accessing global vars in functions in parfor loops

Hi, I am trying to use global variables to control function behavior to see which option works best (so using globals is only a temporary solution and the global vars will not be changed during run-time)

here's the code:

 function parfor_globals
    global TESTVAR_A
    TESTVAR_A = 3;

    parfor i = 1:2
     disp(TESTVAR_A)
     parfor_globals__sub();
    end
 end

 function parfor_globals__sub()
    global TESTVAR_A;

    if isempty(TESTVAR_A)
        disp('empty')
    else
        disp('not empty')
    end
 end

the problem is that in parfor_globals__sub() the 'TESTVAR_A' does not contain the value set at the beginning of the code, as you can see from the output:

 >> parfor_globals
     3
 empty
     3
 empty

I am aware that within parfor-loops, global vars cannot be changed across workers. This is not an issue for me as I do not intend to change the value during runtime.

Is there any solution available for me?

-- Jakob (tested with R2016b and R2018b)

[Adam]

I'd be surprised if global variables worked at all in parfor loops, to be honest! They would cause no end of potential chaos. The fact that you only use them in a certain way doesn't really matter because they have the capability to be misused across workers and the main thread, which I would have thought would simply make them unusable in parallel code.

I would not think you would ever want to either, even if it were possible because the potential for bugs would be way higher than just passing data explicitly.

[thengineer]

I know I'm probably asking too much here. Guess I'll have to do this without parfor then. Actually I was hoping for some special construct like 'parallel.pool.Constant' that would make the data just available, but well...

Answer 1

[Steven Lord]

See Edric's answer to this question.