begin_ensure.rb

def long_method
  @running = true
  begin
    really_long_code
  ensure
    @running = false
  end
end

long_method # => NameError: undefined local variable or method `really_long_code' for #<Object:0x102310508>
puts @running # => false

begin_rescue_ensure.rb

def long_method
  @running = true
  begin
    really_long_code
  rescue
  ensure
    @running = false
  end
end

long_method # => nil
puts @running # => false

ensure.rb

def long_method
  @running = true
  return if @running
  really_long_code
ensure
  @running = false
end

long_method # => nil
puts @running # => false

return_begin_ensure.rb

def long_method
  @running = true
  return
  begin
    really_long_code
  ensure
    @running = false
  end
end

long_method # => nil
puts @running # => true