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folly/FBString.h

fbstring is a drop-in replacement for std::string. The main benefit of fbstring is significantly increased performance on virtually all important primitives. This is achieved by using a three-tiered storage strategy and by cooperating with the memory allocator. In particular, fbstring is designed to detect use of jemalloc and cooperate with it to achieve significant improvements in speed and memory usage.

fbstring supports x32 and x64 architectures. Porting it to big endian architectures would require some changes.

Storage strategies


  • Small strings (<= 23 chars) are stored in-situ without memory allocation.

  • Medium strings (24 - 255 chars) are stored in malloc-allocated memory and copied eagerly.

  • Large strings (> 255 chars) are stored in malloc-allocated memory and copied lazily.

Implementation highlights


  • 100% compatible with std::string.

  • Thread-safe reference counted copy-on-write for strings "large" strings (> 255 chars).

  • Uses malloc instead of allocators.

  • Jemalloc-friendly. fbstring automatically detects if application uses jemalloc and if so, significantly improves allocation strategy by using non-standard jemalloc extensions.

  • find() is implemented using simplified Boyer-Moore algorithm. Casual tests indicate a 30x speed improvement over string::find() for successful searches and a 1.5x speed improvement for failed searches.

  • Offers conversions to and from std::string.

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