From: SunRaySon <sunrayson@...>
Date: 2007-02-18T16:44:36+09:00
Subject: Re: Does it make sense to flush and close?

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I think the following If you set "file.sync = true" it would do the same and
you don't have to write "file.flush" every time you use a "file.write".

On 2/17/07, Garance A Drosehn <drosihn@gmail.com> wrote:
>
> On 2/15/07, Mischa Berger <mischa78@xs4all.nl> wrote:
> >
> > Hi everyone,
> >
> > Consider the following code:
> >
> > # Save the file on the file system
> > File.open(self.temp_path, 'wb') do |f|
> >   while buff = myfile_field.read(4096)
> >     f.write(buff)
> >     f.flush
> >   end
> > end
> >
> > Is there any benefit in flushing in the code above?
> >
> > I'm trying to grasp what exactly happens and if there are any benefits
> > or drawbacks.
>
>
> In most situations, the extra calls flush are nothing but a drawback, in
> that they are a performance penalty.  That's why the operating system
> caches up the writes in the first place -- to speed things up.
>
> But in some situations, it might considered a benefit.  For instance if
> you're concerned that the destination might run out of disk space, then
> it might be to your advantage to *immediately* find out when that
> happens.  Without those extra calls to flush, if you *do* run out of disk
> space, then the code has no way of knowing how much of the data
> actually made it to the disk.  Consider, for instance, if you were writing
> a huge file to multiple USB-key devices.  If code knew exactly when the
> first one was full, then it could flip to a new floppy and continue
> writing.
> (there are other solutions to that specific example, but it *could* be
> worthwhile to simply write the data and catch the error when the output
> device is full).
>
> The extra calls to flush could also be a benefit if some other process
> is monitoring the destination file, just to keep track of how far along
> the first process is.  Someone doing a 'tail -f', for instance.
>
> Most of the time it is not worth it to do the calls to flush, especially
> if you're in a tight loop like the one in your example, but in some
> special circumstances it can be worth the performance penalty.
>
> --
> Garance Alistair Drosehn     =             drosihn@gmail.com
> Senior Systems Programmer
> Rensselaer Polytechnic Institute;             Troy, NY;  USA
>

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