STL
Folly
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STL | Folly | |
---|---|---|
154 | 90 | |
9,698 | 27,072 | |
1.3% | 1.0% | |
9.6 | 9.8 | |
7 days ago | 2 days ago | |
C++ | C++ | |
GNU General Public License v3.0 or later | 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.
STL
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Show HN: Logfmtxx – Header only C++23 structured logging library using logfmt
Again, they are barely functional.
MSVC chokes on many standard-defined constructs: https://github.com/microsoft/STL/issues/1694
clang does not claim to be "mostly usable" at all - most papers are not implemented: https://clang.llvm.org/cxx_status.html#cxx20
And gcc will only start ot be usable with CMake when version 14 is released - that has not happened yet.
And, as I mentioned before, IDE support is either buggy (Visual Studio) or non-existing (any other IDE/OS). So you're off to writing in a text editor and hoping your compiler works to a somewhat usable degree. Yes, at some point people should start using modules, I agree, but to advise library maintainers to ship modularized code... the tooling just isn't there yet.
I mean, the GitHub issue is Microsoft trying to ship their standard library modularized, they employ some of the most capable folks on the planet and pay them big money to get that done, while metaphorically sitting next to the Microsoft compiler devs, and they barely, barely get it done (with bugs, as they themselves mention). This is too much for most other library maintainers.
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Cpp2 and cppfront – An experimental 'C++ syntax 2' and its first compiler
Notice that there are in practice three distinct implementations of the C++ standard library. They're all awful to read though, here's Microsoft's std::vector https://github.com/microsoft/STL/blob/main/stl/inc/vector
However you're being slightly unfair because Rust's Vec is just defined (opaquely) as a RawVec plus a length value, so let's link RawVec, https://doc.rust-lang.org/src/alloc/raw_vec.rs.html -- RawVec is the part responsible for the messy problem of how to actually implement the growable array type.
Still, the existence of three C++ libraries with slightly different (or sometimes hugely different) quality of implementation means good C++ code can't depend on much beyond what the ISO document promises, and yet it must guard against the nonsense inflicted by all three and by lacks of the larger language. In particular everything must use the reserved prefix so that it's not smashed inadvertently by a macro, and lots of weird C++ idioms that preserve performance by sacrificing clarity of implementation are needed, even where you'd ordinarily sacrifice to get the development throughput win of everybody know what's going on. For example you'll see a lot of "pair" types bought into existence which are there to squirrel away a ZST that in C++ can't exist, using the Empty Base Optimisation. In Rust the language has ZSTs so they can just write what they meant.
- C++ Specification vs Implementation
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C++23: Removing garbage collection support
Here is Microsoft's implementation of map in the standard library. I think of myself as a competent programmer / computer scientist. I couldn't write this: https://github.com/microsoft/STL/blob/f392449fb72d1a387ac502...
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std::condition_variable wait for (very) long time
Be careful on Windows, the MSVC STL implementation uses the system time, so it can be badly impacted by clock adjustments: https://github.com/microsoft/STL/issues/718
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Compiler explorer: can you use C++23 std lib modules with MSVC already?
Can you provide a link? If it affects import std;, I'd like to add it to my tracking issue.
- Learn to write production quality STL like classes
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MSVC C++23 Update
Do you have a list of the bugs you've filed and their current status, like the one I have for the STL? I saw you mentioned 3 bugs 7 months ago, 2 of which were fixed in 17.6 and the third of which was a duplicate of an active bug ("deducing this" is known to not yet work with modules, which is why we don't define the feature-test macro to claim full support).
- C++/CLI wrap of a C++ class that includes <future> in public header
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Has Boost lost its charm?
Yep. And look at our implementation's name: https://github.com/microsoft/STL
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?
EA Standard Template Library - EASTL stands for Electronic Arts Standard Template Library. It is an extensive and robust implementation that has an emphasis on high performance.
abseil-cpp - Abseil Common Libraries (C++)
asio - Boost.org asio module
Boost - Super-project for modularized Boost
robin-hood-hashing - Fast & memory efficient hashtable based on robin hood hashing for C++11/14/17/20
Seastar - High performance server-side application framework
tracy - Frame profiler
parallel-hashmap - A family of header-only, very fast and memory-friendly hashmap and btree containers.
gcc
EASTL - Obsolete repo, please go to: https://github.com/electronicarts/EASTL
llvm-project - The LLVM Project is a collection of modular and reusable compiler and toolchain technologies.
OpenFrameworks - openFrameworks is a community-developed cross platform toolkit for creative coding in C++.