default Map<SystemStreamPartition, String> beforeCheckpoint(Map<SystemStreamPartition, String> offsets) {
    return offsets;
  }
Called before writing the checkpoint for each Task in the Container processing SSPs on this system.
Implementations may modify the Task offsets to be checkpointed, or return the provided offsets as-is.

@param offsets offsets about to be checkpointed.
@return potentially modified offsets to be checkpointed.
samza-api/src/main/java/org/apache/samza/checkpoint/CheckpointListener.java