BESPlugin.h

// BESPlugin.h
 
// This file is part of bes, A C++ back-end server implementation framework
// for the OPeNDAP Data Access Protocol.
 
// Copyright (c) 2004-2009 University Corporation for Atmospheric Research
// Author: Patrick West <pwest@ucar.edu> and Jose Garcia <jgarcia@ucar.edu>
// and James Gallagher <jgallagher@gso.uri.edu>
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
//
// You can contact University Corporation for Atmospheric Research at
// 3080 Center Green Drive, Boulder, CO 80301
 
// (c) COPYRIGHT University Corporation for Atmospheric Research 2004-2005
// Please read the full copyright statement in the file COPYRIGHT_UCAR.
//
// Authors:
//      pwest       Patrick West <pwest@ucar.edu>
//      jgarcia     Jose Garcia <jgarcia@ucar.edu>
//      jimg        James Gallagher <jgallagher@gso.uri.edu>
 
#ifndef T_BESPlugin_h
#define T_BESPlugin_h
 
#include <dlfcn.h>
#include <string>
#include <iostream>
 
#include "BESObj.h"
#include "BESInternalFatalError.h"
#include "BESInternalError.h"
#include "BESDebug.h"
 
#undef UNPLUG_HANDLERS

class NoSuchLibrary: public BESInternalFatalError {
public:
    NoSuchLibrary(const std::string &msg, const std::string &file, int line) :
            BESInternalFatalError(msg, file, line)
    {
    }
};

class NoSuchObject: public BESInternalFatalError {
public:
    NoSuchObject(const std::string &msg, const std::string &file, int line) :
            BESInternalFatalError(msg, file, line)
    {
    }
};

 
template<typename M>
class BESPlugin: public BESObj {
private:
    std::string d_filename; // Library filename
    void *d_lib = nullptr; // Open library handle

    void *get_lib() {
        if (!d_lib) {
            d_lib = dlopen(d_filename.c_str(), RTLD_LAZY /*RTLD_NOW*/ | RTLD_GLOBAL);
            BESDEBUG( "bes", "BESPlugin: plug in handler:" << d_filename << ", " << d_lib << std::endl);
            if (d_lib == nullptr) {
                throw NoSuchLibrary(std::string(dlerror()), __FILE__, __LINE__);
            }
        }
 
        return d_lib;
    }
 
public:
    BESPlugin() = delete;
    BESPlugin(const BESPlugin &p) = delete;

    explicit BESPlugin(const std::string &filename) : d_filename(filename) { }
 
    ~BESPlugin() override = default;
 
    BESPlugin &operator=(const BESPlugin &p) = delete;

    M* instantiate() {
        void *maker = dlsym(get_lib(), "maker");
        if (!maker) {
            throw NoSuchObject(std::string(dlerror()), __FILE__, __LINE__);
        }
 
        typedef M *(*maker_func_ptr)();
        maker_func_ptr my_maker = *reinterpret_cast<maker_func_ptr*>(&maker);
        M *my_M = my_maker();
 
        return my_M;
    }
 
    void dump(std::ostream &strm) const override  {
        strm << "BESPlugin::dump - (" << std::ios::hex << this << ")" << std::endl;
        strm << "    plugin name: " << d_filename << std::endl;
        strm << "    library handle: " << std::ios::hex << d_lib << std::endl;
    }
};
 
#endif // T_BESPlugin_h