Why do I get Library was not found Error while using external library in parpool?

Hi,

I would like to call external library functions in parallel.

I am using the code below.

clear all
if ~libisloaded('shrlibsample')
   addpath(fullfile(matlabroot,'extern','examples','shrlib'))
   loadlibrary('shrlibsample')
end

struct.p1 = 4; struct.p2 = 7.3; struct.p3 = -290;

parpool('AttachedFiles',{'shrlibsample.mexw64','shrlibsample.h','shrlibsample.c', 'shrhelp.h'}); 

parfor i=1:4
[res,st] = calllib('shrlibsample','addStructByRef',struct);
end

unloadlibrary shrlibsample

But, when running this code, I am getting error- ERROR: Library was not found

How to fix this?

Answer 1

[MathWorks Support Team]

This error means that the library you are trying to call is not available in parallel workers.

Although, you have added required files to the parallel pool using 'AttachedFiles', the reason why this error is thrown is that those libraries are not loaded in parallel workers.

In order to have libraries available in those workers, please load libraries in each worker.

So, to fix this issue, please use  loadlibrary  to load libraries in each worker.

clear all;
addpath(fullfile(matlabroot,'extern','examples','shrlib'))
struct.p1 = 4; struct.p2 = 7.3; struct.p3 = -290;

parpool('AttachedFiles',{'shrlibsample.mexw64','shrlibsample.h','shrlibsample.c', 'shrhelp.h'}); 

parfor i=1:4
    if ~libisloaded('shrlibsample')
        loadlibrary('shrlibsample')
    end
[res,st] = calllib('shrlibsample','addStructByRef',struct);
end

unloadlibrary shrlibsample