Error message in the console when using batch

Im using batch, where we call the myFUN 30 times (this function procces an image)

for k=1:30
    job(nn)=batch(@myFUN,1,{matfiles,k,Parameters,base_folder,saveflag,Plot_Figures},'CaptureDiary',true);
    
end

In that function I have an error message that tells me that this image could not be processed for some reason

fprintf(fileID,'%s Number of initial sources=0, unprocessed roi\n',Sample.TagName); 

How can I make that error message appear in the console when I am using batch?

[Raymond Norris]

@Sandra Martinez all good answers here.

Just to clarify, is the "error message" you're talking about the fprintf statement you're showing? That is, you want the fprintf statement to be displayed in your MATLAB console (as a pseudo error)?

Or was the call to fprintf erroring out (perhaps Sample is undefined) and you want to display the MATLAB error?

[Sandra Martinez]

Thanks for the answers. My conclusion after reading the answers is that you cannot get a message to appear in the middle of the process when using Batch. ValueStore is not avilable at MAtlab2021.

Therefore I chose to save as a text (as Walter suggested) that is part of the job object. At the end of the process Im able to know if there was any error.

Answer 1

[Walter Roberson]

fetchOutputs() in a try/catch environment. It will succeed if there was no error, and will throw an error if there was an error encountered. Inside the catch block, check the Tasks.Error property of the job; it should be error information.

https://www.mathworks.com/help/parallel-computing/parallel.job.fetchoutputs.html

Tip

To see if any of the tasks on the job j failed after encountering an error, check if j.Tasks.Error is empty. If the returned array is empty, none of the tasks on the job j encountered any errors.

If some tasks completed successfully, you can use the OutputArguments property of a task to access the output arguments of that task directly.

[Sandra Martinez]

Hi Walter,

I understand that this would give me the information once the process is finished, if I access that value. What I would like is to print on the screen an error message written by me, which notifies the user that this image will not be processed (explaining the reasons) and will move on to the next one.

Maybe the only way to do it is for the error message to be an output of my function. But I would like it to appear on the console.

[Walter Roberson]

In your catch block detect the particular error() that you emit when the image is not readable. Display the relevant error message. Otherwise display some other error message.

[Walter Roberson]

The alternative is to emit the error message as text, and to pick it up by examining the Diary property of the job. However, this will pick up all text emitted. (You could in theory post-process the text picked up from Diary)

There is no "display in console" type of function.

As an alternative, you might consider using parfeval() instead of batch(). Using parfeval() would allow you to construct parallel.pool.DataQueue or parallel.pool.PollableDataQueue objects, which could then be used to send text back to the client .

[Sandra Martinez]

Thank you Walter for the suggestion of saving the error message as text,

Answer 2

[Edric Ellis]

As mentioned by @Walter Roberson you can use the Diary property of the job to view this information. Another (more intrusive) option if you wish is to use ValueStore to record the messages. There's an example on that documentation page showing how a batch job can record progress into the ValueStore, and also how the client can register a callback function that gets called automatically whenever an entry is added to the ValueStore.

[Sandra Martinez]

Thanks Edric, ValueStore is not avilable at MAtlab2021.

Unfortunately, I am Argentina and at the moment (as I believe you know something about our president's decisions) they have canceled all previously awarded research projects. So we can't buy new versions of sfotwears.