Sharing C mex variables Between Client and parallel Workers

How can I use a structure variable defined in C mex file and assigned in Client before entering spmd workers, inside this parallel workers with the same values?

When a global structure variable values changes insided C mex function in matlab client then the same C mex function is executed from the spmd parallel workers; the values of the global structure variable is returned to zeros inside the parallel worker (I'm using mexMakeMemoryPersistent function).

How can I share the structure variable between Client and parallel Workers?

Answer 1

[Walter Roberson]

mexMakeMemoryPersistent is the equivalent of persistent and is not the equivalent of global .

If you need changes in one worker (or on the client) to affect all of the workers, then you need to do one of:

• program shared memory (operating system specific; Mac and Linux use POSIX standard shared memory, Windows does its own shared memory)
• matFile() to access a shared file (I am not really confident this will work reliably)
• memmapfile() https://www.mathworks.com/help/matlab/ref/memmapfile.html
• use dataqueues to send between client and workers, with the client acting as the switchyard to distribute any changes to all workers

[Amr Mohamed]

-Aren't file memmapfile(), and use dataqueues to send between client and workers for variables not in a C mex (defined inside matlab)? I need to do that inside the C mex file.

I don't think those solutions may help me; As I have a complex C structure variable which contains many variables and pointers inside a C mex file and I want to fill this strucure variable from matlab client to be used inside matlab parallel workers.

[Walter Roberson]

https://www.mathworks.com/help/matlab/matlab_external/call-matlab-functions-from-mex.html

I have a complex C structure variable which contains many variables and pointers

Classical workers are in different processes; pointers shared would be useless, unless the pointers were to shared memory that was mapped into a fixed address location inside the process.

There is a File Exchange contribution for Shared Memory for Mac and Linux (not Windows). Reports are that it worked until MATLAB changed the headers for variables when it changed representation of complex a couple of releases ago, so it might potentially be repairable for current versions.