[Swift-user] moving files during runtime

[Michael Wilde]

Hi Khushbu,

> ...In the shell script for the app, I actually do a
> move of the file that was produced in my previous iteration to my
> current iteration. However when Swift runs, I just see lot of links.
> Basically file in iteration 4 has a symbolic link to file in iteration
> 3, 3 to 2 and so on. This works ok for couple of iterations, but after
> a while system seem to fail with message “ unable to follow links”.
> Since we are trying to run over 100’s of iterations, I would like to
> know if there is a way to tell swift to just copy or move the file
> than to create symbolic links.

I'm assuming that since each iteration of this process depends on the prior iteration, they all run serially.

If thats the case, you can use either a foreach loop or an iterate statement, and just let Swift do all the copying in a natural way:

type file;
file f[];
file first<"initial.data">;

f[0] = first;
foreach i in [1:100] {
  f[i] = myApp(f[i-1]);
}

(I didnt test this, but something similar should work for your application)

Whats happening in your current case is that your app script is "breaking the rules" by trying to preserve data objects from the Swift pre-job "sandbox" directory (as explained in User Guide sections 5.1 and 5.2:
  http://www.ci.uchicago.edu/swift/guides/trunk/userguide/userguide.html#_mapping_of_app_semantics_into_unix_process_execution_semantics

and 

http://www.ci.uchicago.edu/swift/guides/trunk/userguide/userguide.html#_how_swift_implements_the_site_execution_model

I could explain a few ways to make your current approach work, but I think the approach above is much more natural and also safer and less brittle - less vulnerable to breakage if we change the Swift runtime model. (For example, you could do the cp in your app script rather than an mv, or you could Swift to do cp's rather than links by specifying the "scratch" tag in your sites.xml entry. But I didn't tell you either of these things because they are not good practice ;)

- Mike