[glibmm] Make SignalTimeout, SignalIdle::connect_once() more thread safe.

[Murray Cumming <murrayc src gnome org>]

commit 08c585e5f327bde1ddc25002fc4f97db03600f73
Author: Kjell Ahlstedt <kjell ahlstedt bredband net>
Date:   Thu Mar 22 19:06:33 2012 +0100

    Make SignalTimeout,SignalIdle::connect_once() more thread safe.
    
    * glib/glibmm/main.cc: Don't create a sigc::connection in the connect_once()
    methods. Bug #396963.

 ChangeLog           |    7 ++++++
 glib/glibmm/main.cc |   58 +++++++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 59 insertions(+), 6 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 5ccd957..47fcd2e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2012-03-22  Kjell Ahlstedt  <kjell ahlstedt bredband net>
+
+	Make SignalTimeout,SignalIdle::connect_once() more thread safe.
+
+	* glib/glibmm/main.cc: Don't create a sigc::connection in the connect_once()
+	methods. Bug #396963.
+
 2012-03-30  Murray Cumming  <murrayc murrayc com>
 
 	Regenerate .defs files.
diff --git a/glib/glibmm/main.cc b/glib/glibmm/main.cc
index 91da784..cf1b7c6 100644
--- a/glib/glibmm/main.cc
+++ b/glib/glibmm/main.cc
@@ -84,7 +84,7 @@ void* SourceConnectionNode::notify(void* data)
     g_source_destroy(s);
 
     // Destroying the object triggers execution of destroy_notify_handler(),
-    // eiter immediately or later, so we leave that to do the deletion.
+    // either immediately or later, so we leave that to do the deletion.
   }
 
   return 0;
@@ -214,6 +214,26 @@ static gboolean glibmm_source_callback(void* data)
   return 0;
 }
 
+/* Only used by SignalTimeout::connect_once() and SignalIdle::connect_once().
+ * These don't use Glib::Source, to avoid the unnecessary overhead
+ * of a completely unused wrapper object.
+ */
+static gboolean glibmm_source_callback_once(void* data)
+{
+  SourceConnectionNode* const conn_data = static_cast<SourceConnectionNode*>(data);
+
+  try
+  {
+    // Recreate the specific slot from the generic slot node.
+    (*static_cast<sigc::slot<void>*>(conn_data->get_slot()))();
+  }
+  catch(...)
+  {
+    Glib::exception_handlers_invoke();
+  }
+  return 0; // Destroy the event source after one call
+}
+
 static gboolean glibmm_iosource_callback(GIOChannel*, GIOCondition condition, void* data)
 {
   SourceCallbackData *const callback_data = static_cast<SourceCallbackData*>(data);
@@ -251,6 +271,29 @@ static gboolean glibmm_child_watch_callback(GPid pid, gint child_status, void* d
   return 0;
 }
 
+static void glibmm_signal_connect_once(const sigc::slot<void>& slot, int priority,
+                                       GSource* source, GMainContext* context)
+{
+  SourceConnectionNode* const conn_node = new SourceConnectionNode(slot);
+
+  if (priority != G_PRIORITY_DEFAULT)
+    g_source_set_priority(source, priority);
+
+  g_source_set_callback(
+    source, &glibmm_source_callback_once, conn_node,
+    &SourceConnectionNode::destroy_notify_callback);
+
+  g_source_attach(source, context);
+  // GMainContext holds a reference to source until the source is dispatched and
+  // glibmm_source_callback_once() returns 0. Even if that has happened now
+  // (in another thread), conn_node and source still exist.
+  // SourceConnectionNode::destroy_notify_callback() has not been called,
+  // because the initial reference to source remains until the following call
+  // to g_source_unref().
+  conn_node->install(source);
+  g_source_unref(source);
+}
+
 } // anonymous namespace
 
 
@@ -315,7 +358,8 @@ sigc::connection SignalTimeout::connect(const sigc::slot<bool>& slot,
 void SignalTimeout::connect_once(const sigc::slot<void>& slot,
                                  unsigned int interval, int priority)
 {
-    connect(sigc::bind_return(slot, false), interval, priority);
+  GSource* const source = g_timeout_source_new(interval);
+  glibmm_signal_connect_once(slot, priority, source, context_);
 }
 
 /* Note that this is our equivalent of g_timeout_add_seconds(). */
@@ -344,7 +388,8 @@ sigc::connection SignalTimeout::connect_seconds(const sigc::slot<bool>& slot,
 void SignalTimeout::connect_seconds_once(const sigc::slot<void>& slot,
                                          unsigned int interval, int priority)
 {
-    connect_seconds(sigc::bind_return(slot, false), interval, priority);
+  GSource* const source = g_timeout_source_new_seconds(interval);
+  glibmm_signal_connect_once(slot, priority, source, context_);
 }
 
 SignalTimeout signal_timeout()
@@ -384,7 +429,8 @@ sigc::connection SignalIdle::connect(const sigc::slot<bool>& slot, int priority)
 
 void SignalIdle::connect_once(const sigc::slot<void>& slot, int priority)
 {
-    connect(sigc::bind_return(slot, false), priority);
+  GSource* const source = g_idle_source_new();
+  glibmm_signal_connect_once(slot, priority, source, context_);
 }
 
 SignalIdle signal_idle()
@@ -795,7 +841,7 @@ Source::Source()
 {
   g_source_set_callback(
       gobject_, &glibmm_dummy_source_callback,
-      new SourceCallbackData(this), // our persistant callback data object
+      new SourceCallbackData(this), // our persistent callback data object
       &SourceCallbackData::destroy_notify_callback);
 }
 
@@ -805,7 +851,7 @@ Source::Source(GSource* cast_item, GSourceFunc callback_func)
 {
   g_source_set_callback(
       gobject_, callback_func,
-      new SourceCallbackData(this), // our persistant callback data object
+      new SourceCallbackData(this), // our persistent callback data object
       &SourceCallbackData::destroy_notify_callback);
 }