This looks like a good candidate for the JointJS Petri Net shapes plugin (joint.shapes.pn.js). See a demo at: http://jointjs.com/demos/pn. You can download the plugin from here: http://jointjs.com/download. Then use:
var place = new joint.shapes.pn.Place({
position: { x: 140, y: 50 },
tokens: 1
});