I have a piece of code which looks like this:


    <code here>


so basically a Table which I parallelize. Each element of this parallelized table being itself a Table which I want to monitor.

I receive this error message:

FrontEndObject::notavail: A front end is not available; certain operations require a front end.

This error originates from the Monitor[]. I suspect that because my first Table is parallelized, somehow the dynamic cell into which Monitor[] will write to is not connected to any Front End or something...

How would I solve this issue?

  • $\begingroup$ What happened when you started a front end? $\endgroup$ Commented Jul 3, 2014 at 10:49
  • $\begingroup$ from help, it says: generates a monitor cell that shows the continually updated current value...In a notebook, the monitor cell normally appears directly after the cell in which Monitor[expr,mon] is evaluated so clearly Monitor requires a frontend. Can't be used in script/batch. $\endgroup$
    – Nasser
    Commented Jul 3, 2014 at 11:28
  • $\begingroup$ @OleksandrR. Can you start a front end for each parallel kernel and use Monitor? $\endgroup$
    – acl
    Commented Jul 3, 2014 at 11:46
  • $\begingroup$ In case it is not clear, I have a Front End running for my master kernel. How would I start a Front End for each child kernels ? $\endgroup$
    – coussin
    Commented Jul 3, 2014 at 13:22
  • $\begingroup$ Or rather, each child kernels should use the Front End used by my master kernel... $\endgroup$
    – coussin
    Commented Jul 3, 2014 at 13:33

1 Answer 1


As pointed in the comments by @Nasser, Monitor needs a front end, so it should be outside ParallelTable. It also needs a variable that acts as a "counter" and that is shared among all the kernels participating in the calculation, for that you can use SetSharedVariable. Therefore, a solution to your question would be:

iter = 0
   iter += 1;
   , {1000}
   ], ProgressIndicator[iter, {0, 1000}]];

Its is true that its questionable if the cost of keeping the iteration counter updated makes parallelism worthwhile, as pointed by @mfvonh. This should be evaluated case by case, and its not impossible that its advantageous. I have found this trick useful at least once.


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