lots-of-parallel-builders.nix

with (import <nixpkgs> {});
with lib;
let
    forceRebuild = "1";
    dummy = index: stdenv.mkDerivation {
      name = "dummy-${forceRebuild}-${toString index}";
      builder = writeScript "sleeping-builder" ''
         #!/bin/sh
         echo "dummy ${toString index} is building" > $out
         ${coreutils}/bin/sleep 10
      '';
    };
    indices = genList id 1000;
    dummyDerivations = map (index: "dummy-${toString index} : ${dummy index}") indices;
in writeTextFile {
   name = "toplevel";
   text = ''
     ${builtins.concatStringsSep "\n" dummyDerivations}
   '';
}