FFI Global Initializer

Problem

You are working with a library via Pony’s C-FFI and need to initialize the library before you can use it. And you’d like to do this initialization once and only once.

Solution

Pony’s primitives can serve a variety of design purposes. Here we will use a primitive to initialize our imaginary C library.

use @magic_global_initialization[None]()

primitive LibraryInitializer
  fun _init() =>
    @magic_global_initialization()

Discussion

Only a single instance of a Pony primitive will exist in our binary. User defined primitives are singletons. We can combine this with the fact that primitives have an _init function that is called when the primitive is created.

Wrapping our “should only be done once” initialization code in a primitive’s _init method is a good way to ensure that the initialization code is only run once. It is important to note that this approach doesn’t protect you from someone mistakenly calling the initializer via C-FFI directly again,

If we need to teardown the library, we can add a _final method to LibraryInitializer which will be executed on program shutdown.

use @magic_global_initialization[None]()
use @magic_global_shutdown[None]()

primitive LibraryInitializer
  fun _init() =>
    @magic_global_initialization()

  fun _final() =>
    @magic_global_shutdown()