From: Daniel N <has.sox@...>
Date: 2006-08-03T23:39:36+09:00
Subject: Re: How to tell when IO::popen is finished?

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On 8/4/06, ara.t.howard@noaa.gov <ara.t.howard@noaa.gov> wrote:
>
> On Thu, 3 Aug 2006, Daniel N wrote:
>
> > Hi,
> >
> > I've just installed and had some success with the gnuplot library.
> >
> > I'm saving the output to a png file (plot.terminal "png") and this all
> works
> > well, but when I try to use the file it isn't finished writing it yet
> and I
> > get an exception.
> >
> > I've used
> >
> > Gnuplot.open(  ) do |gp|
> > ....
> > end
> >
> > while(!File.exists?("/test2.png") || File.zero?("/test2.png") )
> > sleep 0.1
> > end
> >
> > In an attempt to wait until the file is written before I try to do
> anything
> > with it, but this seems a bit too hackish.
> >
> > Can I capture the Gnuplot.open into a variable and check it?  The last
> > statement in the Gnuplot.open is a call to
> > IO::popen( cmd, "w") { |io| yield io }
> >
> > but if I test the class of what is returned it is
> > Gnuplot::Plot
> >
> > not anything to do with IO
> >
> > Is there a way that I can test the IO::popen to tell when it's finished?
>
>
>
> can you show the code?  that pipe will be automatically closed once the
> yield
> has returned.
>
> -a
> --
> we can never obtain peace in the outer world until we make peace with
> ourselves.
> - h.h. the 14th dali lama
>
> I'm using Gnuplot the open method is

  def Gnuplot.open( persist=true )
    cmd = Gnuplot.gnuplot( persist ) or raise 'gnuplot not found'
    IO::popen( cmd, "w") { |io| yield io }
  end


Then my method

def make_chart( )
Gnuplot.open() do |gp|
  Gnuplot::Plot.new(gp) do |plot|
    plot.terminal  "png"
    plot.output  "/test2.png"

    plot.title  "Array Plot Example"
    plot.ylabel "x"
    plot.xlabel "x^2"

    x = (0..200).collect { |v| v.to_f }
    y = x.collect { |v| v ** 2 }

    plot.data << Gnuplot::DataSet.new( [x, y] ) do |ds|
      ds.with = "lines"
      ds.notitle
      ds.linewidth = 6

    end
  end

end
end

make_chart

while(!File.exists?("/test2.png") || File.zero?("/test2.png") )
sleep 0.1
end

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