1 files changed, 69 insertions, 0 deletions
diff --git a/ACE/examples/Export/dll.h b/ACE/examples/Export/dll.h
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+// $Id$
+
+// To use the export macros with a DLL, a file will need to be
+// created (see ACE_wrapper/bin/generate_export_file.pl) and
+// included.  This file defines Test_Export (and the
+// TEST_SINGLETON_* macros).
+#include "test_export.h"
+
+#include "ace/Singleton.h"
+#include "ace/Null_Mutex.h"
+
+#define RETVAL 42
+
+// To expose a function outside of a DLL, use the *_Export
+// at the beginning of the function declaration.
+
+Test_Export int test_function ();
+
+// To expose data, put use the *Export at the beginning
+// of the variable declaration.  The extern is required when
+// building static libraries.
+
+extern Test_Export int test_variable;
+
+// To expose a class, put the *_Export between "class"
+// and the class name.
+
+class Test_Export test_class
+{
+public:
+  int method ();
+};
+
+// ACE_Singleton and its relatives are special cases.  The problem is
+// that ACE_Singleton is a template.  If the singleton is used in both
+// the DLL and the executable linking the DLL, then two instances of
+// the singleton will be used (which defeats the purpose of a Singleton).
+//
+// This occurs because the ACE_Singleton template is expanded in both
+// places because Visual C++ and Borland C++ do this automatically by
+// including the template source.  This in turn creates two copies of
+// the static member variable.
+//
+// So to get around this problem, the *_SINGLETON_DECLARE macro is
+// used to instruct the compiler to not create the second copy in the
+// program.  This macro solution does not work for Borland C++, so for
+// this compiler you must explicitly disable the template instantiation
+// using a #pragma (or use the other workaround below).
+//
+// Another workaround for this is to not to expose the Singleton itself
+// to the outside world, but to instead supply a function or static
+// member function that returns the singleton to the executable
+// (like get_dll_singleton () does below).
+
+#if defined (__BORLANDC__)
+# if !defined (TEST_BUILD_DLL)
+#   pragma option push -Jgx
+# endif
+#endif
+TEST_SINGLETON_DECLARE (ACE_Singleton, test_class, ACE_Null_Mutex)
+#if defined (__BORLANDC__)
+# if !defined (TEST_BUILD_DLL)
+#   pragma option pop
+# endif
+#endif
+
+typedef ACE_Singleton<test_class, ACE_Null_Mutex> TEST_SINGLETON;
+
+Test_Export test_class *get_dll_singleton ();