Implement best checkpointer

pymarlin/utils/checkpointer/checkpoint_utils.py

@@ -4,7 +4,7 @@
 
 import os
 import re
-from typing import Optional, Dict
+from typing import Optional, Dict, Tuple, Callable
 from abc import ABC, abstractmethod
 from operator import itemgetter
 from dataclasses import dataclass
@@ -291,3 +291,99 @@ def check_mk_dir(self, dirpath: str) -> None:
             os.makedirs(dirpath)
         assert os.path.isdir(dirpath), "supplied checkpoint dirpath "\
             "is not a directory"
+
+
+@dataclass
+class BestCheckpointerArguments(DefaultCheckpointerArguments):
+    """Additional arguments for checkpointer
+
+    metric_name: name of metric where minimal is defined as best. Must be a registered buffer in module interface
+    save_every_epoch: whether to produce a checkpointer every epoch in addition to latest and best.
+    load_best: whether to load best or latest checkpoint. Default behavior is to load latest.
+    """
+    metric_name: str = "val_perplexity"
+    init_metric_val: Optional[float] = None
+    criteria: Optional[Tuple[str, Callable]] = "min"
+    save_every_epoch: bool = False  # not usually necessary in practice
+    load_best: bool = False  # default to load latest
+
+
+class BestCheckpointer(DefaultCheckpointer):
+    """
+    Saves best and latest checkpoint. Best checkpoint is defined as the smallest value of a given parameter in the
+    module interface. Therefore this checkpointer works by relying on the parameter defined in metric_name existing as a
+    single value. By default it checks "val_perplexity" which is a registered buffer in `AbstractUserMessageReplyModule`
+    that gets updated after every call to `on_end_val_epoch`.
+    """
+    def __init__(self, args: BestCheckpointerArguments):
+        super().__init__(args)
+        self.best_checkpoint_name = f"{self.args.file_prefix}_best_checkpoint.{self.args.file_ext}"
+        self.latest_checkpoint_name = f"{self.args.file_prefix}_latest_checkpoint.{self.args.file_ext}"
+        if self.args.criteria == 'min':
+            self.criteria_func = lambda new, old: new < old
+            self.best_metric = float('inf')
+        elif self.args.criteria == 'max':
+            self.criteria_func = lambda new, old: new > old
+            self.best_metric = -float('inf')
+        else:
+            self.criteria_func = self.args.criteria
+            self.best_metric = self.args.init_metric_value
+
+        if self.args.init_metric_value is not None:
+            self.best_metric = self.args.init_metric_value
+
+    def save(self, checkpoint_state: Checkpoint, index: int, force=False) -> str:
+        """
+        Saves trainer, optimizer, and module interface state.
+
+        Args:
+            checkpoint_state: instance of `Checkpoint` which contains trainer, optimizer, and module interface state
+            index: current epoch number
+            force: whether to force a save even if period of checkpointing does not line up
+
+        Returns:
+            list of paths checkpoint state was saved to
+        """
+        paths = []
+        if self.args.save_every_epoch:
+            paths.append(super().save(checkpoint_state, index, force))
+        if self.args.checkpoint and ((index % self.args.period == 0) or force):
+            # TODO grab this from logged metrics instead
+            metric = float(checkpoint_state.module_interface_state[self.args.metric_name])
+
+            # optiionally save best
+            if self.criteria_func(metric, self.best_metric):
+                self.best_metric = metric
+                best_path = os.path.join(self.args.save_dir, self.best_checkpoint_name)
+                torch.save(checkpoint_state.__dict__, best_path)
+                paths.append(best_path)
+
+            # save latest
+            latest_path = os.path.join(self.args.save_dir, self.latest_checkpoint_name)
+            torch.save(checkpoint_state.__dict__, latest_path)
+            paths.append(latest_path)
+        return paths
+
+    def load(self) -> Checkpoint:
+        """
+        Optionally loads a checkpoint from a given directory. Either loads a specified filename, the best checkpoint, or
+        the latest checkpoint. Raises a `ValueError` upon failure to load checkpoint.
+
+        Returns:
+            An instance of `Checkpoint`
+        """
+        if self.args.load_dir:
+            if self.args.load_filename:
+                load_path = os.path.join(self.args.load_dir, self.args.load_filename)
+            elif self.args.load_best:
+                load_path = os.path.join(self.args.load_dir, self.best_checkpoint_name)
+            else:
+                load_path = os.path.join(self.args.load_dir, self.latest_checkpoint_name)
+
+            # TODO how to set best metric to match loaded checkpoint?
+            self.logger.debug(f"loading checkpoint from {load_path}")
+            checkpoint = torch.load(load_path, map_location=torch.device('cpu'))
+            self.logger.debug('Checkpoint loaded')
+            return Checkpoint(**checkpoint)
+
+        return Checkpoint()