C++ Introspection and Object persistency Through JIL David Lawrence Ph. D. Jefferson Lab, Newport News VA

Introspection and Object Persistency Introspection: Ability for a program to query the structure of its classes from within the program. Object Persistency: Writing the data portion of an object to a file so that it can be re-created later by another program.

Motivation for JIL Add object persistency support to existing CODA file format Implement C++ object persistence in DANA framework Make general use tool for object persistence without requiring access to C++ source (only headers)

Serializers Files are 1-dimensional things. In order to write a multi-dimensional “object” into a file, it must be serialized. A corresponding deserializer must also be written to reconstitute the object later. In addition, a file format specification is needed to keep track of what objects are in the file along with locations and sizes.

Multiple Approaches To Creating Serializers Write generic serializer based on introspective information C++ parser/interpreter (ROOT) Write class definitions in XML format and generate C++ headers Hand coded serializers

A Simple Example

Use Gnu Debugger (gdb) to mine class/struct structure

XML representation of “myClass”

(De)Serializer Routines change complex structures into “simple” type problem

Writing objects to a file

Reading objects from a file

Serialization time vs. # events

Multi-Threading

Summary JIL provides a mechanism to add object persistency through files to C++ projects JIL can use either C++ code or XML as the source from which to generate serializer methods JIL can be used to make 3rd party objects persistent without modifying the 3rd party source code

Summary JIL optionally uses bzip2 compression JIL is multi-thread enabled (not just thread- safe) JIL allows customized backends to support legacy file formats