Add Gio::giomm_SignalProxy_async_callback() with C linkage

and use it instead of SignalProxy_async_callback().
Part of issue #1

2 files changed, 38 insertions, 5 deletions

diff --git a/gio/giomm/slot_async.cc b/gio/giomm/slot_async.cc
index db23dbf5..d06bf9a5 100644
--- a/gio/giomm/slot_async.cc
+++ b/gio/giomm/slot_async.cc
@@ -20,9 +20,14 @@
 
 namespace Gio
 {
-
+extern "C"
+{
+// A function with external linkage and C linkage does not get a mangled name.
+// Even though giomm_SignalProxy_async_callback is declared in a named namespace,
+// the linker does not see the namespace name, only 'giomm_SignalProxy_async_callback'.
+// Therefore the function name shall have a prefix, hopefully unique.
 void
-SignalProxy_async_callback(GObject*, GAsyncResult* res, void* data)
+giomm_SignalProxy_async_callback(GObject*, GAsyncResult* res, void* data)
 {
   Gio::SlotAsyncReady* the_slot = static_cast<Gio::SlotAsyncReady*>(data);
 
@@ -38,5 +43,13 @@ SignalProxy_async_callback(GObject*, GAsyncResult* res, void* data)
 
   delete the_slot;
 }
+} // extern "C"
+
+//TODO: Remove SignalProxy_async_callback when we can break ABI and API.
+void
+SignalProxy_async_callback(GObject* source_object, GAsyncResult* res, void* data)
+{
+  giomm_SignalProxy_async_callback(source_object, res, data);
+}
 
 } // namespace Gio
diff --git a/gio/giomm/slot_async.h b/gio/giomm/slot_async.h
index ed76b5b4..cc38cf84 100644
--- a/gio/giomm/slot_async.h
+++ b/gio/giomm/slot_async.h
@@ -24,14 +24,34 @@
 
 namespace Gio
 {
+extern "C"
+{
+/** Callback function, used in combination with Gio::SlotAsyncReady.
+ *
+ * Example:
+ * @code
+ * _WRAP_METHOD(void acquire_async(const Gio::SlotAsyncReady& slot{callback},
+ *   const Glib::RefPtr<Gio::Cancellable>& cancellable{.?}), g_permission_acquire_async,
+ *   slot_name slot, slot_callback Gio::giomm_SignalProxy_async_callback)
+ * @endcode
+ *
+ * @newin{2,78}
+ */
+GIOMM_API
+void giomm_SignalProxy_async_callback(GObject*, GAsyncResult* res, void* data);
 
+} // extern "C"
+
+//TODO: Remove SignalProxy_async_callback when we can break ABI and API.
 /** Callback function, used in combination with Gio::SlotAsyncReady.
  *
+ * Prefer giomm_SignalProxy_async_callback() as a callback from a C function.
+ *
  * Example:
  * @code
- * _WRAP_METHOD(void acquire_async(const SlotAsyncReady& slot{callback},
- *   const Glib::RefPtr<Cancellable>& cancellable{.?}), g_permission_acquire_async,
- *   slot_name slot, slot_callback SignalProxy_async_callback)
+ * _WRAP_METHOD(void acquire_async(const Gio::SlotAsyncReady& slot{callback},
+ *   const Glib::RefPtr<Gio::Cancellable>& cancellable{.?}), g_permission_acquire_async,
+ *   slot_name slot, slot_callback Gio::SignalProxy_async_callback)
  * @endcode
  */
 GIOMM_API