Geant4 User's Guide
For Application Developers
Detector Definition and Response
4.6 Object Persistency
4.6.1 Persistency in Geant4
Object persistency is provided by Geant4 as an optional category, so that the
user may run Geant4 with or without an object database management system
When a usual (transient) object is created in C++, the object is placed onto the application heap and it ceases to exist when the application terminates. Persistent objects, on the other hand, live beyond the termination of the application process and may then be accessed by other processes (in some cases, by processes on other machines).
C++ does not have, as an intrinsic part of the language, the ability to store and retrieve persistent objects. Geant4 provides an abstract framework for persistency of hits, digits and events.
An example which demonstrates an implementation of object persistency using one of the tools accessible through the available interface, is provided in examples/extended/persistency.