meta/folly on Hacker News

…trials and look at the minimum observed time, which is when there will have been ~no interruptions. https://github.com/facebook/folly/blob/main/folly/docs/Bench...

comment by loeg · 2026-01-14 · in A 40-line fix eliminated a 400x performance gap

…Not saying those are precisely on point, though; just thought some of the ideas were similar. [0]: https://github.com/facebook/folly/blob/main/folly/docs/Poly.... [1]: https://github.com/microsoft/proxy

comment by aw1621107 · 2025-12-19 · in Common Rust Lifetime Misconceptions

…Folly's definition [1]. [0] https://community.intel.com/t5/Intel-Moderncode-for-Parallel... [1] https://github.com/facebook/folly/blob/d2e6fe65dfd6b30a9d504...

comment by charleshn · 2025-12-08 · in Spinlocks vs. Mutexes: When to Spin and When to Sleep

…in C++ in a very similar way as Rust. E.g., APIs can take folly::Synchronized<T>::RLockedPtr: https://github.com/facebook/folly/blob/76f81836a2ccb6cd3bc7d...

comment by loeg · 2025-09-23 · in The allure of new languages vs. the necessity of problem-solving

…mostly historical, though it's relatively common to use a 128 byte line size on x86, still. E.g., https://github.com/facebook/folly/blob/main/folly/lang/Align... (Sandy Bridge was a 2011 CPU). (Clang's impl of the std version of these…

comment by loeg · 2025-09-15 · in Analyzing the memory ordering models of the Apple M1

…every single time they need to do some basic things (like for example version upgrades). Example: https://github.com/facebook/folly/blob/main/build.sh

comment by dev_l1x_be · 2025-09-15 · in RustGPT: A pure-Rust transformer LLM built from scratch

https://github.com/facebook/folly/blob/main/folly/chrono/Har...

comment by loeg · 2025-08-16 · in OpenBSD is so fast, I had to modify the program slightly to measure itself

…on escape-heavy strings. [1] https://source.chromium.org/chromium/_/chromium/v8/v8/+/5cbc... [2] https://github.com/facebook/folly/commit/2f0cabfb48b8a8df84f...

comment by ot · 2025-08-04 · in How we made JSON.stringify more than twice as fast

Bingo. https://github.com/facebook/folly/commit/4d932ecc53c7a722671...

comment by loeg · 2025-05-07 · in Matt Godbolt sold me on Rust by showing me C++

…[3]: https://research.facebook.com/publications/hive-a-warehousin... [4]: https://github.com/facebook/folly/tree/main

comment by smitelli · 2024-12-04 · in Meta built large-scale cryptographic monitoring

…some are better at certain workloads than the rest. DistributedMutex and SharedMutex come to mind ( https://github.com/facebook/folly/blob/main/folly/synchroniz... , https://github.com/facebook/folly/blob/main/folly/SharedMute... ) Just…

comment by uvdn7 · 2024-10-02 · in The Fastest Mutexes

…look at it? Wondering if there are any advantages. The api seems fairly similar to me at a glance. https://github.com/facebook/folly/tree/main/folly/experiment...

comment by dkasper · 2024-09-26 · in Show HN: Coros – A Modern C++ Library for Task Parallelism

…disprove your wrong assertions as opposed to providing references that justify your position: Folly https://github.com/facebook/folly : "It complements (as opposed to competing against) offerings such as Boost and of course std. In fact,…

comment by Maxatar · 2024-08-06 · in C++'s `noexcept` can sometimes help or hurt performance

▲ 1

Folly: An open-source C++ library developed and used at Facebook

story by tosh · 2024-07-24 · 0 comments

…used to test its core synchronization primitives, but I don't think it's as sophisticated as loom. https://github.com/facebook/folly/blob/main/folly/test/Deter...

comment by ot · 2024-07-06 · in Properly testing concurrent data structures

Easily solved manually reserving exponentially. All my projects use some variation of this: https://github.com/facebook/folly/blob/9f125c94e10fd01f5567c... But I've burned myself on this a few times before.

