If a CAPI window is busy and unresponsive you can use the break gesture
Meta+Ctrl+C
to regain control.
Note that this break gesture is specific to the window system your CAPI program is running in.
On GTK+ and Motif you can configure the break gesture by calling the function
set-interactive-break-gestures
.
CAPI User Guide (Unix version) - 30 Aug 2011