pg_test.rb

require 'pg'
class Context
  attr_reader :connections
  def initialize
    @connections = {}
  end

  def connection
    @connections.fetch(Process.pid) { @connections[Process.pid] = PG.connect( dbname: 'test' ) }
  end
end

context = Context.new
p context.connection.exec( "SELECT current_database();" ).to_a
parent_pid = Process.pid

fork do
  at_exit do
    IO.for_fd(context.connections[parent_pid].socket).close
  end
end

Process.wait
p context.connection.exec( "SELECT current_database();" ).to_a