comment by mandarax8 · 2024-06-09 · in Compilers are too smart

Modern hash table implementations use vector instructions for lookups: - Folly: https://github.com/facebook/folly/blob/main/folly/container/... - Abseil: https://abseil.io/about/design/swisstables

comment by alexhutcheson · 2024-06-04 · in Intel's Lion Cove Architecture Preview

Nope, given that it has a plugin architecture and in time it would have been everywhere. https://github.com/facebook/folly/commit/b1391e1c57be71c1e2a...

comment by pajko · 2024-03-31 · in Ask HN: How bad is the xz hack?

yes, like this one: https://github.com/facebook/folly/pull/2153

comment by jdright · 2024-03-30 · in Backdoor in upstream xz/liblzma leading to SSH server compromise

…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…

comment by loeg · 2024-03-01 · in A lock-free ring-buffer with contiguous reservations (2019)

…but uses some sort of SeqCst barrier between the store and the 2nd load (with acquire semantics): https://github.com/facebook/folly/blob/main/folly/synchroniz...

comment by loeg · 2024-03-01 · in A lock-free ring-buffer with contiguous reservations (2019)

folly provides functions to resize std::string & std::vector without initialization [0]. [0] https://github.com/facebook/folly/blob/3c8829785e3ce86cb821c...

comment by terrelln · 2023-10-27 · in Appending to an std:string character-by-character: how does the capacity grow?

It is doable, `folly::Expected` supports that: https://github.com/facebook/folly/blob/main/folly/test/Expec...

comment by ot · 2023-09-30 · in How to Use Monadic Operations for `std:optional` in C++23

…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...

comment by ot · 2023-07-02 · in A compressed indexable bitset

…was a non-negotiable. [1] https://github.com/ot/ds2i/ [2] https://github.com/pisa-engine/pisa [3] https://github.com/facebook/folly/blob/main/folly/experiment...

comment by ot · 2023-07-01 · in A compressed indexable bitset

C++ with folly's SCOPE_EXIT {} construct: https://github.com/facebook/folly/blob/main/folly/ScopeGuard...

comment by loeg · 2023-06-21 · in Defer for Shell (2020)

…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/sy…

comment by ot · 2023-06-18 · in A single line of code made a 24-core server slower than a laptop (2021)

…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

comment by personjerry · 2023-06-17 · in Ask HN: What are some of the most elegant codebases in your favorite language?

▲ 1

Growing std::vector by a factor that allows memory reuse (2020)

story by nequo · 2023-05-06 · 0 comments

…in the standard library this even spells out that the result has "at least the specified capacity" https://github.com/facebook/folly/blob/main/folly/container/... F14 is a linear map but I couldn't immediately find actual API…

comment by tialaramex · 2023-04-12 · in Deduplicate a slice in Go, use sort or a map?

…com/SerenityOS/serenity/blob/master/Kernel/Lo... I don't know why the article doesn't touch on these. https://github.com/facebook/folly/blob/main/folly/docs/Synch... https://github.com/facebook/folly/blob/main/folly/Synchroniz...

comment by loeg · 2023-04-06 · in MutexProtected: A C++ Pattern for Easier Concurrency

…? https://en.cppreference.com/w/cpp/atomic/atomic * folly::Synchronized, mentioned by ot57? https://github.com/facebook/folly/blob/main/folly/docs/Synch... * Boost synchronized data structures, -mentioned by mchicken 53?…

comment by einpoklum · 2023-04-06 · in MutexProtected: A C++ Pattern for Easier Concurrency

…object. It is generally the preferred synchronization utility at Meta and thus it is widely used. https://github.com/facebook/folly/blob/main/folly/docs/Synch...

comment by ot · 2023-04-06 · in MutexProtected: A C++ Pattern for Easier Concurrency

https://github.com/facebook/folly/blob/main/folly/docs/Synch...

comment by ajtulloch · 2023-04-06 · in MutexProtected: A C++ Pattern for Easier Concurrency

