Wait until another instance of MATLAB is finished executing

I am running a secondary MATLAB instance from within my primary MATLAB window:

% in the primary MATLAB instance
eval(['!matlab -nodesktop -r  execute(' input ')&']) % this runs execute.m in the secondary MATLAB instance

where execute(input) is a function that calls for a variable named input.

While the execution time of the secondary instance (i.e. execute.m) could be quite long, I would like the primary instance to wait until this execution is finished.

Note: I know I can fetch the PID and number of different MATLAB consoles (instances) running in the system at each moment via

[status,result] = system('tasklist /FI "imagename eq matlab.exe" ')

and wait until the number of instances/PID is equivalent to what it was before opening any secondary instances, but is there any better way to address this issue?