# nodus.checkpoint

> The checkpoint handshake and gang checkpoints (resources.md §8, distributed-training.md §10.3).

Source: https://nodus-platform-site.pages.dev/docs/reference/python/nodus-checkpoint/
Build revision: 211ad9f836655b1c3a2668c4693e442471f28614

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The checkpoint handshake and gang checkpoints (resources.md §8, distributed-training.md §10.3).

Nodus owns checkpoint cadence and storage; programs write their own files into `nodus.state_dir()`. Before a snapshot the node sends `checkpoint.request`: `on_request(callback)` saves, then `ack()` tells the node the files are consistent. Restoring files never restores process memory: a restarted program loads what it saved.

## `ack`

```python
ack(seq: str | None = None) -> None
```

Tell the node the checkpoint files are complete for request `seq` (the latest one by default).

## `handle`

```python
handle(message: dict[str, Any]) -> None
```

Process one message from the events socket.

## `on_request`

```python
on_request(callback: Callable[[], None]) -> None
```

Call `callback` (then `ack()`) whenever the node asks for a checkpoint; a no-op outside Nodus.

## `requested`

```python
requested() -> bool
```

True while a checkpoint request is pending; poll it at safe points in a training loop.

## `subscribe`

```python
subscribe() -> None
```

Listen for checkpoint requests without a callback: poll `requested()` and call `ack()` after saving.