1. Using Shared Libraries
The traditional way
Is code equals to code?
Some words about configuration.
Benefits

2. The traditional way - comparison
The past:
1 Executable
Many object files/libraries, all linked into one executable at link time
Gaudi:
Very few object files/libraries linked in
Process aquires it’s “personality” at run-time
Dynamic linkage of images
Execution of code within these images
GAUDI
M.Frank LHCb/CERN

3. Is Code equals to code? Usually most of the code is never executed
Why carry the useless ballast with you?
Example(s):
Why link against Objy implementation, if I just want to copy a few events with ROOT to work at home?
Why should a link after fixing a bug in a module?
Why should I always link against reconstruction code, if it is unclear wether it will be ever called?
The dependencies grow and grow and grow
Lean component modules tend to have manageable dependencies
GAUDI
M.Frank LHCb/CERN

4. What type of code exists?
Static libraries
Code to be duplicated for each image
Code which is aware of running in an executable or a shared image:
Gaudi System class
FactoryTable (wait for next slides)
Basic Bootstrap
IIDs, CLIDs, …
GAUDI
M.Frank LHCb/CERN

5. What type of code exists?
Implicitly linked libraries
Equivalent to tradition shared libraries
Public implementation code
All symbols are exported
Base classes
e.g. Converter, Service, ConversionSvc, MsgStream,…
GAUDI
M.Frank LHCb/CERN

6. What type of code exists?
Explicitly linked libraries
Loaded on demand using LoadLibrary(), dlopen(),…
Component libraries
Private implementation code
No symbols are exported
objdump -> no output (unless --dynamic-syms)
Single entry point
extern “C” std::list<const IFactory&>& getFactoryEntries()
Access to all implemented factories
GAUDI
M.Frank LHCb/CERN

7. Benefits Process depends on configuration Modules become manageable
PATH
LD_LIBRARY_PATH
Modules become manageable
Minimize dependencies
Upgrades are simple
No link step is involved
Efficient use of resources
GAUDI
M.Frank LHCb/CERN

8. Side Remarks
Macros: GaudiDllCall, GaudiDllData, … used to export code on NT are gone
Analyse archive library file directly: xdfol.exe
Explicitly generate file with transfer vectors
Fortran
Shared libraries may not have unresolved refs to F77 code
Force link into executable
DLLs use routine pointers filled at image activation by analysing invoking executable file
GAUDI
M.Frank LHCb/CERN