From: Stefano Crocco <stefano.crocco@...>
Date: 2009-12-10T20:58:18+09:00
Subject: Re: How do I ensure that File.write finished?

On Thursday 10 December 2009, Emil Kampp wrote:
> |Hi there.
> |
> |I am trying to make a form to update the values in a yml file (my
> |applications configuration file). This is working kind of fine.
> |Sometimes it works, sometimes not.
> |
> |I have confirmed (through logging) that a content for +string+ is always
> |there. So there is always something trying to be written into the yml
> |file, but still sometimes it ends up being empty. And an empty
> |configuration file is no good!
> |
> |[code]
> |# server-controller (user generated controller in rails)
> |  def update
> |    # This inserts a new setting into the hash
> |    unless params[:new_setting][:key].blank? and
> |params[:new_setting][:value].blank?
> |      params[:settings].collect{ |env, settings|
> |settings[params[:new_setting][:key].to_sym] =
> |params[:new_setting][:value].to_s }
> |    end
> |
> |    # This writes the hash to the file (See the second snippet for
> |details)
> |    ServerSystem::update_configuration(params[:settings])
> |
> |    # Redirects to the action that restarts the server to load the new
> |configurations
> |    redirect_to admin_server_restart_path
> |  end
> |[/code]
> |
> |[code]
> |# Custom class
> |    def update_configuration(settings)
> |      string = settings.to_yaml
> |      File.new(APP_CONFIG_FILE, "w").write string
> |    end
> |[/code]
> |
> |The problem is that the setup is dodgy, sometimes it works, sometimes it
> |looks like the server is restarted before the content of +string+ is
> |written to the configuration file.
> |How can I ensure that the content has been written before executing next
> |line of code (the restart in this case)?
> |

I'm not sure, but maybe the fact you're not closing the file after writing has 
something to do with that. Try replacing the last line of update_configuration 
with:

File.open(APP_CONFIG_FILE, 'w'){|f| f.write string}

When given a block, File.open closes the file after calling the block, which 
should ensure that everything you wrote to file should have actually been 
written.

I hope this helps

Stefano