How do I ensure that File.write finished?

Ruby
#1

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!

# 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
# Custom class
    def update_configuration(settings)
      string = settings.to_yaml
      File.new(APP_CONFIG_FILE, "w").write string
    end

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)?

#2

On Thursday 10 December 2009, Emil K. wrote:

|
|
|[code]
|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

#3

2009/12/10 Stefano C. [email protected]:

|configuration file is no good!
| end
|
|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.

That’s definitively the reason.

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.

[ADV]: see also
http://blog.rubybestpractices.com/posts/rklemme/001-Using_blocks_for_Robustness.html

Cheers

robert

#4 
 File.new(APP_CONFIG_FILE, "w").write string

This file is never closed, so if the process is exited without running
its finalizers for some reason, buffered data could be lost.

-r

#5

It seems that that did the job. Thank you very much :slight_smile: