[FFI] FFI::AutoPointer#free causes FFI::AutoPointer#autorelease? to cast NullPointerException

[Burgestrand]

require "ffi"

class Releasable < FFI::AutoPointer
  def self.release(pointer)
    puts "Release"
    # no op
  end
end

p = FFI::Pointer.new(1)
r = Releasable.new(p)
r.free
p r.autorelease? # => NullPointerException

It’s because when AutoPointer#free is called, the reaper (managed for releasing the pointer) is reassigned to null. This causes AutoPointer#autorelease? to fail, since reaper is now no longer.