gdl.h

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#ifndef  GDYNAMICLIB_H
#define  GDYNAMICLIB_H  1
 
#include "glogger.h"
 
// c++ plugin loading functions
// documentation: http://www.faqs.org/docs/Linux-mini/C++-dlopen.html
#include <dlfcn.h>
 
// c++
#include <sys/stat.h> // to check if file exists
#include <string>
#include <iostream>
 
typedef void *dlhandle;
 
static dlhandle load_lib(const std::string &path);
 
static void close_lib(dlhandle handle);
 
// exit codes: 1000s
#define EC__DLNOTFOUND       1001
#define EC__FACTORYNOTFOUND  1002
#define EC__DLHANDLENOTFOUND 1003
 
 
struct DynamicLib {
 
private:
    std::string dlFileName;  // dynamic library file
 
    bool doesFileExists(const std::string &name) {
        struct stat buffer;
        return (stat(name.c_str(), &buffer) == 0);
    }
 
    std::shared_ptr<GLogger> log;
 
public:
    // default constructor
    DynamicLib() = default;
 
    // path here is the filename
    DynamicLib(std::shared_ptr<GLogger> logger, std::string path) : dlFileName(path), log(std::move(logger)), handle(nullptr) {
 
        log->debug(CONSTRUCTOR, "Instantiating ", path);
        log->debug(NORMAL, "Trying ", dlFileName);
 
        // trying $GEMC/lib/ + path if not found
        if (!doesFileExists(dlFileName)) {
            log->debug(NORMAL, dlFileName, "Not found...");
            dlFileName = std::string(getenv("GEMC")) + "/lib/" + path;
            log->debug(NORMAL, "Trying ", dlFileName);
        }
 
        // trying $GEMC/lib64/ + path if not found
        if (!doesFileExists(dlFileName)) {
            log->debug(NORMAL, dlFileName, "Not found...");
            dlFileName = std::string(getenv("GEMC")) + "/lib64/" + path;
            log->debug(NORMAL, "Trying ", dlFileName);
        }
 
        if (doesFileExists(dlFileName)) {
            handle = load_lib(dlFileName);
            log->info(0, "Loaded ", dlFileName);
            if (handle == nullptr) {
                char const *const dlopen_error = dlerror();
                log->error(EC__DLHANDLENOTFOUND, "File ", dlFileName, " found, but handle is null. Error: ",
                           dlopen_error);
            }
        } else {
            log->error(EC__DLNOTFOUND, "could not find ", dlFileName);
        }
    }
 
    dlhandle handle = nullptr;   // posix handle of the dynamic library
 
    ~DynamicLib() {
        if (handle != nullptr) {
            close_lib(handle);
            log->debug(DESTRUCTOR, "Destroying ", dlFileName);
        }
    }
 
 
};
 
 
static dlhandle load_lib(const std::string &path) {
 
    return dlopen(path.data(), RTLD_NOW);
    // get a handle to the lib, may be nullptr.
    // RTLD_NOW ensures that all the symbols are resolved immediately:
    // if a symbol cannot be found, the program will crash now instead of later.
}
 
static void close_lib(dlhandle handle) {
    dlclose(handle);
}
 
#endif