Dual Parfor from different scripts

So I have a Launcher.m script which executes a function.m using parfor. The function.m also has its own parfor. Will this work?

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/parallel-computing/nested-parfor-loops-and-for-loops.html

it will be accepted but will execute the second one in serial order

[Rishi Balasubramanian]

That was quick, thank you.

[Rishi Balasubramanian]

Is there a way to run both the parfors. The function.m uses parfor within. That must be driven for values [1, 2, 3, 4, 4.2, 4.4, 4.6, 4.8] for which I use parfor?

[Walter Roberson]

The nested parfor will be executed in serial, in reverse order. It is not possible to initiate parallel constructs within parallel constructs and have the nested ones operate in parallel.

(Though I am not certain what would happen if you were to parfeval() or batch() within a parallel construct.)

[Walter Roberson]

Looks like parfeval() and parfor() cannot initiate parfeval() ...

p = parpool();

Starting parallel pool (parpool) using the 'Processes' profile ...
Connected to the parallel pool (number of workers: 2).

outer_results = parfevalOnAll(p, @test_outer, 0, p)

outer_results = 
 FevalOnAllFuture with properties: 

                   ID: 5
             Function: @test_outer
       CreateDateTime: 02-Feb-2023 02:33:51
        StartDateTime: 02-Feb-2023 02:33:51
      RunningDuration: 0 days 0h 0m 0s
                State: running
                Error: [1x2 cell]

celldisp(outer_results.Error)

 
ans{1} =
 
  ParallelException with properties:

     identifier: 'MATLAB:parallel:future:NoFevalOnWorkers'
        message: 'Workers cannot execute parfeval or parfevalOnAll.'
          cause: {}
    remotecause: {[1×1 MException]}
          stack: [2×1 struct]
     Correction: []

 
 
ans{2} =
 
  ParallelException with properties:

     identifier: 'MATLAB:parallel:future:NoFevalOnWorkers'
        message: 'Workers cannot execute parfeval or parfevalOnAll.'
          cause: {}
    remotecause: {[1×1 MException]}
          stack: [2×1 struct]
     Correction: []

 

parfor K = 1 : p.NumWorkers
    test_outer(p);
end

Analyzing and transferring files to the workers ...done.
outer about to start inner, ID = 67

Error using parallel.ProcessPool/parfevalOnAll
Workers cannot execute parfeval or parfevalOnAll.

Error in solution>test_outer (line 13)
inner_results = parfevalOnAll(p, @test_inner, 0, ID)

function test_outer(p)
   ID = randi(99);
   fprintf('outer about to start inner, ID = %d\n', ID);
   inner_results = parfevalOnAll(p, @test_inner, 0, ID)
   celldisp(inner_results.Error)
   fprintf('outer fininished inners, ID = %d\n', ID);
end

function test_inner(ID)
   subID = randi(99);
   fprintf('inner ID %d subid %d reporting!\n', ID, subID);
end