C Introspection and Object persistency Through JIL

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C Introspection and Object persistency Through
JIL

• David Lawrence Ph. D.
• Jefferson Lab, Newport News VA

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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.

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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)

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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.

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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

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A Simple Example
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Use Gnu Debugger (gdb) to mine class/struct
structure
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XML representation of myClass
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(De)Serializer Routines change complex structures
into simple type problem
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(No Transcript)
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Writing objects to a file
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Reading objects from a file
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Serialization time vs. events
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Multi-Threading
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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

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Summary

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