How to Use runtime.SetFinalizer in Go

Use runtime.SetFinalizer to attach a cleanup function to a Go object that the garbage collector will run when the object becomes unreachable. This is essential for releasing resources allocated outside Go's memory management, such as C library handles.

import "runtime"

type Resource struct {
    handle uintptr
}

func (r *Resource) cleanup() {
    // Release external resource, e.g., C.free(r.handle)
}

func NewResource() *Resource {
    r := &Resource{handle: allocateExternalResource()}
    runtime.SetFinalizer(r, (*Resource).cleanup)
    return r
}

runtime.SetFinalizer tells Go to run a specific cleanup task when an object is no longer needed and is about to be deleted. It acts like a safety net for resources like file handles or C memory that Go doesn't automatically manage. Think of it as a 'delete me' tag that the system processes only when the object is truly abandoned.