Trace_stat_summary.Span_folderAccumulator for the span field of t.
type acc = {per_span : span_acc Span.Map.t;seen_atoms_durations_in_block : float list Span.Map.t;timestamp_before : float;}val create :
float ->
int ->
([< `Add of int32
| `Checkout of int32
| `Commit of Def.commit
| `Copy of int32
| `Find of int32
| `Mem of int32
| `Mem_tree of int32
| `Remove of int32 ],
acc,
Span.Val.t Span.Map.t)
Utils.Parallel_folders.folder