Reddit Programming

Been going back and forth on this for a while. The common wisdom these days is "just use Virtual Threads, reactive is dead", and honestly it's hard to argue against the DX argument. But I kept having this nagging feeling that for workloads mixing I/O and heavy CPU (think: DB query -> BCrypt verify -> JWT sign), the non-blocking model might still have an edge that wasn't showing up in the benchmarks I could find. The usual suspects all had blind spots for my use case: TechEmpower (https://github.com/TechEmpower/FrameworkBenchmarks) is great but it's raw CRUD throughput, chrisgleissner's loom-webflux-benchmarks (https://github.com/chrisgleissner/loom-webflux-benchmarks) (probably the most rigorous comparison out there) simulates DB latency with artificial delays rather than real BCrypt, and the Baeldung article on the topic (https://www.baeldung.com/java-reactor-webflux-vs-virtual-threads) is purely theoretical. None of them tested "what happens when your event-loop is free during the DB wait, but then has to chew through 100ms of BCrypt right after". So I built two identical implementations of a Spring Boot account service and hammered them with k6. The setup Stack A: Spring WebFlux + R2DBC + Netty Stack B: Spring MVC + Virtual Threads + JDBC + Tomcat i9-13900KF, 64GB DDR5, OpenJDK 25.0.2 (Temurin), PostgreSQL local with Docker 50 VUs, 2-minute steady state, runs sequential (no resource sharing between the two) 50/50 deterministic VU split between two scenarios Scenario 1 - Pure CPU: BCrypt hash (cost=10), zero I/O WebFlux offloads to Schedulers.boundedElastic() so it doesn't block the event-loop. VT just runs directly on the virtual thread. WebFlux VT median 62ms 55ms p(95) 69ms 71ms max 88ms 125ms Basically a draw. VT wins slightly on median because there's no dispatch overhead. WebFlux wins on max because boundedElastic() has a larger pool to absorb spikes when 50 threads are all doing BCrypt simultaneously. Nothing surprising here, BCrypt monopolizes a full thread in both models, no preemption possible in Java. Scenario 2 - Real login: SELECT + BCrypt verify + JWT sign WebFlux VT median 80ms 96ms p(90) 89ms 110ms p(95) 94ms 118ms max 221ms 245ms WebFlux wins consistently, −20% on p(95). The gap is stable across all percentiles. My read on why: R2DBC releases the event-loop immediately during the SELECT, so the thread is free for other requests while waiting on Postgres. With JDBC+VT, the virtual thread does get unmounted from its carrier thread during the blocking call, but the remounting + synchronization afterward adds a few ms. BCrypt then runs right after, so that small overhead gets amplified consistently on every single request. Small note: VT actually processed 103 more requests than WebFlux in that scenario (+0.8%) while showing higher latency, which rules out "WebFlux wins because it was under less pressure". The 24ms gap is real. Overall throughput: 123 vs 121 req/s. Zero errors on both sides. Caveats (and I think these matter): Local DB, same machine. With real network latency, R2DBC's advantage would likely be more pronounced since there's more time freed on the event-loop per request Only 50 VUs, at 500+ VUs the HikariCP pool saturation would probably widen the gap further Single run each, no confidence intervals BCrypt is a specific proxy for "heavy CPU", other CPU-bound ops might behave differently Takeaway If your service is doing "I/O wait then heavy CPU" in a tight loop, the reactive model still has a measurable latency advantage at moderate load, even in 2026. If it's pure CPU or light I/O, Virtual Threads are equivalent and the simpler programming model wins hands down. Full report + methodology + raw k6 JSON: https://gitlab.com/RobinTrassard/codenames-microservices/-/blob/account-java-version/load-tests/results/BENCHMARK_REPORT.md  submitted by /u/Lightforce_ (https://www.reddit.com/user/Lightforce_)

2 views01:39

Reddit Programming

[link] (https://gitlab.com/RobinTrassard/codenames-microservices/-/blob/account-java-version/load-tests/results/BENCHMARK_REPORT.md) [comments] (https://www.reddit.com/r/programming/comments/1rnda23/i_couldnt_find_a_benchmark_testing_webflux_r2dbc/)

3 views01:39

Reddit Programming

I ported Daniel Lemire's fast_float to c99
https://www.reddit.com/r/programming/comments/1rnswm5/i_ported_daniel_lemires_fast_float_to_c99/

It's a single-header drop in that's been exhaustively tested against the fast_float suite and is benchmarking slightly faster than the cpp. simd, portable, single-header, no allocation, so hot right now  submitted by /u/foobear777 (https://www.reddit.com/user/foobear777)
[link] (http://github.com/kolemannix/ffc.h) [comments] (https://www.reddit.com/r/programming/comments/1rnswm5/i_ported_daniel_lemires_fast_float_to_c99/)

3 views08:19

Reddit Programming

Looking for textbook📚: Finite Automata and Formal Languages: A Simple Approach, by A. M. Padma Reddy, published by Pearson Education India. 📚
https://www.reddit.com/r/programming/comments/1rnu1d1/looking_for_textbook_finite_automata_and_formal/

Hi everyone, My university syllabus for Theory of Computation / Automata Theory recommends the book: Finite Automata and Formal Languages: A Simple Approach — A. M. Padma Reddy Has anyone here used this book before or know where I could: • access a legal PDF or ebook
• borrow it through a digital library
• find lecture notes or alternative books that cover the same topics If not, I'd also appreciate recommendations for good alternative textbooks covering: Module I: Introduction to Finite Automata Central Concepts of Automata Theory Deterministic Finite Automata (DFA) Nondeterministic Finite Automata (NFA) Applications of Finite Automata Finite Automata with ε-Transitions Module II: Regular Expressions Regular Languages Properties Module III: Properties of Regular Languages Context-Free Grammars Module IV: Pushdown Automata Context-Free Languages Module V: Turing Machines Undecidability Any help or recommendations would be appreciated. Thanks! 🙏 Thanks in advance! 📚  submitted by /u/Broad-Ad2003 (https://www.reddit.com/user/Broad-Ad2003)
[link] (https://www.google.com/search?q=Finite+Automata+and+Formal+Languages%3A+A+Simple+Approach%2C+by+A.+M.+Padma+Reddy&rlz=1C1VDKB_enIN1111IN1112&oq=Finite+Automata+and+Formal+Languages%3A+A+Simple+Approach%2C+by+A.+M.+Padma+Reddy&gs_lcrp=EgZjaHJvbWUyBggAEEUYOTIGCAEQRRhBMgYIAhBFGEEyBggDEEUYPDIGCAQQRRhB0gEHNjQzajBqN6gCALACAA&sourceid=chrome&ie=UTF-8) [comments] (https://www.reddit.com/r/programming/comments/1rnu1d1/looking_for_textbook_finite_automata_and_formal/)

3 views08:20

Reddit Programming

Avoiding Modern C++ | Anton Mikhailov
https://www.reddit.com/r/programming/comments/1rnu5lj/avoiding_modern_c_anton_mikhailov/

submitted by /u/BlueGoliath (https://www.reddit.com/user/BlueGoliath)
[link] (https://www.youtube.com/watch?v=ShSGHb65f3M) [comments] (https://www.reddit.com/r/programming/comments/1rnu5lj/avoiding_modern_c_anton_mikhailov/)

3 views08:21

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