cppinsights
Folly
cppinsights | Folly | |
---|---|---|
24 | 90 | |
3,693 | 27,118 | |
- | 0.6% | |
8.1 | 9.8 | |
28 days ago | 5 days ago | |
C++ | C++ | |
MIT License | Apache License 2.0 |
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.
cppinsights
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C++ Insights – See your source code with the eyes of a compiler
Sorry, I don't know about an Emacs plugin. All the plugins/extensions I'm aware of are listed in the Readme.md: https://github.com/andreasfertig/cppinsights/#c-insights--vi...
I'm happy to add an entry for Emacs once somebody develops a plugin for that editor.
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C++20 Idioms for Parameter Packs
Thank you! This is exactly the sort of thing I was looking for.
I found the source at https://github.com/andreasfertig/cppinsights
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Why does ![]{} equate to 0?
You can put it into https://cppinsights.io/ and see the conversions that happen under the hood.
- C++ lernen
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BitMasks in 2023
I tried this at https://cppinsights.io/ to see what is generated for something like:
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Ask HN: Best way to learn C++ in 2022
> https://cppinsights.io/ it's a must so you can investigate what gets generated by templates behind the scenes.
> http://eel.is/c++draft/ bookmark this, you will need it!
Now, about books I would suggest the latest "A tour of C++" by Bjarne Stroustrup; it's ideal for experienced programmers that want to learn modern C++ rather fast.
Other books would be Scott Meyers' Effective Series, Andrei Alexandrescu and Herb Sutter are a must, and of course Jason Turner's "C++ Weekly" series [1]; of course apart from the books, the links I have originally shared are more than enough to cover everything around C++.
[1] https://www.youtube.com/c/lefticus1/videos
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Ask HN: Where can I find C++ by Example?
https://cppinsights.io/ it's a must so you can investigate what gets generated by templates behind the scenes.
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Ask HN: Any tool to look C++ interpretation template form syntax to substitution
Try https://cppinsights.io. For example, go to https://cppinsights.io/s/8401262a and click the play button at the top left.
If you're doing something more complex, you might need metashell. See http://metashell.org/manual/how_to/index.html#see-what-templ.... But you have to really, deeply, love C++ to get much out of it.
- Question on a For each loop.
- Can anyone recommend a good book/resource on C++/C++ compilers? With detailed discussions of what happens "under the hood".
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
What are some alternatives?
LLVM-Guide - LLVM (Low Level Virtual Machine) Guide. Learn all about the compiler infrastructure, which is designed for compile-time, link-time, run-time, and "idle-time" optimization of programs. Originally implemented for C/C++ , though, has a variety of front-ends, including Java, Python, etc.
abseil-cpp - Abseil Common Libraries (C++)
lsif-clang - Language Server Indexing Format (LSIF) generator for C, C++ and Objective C
Boost - Super-project for modularized Boost
GSL - Guidelines Support Library
Seastar - High performance server-side application framework
gcem - A C++ compile-time math library using generalized constant expressions
parallel-hashmap - A family of header-only, very fast and memory-friendly hashmap and btree containers.
fccf - fccf: A command-line tool that quickly searches through C/C++ source code in a directory based on a search string and prints relevant code snippets that match the query.
EASTL - Obsolete repo, please go to: https://github.com/electronicarts/EASTL
Xoshiro-cpp - Header-only Xoshiro/Xoroshiro PRNG wrapper library for modern C++ (C++17/C++20)
OpenFrameworks - openFrameworks is a community-developed cross platform toolkit for creative coding in C++.