Add internal helper GContextSpecificGroup

Add a new internal helper called GContextSpecificGroup.

This is a mechanism for helping to maintain a group of context-specific
monitor objects (eg: GAppInfoMonitor, GUnixMountMonitor).

https://bugzilla.gnome.org/show_bug.cgi?id=742599

gio/gcontextspecificgroup.h

@@ -0,0 +1,47 @@
+/*
+ * Copyright © 2015 Canonical Limited
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the licence, 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Ryan Lortie <desrt@desrt.ca>
+ */
+
+#ifndef __G_CONTEXT_SPECIFIC_GROUP_H__
+#define __G_CONTEXT_SPECIFIC_GROUP_H__
+
+#include <glib-object.h>
+
+typedef struct
+{
+  GHashTable *table;
+  GMutex      lock;
+} GContextSpecificGroup;
+
+gpointer
+g_context_specific_group_get (GContextSpecificGroup *group,
+                              GType                  type,
+                              goffset                context_offset,
+                              GCallback              start_func);
+
+void
+g_context_specific_group_remove (GContextSpecificGroup *group,
+                                 GMainContext          *context,
+                                 gpointer               instance,
+                                 GCallback              stop_func);
+
+void
+g_context_specific_group_emit (GContextSpecificGroup *group,
+                               guint                  signal_id);
+
+#endif /* __G_CONTEXT_SPECIFIC_GROUP_H__ */