Issue using a parfor loop to control two instruments at the same time

Hi all,

I am trying to control two instruments, 1) to tell a laser to sweep a range of wavelengths, 2) signal and read data from a NI data aquisition unit. As I am trying to record the signal as the laser sweeps I need both to run at the same time hence the parfor. I have tested the code individually and they are working my issue is getting them to work in a parfor loop. I am new to using libaries and setting up parpools so I might be doing something stupid (fingercrossed).

When I run the code below, i get the error ---> Library was not found

Below is the relevent code.

function output = main4
main1; %<------ Connects to laser and starts connection etc (WORKS FINE)
dq = MCTsetup %<----- Connects to data logger (WORKS FINE)
readout = 1;

delete(gcp('nocreate'));
parpool('AttachedFiles',{'MIRcatSDK'});

parfor i=1:2
    if i == 1
        pause(0.1);
        runlasersweep; %<------ begins laser sweep scan (Code below)
    end
    if i == 2
        readout = read(dq, seconds(5));  %<------ begins the data logger
    end
end

main3; %<---- turn off laser emission (WORKS FINE)
output = readout;
end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%runlasersweep - code
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

function runlasersweep
load('MIRcatSDKconstants.mat');
fprintf('========================================================\n');
ret = calllib('MIRcatSDK','MIRcatSDK_StartSweepScan', ...
    single(1200), single(1900), single(500), ... 
    MIRcatSDK_UNITS_CM1, uint16(1), true, uint8(1));
if MIRcatSDK_RET_SUCCESS == ret
    fprintf(' Successful\n' );
else
    % If the operation fails, unload the library and raise an error.
    fprintf(' Failure\n' );
    calllib('MIRcatSDK','MIRcatSDK_DeInitialize');
    unloadlibrary MIRcatSDK;
    error('Error! Code: %d', ret);
end
isScanInProgress = true;
isScanInProgressPtr = libpointer('bool', isScanInProgress);
isScanActive = false;
isScanActivePtr = libpointer('bool', isScanActive);
isScanPaused = false;
isScanPausedPtr = libpointer('bool', isScanPaused);
curScanNum = uint16(0);
curScanNumPtr = libpointer('uint16Ptr', curScanNum);
curScanPercent = uint16(0);
curScanPercentPtr = libpointer ('uint16Ptr', curScanPercent);
curWW = single(0);
curWWPtr = libpointer('singlePtr', curWW);
isTECinProgress = false;
isTECinProgressPtr = libpointer('bool', isTECinProgress);
isMotionInProgress = false;
isMotionInProgressPtr = libpointer('bool', isMotionInProgress);
units = uint8(0);
unitsPtr = libpointer('uint8Ptr', units);
fprintf('========================================================\n');
fprintf('Test: Get Scan Status\n');
while isScanInProgress
    calllib('MIRcatSDK','MIRcatSDK_GetScanStatus', ...
        isScanInProgressPtr, isScanActivePtr, isScanPausedPtr, ...
        curScanNumPtr, curScanPercentPtr, curWWPtr, unitsPtr, ...
        isTECinProgressPtr, isMotionInProgressPtr);
    isScanInProgress = isScanInProgressPtr.value;
    isScanActive = isScanActivePtr.value;
    isScanPaused = isScanPausedPtr.value;
    curScanNum = curScanNumPtr.value;
    curScanPercent = curScanPercentPtr.value;
    curWW = curWWPtr.value;
    units = unitsPtr.value;
    isTECinProgress = isTECinProgressPtr.value;
    isMotionInProgress = isMotionInProgressPtr.value;
    fprintf(['\tIsScanInProgress: %d \tIsScanActive: %d \tisScanPaused: %d', ...
        '\tcurScanNum: %d \tcurWW: %.3f \tunits: %u \tcurScanPercent: %.2f', ...
        '\tisTECinProgress: %d \tisMotionInProgress: %d\n'], ...
        isScanInProgress, isScanActive, isScanPaused, curScanNum, curWW, ...
        units, curScanPercent, isTECinProgress, isMotionInProgress);
    pause(0.3);
end
end

[Matt J]

Please show error messages in full.

Also, consider using parfeval rather than parfor.

Also, are you sure the two instrument units aren't supposed to be synchronized in some way? The Parallel Computing Toolbox will run parallel jobs asynchronously.

Answer 1

[Raymond Norris]

Hi @james ingham,

I see a couple of potential issues

main1; %<------ Connects to laser and starts connection etc (WORKS FINE)
dq = MCTsetup %<----- Connects to data logger (WORKS FINE)
readout = 1;

Your setup is happening on the client side, but you're actual compute is on the workers. Getting a "library not found" error could be because

• You've initialized on the client but the worker has no idea what you're talking about (the initialization didn't happen there)
• The client path might have the dll/library on its path, but the workers don't, so it can't find the library

So the assignment to dq might happen in the parallel code. Not sure about the call to main1.

delete(gcp('nocreate'));
parpool('AttachedFiles',{'MIRcatSDK'});

I wouldn't suggest deleting and restarting a parallel pool within your code. This is better left outside of the code at it can be costly to retstart everytime you run your code. If MATLAB needs a pool, it'll start one. If you want to tailor it (size, attached files), start it up before calling your code (only if needed).

parfor i=1:2
    if i == 1
        pause(0.1);
        runlasersweep; %<------ begins laser sweep scan (Code below)
    end
    if i == 2
        readout = read(dq, seconds(5));  %<------ begins the data logger
    end
end

Although you have a loop of two iterations, I think a spmd block would work better.

spmd
    if labindex==1
        pause(0.1)
        runlasersweep
    else
        readout = read(dq, seconds(5));
    end
end

As you've written it, readout is a temporary variable, not a sliced or reduction. Therefore, when you assign output below, you're really assigining it to the value 1 (the value before you entered the parfor), not what you assigned from calling read.

Secondly, as @Matt J points out, I think you need to synchronize the two workers. What happens if you read from the DAQ board before the laser starts? Is read a single shot? If not, what tells it to stop reading? With spmd, you'll be able to send message between the workers (i.e., when to start and stop).

main3; %<---- turn off laser emission (WORKS FINE)
output = readout;

Based on above, main3 might need to be done inside the parallel code.