tests: Check thread safety of GParamSpecPool

Aside from checking that we're accessing the global GParamSpecPool
without necessarily initializing GObjectClass, we should also verify
that we're doing so safely without the class init lock.

gobject/tests/properties-introspection.c

@@ -49,12 +49,66 @@ properties_introspection (void)
   g_test_trap_assert_stderr ("");
 }
 
+static gpointer
+inspect_func (gpointer data)
+{
+  unsigned int *n_checks = data; /* (atomic) */
+
+  gpointer klass = NULL;
+  do
+    {
+      klass = g_type_default_interface_ref (my_testable_get_type ());
+    }
+  while (klass == NULL);
+
+  GParamSpec *pspec = NULL;
+  do
+    {
+      pspec = g_object_interface_find_property (klass, "check");
+    }
+  while (pspec == NULL);
+
+  g_type_default_interface_unref (klass);
+
+  g_atomic_int_inc (n_checks);
+
+  return NULL;
+}
+
+#define N_THREADS 10
+
+static void
+properties_collision (void)
+{
+  GThread *threads[N_THREADS];
+  unsigned int n_checks = 0; /* (atomic) */
+
+  g_test_summary ("Verify that multiple threads create a single GParamSpecPool.");
+
+  for (unsigned int i = 0; i < N_THREADS; i++)
+    {
+      char *t_name = g_strdup_printf ("inspect [%d]", i);
+      threads[i] = g_thread_new (t_name, inspect_func, &n_checks);
+      g_assert_nonnull (threads[i]);
+      g_free (t_name);
+    }
+
+  while (g_atomic_int_get (&n_checks) != N_THREADS)
+    g_usleep (50);
+
+  for (unsigned int i = 0; i < N_THREADS; i++)
+    g_thread_join (threads[i]);
+}
+
+#undef N_THREADS
+
 int
 main (int argc, char *argv[])
 {
   g_test_init (&argc, &argv, NULL);
 
   g_test_add_func ("/properties/introspection", properties_introspection);
+  g_test_add_func ("/properties/collision", properties_collision);
 
   return g_test_run ();
 }