Execute functions and read input simultaneously in Matlab

I have an mp3 file which needs to go through different functions (blocks) in series. The input of each block is taken from the output of the previous block. Block C needs the longest time to process (eg. 10s). The problem is, instead of waiting the 10s, I wish to read another frame of mp3 while waiting the block C to finish its process. Any idea on the solution?

Answer 1

[Walter Roberson]

If you have the parallel computing toolbox then you can use spmd.

framesize = 4096;
P = parpool(4);
spmd 
  if labindex == 1

    end 
  end

spmd 
  if labindex == 1 
    afr = dsp.AudioFileReader(Filename, 'SamplesPerFrame', framesize);
    while ~isDone(afr) 
      frame = step(afr);
      labSend(frame, 2);
    end
    labSend([], 2)
    release(afr) 

    elseif labindex == 2
      while true
        frame = labReceive(1);
        if isempty(frame) 
          labSend([], 3)
          break
        end
        Bres = BlockB(frame);
        labSend(Bres, 3);
      end

    elseif labindex == 3
       while true
         Bres = labReceive(2);
         if isempty(Bres) 
           labSend([], 4)
           break
         end
         Cres = BlockC(Bres) ;
         labSend(Cres, 4) 
      end

    else
      while true 
        Cres = labReceive(3);
        if isempty(Cres) 
           break 
        end 
        Dres = BlockD(Cres) ;
      end
    end

[Star]

Thanks Walter. May I know why we need the first spmd loop?

    spmd 
       if labindex == 1
       end 
    end

[Walter Roberson]

I had the dsp initialization there but moved it and forgot to remove the step.

[Star]

Hi Walter,

My project goes like this.

labindex1 decode the first 1137 bits (i=0:1137),

labindex2 decode starting from bit #1393 (i=1393:2372)

and labindex3 decode starting from bit #2373 (i=2373:2687).

However, there is a function block in labindex3 which need to retrieve the information of i=0:64. How do I send (i=0:64) from labindex1 to labindex3?

Thank you.

[Walter Roberson]

labSend(DataToSend, 3)

And to receive it,

labReceive()

[Star]

Hi Walter, thanks for the reply.

How to receive a data array by using labReceive()? I have tried three methods but all of them causes an error.

Initialized data array: table_select(1:4,1:3) = uint8(0);

Method #1:

table_select(1:4,1:3) = labReceive(1);

Error:

Error using decoder_spmd_2g4>(spmd body) (line 594)
Error detected on worker 2.
Assignment has fewer non-singleton rhs dimensions than non-singleton subscripts

Method #2:

table_select = labReceive(1);

Error:

Error using decoder_spmd_2g4>(spmd body) (line 705)
Error detected on worker 2.
Attempted to access table_select(1,2); index out of bounds because size(table_select)=[4,1].

Method #3:

table_select(:) = labReceive(1);

Error:

Error using decoder_spmd_2g4>(spmd body) (line 594)
In an assignment  A(:) = B, the number of elements in A and B must be the same.

Thank you.

[Walter Roberson]

what is size() of the item you labSend() ?

[Star]

Hi Walter, this is part of my coding:

function [PCM, output] = mp3(song)

table_select(1:4,1:3) = uint8(0);

spmd
if labindex == 1
    while true
        row_index = 1;
        if ( blocksplit_flag(row_index))
            for region=1:2
                table_select(row_index,region) = uint8( reformbit (y(remd:remd+4))); 
            end
        else
            for region=1:3
                table_select(row_index,region) = uint8( reformbit (y(remd:remd+4)));
            end
           
            labSend(table_select(row_index,:), 2);
			
        end
		
else labindex == 2
    while true	
        row_index = 1;
            table_select(1:4,1:3) = labReceive(1);
            if (blocksplit_flag(row_index,1) == 1 && block_type(row_index) == 2)
                [a0 lin0 max0] = huffman(table_select(row_index,1));
		  [a1 lin1 max1] = huffman(table_select(row_index,2));                                    
				
	      else
		  [a0 lin0 max0] = huffman(table_select(row_index,1));
		  [a1 lin1 max1] = huffman(table_select(row_index,2));
		  [a2 lin2 max2] = huffman(table_select(row_index,3));
				
	      end
	end
end
end
end

Thank you.

[Walter Roberson]

you are sending a single row but receive into 4 rows. Are you wanting to copy the same one row to all four rows of the matrix ?

[Star]

Hi Walter, is your answer provided above involve a job scheduler?

[Walter Roberson]

No. Job scheduler is only needed if you are using the Distributed Computing Toolbox, which would be for running computing on a cluster. Job schedulers are not required for running only on the resources of the local computer.

