Folly
cppcoro
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Folly | cppcoro | |
---|---|---|
90 | 24 | |
27,072 | 3,230 | |
1.0% | - | |
9.8 | 0.0 | |
1 day ago | 4 months ago | |
C++ | C++ | |
Apache License 2.0 | MIT License |
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
cppcoro
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Struggle with C++ 20 Coroutines
PS: Take a look at cppcoro; this might help as well, especially generator<>, if you're looking to generate numbers, and stuff;
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Does C++23 have a coroutine task promise type?
This is the only viable implementation.
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Stop Comparing Rust to Old C++
Kind of sounds like whatever library you were using provided leaky abstractions. Something like cppcoro provides really good abstractions for coroutines, the user really doesn't need to understand why any of it works.
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Sane coroutine imitation with macros; copyable, serializable, and with reflection
Is there a usecase for copying/serializing such coroutines? If not, I would use the normal C++20 coroutines (cppcoro?).
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Is Tokio::sync::Mutex lock-free?
C++ has the popular CppCoro library. Async_mutex is its equivalent of Tokio::sync::Mutex, providing exclusive access to data shared between tasks.
- My experience with C++ 20 coroutines
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My thoughts and dreams about a standard user-space I/O scheduler
Because the whole application is running under a single thread there is no need for atomic operations in synchronization primitives(which most of the time requires seq_cst memory order and CMPXCHG which is an expensive instruction in CPU). for example what async_mutex would look like if it knows it's running in a single-threaded scheduler (a non-atomic state variable and waiters queue).
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[Discussion] What are some old C++ open source projects you wish were still active?
Maybe not old, but I wish cppcoro was still updated. It was such a nice start!
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A high-level coroutine explanation
You can get generator<> from https://github.com/lewissbaker/cppcoro
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C++ Coroutines Do Not Spark Joy
It is possible to compose them more easily than described in the article; Lewis Baker's cppcoro library for example provides a recursive_generator<> type[0] that allows this without using any macros. It's up to the library part of coroutines to make things easy, end users are not expected to write low-level coroutine code themselves.
I wonder about the allocation elision. Return value optimization became mandatory, and some compilers can already elide calls to new/delete and malloc()/free() in normal code, so perhaps it will be possible to guarantee allocation elision in the future in the most used cases.
[0]: https://github.com/lewissbaker/cppcoro#recursive_generatort
What are some alternatives?
abseil-cpp - Abseil Common Libraries (C++)
libunifex - Unified Executors
Boost - Super-project for modularized Boost
drogon - Drogon: A C++14/17/20 based HTTP web application framework running on Linux/macOS/Unix/Windows
Seastar - High performance server-side application framework
C-Coroutines - Coroutines for C.
parallel-hashmap - A family of header-only, very fast and memory-friendly hashmap and btree containers.
Flow - Flow is a software framework focused on ease of use while maximizing performance in closed closed loop systems (e.g. robots). Flow is built on top of C++ 20 coroutines and utilizes modern C++ techniques.
EASTL - Obsolete repo, please go to: https://github.com/electronicarts/EASTL
coproto - A protocol framework based on coroutines
OpenFrameworks - openFrameworks is a community-developed cross platform toolkit for creative coding in C++.
uvloop - Ultra fast asyncio event loop.