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13692 :: when using "nim r prg.nim" on a cached binary, the startup time is quite slow

• rarino (orginal) [2026-02-05T20:27:28+01:00] view original

  As I understand, "nim r prg.nim" does the following: it compiles a program if necessary and then it launches the binary. However, if the binary is in the cache and the source hasn't changed, it simply launches the binary.

  However, when it simply launches the binary, it happens quite slowly. Let's take a simple "hello world" example:

  
  $ time nim r hello.nim
  667 msec (compile time + launch)
  
  $ time nim r hello.nim
  106 msec (nothing changed, thus no compilation, just launch)
  
  $ nim c hello.nim
  $ time ./hello
  5 msec
  Run

  Why is "nim r hello.nim" 20x slower when it just needs to launch the cached binary (2nd case)?

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• Araq (orginal) [2026-02-05T23:57:25+01:00] view original

  I'm not sure but my guess is it's slow because it computes file checksums and doesn't look at the file timestamps.

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