Folly
cs_libguarded
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Folly | cs_libguarded | |
---|---|---|
90 | 10 | |
27,072 | 218 | |
0.8% | 0.0% | |
9.8 | 5.0 | |
about 11 hours ago | about 1 month ago | |
C++ | C++ | |
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
cs_libguarded
- MutexProtected: A C++ Pattern for Easier Concurrency
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Using shared_ptr for reloadable config
I know this article was trying to come up with an excuse to use a shared_ptr, but atomic smart pointers are a lot more error prone than wrapping mutexes in an appropriate interface that hides the complexity and forces you to use them correctly.
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Ban thread locking classes/functions?
The approach I would recommend would be to use mutexes but wrap them in a convenience library designed to make them difficult to misuse: https://github.com/copperspice/cs_libguarded
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FreeRTOS Guarded Data Structure
I was inspired by the great copperspice library libguarded and wanted something similar for when I have to go back to micro's and FreeRTOS. The basic idea of the library is to prevent access to a shared data structure unless the mutex lock associated with it is also acquired. This is to prevent situations where someone forgets to get the lock before reading or writing to shared memory.
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Strategies for serialization of a class in a concurrent fashion
I'm personally partial to the basic guarded type from https://github.com/copperspice/cs_libguarded due to its simplicity.
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Why Rust mutexes look like they do
The Rust strategy for mutexes sounds a lot like libguarded, which now that I've read this article is occurs to me that the former was likely have been the inspiration for the latter.
This is pretty much what libguarded does.
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How would you recommend implementing an iterator that holds a resource?
Also I don't think that operating this way is good to begin with. See how libGuard operates - it is way way cleaner and more flexible https://github.com/copperspice/cs_libguarded
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A C++ locking wrapper
have you heard of https://github.com/copperspice/cs_libguarded ? it sounds like a similar idea, but supports other stuff like rcu as well
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Having fun overloading the operator->
https://github.com/copperspice/cs_libguarded#cslibguarded
What are some alternatives?
abseil-cpp - Abseil Common Libraries (C++)
ultimatepp - U++ is a C++ cross-platform rapid application development framework focused on programmer's productivity. It includes a set of libraries (GUI, SQL, Network etc.), and integrated development environment (TheIDE).
Boost - Super-project for modularized Boost
concurrencpp - Modern concurrency for C++. Tasks, executors, timers and C++20 coroutines to rule them all
Seastar - High performance server-side application framework
concurrent-resource - A header-only C++ library that allows easily creating thread-safe, concurrency friendly resources.
parallel-hashmap - A family of header-only, very fast and memory-friendly hashmap and btree containers.
freertos-addons - Additions to FreeRTOS
EASTL - Obsolete repo, please go to: https://github.com/electronicarts/EASTL
rwspinlock - Slim, simple, cross-process, reader-writer unfair fast spin lock for Windows
OpenFrameworks - openFrameworks is a community-developed cross platform toolkit for creative coding in C++.
lock_ios - iostream synchronization manipulator for concurrency