printoperation: add some assertions

Let's assert that we schedule the idle callback exactly once.

These assertions are not perfect because if the callback executes before
we schedule it, then the assertion itself would be a use-after-free,
since I'm using the PrinterFinder to track whether the callback that
frees it has been scheduled. But in practice when using loupe's print
dialog, I was noticing the callback scheduled twice before it was
executed. The assertion would have caught this problem.

diff --git a/gtk/print/gtkprintoperation-unix.c b/gtk/print/gtkprintoperation-unix.c
index 4d592eeb6cddeb07064dae1d72f3180a95772511..ab69e1970be0aaa53cf207a8d6a6eed2c68187f5 100644 (file)
--- a/gtk/print/gtkprintoperation-unix.c
+++ b/gtk/print/gtkprintoperation-unix.c
@@ -1056,6 +1056,7 @@ gtk_print_run_page_setup_dialog_async (GtkWindow            *parent,
 struct _PrinterFinder
 {
   gboolean found_printer;
+  gboolean scheduled_callback;
   GFunc func;
   gpointer data;
   char *printer_name;
@@ -1088,6 +1089,14 @@ find_printer_idle (gpointer data)
   return G_SOURCE_REMOVE;
 }
 
+static void
+schedule_finder_callback (PrinterFinder *finder)
+{
+  g_assert (!finder->scheduled_callback);
+  g_idle_add (find_printer_idle, finder);
+  finder->scheduled_callback = TRUE;
+}
+
 static void
 printer_added_cb (GtkPrintBackend *backend,
                   GtkPrinter      *printer,
@@ -1120,7 +1129,7 @@ printer_added_cb (GtkPrintBackend *backend,
     }
 
   if (finder->found_printer)
-    g_idle_add (find_printer_idle, finder);
+    schedule_finder_callback (finder);
 }
 
 static void
@@ -1139,7 +1148,7 @@ printer_list_done_cb (GtkPrintBackend *backend,
    * above, then we're finished.
    */
   if (finder->backends == NULL && !finder->found_printer)
-    g_idle_add (find_printer_idle, finder);
+    schedule_finder_callback (finder);
 }
 
 static void
@@ -1229,7 +1238,7 @@ find_printer (const char *printer,
 
   if (finder->backends == NULL)
     {
-      g_idle_add (find_printer_idle, finder);
+      schedule_finder_callback (finder);
       return;
     }