Fix callback races in glibmm when source is destructed

It is normal situation when glib main loop iterates sources on one
thread where it checks whether source is still active and its callback
functions can be called and glibmm Source being destroyed on other
thread. Glibmm should check once again that callback_data and
callback_funcs fields are still valid and GSource was not marked
as inactive while its callback handlers are called.

Fixes #41

1 files changed, 23 insertions, 7 deletions

diff --git a/glib/glibmm/main.cc b/glib/glibmm/main.cc
index e4095405..3ca2c739 100644
--- a/glib/glibmm/main.cc
+++ b/glib/glibmm/main.cc
@@ -149,13 +149,23 @@ SourceCallbackData::destroy_notify_callback(void* data)
 static SourceCallbackData*
 glibmm_source_get_callback_data(GSource* source)
 {
-  g_return_val_if_fail(source->callback_funcs != nullptr, nullptr);
+  /* There is race between iteration of sources in main loop
+   * that checks whether they are still active and source
+   * destruction happening in other threads.
+   */
+  gpointer callback_data = source->callback_data;
+  GSourceCallbackFuncs* callback_funcs = source->callback_funcs;
+
+  g_return_val_if_fail(callback_funcs != nullptr, nullptr);
+
+  if (g_source_is_destroyed(source))
+    return nullptr;
 
   GSourceFunc func;
   void* user_data = nullptr;
 
   // Retrieve the callback function and data.
-  (*source->callback_funcs->get)(source->callback_data, source, &func, &user_data);
+  (*callback_funcs->get)(callback_data, source, &func, &user_data);
 
   return static_cast<SourceCallbackData*>(user_data);
 }
@@ -920,7 +930,10 @@ Source::~Source() noexcept
   if (gobject_)
   {
     SourceCallbackData* const data = glibmm_source_get_callback_data(gobject_);
-    data->wrapper = nullptr;
+
+    if (data) {
+      data->wrapper = nullptr;
+    }
 
     GSource* const tmp_gobject = gobject_;
     gobject_ = nullptr;
@@ -940,7 +953,10 @@ Source::connect_generic(const sigc::slot_base& slot)
   // Don't override the callback data.  Reuse the existing one
   // calling SourceCallbackData::set_node() to register conn_node.
   SourceCallbackData* const data = glibmm_source_get_callback_data(gobject_);
-  data->set_node(conn_node);
+
+  if (data) {
+    data->set_node(conn_node);
+  }
 
   conn_node->install(gobject_);
   return connection;
@@ -972,7 +988,7 @@ inline // static
   Source::get_wrapper(GSource* source)
 {
   SourceCallbackData* const data = glibmm_source_get_callback_data(source);
-  return data->wrapper;
+  return (data) ? data->wrapper : nullptr;
 }
 
 // static
@@ -982,7 +998,7 @@ Source::prepare_vfunc(GSource* source, int* timeout)
   try
   {
     Source* const self = get_wrapper(source);
-    return self->prepare(*timeout);
+    return (self) ? self->prepare(*timeout) : 0;
   }
   catch (...)
   {
@@ -999,7 +1015,7 @@ Source::check_vfunc(GSource* source)
   try
   {
     Source* const self = get_wrapper(source);
-    return self->check();
+    return (self) ? self->check() : 0;
   }
   catch (...)
   {