…people use Result in Rust. (And C++ std::optional<T> is somewhat similar to Rust's Option<T> type.) https://github.com/facebook/folly/blob/main/folly/Expected.h...

comment by loeg · 2023-03-14 · in Switching from C++ to Rust

You have to use something similar to https://github.com/facebook/folly/tree/main/folly/experiment... to solve this problem. It's a nasty bug that everyone encounters when first working with coroutines. (Similarly everyone will encounter…

comment by somerando7 · 2022-10-04 · in C++20 coroutines: “The bug is in the C++ standard, not GCC.” (2020)

https://github.com/facebook/folly/blob/main/folly/docs/Packe... is pretty awesome and I’ve personally gotten big wins from it. The parent mentioned Bloom Filters, HyperLogLog-type stuff is on that family tree and also very interesting and…

comment by benreesman · 2022-07-22 · in Ask HN: What are some cool but obscure data structures you know about?

…for this (see folly::dynamic[1]). We make extensive use of this at my (non-Facebook) job. [1] https://github.com/facebook/folly/blob/master/folly/docs/Dyn...

comment by ollien · 2022-05-26 · in Parsing JSON faster with Intel AVX-512

https://github.com/facebook/folly/blob/main/folly/docs/Overv... This has library contents: it’s a mix of various utilities - type conversion, data structures, memory management, random numbers, concurrency, etc.

comment by ximeng · 2022-01-07 · in Folly: An open-source C++ library developed and used at Facebook

The docs have a bit more detail about what is included: https://github.com/facebook/folly/blob/main/folly/docs/Overv...

comment by MarkSweep · 2022-01-07 · in Folly: An open-source C++ library developed and used at Facebook

▲ 95

Folly: An open-source C++ library developed and used at Facebook

story by u1tron · 2022-01-07 · 83 comments

Ideally they should be turned into open source projects. Google's https://abseil.io and Facebook's https://github.com/facebook/folly come to mind.

comment by floatboth · 2021-12-25 · in Fix the unit test and open a giant hole everywhere

…callable and can be moved but not copied). That's often preferable for storing functors. Example: https://github.com/facebook/folly/blob/main/folly/docs/Funct...

comment by MauranKilom · 2021-12-13 · in The Evolutions of Lambdas in C++14, C++17 and C++20

…For example, Facebook's Folly has been updated to use coroutines and is being widely adopted at FB: https://github.com/facebook/folly/tree/main/folly/experiment...

comment by pavlov · 2021-11-01 · in C++ Coroutines Do Not Spark Joy

…an even better performance implementation using sqrt. Might make sense to port that over to Rust. https://github.com/facebook/folly/blob/master/folly/stats/TD...

comment by rogers18445 · 2021-09-15 · in How percentile approximation works and why it's more useful than averages

Edit: Links to repos: https://github.com/pytorch/pytorch https://github.com/tensorflow/tensorflow https://github.com/facebook/folly

comment by pdevr · 2021-08-24 · in Ask HN: What are the best publicly available FAMANG code repos?

For example folly's vector performs this optimization: https://github.com/facebook/folly/blob/master/folly/docs/FBV...

comment by kevincox · 2021-06-15 · in Linux with “memory folios”: a 7% performance boost when compiling the kernel

…) good ( https://software.intel.com/content/www/us/en/develop/documen... ) options ( https://github.com/facebook/folly/tree/master/folly/concurre... ) out there." There are plenty of practical solutions to the safe memory reclamation…

comment by pkhuong · 2021-06-01 · in Libdill: Structured Concurrency for C (2016)

…ticks? http://www.cs.columbia.edu/~nahum/w6998/papers/sosp87-timing... Production implementation: https://github.com/facebook/folly/blob/master/folly/io/async...

comment by EquallyJust · 2021-05-25 · in Need Something Sorted? Sleep on It

folly::Function was added for exactly this reason I think https://github.com/facebook/folly/blob/master/folly/docs/Fun...

comment by aptxkid · 2021-04-16 · in Why C++ Is Terrifying