code: @Reference(name = BASE_INSTANCE,
                 service = ContextService.class,
                 cardinality = ReferenceCardinality.OPTIONAL,
                 policy = ReferencePolicy.DYNAMIC,
                 policyOption = ReferencePolicyOption.GREEDY,
                 target = "(id=unbound)")
      protected void setBaseInstance(ServiceReference<ContextService> ref) {
          lock.writeLock().lock();
          try {
              threadContextConfigurations = null;
          } finally {
              lock.writeLock().unlock();
          }
      }
docs: Declarative Services method for setting the service reference to the base contextService instance.
  
  @param ref reference to the service