# Creating userimg.jl files

If you want to save more precompile information, one option is to create a "userimg.jl" file with which to build Julia. This is only supported for @snoopc. Instead of calling SnoopCompile.parcel and SnoopCompile.write, use the following:

# Use these two lines if you want to add to your userimg.jl
pc = SnoopCompile.format_userimg(reverse!(data[2]))
SnoopCompile.write("/tmp/userimg_Images.jl", pc)

Now move the resulting file to your Julia source directory, and create a userimg.jl file that includes all the package-specific precompile files you want. Then build Julia from source. You should note that your latencies decrease substantially.

There are serious negatives associated with a userimg.jl script:

• Your julia build times become very long
• Pkg.update() will have no effect on packages that you've built into julia until you next recompile julia itself. Consequently, you may not get the benefit of enhancements or bug fixes.
• For a package that you sometimes develop, this strategy is very inefficient, because testing a change means rebuilding Julia as well as your package.

A process similar to this one is also performed via PackageCompiler.