Make atexit callbacks threadsafe (#930)

src/hb-common.cc

@@ -724,8 +724,14 @@ static HB_LOCALE_T C_locale;
 static void
 free_C_locale (void)
 {
-  if (C_locale)
-    HB_FREE_LOCALE (C_locale);
+retry:
+  HB_LOCALE_T locale = (HB_LOCALE_T) hb_atomic_ptr_get (&C_locale);
+
+  if (!hb_atomic_ptr_cmpexch (&C_locale, locale, nullptr))
+    goto retry;
+
+  if (locale)
+    HB_FREE_LOCALE (locale);
 }
 #endif
 

src/hb-ft.cc

@@ -423,7 +423,12 @@ static hb_font_funcs_t *static_ft_funcs = nullptr;
 static
 void free_static_ft_funcs (void)
 {
-  hb_font_funcs_destroy (static_ft_funcs);
+retry:
+  hb_font_funcs_t *ft_funcs = (hb_font_funcs_t *) hb_atomic_ptr_get (&static_ft_funcs);
+  if (!hb_atomic_ptr_cmpexch (&static_ft_funcs, ft_funcs, nullptr))
+    goto retry;
+
+  hb_font_funcs_destroy (ft_funcs);
 }
 #endif
 
@@ -685,7 +690,12 @@ static FT_Library ft_library;
 static
 void free_ft_library (void)
 {
-  FT_Done_FreeType (ft_library);
+retry:
+  FT_Library library = (FT_Library) hb_atomic_ptr_get (&ft_library);
+  if (!hb_atomic_ptr_cmpexch (&ft_library, library, nullptr))
+    goto retry;
+
+  FT_Done_FreeType (library);
 }
 #endif
 

src/hb-glib.cc

@@ -370,7 +370,12 @@ static hb_unicode_funcs_t *static_glib_funcs = nullptr;
 static
 void free_static_glib_funcs (void)
 {
-  hb_unicode_funcs_destroy (static_glib_funcs);
+retry:
+  hb_unicode_funcs_t *glib_funcs = (hb_unicode_funcs_t *) hb_atomic_ptr_get (&static_glib_funcs);
+  if (!hb_atomic_ptr_cmpexch (&static_glib_funcs, glib_funcs, nullptr))
+    goto retry;
+
+  hb_unicode_funcs_destroy (glib_funcs);
 }
 #endif
 

src/hb-icu.cc

@@ -351,7 +351,12 @@ static hb_unicode_funcs_t *static_icu_funcs = nullptr;
 static
 void free_static_icu_funcs (void)
 {
-  hb_unicode_funcs_destroy (static_icu_funcs);
+retry:
+  hb_unicode_funcs_t *icu_funcs = (hb_unicode_funcs_t *) hb_atomic_ptr_get (&static_icu_funcs);
+  if (!hb_atomic_ptr_cmpexch (&static_icu_funcs, icu_funcs, nullptr))
+    goto retry;
+
+  hb_unicode_funcs_destroy (icu_funcs);
 }
 #endif
 

src/hb-ot-font.cc

@@ -217,7 +217,12 @@ static hb_font_funcs_t *static_ot_funcs = nullptr;
 static
 void free_static_ot_funcs (void)
 {
-  hb_font_funcs_destroy (static_ot_funcs);
+retry:
+  hb_font_funcs_t *ot_funcs = (hb_font_funcs_t *) hb_atomic_ptr_get (&static_ot_funcs);
+  if (!hb_atomic_ptr_cmpexch (&static_ot_funcs, ot_funcs, nullptr))
+    goto retry;
+
+  hb_font_funcs_destroy (ot_funcs);
 }
 #endif
 

src/hb-shape.cc

@@ -51,7 +51,12 @@ static const char **static_shaper_list;
 static
 void free_static_shaper_list (void)
 {
-  free (static_shaper_list);
+retry:
+  const char **shaper_list = (const char **) hb_atomic_ptr_get (&static_shaper_list);
+  if (!hb_atomic_ptr_cmpexch (&static_shaper_list, shaper_list, nullptr))
+    goto retry;
+
+  free (shaper_list);
 }
 #endif
 

src/hb-shaper.cc

@@ -44,8 +44,13 @@ static const hb_shaper_pair_t *static_shapers;
 static
 void free_static_shapers (void)
 {
-  if (unlikely (static_shapers != all_shapers))
-    free ((void *) static_shapers);
+retry:
+  hb_shaper_pair_t *shapers = (hb_shaper_pair_t *) hb_atomic_ptr_get (&static_shapers);
+  if (!hb_atomic_ptr_cmpexch (&static_shapers, shapers, nullptr))
+    goto retry;
+
+  if (unlikely (shapers != all_shapers))
+    free ((void *) shapers);
 }
 #endif
 

src/hb-ucdn.cc

@@ -237,7 +237,12 @@ static hb_unicode_funcs_t *static_ucdn_funcs = nullptr;
 static
 void free_static_ucdn_funcs (void)
 {
-  hb_unicode_funcs_destroy (static_ucdn_funcs);
+retry:
+  hb_unicode_funcs_t *ucdn_funcs = (hb_unicode_funcs_t *) hb_atomic_ptr_get (&static_ucdn_funcs);
+  if (!hb_atomic_ptr_cmpexch (&static_ucdn_funcs, ucdn_funcs, nullptr))
+    goto retry;
+
+  hb_unicode_funcs_destroy (ucdn_funcs);
 }
 #endif
 

src/hb-uniscribe.cc

@@ -223,11 +223,19 @@ struct hb_uniscribe_shaper_funcs_t {
 };
 static hb_uniscribe_shaper_funcs_t *uniscribe_funcs;
 
+#ifdef HB_USE_ATEXIT
 static inline void
 free_uniscribe_funcs (void)
 {
+retry:
+  hb_uniscribe_shaper_funcs_t *local_uniscribe_funcs =
+    (hb_uniscribe_shaper_funcs_t *) hb_atomic_ptr_get (&uniscribe_funcs);
+  if (!hb_atomic_ptr_cmpexch (&uniscribe_funcs, local_uniscribe_funcs, nullptr))
+    goto retry;
+
   free (uniscribe_funcs);
 }
+#endif
 
 static hb_uniscribe_shaper_funcs_t *
 hb_uniscribe_shaper_get_funcs (void)