Parfeval with backgorund pool cannot read XML file

Inside the parfeval I am using xml_read with an XML path. This function works properly with a parpool object but not with a backgorundPool

[Animesh]

Can you attach a code snippet for better understanding of the problem?

[Walter Roberson]

Is xml_read from https://www.mathworks.com/matlabcentral/fileexchange/12907-xml_io_tools

Answer 1

[Madheswaran]

Hi Michaela,

I am assuming you are using MATLAB built-in ‘xmlread’ (https://mathworks.com/help/matlab/ref/xmlread.html).

As it is seen from the documentation, ‘backgroundPool’ is a thread based parallel pool.

https://mathworks.com/help/matlab/ref/parallel.backgroundpool.html

As you might have seen in the error message, ‘xmlread’ is unfortunately not supported in thread-based workers because of the use of ‘javaMethod’ function in its implementation.

You can view the errors of scheduled function, using ‘parallel.Future’ object, like mentioned below.

>> f = parfeval(backgroundPool, @xmlread, 1, xmlFilePath);
>> f.Error

ans = 

ParallelException with properties:

identifier: 'parallel:threadpool:DisallowedBuiltin'
message: 'Use of function javaMethod is not supported on a thread-based worker. Use alternatives supported on the background pool.'
cause: {}
remotecause: {[1×1 MException]}
stack: [2×1 struct]
Correction: []

Please note that if a function supports the thread based environment, it would be explicitly mentioned in the Extended Capabilities section of the documentation. Since nothing is mentioned in the documentation page of ‘xmlread’, it is implied that the function is not supported in the thread-based environment.

Hope this helps!