SEAL Reflex, the new Reflection Library Stefan Roiser (for the LCG/SEAL Dictionary work package) LCG Applications Area Meeting, Oct. 6, 2004.

SEAL Reflex, the new Reflection Library

Stefan Roiser(for the LCG/SEAL Dictionary work package)

LCG Applications Area Meeting, Oct. 6, 2004

6. Oct. 2004 Stefan Roiser 2

Content

• Reflection and C++

• The Model

• Use Cases

• Producing reflection information

• Current status, future enhancements

• CHEP ‘04

• Conclusion

6. Oct. 2004 Stefan Roiser 3

Definitions

• Reflection is the ability of a language to introspect it’s own structure at runtime and interact with it in a generic way

• A dictionary provides reflection information about types of a certain language to the user

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What is Reflection?

class Particle { public: double mass(); private: double m_mass; };

Data & Instructions

Without prior

knowledge about

types

Particle p;

std::cout << p.mass();

ClassBuilder(“Particle”). addDataMember(“m_mass”). addFunctionMember(“mass”);

Dictionary

const Type* t = Type::byName(“Particle”);

Object o = t->construct();

cout << *(double*) o.invoke(“mass”);

t->destruct(o);

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Reflection and C++

• Very limited support by the language (RTTI)– Other languages do (e.g. Java, Python,…)

• Several approaches exist, but …– Tied to a system or– Instrumentation of code needed

• Stroustrup proposed XTI (eXtended Type Information)

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Goals

• Enhance C++ with reflection capabilities– non intrusive, automated

• Close to the C++ ISO 14882 standard

• Light and standalone system

• Small memory footprint

• Multi platform– Linux, Windows, Mac OSX, …

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Reflection Model

Type

TypeBase

Scope

ScopeBase

Member

Class

PropertyList

…

Function

Typedef

Reference

PointerNamespace

InstTemplate

TemplFamilyInstTFunction

InstTClass

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Reflection Use Cases

const Type * t = Type::byName(“Particle”);

size_t s = t->sizeOf();

bool t = t->isClass();

• Types– Retrieve a specific type– Introspect the actual type

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Reflection Use Cases (ctd.)

• Classes– Inspect inheritance tree – Create / delete instances

const Class * c = t->asClass();

const Base * b = c->base(0);

Object o = c->construct();c->destruct(o);

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Reflection Use Cases (ctd.)

• Data Members– Get / set values– Retrieve offset relative to beginning of class

const DataMember * dm = c->dataMember(0);

double d = *(double*) dm->get(v);

size_t s2 = dm->offset();

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Reflection Use Cases (ctd.)

const FunctionMember * fm = c->functionMember(0);

const Type * rt = fm->type()->asFunction()->returnType();

void * r = fm->invoke(o);

• Function Members– Inspect return and parameter types– Invoke a function and retrieve return values

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Reflection Use Cases (ctd.)• All Types

– Reference, Pointer, PointerToMember, Array, Enum, Union, Fundamental, Class, Function

• Typedefs• Scopes

– Search scopes– Retrieve scopes

• Additional Properties– For Types, Scopes

and Members– Everything that does

not fit ISO standard– Any type supported

• CV qualifiers• Templates

– Inspect families– Look for instantiations

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System Overview

.h_dict.cpp

gcc_xml.xml

gendict.py

lcgdict

.xml

TypeSelection

make.so.cpp _dict.so

make

Reflex.so

UserProgram

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[lxplus]~>

Dictionary Creation<lcgdict> <class name=“Particle”/></lcgdict>

#include “Particle.h”class Particle_dict { public: Particle_dict(); };void* stubfun(void* o) { return (void*)((Particle*)o)->mass(); }Particle_dict::Particle_dict() {ClassBuilder<Particle>(“Particle”).addDataMember<double>(”m_mass”,Offset(Particle,m_mass),PRIVATE).addFunctionMember<double(void)>(”mass”,&stubfun,0,0,PUBLIC); }static Particle_dict instance;

