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Written by Christoph Berger on 2025-01-15 at 15:22

Clean up what the GC can't clean up

Gophers coming from OOP languages may occasionally miss a finalizer in Go. Fret no more: With the AddCleanup function, new in Go 1.24, you can close files, disconnect DB connections, and clean up other resources once the object containing these resources becomes unreachable.

Here is how it works:

• The first parameter of AddCleanup is the object whose resources to clean up.

• The second parameter is a function that expects a resource object to clean up.

• The third parameter is the resource object to be passed to the aforementioned function.

If the object containing the resource becomes unreachable, hence due for garbage collection, the cleanup function is called.

A small but important caveat: The cleanup function must not refer to the object containing the resources. Otherwise, the object would always be referenced by reachable code and would never become subject to garbage collection; hence, the cleanup function would never run.

The example in the screenshot and in the playground is simplified as much as possible. The object is a temporary file, and the cleanup function removes the file from disk.

https://go.dev/play/p/05BWkHUHWZo?v=gotip

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