The strange details of std::string at Facebook

on YouTube ↗31m

" summary

Shows concrete internals: GCC 4 uses a 25-byte global empty string plus copy-on-write with refcount-minus-one, while Facebook's fbstring uses a 24-byte struct with SSO storing up to 23 in-situ bytes and stores flags in low bits via JMalloc buckets. Replacing std::string at Facebook in 2012 yields a 1% performance win company-wide. Covers perf and perf counters, a cache-line–trashing c_str bug at a page boundary, the attempted removal of the null terminator, and tradeoffs after GCC5 switches to a 32-byte std::string with only 15-byte SSO.

AI-written summary · about

" chapters (15)

1. 0:00Introduction to std::string
2. 1:06Why strings matter at Facebook
3. 2:11How GCC implements std::string
4. 5:32GCC string optimizations
5. 6:39FB string vs GCC string
6. 8:23Small string optimization in FB string
7. 13:21Clang and Microsoft string implementations
8. 14:45Performance comparison of FB and GCC strings
9. 17:15Replacing standard string with FB string
10. 19:00Removing the null terminator
11. 21:08The const c_str() problem
12. 23:17The most complex bug in FB string
13. 26:05GCC 5’s new string layout
14. 29:16GCC 5 vs FB string trade-offs
15. 30:19Conclusion and future of std::string

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