ACE/examples/Export/dll.h

   1 // To use the export macros with a DLL, a file will need to be
   2 // created (see ACE_wrapper/bin/generate_export_file.pl) and
   3 // included.  This file defines Test_Export (and the
   4 // TEST_SINGLETON_* macros).
   5 #include "test_export.h"
   6
   7 #include "ace/Singleton.h"
   8 #include "ace/Null_Mutex.h"
   9
  10 #define RETVAL 42
  11
  12 // To expose a function outside of a DLL, use the *_Export
  13 // at the beginning of the function declaration.
  14
  15 Test_Export int test_function ();
  16
  17 // To expose data, put use the *Export at the beginning
  18 // of the variable declaration.  The extern is required when
  19 // building static libraries.
  20
  21 extern Test_Export int test_variable;
  22
  23 // To expose a class, put the *_Export between "class"
  24 // and the class name.
  25
  26 class Test_Export test_class
  27 {
  28 public:
  29   int method ();
  30 };
  31
  32 // ACE_Singleton and its relatives are special cases.  The problem is
  33 // that ACE_Singleton is a template.  If the singleton is used in both
  34 // the DLL and the executable linking the DLL, then two instances of
  35 // the singleton will be used (which defeats the purpose of a Singleton).
  36 //
  37 // This occurs because the ACE_Singleton template is expanded in both
  38 // places because Visual C++ and Borland C++ do this automatically by
  39 // including the template source.  This in turn creates two copies of
  40 // the static member variable.
  41 //
  42 // So to get around this problem, the *_SINGLETON_DECLARE macro is
  43 // used to instruct the compiler to not create the second copy in the
  44 // program.  This macro solution does not work for Borland C++, so for
  45 // this compiler you must explicitly disable the template instantiation
  46 // using a #pragma (or use the other workaround below).
  47 //
  48 // Another workaround for this is to not to expose the Singleton itself
  49 // to the outside world, but to instead supply a function or static
  50 // member function that returns the singleton to the executable
  51 // (like get_dll_singleton () does below).
  52
  53 #if defined (__BORLANDC__)
  54 # if !defined (TEST_BUILD_DLL)
  55 #   pragma option push -Jgx
  56 # endif
  57 #endif
  58 TEST_SINGLETON_DECLARE (ACE_Singleton, test_class, ACE_Null_Mutex)
  59 #if defined (__BORLANDC__)
  60 # if !defined (TEST_BUILD_DLL)
  61 #   pragma option pop
  62 # endif
  63 #endif
  64
  65 typedef ACE_Singleton<test_class, ACE_Null_Mutex> TEST_SINGLETON;
  66
  67 Test_Export test_class *get_dll_singleton ();