Add macros to handle constructor functions on the compilers that support it

This is only supported on some compilers, so we define G_HAS_CONSTRUCTORS
when it is supported. However, when it is supported we guarantee that
both constructors and destructors work, in executables as well as shared
libraries (including runtime unloading of shared libraries).

Usage is a bit unorthodox, as some compilers need to use #pragma to
implement constructors, and #pragma can't be used in macros.

The canonical way to use this:

  #ifdef G_DEFINE_CONSTRUCTOR_NEEDS_PRAGMA
  #pragma G_DEFINE_CONSTRUCTOR_PRAGMA_ARGS(my_constructor)
  #endif
  G_DEFINE_CONSTRUCTOR(my_constructor)

  static void my_constructor (void)
  {
    ...

  #ifdef G_DEFINE_DESTRUCTOR_NEEDS_PRAGMA
  #pragma G_DEFINE_DESTRUCTOR_PRAGMA_ARGS(my_destructor)
  #endif
  G_DEFINE_DESTRUCTOR(my_destructor)

  static void my_destructor (void)
  {
    ...

1 files changed, 93 insertions, 0 deletions

diff --git a/glib/gmacros.h b/glib/gmacros.h
index 2b340cb0d..4fc20bf36 100644
--- a/glib/gmacros.h
+++ b/glib/gmacros.h
@@ -318,4 +318,97 @@
 #define GLIB_DEPRECATED_FOR(f) G_DEPRECATED_FOR(f)
 #endif
 
+/*
+  If G_HAS_CONSTRUCTORS is true then the compiler support *both* constructors and
+  destructors, in a sane way, including e.g. on library unload. If not you're on
+  your own.
+
+  Some compilers need #pragma to handle this, which does not work with macros,
+  so the way you need to use this is (for constructors):
+
+  #ifdef G_DEFINE_CONSTRUCTOR_NEEDS_PRAGMA
+  #pragma G_DEFINE_CONSTRUCTOR_PRAGMA_ARGS(my_constructor)
+  #endif
+  G_DEFINE_CONSTRUCTOR(my_constructor)
+  static void my_constructor(void) {
+   ...
+  }
+
+*/
+
+#if  __GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 7)
+
+#define G_HAS_CONSTRUCTORS 1
+
+#define G_DEFINE_CONSTRUCTOR(_func) static void __attribute__((constructor)) _func (void);
+#define G_DEFINE_DESTRUCTOR(_func) static void __attribute__((destructor)) _func (void);
+
+#elif _MSC_VER >= 1500
+/* Visual studio 2008 and later has _Pragma */
+
+#define G_HAS_CONSTRUCTORS 1
+
+#define G_DEFINE_CONSTRUCTOR(_func) \
+  static void _func(void); \
+  static int _func ## _wrapper(void) { _func(); return 0; } \
+  __pragma(section(".CRT$XCU",read)) \
+  __declspec(allocate(".CRT$XCU")) static int (* _array ## _func)(void) = _func ## _wrapper;
+
+#define G_DEFINE_DESTRUCTOR(_func) \
+  static void _func(void); \
+  static int _func ## _constructor(void) { atexit (_func); return 0; } \
+  __pragma(section(".CRT$XCU",read)) \
+  __declspec(allocate(".CRT$XCU")) static int (* _array ## _func)(void) = _func ## _constructor;
+
+#elif defined (_MSC_VER)
+
+#define G_HAS_CONSTRUCTORS 1
+
+/* Pre Visual studio 2008 must use #pragma section */
+#define G_DEFINE_CONSTRUCTOR_NEEDS_PRAGMA 1
+#define G_DEFINE_DESTRUCTOR_NEEDS_PRAGMA 1
+
+#define G_DEFINE_CONSTRUCTOR_PRAGMA_ARGS(_func) \
+  section(".CRT$XCU",read)
+#define G_DEFINE_CONSTRUCTOR(_func) \
+  static void _func(void); \
+  static int _func ## _wrapper(void) { _func(); return 0; } \
+  __declspec(allocate(".CRT$XCU")) static int (*p)(void) = _func ## _wrapper;
+
+#define G_DEFINE_DESTRUCTOR_PRAGMA_ARGS(_func) \
+  section(".CRT$XCU",read)
+#define G_DEFINE_DESTRUCTOR(_func) \
+  static void _func(void); \
+  static int _func ## _constructor(void) { atexit (_func); return 0; } \
+  __declspec(allocate(".CRT$XCU")) static int (* _array ## _func)(void) = _func ## _constructor;
+
+#elif defined(__SUNPRO_C)
+
+/* This is not tested, but i believe it should work, based on:
+ * http://opensource.apple.com/source/OpenSSL098/OpenSSL098-35/src/fips/fips_premain.c
+ */
+
+#define G_HAS_CONSTRUCTORS 1
+
+#define G_DEFINE_CONSTRUCTOR_NEEDS_PRAGMA 1
+#define G_DEFINE_DESTRUCTOR_NEEDS_PRAGMA 1
+
+#define G_DEFINE_CONSTRUCTOR_PRAGMA_ARGS(_func) \
+  init(_func)
+#define G_DEFINE_CONSTRUCTOR(_func) \
+  static void _func(void);
+
+#define G_DEFINE_DESTRUCTOR_PRAGMA_ARGS(_func) \
+  fini(_func)
+#define G_DEFINE_DESTRUCTOR(_func) \
+  static void _func(void);
+
+#else
+
+/* constructors not supported for this compiler */
+
+#endif
+
+
+
 #endif /* __G_MACROS_H__ */