DynLib.h

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// # DynLib.h: Class to handle loadig of dynamic libraries
// # Copyright (C) 2009
// # Associated Universities, Inc. Washington DC, USA.
// #
// # This library is free software; you can redistribute it and/or modify it
// # under the terms of the GNU Library General Public License as published by
// # the Free Software Foundation; either version 2 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 Library General Public
// # License for more details.
// #
// # You should have received a copy of the GNU Library General Public License
// # along with this library; if not, write to the Free Software Foundation,
// # Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
// #
// # Correspondence concerning AIPS++ should be addressed as follows:
// #        Internet email: casa-feedback@nrao.edu.
// #        Postal address: AIPS++ Project Office
// #                        National Radio Astronomy Observatory
// #                        520 Edgemont Road
// #                        Charlottesville, VA 22903-2475 USA
 
#ifndef CASA_DYNLIB_H
#define CASA_DYNLIB_H
 
// # Includes
#include <casacore/casa/aips.h>
#include <string>
 
namespace casacore {  // # NAMESPACE CASACORE - BEGIN
 
// <summary>
// Class to handle loading of dynamic libraries
// </summary>
// <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="" demos="">
// </reviewed>
 
// <use visibility=export>
 
// <prerequisite>
//    <li> Basic knowledge of the dlopen function family
// </prerequisite>
 
// <synopsis>
// This class makes it possible to load a dynamic library and execute an
// initialization function. Furthermore, one can get a pointer to any function
// in the dynamic library and close the library.
//
// The search path of the shared library is as follows:
// <ul>
//  <li> If the environment library CASACORE_LDPATH is defined, it is tried to
//       find the library using that path.
//  <li> If not defined or not found, the system's (DY)LD_LIBRARY_PATH is used.
//  <li> The library looked for has the name 'prefix'libname'suffix'.
//       <br>As prefix first "lib" is used, thereafter the given one
//       (e.g., "libcasa_").
//       <br>As suffix first ".so" is used, thereafter ".dylib" (for OS-X).
// </ul>
//
// It is a wrapper around functions dlopen, dlsym, and dlclose.
// If dlopen and so are not supported on a platform, the class acts as if
// the shared library could not be found.
// </synopsis>
 
// <example>
// <srcblock>
//    DynLib dl("derivedmscal", "libcasa_", "register_derivedmscal");
//    AlwaysAssert (dl.getHandle());
// </srcblock>
// Using this
//  loads the shared library <src>libcasa_derivedmscal.so</src> and
//  executes the given register initialization function.
// </example>
 
// <motivation>
// dlopen is a standard UNIX system call, but some operating systems
// do not support it or have different function names (notably Windows).
// In this way use of dynamic libraries is centralized and can easily b
// tailored as needed.
// </motivation>
 
class DynLib {
 public:
  // Load the dynamic library. It is tried with prefixes <src>prefix</src>
  // and "lib" (in that order) and with suffix ".so" or ".dylib" (for Apple).
  // No library version number is used.
  // If not loaded successfully, an exception is thrown.
  // <br>If a non-empty funcName is given, that function is looked up and
  // executed for initialization purposes. Its signature must be
  // <src>void func()</src>.
  // Note that the function name should not be mangled, thus declared
  // <src>extern "C"</src>.
  // An exception is thrown if the library is loaded successfully, but
  // <src>funcName</src> could not be found.
  // <br>If <src>closeOnDestruction=True</src>, the dynamic library is
  // closed on destruction of the DynLib object.
  DynLib(const std::string& library, const std::string& prefix = std::string(),
         const std::string& funcName = std::string(), bool closeOnDestruction = True);
 
  // The same as above, but it is tried with and without the given version
  // (in that order).
  DynLib(const std::string& library, const std::string& prefix, const std::string& version,
         const std::string& funcName, bool closeOnDestruction = True);
 
  // Load the dynamic library with the given name, prefix, and suffix.
  // If not loaded successfully, the internal handle is NULL.
  // <br>If <src>closeOnDestruction=True</src>, the dynamic library is closed
  // when the DynLib object is destructed.
  DynLib(const std::string& library, Bool closeOnDestruction, const std::string& prefix = "lib",
#ifdef __APPLE__
         const std::string& suffix = ".dylib");
#else
         const std::string& suffix = ".so");
#endif
 
  // Close the dynamic library if told so in the constructor.
  ~DynLib();
 
  // Get a pointer to a function in the dynamic library.
  // The pointer has to be casted with a reinterpret_cast to a function
  // pointer with the correct signature. When compiling with -pedantic the
  // compiler will give a warning for such a cast, because on some systems
  // (in particular some micro-controllers) a data pointer differs from a
  // function pointer. However, that problem cannot be solved.
  // For example:
  // <srcblock>
  //   typedef Int MyFunc(Int, Int);
  //   void* initfunc = DynLib::getFunc (mod, ("register_"+name).c_str());
  //   if (initFunc) {
  //     MyFunc* func = reinterpret_cast<MyFunc*>(initfunc);
  //     Int result = func(1,2);
  //   }
  // </srcblock>
  // casts to a function returning Int and taking two Ints.
  // <br>A null pointer is returned if the function could not be found.
  void* getFunc(const std::string& funcName);
 
  // Get the dynamic library handle.
  void* getHandle() const { return itsHandle; }
 
  // Get the possible error.
  const std::string& getError() const { return itsError; }
 
 private:
  // Try to open the library with some prefixes, suffixes and versions
  // and to execute the initialization function.
  // If successful, itsHandle is filled. Otherwise an exception is thrown.
  void attach(const std::string& name, const std::string& prefix, const std::string& version,
              const std::string& funcName);
 
  // Try to open the library with some prefixes, suffixes and versions
  // If successful, itsHandle is filled and the full library name is
  // returned. Otherwise an empty name is returned.
  std::string tryOpen(const std::string& name, const std::string& libdir, const std::string& prefix,
                      const std::string& version);
 
  // Open (load) the dynamic library.
  void open(const std::string& name);
 
  // Close (unload) the dynamic library (if opened).
  void close();
 
  // Try if the library can be opened using CASACORE_LDPATH.
  std::string tryCasacorePath(const std::string& library, const std::string& prefix,
                              const std::string& version);
 
  // # Handle to dynamic library; note that the pointer is not owned, so the
  // # generated copy ctor and assignment are fine.
  void* itsHandle;
  Bool itsDoClose;
  std::string itsError;
};
 
}  // namespace casacore
 
#endif