Starting a Background Instance of Matlab on Mac OS X

Question

In Windows you can use the following command in Matlab to start a new instance of MATLAB which will run in the background (ie you can keep executing commands in your first version of MATLAB).

system('matlab &')

An analogous call in OSX,

system([matlabroot '/bin/matlab &'])

however results in the display of the splash image, then nothing. If I take out the ampersand, the new instance opens as expected. Unfortunately, this won't work for me, I really need to be able to control the first instance of MATLAB while the second is running.

Does anyone know why this discrepancy between the operating systems exists? By the way, I'm using OSX 10.7, Windows 7 64 bit, and MATLAB R2012a on Mac and R2012b on PC.

As some background, I'm trying to write a generic tester for an interactive command line interface that uses the input() function extensively.

Edit: I should have mentioned that the command

/Applications/MATLAB_R2012a.app/bin/matlab &

works as expected from the OSX terminal. In other words, a new instance of MATLAB opens and new commands can be entered into the terminal. So this problem seems to be specific to the system() function in OSX matlab.

Also, I tried adding that command to a bash script and calling the script from matlab, but had the same problem that I did with putting the command into the system() function.

Thanks

Answer 1

This is a long shot, but it might be happening because when you invoke the new instance of Matlab from Matlab with the system() command on Unix or OS X, the matlab_helper process forks and runs a shell process to run the new application. If you omit the ampersand, the shell blocks and waits for the program to finish, and system() waits for it, so the first Matlab locks up. And (here's the speculation part) if you add the ampersand, Matlab launches in the background, and then the forked shell exits, which then causes the new Matlab process to exit because its parent process (the shell) has exited. (Windows doesn't have the same parent/child process relationships, process launch mechanism, or shells, which would explain the different behavior.)

You could try prefixing the command with nohup , which protects processes from getting killed by SIGHUP, which might be what's happening here to your second Matlab process.

system(['nohup ' matlabroot '/bin/matlab &'])

You could also try using the OS X open command to launch a new independent instance. Something like this. You may need to fiddle with the options and path, but -n should be what gives you a new instance. It should be pointing at /Applications/MATLAB_R2012a.app ; I'm assuming that's what matlabroot is returning on OS X.

system(['open -na ' matlabroot])

You could also try running it from the Java process-launching features from within Matlab instead of with system() . Runtime.exec() doesn't block like system() does, and there may be other quirks to system() , like the matlab_helper architecture. Try launching it with java.lang.Runtime from Matlab.

jrt = java.lang.Runtime.getRuntime();
newMatlabProcess = jrt.exec([matlabroot '/bin/matlab']);

You can try the other command line variants above using this mechanism too, and you may need to redirect stdout to /dev/null, since the new processes input and output are buffered in to that newMatlabProcess object.

Answer 2

You can use applescript to do this. I do something like this:

! osascript -e "tell application \"Terminal\" to do script \"cd `pwd`;matlab -nojvm -nosplash -r 'why'\""

This example opens a new Matlab instance, in the current directory, and runs the command "why". You can remove the "-nojvm" if you need java in your background Matlab process