Is it possible to load and modify the same .mat file in two instances of matlab?

I am attempting to parallelize my Matlab code without using the parallel computing toolbox, since parfor cannot be compiled using mcc, as far as I know.

Would I run into any issues if I ran the following code simultaneously on two or more Matlab instances?

function simulate(input_data,index,foo,bar)
   load(foo);
   load(bar);
   tempdata = subfunction(input_data(index,:));
   if all(tempdata(:,2) <10)
      foo_data= vertcat(foo_data,[tempdata,input_data(index,end)]);
   else
      bar_data = vertcat(bar_data,[tempdata,input_data(index,end)]);
   end
   save(foo,'foo_data');
   save(bar,'bar_data');
 end

(where subfunction is another .m file in the current working directory)

Each instance of matlab would have a different index input.

Thanks in advance!

[José-Luis]

I think that would depend on your OS more than on Matlab.

[Margaret]

I'm planning to compile my code using mcc, and run my code in parallel job tasks. I'm still trying to figure out how the m-code would handle the i/o. So, my OS would be Linux?

Answer 1

[Bruno Pop-Stefanov]

I don't know if your code would work but trying to access a single resource from two different processes sounds like a bad idea. I can't speak for MATLAB, but in general, for safety reasons, when a process opens a file (a resource), the file is locked until the process releases it. Assuming that you could access your data in two instances of MATLAB, you don't know how and in which order each unit of data is accessed at a lower, byte level. You could end up with deleted segments of your data, or with duplicated data. If you really want to run two instances of MATLAB, I would recommend to split your data in two and give one side each.

[Margaret]

Thanks a lot! I didn't think about that.

On that note, would you know if its possible to concatenate multiple .mat files without having to load them all first?

[Bruno Pop-Stefanov]

You can append new variables to a .mat file that already exists using

save(filename,variables,'-append')

but I don't think you can concatenate matrices from two different .mat files without loading the data and doing the concatenation in your code. Someone should double check me on this but that's what has been said in a previous question: http://www.mathworks.com/matlabcentral/answers/63010-concatenating-mat-files-into-a-single-file

[Margaret]

Thanks again Bruno! You've been a great help.

[Walter Roberson]

I do seem to recall that the parts of a .mat file can be concatenated, but possibly not the header as well... that part I do not recall. Also if a variable occurs in multiple places, the last version of it would hold; they would not be concatenated together.