Why do I get error when I use loadlibrary inside an SPMD block in MATLAB 7.12 ( R2011a)?

I am using LOADLIBRARY to load a library on SPMD workers.

matlabpool open local 4 

spmd 

              loadlibrary('testDLL2') 

end

When I execute this code on my MATLAB I receive the following error:

 Lab 1: 

   Warning: File not found or permission denied 

   > In loadlibrary>deltempfiles at 636 

     In loadlibrary at 436 

     In remoteBlockExecution at 47 

 ??? Error using ==> spmd_feval at 8 

 Error detected on lab(s) 1 

 Caused by: 

     Failed to preprocess the input file. 

      Output from preprocessor is:The process cannot access the file because it is being used by 

      another process. 

     Error stack: 

     loadlibrary.m at 441

Answer 1

[MathWorks Support Team]

This is a limitation of SPMD and LOADLIBRARY when used together on a shared file system.

When LOADLIBRARY is executed it runs preprocessor to parse the library header file. During the pre-processor execution LOADLIBRARY generates temporary files, which are destroyed after LOADLIBRARY operation completes.

The LOADLIBRARY always generates files with the same filename when loading a specific library.

When LOADLIBRARY is executed inside of SPMD on a MATLAB pool of N workers, there are N instances of LOADLIBRARY executing concurrently. These instances create a race condition for generating and deleting the temporary files. This race condition leads the error in question.

To work around this issue, the loading of libraries has to be serialized on the workers using the LABBARRIER command as shown in the example below:

spmd 

      for i = 1:numlabs 

          if i == labindex 

              loadlibrary('testDLL2') 

          end 

          labBarrier 

      end 

end 

spmd 

      calllib('testDLL2','addTwoNumbers',5,6) 

end