March 27, 2007HPC 07 - Norfolk, VA1 C++ Reflection for High Performance Problem Solving Environments Tharaka Devadithya 1, Kenneth Chiu 2, Wei Lu 1 1. Computer Science Department, Indiana University 2. Department of Computer Science, State University of New York, Binghamton

Outline Reflection Overview Problem Solving Environments (PSEs) Motivation and Goals C++ Reflection Library Performance Applications Related Work March 27, 2007HPC 07 - Norfolk, VA2

March 27, 2007HPC 07 - Norfolk, VA3 Reflection Involves accessing type information Two main types  Compile-time reflection E.g., Boost type traits  Run-time reflection Some languages support reflection as part of their standard specifications  E.g., Java, C#, Python C++ supports Run-Time Type Information (RTTI)  Very limited features

March 27, 2007HPC 07 - Norfolk, VA4 Implementing Run-time Reflection Include additional metadata to compiled code. Compilers of languages that support reflection generates this metadata and inserts into the binary. Since C++ compiler does not generate this metadata, it must be generated as a separate step.

March 27, 2007HPC 07 - Norfolk, VA5 Problem Solving Environments (PSEs) Provides all the computational facilities necessary to solve a target class of problems. A scientist or engineer should be able to dynamically couple tasks or computations, such that the composite will lead to solving some problem. Examples  Symbolic manipulation for basic mathematical expressions  Visualization packages for 2-, 3-, and 4-D phenomena  Geometric modelers for a broad class of shapes

March 27, 2007HPC 07 - Norfolk, VA6 How Reflection Aids PSE Need to dynamically couple tasks or computations. It should be possible for the back-end to dynamically invoke functionalities  become known only during run-time. Reflection provides a powerful and flexible method invocation ability.  E.g., request the application to dynamically load a library and invoke an arbitrary method in it.

March 27, 2007HPC 07 - Norfolk, VA7 Need for Reflection in C++ Reflection is not supported by modern languages used in High Performance Computing (HPC). Attempts to incorporate reflection capabilities to C++ are either  intrusive, or  not fully compliant with the C++ standard specification PSE developers for HPC domains have to depend on another language (e.g., Java) to “wrap” each component with a reflection enabled interface.  Multiple language skill required  Overhead in transferring data

March 27, 2007HPC 07 - Norfolk, VA8 Benefits of Reflection Develop generic algorithms. E.g., classType = ClassType::getClass(“Service1”); obj = classType.createInstance(); obj.invoke(“method1”); Capabilities resulting from this generality.  Object serialization Results in a generic object persistence framework  Interface to a Scripting Environment E.g., provide a Python interface to HPC code without needing language bindings for each invocation.  Object Instantiation More flexible approach than using the Factory pattern.

March 27, 2007HPC 07 - Norfolk, VA9 Goals Run-time access to members.  Invoke member functions  Read from / write to data members Standard compliant.  Increases portability Relatively efficient.  Minimize overhead of indirect invocations Non-intrusive.  Can be used with existing code  Avoid programmer errors

March 27, 2007HPC 07 - Norfolk, VA10 C++ Reflection Library Consists of  a small set of core classes, and  another set of generated classes to store and present the type-specific, metadata information. generated by parsing the user-supplied target classes. Employs 2 main types of classes  Meta classes  Member classes

Code Generation Meta-data generated using source files (header files defining classes).

March 27, 2007HPC 07 - Norfolk, VA12 Meta classes Maintains information about user defined classes.  Name and type  List of data members and member functions  Inheritance information Interface to instantiate a class. Example ClassType *ct = ClassType::getClass("ClassA"); string className = ct->name(); classAObj = ct->createInstance();

March 27, 2007HPC 07 - Norfolk, VA13 Member classes Encapsulate the members of a class. Provide means of indirectly accessing them, given their names at run-time. 2 Types  Data members DataMember dm = ct->getDataMember("f1"); dm.ref (&classAObj) = 1234;  Member functions MemberFunction mf = ct->getMemberFunction("m1"); mf.invoke (&classAObj);

March 27, 2007HPC 07 - Norfolk, VA14 Sample Usage XMLDocument dom; dom.parse(...); classType = ClassType::getClass("Service"); obj = classType.createInstance(); operationName = dom.getRoot()->getName(); memberFunction = classType.getMemberFunction(operationName); Arguments args; extractArgs(memberFunction, dom.getRoot(), args); memberFunction.genericInvoke (*obj, args);

Performance Invocation time Reflection overhead  with 100 invocations  with 100,000 invocations Reflection Vs. generated code March 27, 2007HPC 07 - Norfolk, VA15

Invocation Times March 27, 2007HPC 07 - Norfolk, VA16

Reflection Overhead (100 invocations) March 27, 2007HPC 07 - Norfolk, VA17

Reflection Overhead (100,000 invocations) March 27, 2007HPC 07 - Norfolk, VA18

Reflection Vs. Generated Code March 27, 2007HPC 07 - Norfolk, VA19

Applications Remote method invocation  Requires ability to invoke a method, given the class and method names along with the arguments at runtime. Solving Large Sparse Linear Systems of Equations  Need to try out different strategies.  A PSE could help the algebraist by providing a set of components out of which he or she can choose the ones that provide the functionalities required by the current strategy. Unit testing framework  Prefix each test member function name with some predefined word, (E.g., “testXXXX()”) March 27, 2007HPC 07 - Norfolk, VA20

Related Work Some other approaches to reflection in C++  SEAL Reflex  Meta Object Protocol (MOP)  CppReflect All the above approaches are either,  intrusive, or  not fully compliant with the C++ standard specification March 27, 2007HPC 07 - Norfolk, VA21

Questions March 27, 2007HPC 07 - Norfolk, VA22