[racket] Curious error messages

From: Sam Tobin-Hochstadt (samth at cs.indiana.edu)
Date: Thu Dec 4 11:34:46 EST 2014

On Thu Dec 04 2014 at 9:36:08 AM Robby Findler <robby at eecs.northwestern.edu>

> On Wed, Dec 3, 2014 at 10:30 PM, Prabhakar Ragde <plragde at uwaterloo.ca>
> wrote:
> > I'm currently using Racket 6.1. For some time now, when editing Scribble
> > files in DrRacket, I've been getting "file has changed on disk" messages
> > when trying to save or render - not consistently, just every so often.
> These
> > are files I am not editing in anything other than DrRacket. I click
> "ignore"
> > and everything works fine, but it is annoying.
> This is definitely a bug somewhere and I've had not a lot of luck
> tracking it down.

> I guess that what's happening is something is actually changing the
> file on the disk (perhaps DrRacket itself) and it shouldn't.
> So if you can figure out what feature of DrRacket is making this
> happen or verify that the file is actually not changing on the disk,
> either of those would be helpful.

Here's a thought on tracking it down:

* Run DrRacket under strace, looking at the calls to `open()` and `write()`.

* Add to relevant places in DrRacket something like this:
   (access string F_OK)

where `access` is an FFI call to the C library access function, and F_OK is
the appropriate constant. Then those messages will appear in the strace
output, so you can see what DrRacket is doing right around the time it
opens or writes to the relevant file.

I got this trick from here:
https://people.gnome.org/~federico/news-2006-03.html#09 where it's used to
plot timelines (also cool) but it might be useful for debugging in this

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