hscale=auto;
compress=yes;
angle = 5;
a, b, c;

mark top1;
a->b: Message 1;
b->c: Message 2;
mark src2 [centerline=source];
mark dst2 [centerline=destination];
box c--c: Processing;
mark center_box [centerline=yes];
vspace 5;
c->c: Msg 3 [side=left];
mark src3 [centerline=source];
b<-c: Message 4;
mark dst3 [offset=+5];
parallel symbol arc at b 
    [fill.color=aqua, draw_time=after_default];
text at b+ +6: exit condition;
a<-b: Message 5;

vertical pointer dst2>>src3:cause 
     [line.radius=5, arrow.endType=empty];
vertical pointer dst3>src2 at b-:repeat 
     [line.radius=5, arrow.endType=empty];
vertical range top1->center_box at c+:First part;

