4 ms·

LMDB is the only one here in C, so the interop is probably what makes LMDB so slow in here

• apatheticonion 2y ago
  Curious, what overhead is there calling C code from other languages?
  • atombender 2y ago
    Go doesn't use the C calling convention, but has its own growable stack system and goroutine scheduler that maps to goroutines to threads. So a goroutine can't just call a C function directly. In order to interface with C code safely, Go's runtime has to jump to the system stack and do some additional setup, make the call, and then switch back. (Adding to that, if the call takes too long, this prevents other goroutines on the same OS thread from running, so the scheduler must jump in and move those goroutines to a different thread.) All of this is expensive, though we are talking about nanoseconds, not milliseconds. Performance is mostly a problem when doing lots of very quick calls (e.g. you're writing a game engine interacting with something like OpenGL) or lots of slow calls (causing scheduler trashing).
    • apatheticonion 2y ago
      Thanks! Is this also the case even Rust consumes a C library?
      • atombender 2y ago
        No, my understanding is that Rust uses normal stacks, and it uses a classic threading model, so aside from async, calling C doesn't need to any runtime stuff.
        • steveklabnik 2y ago
          That is correct, and was a major motivation for dropping green threads way back in 2014.