If you run multiple instances of Arnold on a computer, they will all share a single license. Arnold licenses are per-computer, not per-CPU or per-core or per-user.

In the license file, the share= attribute (line 3) controls how the licenses are shared. Arnold uses share=h, which means all processes running on the same host (aka computer) will share the same license.

HOST localhost 0000DEADBEEF 5053
ISV solidangle
LICENSE solidangle arnold 400 permanent 1 share=h min_timeout=120
  start=17-oct-2012 issuer=JB customer=blair issued=17-oct-2012
  replace _ck=00d67b16fa sig="x2M232yijKbUFZ=Mx7MdfzVGiYqz5Vgk6ih1gUt
  vGn1IJyDxwv7FFDrynQwJ3N"