foo.c

// cc -c foo.c -o foo.o
#include <stdlib.h>

void** global_data;

void foo_set(void* data) {
  void** ptr = (void**)malloc(sizeof(data));
  *ptr = data;
  global_data = ptr;
}

void* foo_get() {
  return *global_data;
}

foo.cr

@[Link(ldflags: "#{__DIR__}/foo.o")]
lib LibFoo
  fun set = foo_set(Void*)
  fun get = foo_get : Void*
end

$exit = false

class Foo
  getter name

  def initialize(@name)
  end

  def finalize
    unless @name.empty?
      puts "exit"
      $exit = true
    end
  end
end

def bar
  foo = Foo.new("1")
  puts foo.name
  LibFoo.set(foo as Void*)
end

bar

until $exit
  Foo.new("")
end

1000.times do
  Foo.new("")
end

foo = LibFoo.get as Foo
puts foo.name