class_docstr: Scheduler extension for spans support
class_docstr_tok: ["Scheduler","extension","for","spans","support"]
docstr: Return a synthetic Span which is the sum of all spans
docstr_tok: ["Return","a","synthetic","Span","which","is","the","sum","of","all","spans"]
code: def merge_all(self) -> Span:
      """Return a synthetic Span which is the sum of all spans"""
      return Span.merge(*self.root_spans)
  
imports: from __future__ import annotations
  import uuid
  import weakref
  from collections import defaultdict
  from collections.abc import Hashable, Iterable, Iterator
  from contextlib import contextmanager
  from itertools import islice
  from typing import TYPE_CHECKING, Any
  import dask.config
  from dask.typing import Key
  from distributed.collections import sum_mappings
  from distributed.itertools import ffill
  from distributed.metrics import time
label_desc: Use image node_id 6 for calling the SpansSchedulerExtension obj's underlying member method code with example usage: obj.merge_all() and returns: Span