Folly
Qt
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Folly | Qt | |
---|---|---|
90 | 26 | |
27,072 | 2,273 | |
0.8% | 2.9% | |
9.8 | 10.0 | |
about 8 hours ago | 6 days 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
Qt
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Current Issues With The Qt Project - From The Outside Looking In
Qt mono repo : .. you could check out all submodules and simply use CMake to exactly achieve this. A mono repo also means that if I only use qtbase and declarative, I would need to have all submodules in there? - No
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Why is building a UI in Rust so hard?
For e.g. if you’re writing a framework, you need to interface with Cocoa on MacOS to draw windows, which only provides an Objective C or Swift interface. You can look at the Qt source code and see how they do it: https://github.com/qt/qtbase/tree/067b53864112c084587fa9a507eb4bde3d50a6e1/src/plugins/platforms/cocoa
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Fish (shell) porting to Rust from C++
That's because Qt 6 wholeheartedly converted to CMake for you. (At least it is better than qmake.) In order to support this Qt has this large battery of CMake files [1]. Qt is of course a clear outlier, but you can't expect the same level of support from every other library you want. My points about "anything exotic" still stand.
[1] https://github.com/qt/qtbase/tree/dev/cmake
- A question about how GUI libraries are written.
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A GTK4 Firefox with Libwaita is the next step into the right direction (Please click on the link and upvote my proposal).
What are you talking about? Qt has GTK theme support built-in: https://github.com/qt/qtbase/tree/dev/src/plugins/platformthemes/gtk3
- Ask HN: Why is there no performant remote desktop for Mac/Linux?
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What is this "Portal" which keeps sending notifications when opening the Choose a diskfile window? Is it safe to disable the notifications of it, or will I miss important notifications?
This looks like the Qt bug solved by this commit: https://github.com/qt/qtbase/commit/acaabc9108dfe75530960cf8e3ec4f3602cd82e0
- Where online can I find the Qt6 header files?
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member function definitions should have been like this
Yeah, I'm sure it's completely unheard of. Oh except that it took me all of a couple minutes to find an example of that exact thing in one of the largest, most commonly used C++ frameworks out there.
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Post-mortem of a long-standing bug in video Game Path Of Exile, which was caused by a stale pointer
I don't see any connect in https://github.com/qt/qtbase/blob/dev/src/corelib/tools/qsharedpointer_impl.h, and QPointer isn't a QObject (though I don't know if the latter is actually necessary for signal-slots). One (unreliable) way to test is to see if a QPointer fails to be nulled out when the QObject is blocked by a QSignalBlocker. Alternatively I'd set a data breakpoint on a QPointer and try it out. But I don't have the time right now.
What are some alternatives?
abseil-cpp - Abseil Common Libraries (C++)
Boost - Super-project for modularized Boost
JUCE - JUCE is an open-source cross-platform C++ application framework for desktop and mobile applications, including VST, VST3, AU, AUv3, LV2 and AAX audio plug-ins.
Seastar - High performance server-side application framework
OpenFrameworks - openFrameworks is a community-developed cross platform toolkit for creative coding in C++.
parallel-hashmap - A family of header-only, very fast and memory-friendly hashmap and btree containers.
Cinder - Cinder is a community-developed, free and open source library for professional-quality creative coding in C++.
EASTL - Obsolete repo, please go to: https://github.com/electronicarts/EASTL
Vcpkg - C++ Library Manager for Windows, Linux, and MacOS