[lxplus]~> lcgdict Particle.h -s selection.xml --reflex -I../incl [lxplus]~> lcgdict Particle.h -s selection.xml --reflex -I../incl Parsing File Particle.h with GCC_XML OKGenerating LCG Dictionary (reflex)class Particle[lxplus]~>

[lxplus]~> lcgdict Particle.h -s selection.xml --reflex -I../incl Parsing File Particle.h with GCC_XML OKGenerating LCG Dictionary (reflex)class Particle[lxplus]~> lsParticle.h Particle.xml Particle_dict.cpp[lxplus]~>

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gcc_xml

• “[…] generate an XML description of a C++ program from GCC's internal representation.”

• Any gcc compilable program can be used as input

• lcgdict uses the XML file to produce dictionary files

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Library Sizes

• SEAL ROOT Dictionary: 405 classes

6657.68 6582.30

0

1000

2000

3000

4000

5000

6000

7000

SealROOTDict (KB)

ReflectionReflex

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Library Sizes (ctd.)

CLHEP Dictionary : 56 classes

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Status

• Reflex - new version will be released with SEAL 1_4_2 and 1_5_2– In collaboration with the ROOT team– Idea is common LCG & ROOT dictionary– Several enhancements

• References, Enums, Unions, Typedefs, …

– Closer to ISO standard

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Future Enhancements

• Template types– Full implementation needed

• Measuring the memory footprint– Instructing new / delete– Counting instances

• Unloading libraries– Proper deletion of types / scopes

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Future Enhancements (ctd.)

• Missing Builders – UnionBuilder, EnumBuilder

• STL like iterators– In addition to current implementation

• String parser– Could be used when building types

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Integration with LCG SW

• POOL– Reflex provides sufficient functionality– Integration foreseen

• SEAL Scripting– PyLCGDict will become PyReflex– Work has already started

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Integration with ROOT

• For ROOT I/O – ROOT Meta Classes (e.g. TClass, TMethod) may

be implemented using Reflex – Check of sufficient functionality needed

• For interactive ROOT (CINT) – Creation of CINT data structures needed– Equivalent to existing CINT/Lcgdict gateway in

POOL• Easy for data members• Function members not so straight forward

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Integration with ROOT

.h

lcgdict _dict.so

rootcint CINTcint.so

Reflex

ROOT

CINTDS

TDictionaryCurrent Situation

ReflexDS

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Integration with ROOT

.h

lcgdict _dict.so

rootcint CINTcint.so

Reflex

ROOT

CINTDS

Enabling ROOT I/O

ReflexDS

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Integration with ROOT

.h

lcgdict _dict.so

rootcint CINTcint.so

Reflex

ROOT

CINTDS

ReflexDS

Enabling ROOT I/O& interactive CINT

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Integration with ROOT

.h

lcgdict _dict.so

rootcint CINTcint.so

Reflex

ROOT

CommonDS

Final Goal

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CHEP ‘04

• Other projects showed interest– FreeHEP Java Library– Panoramix

• Improving Standard C++ – Compile time reflection wanted feature– No proposal for the time being

• Summary talk of Core Software– Propose reflection as part of ISO standard

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SW packages• Reflection library

– Current implementation • Reflection, ReflectionBuilder

– New model• Reflex

• DictionaryGenerator– Produce dictionary files for both versions

• Dictionaries CLHEP, STL, ROOT– Standard dictionaries ready to use

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Conclusion• SEAL Dictionaries

– Light, standalone system– Non intrusive, automated code production– Dictionaries for any gcc compileable program

• New system - Reflex - ready for integration– In collaboration with ROOT– Common LCG/ROOT dictionary envisaged– Several enhancements, closer to ISO std– Positive feedback from CHEP’04

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Pointers

• The SEAL project– http://cern.ch/Seal/

• CVS repository– SEAL.cvs.cern.ch:/cvs/SEAL/Dictionary

• access: kserver, ssh, (anonymous) pserver

• gcc_xml– http://www.gccxml.org