Computed the background sources only once
Computed the background sources only once


Former-commit-id: c0c3e15b93e8da3c08e8b02ae77d053257ba8632 [formerly f3a5946985dbebfdeed9246a02a0616c296978c9] [formerly f3a5946985dbebfdeed9246a02a0616c296978c9 [formerly bdf47f10121dbbb49b5970217b36d504e7ac2aa3]]
Former-commit-id: a9b69d4bec7de97dcbf902d0a62ae720633187cc
Former-commit-id: 867376a754a8ce411d12b87052c86bc93a855230
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine