Folly
CppCoreGuidelines
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Folly | CppCoreGuidelines | |
---|---|---|
90 | 306 | |
27,072 | 41,497 | |
0.8% | 0.9% | |
9.8 | 7.6 | |
about 5 hours ago | 8 days ago | |
C++ | Python | |
Apache License 2.0 | GNU General Public License v3.0 or later |
Stars - the number of stars that a project has on GitHub. Growth - month over month growth in stars.
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.
Folly
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Ask HN: How bad is the xz hack?
https://github.com/facebook/folly/commit/b1391e1c57be71c1e2a...
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Backdoor in upstream xz/liblzma leading to SSH server compromise
https://github.com/facebook/folly/pull/2153
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A lock-free ring-buffer with contiguous reservations (2019)
To set a HP on Linux, Folly just does a relaxed load of the src pointer, release store of the HP, compiler-only barrier, and acquire load. (This prevents the compiler from reordering the 2nd load before the store, right? But to my understanding does not prevent a hypothetical CPU reordering of the 2nd load before the store, which seems potentially problematic!)
Then on the GC/reclaim side of things, after protected object pointers are stored, it does a more expensive barrier[0] before acquire-loading the HPs.
I'll admit, I am not confident I understand why this works. I mean, even on x86, loads can be reordered before earlier program-order stores. So it seems like the 2nd check on the protection side could be ineffective. (The non-Linux portable version just uses an atomic_thread_fence SeqCst on both sides, which seems more obviously correct.) And if they don't need the 2nd load on Linux, I'm unclear on why they do it.
[0]: https://github.com/facebook/folly/blob/main/folly/synchroniz...
(This uses either mprotect to force a TLB flush in process-relevant CPUs, or the newer Linux membarrier syscall if available.)
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Appending to an std:string character-by-character: how does the capacity grow?
folly provides functions to resize std::string & std::vector without initialization [0].
[0] https://github.com/facebook/folly/blob/3c8829785e3ce86cb821c...
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Can anyone explain feedback of a HFT firm regarding implementation of SPSC lock-free ring-buffer queue?
My implementation was quite similar to Boost's spsc_queue and Facebook's folly/ProducerConsumerQueue.h.
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A Compressed Indexable Bitset
> How is that relevant?
Roaring bitmaps and similar data structures get their speed from decoding together consecutive groups of elements, so if you do sequential decoding or decode a large fraction of the list you get excellent performance.
EF instead excels at random skipping, so if you visit a small fraction of the list you generally get better performance. This is why it works so well for inverted indexes, as generally the queries are very selective (otherwise why do you need an index?) and if you have good intersection algorithms you can skip a large fraction of documents.
I didn't follow the rest of your comment, select is what EF is good at, every other data structure needs a lot more scanning once you land on the right chunk. With BMI2 you can also use the PDEP instruction to accelerate the final select on a 64-bit block: https://github.com/facebook/folly/blob/main/folly/experiment...
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Defer for Shell
C++ with folly's SCOPE_EXIT {} construct:
https://github.com/facebook/folly/blob/main/folly/ScopeGuard...
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Is there any facebook/folly community for discussion and Q&A?
Seems like github issues taking a long time to get any response: https://github.com/facebook/folly
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How a Single Line of Code Made a 24-Core Server Slower Than a Laptop
Can't speak for abseil and tbb, but in folly there are a few solutions for the common problem of sharing state between a writer that updates it very infrequently and concurrent readers that read it very frequently (typical use case is configs).
The most performant solutions are RCU (https://github.com/facebook/folly/blob/main/folly/synchroniz...) and hazard pointers (https://github.com/facebook/folly/blob/main/folly/synchroniz...), but they're not quite as easy to use as a shared_ptr [1].
Then there is simil-shared_ptr implemented with thread-local counters (https://github.com/facebook/folly/blob/main/folly/experiment...).
If you absolutely need a std::shared_ptr (which can be the case if you're working with pre-existing interfaces) there is CoreCachedSharedPtr (https://github.com/facebook/folly/blob/main/folly/concurrenc...), which uses an aliasing trick to transparently maintain per-core reference counts, and scales linearly, but it works only when acquiring the shared_ptr, any subsequent copies of that would still cause contention if passed around in threads.
[1] Google has a proposal to make a smart pointer based on RCU/hazptr, but I'm not a fan of it because generally RCU/hazptr guards need to be released in the same thread that acquired them, and hiding them in a freely movable object looks like a recipe for disaster to me, especially if paired with coroutines https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p05...
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Ask HN: What are some of the most elegant codebases in your favorite language?
Not sure if it's still the case but about 6 years ago Facebook's folly C++ library was something I'd point to for my junior engineers to get a sense of "good" C++ https://github.com/facebook/folly
CppCoreGuidelines
- Learn Modern C++
- C++ Core Guidelines
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Modern C++ Programming Course
You need to talk to Bjarne and Herb...
"C++ Core Guidelines" - https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines
- CLion Nova Explodes onto the C and C++ Development Scene
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Toward a TypeScript for C++"
In addition to the other comments -
TypeScript deliberately takes a "good enough" approach to improving JavaScript, instead of designing an ideal but incompatible approach. For example, its handling of [function parameter bivariance](https://www.typescriptlang.org/docs/handbook/type-compatibil...) is unsound but works much better with the existing JavaScript ecosystem. By contrast, a more academic functional programming language would guarantee a sound type system but would be a huge shift from JavaScript.
By analogy, Herb Sutter is arguing that something like the [C++ Core Guidelines](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines), with tooling help in this new Cpp2 syntax, can bring real improvements to safety. Something like Rust's borrow checker would bring much stricter guarantees, backed by academic research and careful design, but would be incompatible and a huge adjustment.
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MechE student here. Is there benefit to learning C in addition to C++, or can one do everything with C++ that can be done with C?
https://www.youtube.com/watch?v=2olsGf6JIkU
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C++ is everywhere, but noone really talks about it. What are people's thoughts?
Take a look at Effective Modern c++ by Scott Meyers and the ISO c++ core guidelines. These resources are great for learning how to write better, more modern C++. I don't think it would be hard to grasp if you're already familiar with the language, just make sure to actually write some code which makes use of this stuff, otherwise it's easy to forget.
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What are some C++ specific antipatterns that might be missed by C#/Java devs?
Look to the C++ Core Guidelines. It's not perfect, it has some flaws, including some sabotaging advice apparently adopted for political reasons. But at least it has some C++ authorities (Bjarne and Herb) as authors.
- How to improve the code quality
What are some alternatives?
abseil-cpp - Abseil Common Libraries (C++)
Crafting Interpreters - Repository for the book "Crafting Interpreters"
Boost - Super-project for modularized Boost
github-cheat-sheet - A list of cool features of Git and GitHub.
Seastar - High performance server-side application framework
LearnOpenGL - Code repository of all OpenGL chapters from the book and its accompanying website https://learnopengl.com
parallel-hashmap - A family of header-only, very fast and memory-friendly hashmap and btree containers.
git-internals-pdf - PDF on Git Internals
EASTL - Obsolete repo, please go to: https://github.com/electronicarts/EASTL
Power-Fx - Power Fx low-code programming language
OpenFrameworks - openFrameworks is a community-developed cross platform toolkit for creative coding in C++.
clojure-style-guide - A community coding style guide for the Clojure programming language