Re: "clear mex" in octave?

[Joris Mooij]

On Fri, Feb 20, 2009 at 11:57:01AM -0500, Ben Abbott wrote:
> On Friday, February 20, 2009, at 08:53AM, "Joris Mooij" <address@hidden> 
> wrote:
> >On Fri, Feb 20, 2009 at 07:34:32AM -0500, Ben Abbott wrote:
> >> On Feb 19, 2009, at 8:58 AM, Joris Mooij wrote:
> >>
> >>> Hi all,
> >>>
> >>> does anybody know why octave does not automatically reload a mex file
> >>> when I recompile it (using "mkoctfile --mex filename.cpp")? The only
> >>> way I get octave to use the new .mex file is to restart octave, which
> >>> is not very practical (in matlab, MEX files are reloaded  
> >>> automatically).
> >>> Even "clear mex" or "clear all" would not reload the mex files in
> >>> octave.
> >>>
> >>> Thanks for your help,
> >>> Joris
> >>
> >> Are you saying that when running Matlab, "clear mex" actually reloads  
> >> mex files?
> >>
> >> Are you sure?
> >>
> >> Ben
> >
> >Actually I have never tried "clear mex" in Matlab, because Matlab
> >automatically reloads mex files when they are recompiled... at
> >least when the Matlab command prompt is shown.
> 
> In my experience, Matlab does not load mex-files until they are needed (i.e. 
> run).
> 
> >So I am not sure whether "clear mex" actually reloads mex files in
> >Matlab. However, according to the Matlab documentation for 7.0.1
> >(R14SP1) [1], it should.
> 
> The link you provided says: "The command clear mex now clears MEX-functions, 
> but not M- and MEX- functions. Entering clear mex does not clear locked 
> functions or functions that are currently in use. It does however clear 
> breakpoints and persistent variables."
> 
> I may be wrong, but it does not appear to me that Matlab loads a mex file 
> (dll on windows) until it is needed.
> 
> >My actual question is about how to reload mex files in octave after
> >they have changed on disk.
> 
> You should only need to run them. However, the mex file will need to be in 
> your path.
> 
> If my understanding is wrong, I expect someone will correct me shortly.
> 
> Ben


Thank you for your assistance. I believe I have not made myself
sufficiently clear, though, so I will try to pose my question more
verbosely.

I believe that you are correct when you say that Matlab loads mex-files
when they are needed. 

Suppose I have some source mymexfcn.cpp and I have built it using
Matlab's mex compile script, which yields mymexfcn.mexglx.
Then I start Matlab and run mymexfcn:

>> mymexfcn;

Matlab will search for mymexfcn.mexglx in the path and execute it. 
A little while later, it finishes and I get my command prompt back:

>>

Now I change the source mymexfcn.cpp and recompile it, so I get a new
modified mymexfcn.megxlx. I switch back to the Matlab window and run
mymexfcn again:

>> mymexfcn;

Now Matlab runs the new, modified mymexfcn.mexglx: Matlab detects that
mymexfcn.mexglx has changed on disk compared with the version that it
has previously executed. That's nice.

My problem is simply that when I do the same in octave (using "mkoctfile
--mex mymexfcn.cpp" to build mymexfcn.mex), the second call of mymexfcn
actually runs the ORIGINAL version of mymexfcn.mex (i.e. the first
version of mymexfcn.mex that octave has executed during that session),
even though in the meantime the mymexfcn.mex file has changed.

In order to execute the _modified_ mymexfcn.mex in octave, I know of no
other possibility then to quit and restart octave. But that is not
really a practical workflow...


So my question is: is there an easier way to get octave to use the
modified mymexfcn.mex, which does not involve restarting octave?

It could also be that this is just a bug, although I don't know what
octave is supposed to do in this situation. The only relevant
passage in the octave manual that I found
(http://www.gnu.org/software/octave/doc/interpreter/Function-Files.html)
says:
"When Octave defines a function from a function file, it saves the full
name of the file it read and the time stamp on the file. If the time
stamp on the file changes, Octave may reload the file. When Octave is
running interactively, time stamp checking normally happens at most once
each time Octave prints the prompt."

First, it says "Octave [...] MAY reload the file", so it is not clear
whether it will actually do it. Second, it is not clear to me whether
this applies to MEX files as well (is a MEX file a function file?).
Finally, what should one do if octave actually doesn't do a reload? Even
using "clear mymexfcn; mymexfcn" doesn't seem to help...

I would be delighted if anybody could answer this question.

Kind regards,
Joris