Yes, from the command line.
Ctrl-C brings up a list of processes, you can choose the number of the process and kill it. 
If I do it two often it sometimes gets confused but it has got me out of trouble before. 
Russel


On 25 May 2015, at 2:45 pm, Chris Double chris.double@double.co.nz [self-interest] <self-interest@yahoogroups.com> wrote:

Is it possible to interrupt a UI action? I accidentally clicked
"implenters" on a slot named 'parent' and the UI froze for a long time
while it was computing. Can this be canceled in any way?

I also then clicked the 'expand' icon which took even longer and
eventually crashed, probably from an OOM.

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