gutils: avoid race setting prgname from g_option_context_parse()/g_application_run()

g_option_context_parse()/g_application_run()/g_test_init() for
convenience also call g_set_prgname(), when the prgname is unset at this
point. This was racy.

Fix the race by using an atomic compare-and-exchange and only reset the
value, if it is unset still.

gio/gapplication.c

@@ -38,6 +38,7 @@
 #include "gioenumtypes.h"
 #include "gioenums.h"
 #include "gfile.h"
+#include "glib-private.h"
 
 #include "glibintl.h"
 #include "gmarshal-internal.h"
@@ -2526,7 +2527,7 @@ g_application_run (GApplication  *application,
       gchar *prgname;
 
       prgname = g_path_get_basename (argv[0]);
-      g_set_prgname (prgname);
+      GLIB_PRIVATE_CALL (g_set_prgname_once) (prgname);
       g_free (prgname);
     }
 

glib/glib-private.c

@@ -23,6 +23,7 @@
 
 #include "glib-private.h"
 #include "glib-init.h"
+#include "gutilsprivate.h"
 
 #ifdef USE_INVALID_PARAMETER_HANDLER
 #include <crtdbg.h>
@@ -71,6 +72,8 @@ glib__private__ (void)
     g_find_program_for_path,
 
     g_uri_get_default_scheme_port,
+
+    g_set_prgname_once,
   };
 
   return &table;

glib/glib-private.h

@@ -288,6 +288,9 @@ typedef struct {
   /* See guri.c */
   int (* g_uri_get_default_scheme_port) (const char *scheme);
 
+  /* See gutils.c */
+  gboolean (* g_set_prgname_once) (const gchar *prgname);
+
   /* Add other private functions here, initialize them in glib-private.c */
 } GLibPrivateVTable;
 

glib/goption.c

@@ -35,6 +35,7 @@
 
 #include "gprintf.h"
 #include "glibintl.h"
+#include "gutilsprivate.h"
 
 #if defined G_OS_WIN32
 #include <windows.h>
@@ -1813,10 +1814,7 @@ g_option_context_parse (GOptionContext   *context,
       else
 	prgname = platform_get_argv0 ();
 
-      if (prgname)
-	g_set_prgname (prgname);
-      else
-	g_set_prgname ("<unknown>");
+      g_set_prgname_once (prgname ? prgname : "<unknown");
 
       g_free (prgname);
     }

glib/gtestutils.c

@@ -1658,7 +1658,7 @@ void
     }
 
   if (!g_get_prgname () && !no_g_set_prgname)
-    g_set_prgname ((*argv)[0]);
+    g_set_prgname_once ((*argv)[0]);
 
   if (g_getenv ("G_TEST_ROOT_PROCESS"))
     {

glib/gutils.c

@@ -1176,6 +1176,25 @@ g_set_prgname (const gchar *prgname)
   g_atomic_pointer_set (&g_prgname, prgname);
 }
 
+/**
+ * g_set_prgname_once:
+ * @prgname: the name of the program.
+ *
+ * If g_get_prgname() is not set, this is the same as setting
+ * the name via g_set_prgname() and %TRUE is returned. Otherwise,
+ * does nothing and returns %FALSE. This is thread-safe.
+ *
+ * Returns: whether g_prgname was initialized by the call.
+ */
+gboolean
+g_set_prgname_once (const gchar *prgname)
+{
+  /* if @prgname is NULL, then this has the same effect as calling
+   * (g_get_prgname()==NULL). */
+  prgname = g_intern_string (prgname);
+  return g_atomic_pointer_compare_and_exchange (&g_prgname, NULL, prgname);
+}
+
 static gchar *g_application_name = NULL;
 
 /**

glib/gutilsprivate.h

@@ -59,6 +59,8 @@ void _g_unset_cached_tmp_dir (void);
 
 gboolean _g_localtime (time_t timet, struct tm *tm);
 
+gboolean g_set_prgname_once (const gchar *prgname);
+
 G_END_DECLS
 
 #endif /* __G_UTILS_PRIVATE_H__ */