[Star Rats]

Hi Walter, is your answer above considered as Task parallel (Embarrassingly Parallel) or Data parallel (Fine Grained Parallel) ?

Answer 2

[Star]

I want to send 4 rows and receive 4 rows. A more detailed coding is shown below:

function [PCM, output] = mp3(song)
table_select(1:4,1:3) = uint8(0);

spmd
	if labindex == 1
        while true
            row_index = 1;
                for granule = 1:2
                    for channel=1:2
                        if ( blocksplit_flag(row_index))
                            for region=1:2
                                table_select(row_index,region) = uint8( reformbit (y(remd:remd+4))); 
                            end	
                        else
                            for region=1:3
                                table_select(row_index,region) = uint8( reformbit (y(remd:remd+4)));
                            end
                        end
                        row_index = row_index + 1;		
                    end
                end
                labSend(table_select(row_index,:), 2);
        end	
      else labindex == 2
        while true		
            table_select(1:4,1:3) = labReceive(1);
			
                 row_index = 1;
                     for granule = 1:2
			    for channel=1:2
				if (blocksplit_flag(row_index,1) == 1 && block_type(row_index) == 2)
					[a0 lin0 max0] = huffman(table_select(row_index,1));
					[a1 lin1 max1] = huffman(table_select(row_index,2));                                    
				else
					[a0 lin0 max0] = huffman(table_select(row_index,1));
					[a1 lin1 max1] = huffman(table_select(row_index,2));
					[a2 lin2 max2] = huffman(table_select(row_index,3));
				
				end
				row_index = row_index + 1;	
			    end
		        end
	    end
       end
end

[Walter Roberson]

What you labSend is indexed by row so you only send one row .

[Star]

Thanks Walter.

I have face some problem in labSend. The coding is as below:

function [PCM, output] = mp3(song)
table_select(1:4,1:3) = uint8(0);
spmd
	if labindex == 1
	   while true
		%Var b went through several equation
		labSend (b1,2);
			
		row_index = 1;
		for granule = 1:2
		   labSend (granule,2);
		   for channel=1:2
		        labSend (channel,2);
			if ( blocksplit_flag(row_index))
					
			   %Went through several equation
			   for region=1:2
				table_select(row_index,region) = uint8( reformbit (y(remd:remd+4))); 
				labSend(table_select(row_index,:), 2);
			   end	
			else
			   %Went through several equation
			   for region=1:3
			        table_select(row_index,region) = uint8( reformbit (y(remd:remd+4)));
				labSend(table_select(row_index,:), 2);
				remd = remd + 3;
		           end
			end
			row_index = row_index + 1;		
		   end %End of channel
		end %End of granule
			
		   if ( maindata == 0)
			b2 = remd;
			labSend(b2,2);
			labSend(remd,2);	
		   else
			b2 = current_bit - (maindata*8);
			labSend(b2,2);
			labSend(remd,2);
			end
		end
			
	else labindex == 2
		while true	
			b1 = labReceive(1);
			b2 = labReceive(1);
			remd = labReceive(1);
			
			if isempty(frameNumber)
			   labSend(3, []);
			break
			end
			
			row_index = 1;
			for granule = 1:2
				for channel=1:2
					table_select(1:4,1:3) = labReceive(1);
					if (blocksplit_flag(row_index,1) == 1 && block_type(row_index) == 2)
						[a0 lin0 max0] = huffman(table_select(row_index,1));
						[a1 lin1 max1] = huffman(table_select(row_index,2));                                    
					else
						[a0 lin0 max0] = huffman(table_select(row_index,1));
						[a1 lin1 max1] = huffman(table_select(row_index,2));
						[a2 lin2 max2] = huffman(table_select(row_index,3));
					end
					row_index = row_index + 1;	
				end %End of channel
			end %End of granule
		end
	end
end

My Questions are:

1. I manage to labReceive b1 but not b2 and remd. The value for b2 and remd is always zero.

Is it because of the for loop that cause b2 and remd cannot be received?

2. labindex 2 always come first before labindex 1.

I think it is because of the preset value of granule and channel.

How to make labindex 1 run first so that the data needed can be received by labindex 2?

I have tried to run the coding below but it could not work.

Again, the value of granule and channel are always zero.

	row_index = labReceive(1);
	row_index = row_index + 0; 
								
	granule = labReceive(1);
	for ( 0 < granule < 3)
		disp(sprintf('This is granule %d', granule));
							
		channel = labReceive(1);
		for ( 0 < channel < 3)
		disp(sprintf('This is channel %d', channel));	
		%Content
		
		end
	end

Thank you.