript | |
Mozilla Public License 2.0 | GNU General Public License v3.0 or later |
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Activity is a relative number indicating how actively a project is being developed. Recent commits have higher weight than older ones.
For example, an activity of 9.0 indicates that a project is amongst the top 10% of the most actively developed projects that we are tracking.
triple-buffer
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A lock-free single element generic queue
Great write up! I believe the colloquial name for this algorithm is a "lock-free triple buffer". Here's an implementation in Rust (I couldn't find any c/c++ examples) that has extremely thorough comments that might help completely wrap your head around the synchronization ordering. Rust uses the same semantics for atomic primitives as C11, so it should be pretty easy to match up with your implementation. I came to the same conclusion as you to solve an issue I had with passing arbitrarily large data between two threads in an RTOS system I was working with at my day job. It was an extremely satisfying moment, realizing the index variable was sufficient to communicate all the needed information between the two threads.
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Rust Is Hard, Or: The Misery of Mainstream Programming
Rust marks cross-thread shared memory as immutable in the general case, and allows you to define your own shared mutability constructs out of primitives like mutexes, atomics, and UnsafeCell. As a result you don't get rope to hang yourself with by default, but atomic orderings are more than enough rope to devise incorrect synchronizations (especially with more than 2 threads or memory locations). To quote an earlier post of mine:
In terms of shared-memory threading concurrency, Send and Sync, and the distinction between &T and &Mutex and &mut T, were a revelation when I first learned them. It was a principled approach to shared-memory threading, with Send/Sync banning nearly all of the confusing and buggy entangled-state codebases I've seen and continue to see in C++ (much to my frustration and exasperation), and &Mutex providing a cleaner alternative design (there's an excellent article on its design at http://cliffle.com/blog/rust-mutexes/).
My favorite simple concurrent data structure is https://docs.rs/triple_buffer/latest/triple_buffer/struct.Tr.... It beautifully demonstrates how you can achieve principled shared mutability, by defining two "handle" types (living on different threads), each carrying thread-local state (not TLS) and a pointer to shared memory, and only allowing each handle to access shared memory in a particular way. This statically prevents one thread from calling a method intended to run on another thread, or accessing fields local to another thread (since the methods and fields now live on the other handle). It also demonstrates the complexity of reasoning about lock-free algorithms (https://github.com/HadrienG2/triple-buffer/issues/14).
I find that writing C++ code the Rust way eliminates data races practically as effectively as writing Rust code upfront, but C++ makes the Rust way of thread-safe code extra work (no Mutex unless you make one yourself, and you have to simulate &(T: Sync) yourself using T const* coupled with mutable atomic/mutex fields), whereas the happy path of threaded C++ (raw non-Arc pointers to shared mutable memory) leads to pervasive data races caused by missing or incorrect mutex locking or atomic synchronization.
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Notes on Concurrency Bugs
In terms of shared-memory threading concurrency, Send and Sync, and the distinction between &T and &Mutex and &mut T, were a revelation when I first learned them. It was a principled approach to shared-memory threading, with Send/Sync banning nearly all of the confusing and buggy entangled-state codebases I've seen and continue to see in C++ (much to my frustration and exasperation), and &Mutex providing a cleaner alternative design (there's an excellent article on its design at http://cliffle.com/blog/rust-mutexes/).
My favorite simple concurrent data structure is https://docs.rs/triple_buffer/latest/triple_buffer/struct.Tr.... It beautifully demonstrates how you can achieve principled shared mutability, by defining two "handle" types (living on different threads), each carrying thread-local state (not TLS) and a pointer to shared memory, and only allowing each handle to access shared memory in a particular way. This statically prevents one thread from calling a method intended to run on another thread, or accessing fields local to another thread (since the methods and fields now live on the other handle). It also demonstrates the complexity of reasoning about lock-free algorithms (https://github.com/HadrienG2/triple-buffer/issues/14).
I suppose &/&mut is also a safeguard against event-loop and reentrancy bugs (like https://github.com/quotient-im/Quaternion/issues/702). I don't think Rust solves the general problem of preventing deadlocks within and between processes (which often cross organizational boundaries between projects and distinct codebases, with no clear contract on allowed behavior and which party in a deadlock is at fault), and non-atomicity between processes on a single machine (see my PipeWire criticism at https://news.ycombinator.com/item?id=31519951). File saving is also difficult (https://danluu.com/file-consistency/), though I find that fsync-then-rename works well enough if you don't need to preserve metadata or write through file (not folder) symlinks.
- A bug that doesn’t exist on x86: Exploiting an ARM-only race condition
hn-search
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Louis Rossmann: YouTube's Legal Team sent me a letter [video]
If you see a post that ought to have been moderated but hasn't been, the likeliest explanation is that we didn't see it. You can help by flagging it or emailing us at [email protected].
https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...
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An Oil Price-Fixing Conspiracy Caused 27% of All Inflation in 2021
Ok, but please don't post unsubstantive comments to Hacker News.
I understand the reason for repeating these sentiments—it's the same reason why they get upvoted to the top of threads*—but repetition of this kind is what we're most trying to avoid here.
https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so...
https://news.ycombinator.com/newsguidelines.html
* I've marked this one off topic now.
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Validating app for manufacturers enhancing process reliability and efficiency
I was looking for it in the guidelines. There are a couple of conventions for postings. Consider a bit of prior examples: [https://hn.algolia.com/?q=show+hn]
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Show HN: Hacker Search – A semantic search engine for Hacker News
yeah there are only three stories coming up from the site search
https://hn.algolia.com/?q=postgres+clustering
only one is semanthically correct, the other pick up the wrong version of clustering (i.e. k-means instead of multi master writes)
but yeah if one doesn't test the hard cases, how does one know it preserves semantics :D
- Longevity of Recordable CDs, DVDs and Blu-Rays
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The Scientific Method Part 5: Illusions, Delusions, and Dreams
Like dismissing the work of Feyerabend or Wittgenstein without seemingly having read either:
https://hn.algolia.com/?dateRange=pastMonth&page=0&prefix=tr...
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Any Google Analytics Alternatives?
https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
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Russian GRU was behind the attack in Vrbětice, NCOZ confirms
If it's not [flagged], there's no flagging and hence also no flagging ring. baybal2 has been banned on and off for years now https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...
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Gary Killdall, creator of CP/M, wrote Pixar's original 3D renderer [pdf]
The submitted title was "Gary Killdall, creator of CP/M, wrote Pixar's original 3D renderer".
Submitters: If you want to say what you think is important about an article, that's fine, but do it by adding a comment to the thread. Then your view will be on a level playing field with everyone else's: https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so...
(From https://news.ycombinator.com/newsguidelines.html: "Please use the original title, unless it is misleading or linkbait; don't editorialize.")
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Nearsightedness is at epidemic levels – and the problem begins in childhood
Vision therapy for myopia helps some people, but not everyone, likely due to genetic and neuroplasticity differences, https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu.... Nevertheless, many of the principles are useful for children whose eyes and brains are still developing.
What are some alternatives?
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