memory

State snapshot at a given point in time.

Metadata associated with a checkpoint.

A tuple containing a checkpoint and its associated data.

Per-channel result entry from BaseCheckpointSaver.get_delta_channel_history.

Storage-level view of what one channel contributed across the ancestor chain of a target checkpoint:

• writes — on-path deltas oldest→newest as PendingWrite tuples. Always present; possibly empty. Already filtered to one channel. Writes stored at the target checkpoint itself are pending for the next super-step and are excluded.
• seed — the stored value at the nearest ancestor whose channel_values[ch] is populated. Omitted if the walk reached the root without finding any stored value (consumer treats absence as "start empty"). Typically a _DeltaSnapshot for delta channels with finite snapshot frequency, or a plain value for threads migrated from a pre-delta channel type.

Protocol for serialization and deserialization of objects.

• dumps_typed: Serialize an object to a tuple (type, bytes).
• loads_typed: Deserialize an object from a tuple (type, bytes).

Valid implementations include the pickle, json and orjson modules.

An in-memory checkpoint saver.

This checkpoint saver stores checkpoints in memory using a defaultdict.