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Section7-GA-CplusBindingsforGA.rst

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GA++: C++ Bindings for Global Arrays

Overview

GA++ provides a C++ interface to global arrays (GA) libraries. The doxygen documentation of GA++ is located here: https://hpc.pnl.gov/globalarrays/api/cxxapi.shtml. The GA C++ bindings are a layer built directly on top of the GA C bindings. GA++ provides new names for the C bindings of GA functions (For example, GA_Add_patch() is renamed as addPatch()).

GA++ Classes

All GA classes (GAServices, GlobalArray) are declared within the scope of GA namespace.

Namespace issue:Although namespace is part of the ANSI C++ standard, not all C++ compilers support namespaces (A non-instantiable GA class is provided for implementations using compilers without namespace). Note: define the variable _GA_USENAMESPACE_ as 0 in ga++.h if your compiler does not support namespaces.

namespace GA {
    class GAServices;
    class GlobalArray;
};

The current implementation has no derived classes (no (virtual) inheritance), templates, or exception handling. Eventually, more object oriented functionalities will be added, and standard library facilities will be used without affecting the performance.

Initialization and Termination

GA namespace has the following static functions for initialization and termination of Global Arrays.

  • GA::Initialize(): Initialize Global Arrays, allocates and initializes internal data structures in Global Arrays. This is a collective operation.
  • GA::Terminate(): Delete all active arrays and destroy internal data structures. This is a collective operation.
namespace GA {
    _GA_STATIC_ void Initialize(int argc, char *argv[]}, size_t limit = 0);
    _GA_STATIC_ void Initialize(int argc, char *argv[], unsigned long heapSize, unsigned long stackSize, int type, size_t limit = 0);
    _GA_STATIC_ void Terminate();
};
#include <iostream.h>
#include "ga++.h"

int main(int argc, char *argv[]) {
    GA::Initialize(argc, argv, 0);
    cout << "Hello World!\n";
    GA::Terminate();
}

GAServices

GAServices class has member functions that does all the global operations (non-array operations) like Process Information (number of processes, process id, ..), Inter-process Synchronization (sync, lock, broadcast, reduce,..), etc,.

SERVICES Object: GA namespace has a global SERVICES object (of type GAServices), which can be used to invoke the non-array operations. To call the functions (for example, sync()), we invoke them on this SERVICES object (for example, GA::SERVICES.sync()). As this object is in the global address space, the functions can be invoked from anywhere inside the program (provided the header ga++.h is included in that file/program).

Global Array

GlobalArray class has member functions that perform:

  • Array operations
  • One-sided (get/put)
  • Collective array operations
  • Utility operations, etc.