code: def all_known(cls, sources=None, prefixes=None):
          
  
          sources = sources or ("config", "jobs", "raw_subqueues")
  
          queues = set()
  
          if "config" in sources and not prefixes:
              # Some queues are explicitly declared in the config (including all root raw queues)
              cfg = context.get_current_config()
  
              queues_from_config = [
                  t.get("queue")
                  for t in (cfg.get("tasks") or {}).values()
                  if t.get("queue")
              ]
  
              queues_from_config += Queue.get_queues_config().keys()
  
              queues_from_config += [
                  t.get("retry_queue")
                  for t in Queue.get_queues_config().values()
                  if t.get("retry_queue")
              ]
  
              queues |= set(queues_from_config)
  
          if "jobs" in sources:
  
              # This will get all queues from mongodb, including those where we have only non-queued jobs
              for q in context.connections.mongodb_jobs.mrq_jobs.distinct("queue"):
                  if prefixes and not any(q.startswith(p) for p in prefixes):
                      continue
                  queues.add(q)
  
          if "raw_subqueues" in sources:
              for q in Queue.get_queues_config():
                  if prefixes and not any(q + "/" == p for p in prefixes):
                      continue
                  queue_obj = Queue(q)
                  if queue_obj.is_raw and queue_obj.has_subqueues:
                      # TODO: optimize this with a single SUNION on all keys
                      queues |= queue_obj.get_known_subqueues()
  
          return queues
docs: List all currently known queues