class_docstr: Singleton metaclass for :class:`fiftyone.core.frame.Frame`.
  
  This metaclass maintains a weakref dictionary of all in-memory
  :class:`fiftyone.core.frame.Frame` instances keyed by
  ``[collection name][sample ID][frame number]``.
docstr: Syncs the backing documents for all in-memory frames according to
  the following rules:
  
  -   Frames attached to samples whose IDs are in ``sample_ids`` are
      reloaded
  -   Frames attached to samples whose IDs are not in ``sample_ids`` are
      reset
docstr_tok: ["Syncs","the","backing","documents","for","all","in-memory","frames","according","to","the","following","rules",":","-","Frames","attached","to","samples","whose","IDs","are","in","``","sample_ids","``","are","reloaded","-","Frames","attached","to","samples","whose","IDs","are","not","in","``","sample_ids","``","are","reset"]
code: def _sync_docs(cls, collection_name, sample_ids, hard=False):
      """Syncs the backing documents for all in-memory frames according to
      the following rules:
  
      -   Frames attached to samples whose IDs are in ``sample_ids`` are
          reloaded
      -   Frames attached to samples whose IDs are not in ``sample_ids`` are
          reset
      """
      if collection_name not in cls._instances:
          return
  
      samples = cls._instances[collection_name]
  
      sample_ids = set(str(_id) for _id in sample_ids)
      reset_ids = set()
      for sample_id, frames in samples.items():
          if sample_id in sample_ids:
              for frame in frames.values():
                  frame.reload(hard=hard)
          else:
              reset_ids.add(sample_id)
              for frame in frames.values():
                  frame._reset_backing_doc()
  
      for sample_id in reset_ids:
          frames = samples.pop(sample_id)
  
imports: from collections import defaultdict
  import weakref
label_desc: Use image node_id 11 for calling the FrameSingleton obj's underlying member method code with example usage: obj._sync_docs(cls, collection_name, sample_ids, hard) without return types