Compile into a Julia system image

Sometimes it can be useful to 'compile' SpineOpt into a so-called system image. A system image is a binary library that, roughly speaking, 'stores' all the compilation work from a previous Julia session. If you start Julia with a system image, then Julia doesn't need to redo all that work and your code will be fast the first time you run it.

However if you upgrade your version of SpineOpt, any system images you might have created will not reflect that change - you will need to re-generate them.

To compile SpineOpt into a system image just do the following:

1. Install PackageCompiler.jl.

2. Create a file with precompilation statements for SpineOpt:

   a. Start julia with --trace-compile=file.jl.

   b. Call run_spineopt(url...) with a nice DB - one that triggers most of SpineOpt's functionality you need.

   c. Quit julia.

3. Create the sysimage using the precompilation statements file:

   a. Start julia normally.

   b. Create the sysimage with PackageCompiler:

   using PackageCompiler
   create_sysimage(; sysimage_path="SpineOpt.dll", precompile_statements_file="file.jl")

4. Start Julia with --sysimage=SpineOpt.dll to use the generated image.