From: Robert Klemme <shortcutter@...>
Date: 2009-12-10T22:34:10+09:00
Subject: Re: How do I ensure that File.write finished?

2009/12/10 Stefano Crocco <stefano.crocco@alice.it>:
> 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.

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


-- 
remember.guy do |as, often| as.you_can - without end
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