Asynchronous Operations: Use of the Custom Information Dictionary
In the delegate method of a long-running operation, you can store a data object in the _CustomInfo dictionary of the long-running operation and get the list of records processed by the method. You can add to the dictionary any data object needed for a long-running operation by using a SetCustomInfo method.

For a processing operation, the system stores the PXProcessingMessagesCollection<TTable> list of messages in the dictionary. Each message in the list is of the PXProcessingMessage type, which includes a string message and an error level that is of the PXErrorLevel type.
See New way to work with CustomInfo of PXLongOperation at http://asiablog.acumatica.com for more information about the use of the dictionary.