diff --git a/langfun/core/eval/v2/checkpointing.py b/langfun/core/eval/v2/checkpointing.py
index 8c6f163..d09b000 100644
--- a/langfun/core/eval/v2/checkpointing.py
+++ b/langfun/core/eval/v2/checkpointing.py
@@ -92,7 +92,7 @@ def save_state(example: Example):
             )
         )
         writer.add(example)
-        del writer
+        writer.close()
       runner.background_run(save_state, example)
 
   def _file_prefix_and_ext(self, filename: str) -> tuple[str, str]:
@@ -128,6 +128,8 @@ def on_run_abort(
   ) -> None:
     with self._lock:
       if self._sequence_writer is not None:
+        for writer in self._sequence_writer.values():
+          writer.close()
         self._sequence_writer.clear()
 
   def on_run_complete(
@@ -174,6 +176,9 @@ def on_experiment_complete(
     assert experiment.id in self._sequence_writer
     with self._lock:
       if self._sequence_writer is not None:
+        # Make sure the writer is closed without delay so the file will be
+        # available immediately.
+        self._sequence_writer[experiment.id].close()
         del self._sequence_writer[experiment.id]
 
   def on_example_complete(
@@ -207,9 +212,13 @@ def add(self, example: Example):
         return
       self._sequence_writer.add(example_blob)
 
-  def __del__(self):
+  def close(self):
     # Make sure there is no write in progress.
     with self._lock:
-      assert self._sequence_writer is not None
+      if self._sequence_writer is None:
+        return
       self._sequence_writer.close()
       self._sequence_writer = None
+
+  def __del__(self):
+    self.close()