widget/gtk/nsGtkUtils.h

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim:expandtab:shiftwidth=4:tabstop=4:
   3  */
   4 /* This Source Code Form is subject to the terms of the Mozilla Public
   5  * License, v. 2.0. If a copy of the MPL was not distributed with this
   6  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   7
   8 #ifndef nsGtkUtils_h__
   9 #define nsGtkUtils_h__
  10
  11 #include <glib.h>
  12
  13 // Some gobject functions expect functions for gpointer arguments.
  14 // gpointer is void* but C++ doesn't like casting functions to void*.
  15 template <class T>
  16 static inline gpointer FuncToGpointer(T aFunction) {
  17   return reinterpret_cast<gpointer>(
  18       reinterpret_cast<uintptr_t>
  19       // This cast just provides a warning if T is not a function.
  20       (reinterpret_cast<void (*)()>(aFunction)));
  21 }
  22
  23 // Type-safe alternative to glib's g_clear_pointer.
  24 //
  25 // Using `g_clear_pointer` itself causes UBSan to report undefined
  26 // behavior. The function-based definition of `g_clear_pointer` (as
  27 // opposed to the older preprocessor macro) treats the `destroy`
  28 // function as a `void (*)(void *)`, but the actual destroy functions
  29 // that are used (say `wl_buffer_destroy`) usually have more specific
  30 // pointer types.
  31 //
  32 // C++ draft n4901 [expr.call] para 6:
  33 //
  34 //     Calling a function through an expression whose function type E
  35 //     is different from the function type F of the called function’s
  36 //     definition results in undefined behavior unless the type
  37 //     “pointer to F” can be converted to the type “pointer to E” via
  38 //     a function pointer conversion (7.3.14).
  39 //
  40 // §7.3.14 only talks about converting between noexcept and ordinary
  41 // function pointers.
  42 template <class T>
  43 static inline void MozClearPointer(T*& pointer, void (*destroy)(T*)) {
  44   T* hold = pointer;
  45   pointer = nullptr;
  46   if (hold) {
  47     destroy(hold);
  48   }
  49 }
  50
  51 template <class T>
  52 static inline void MozClearHandleID(T& handle, gboolean (*destroy)(T)) {
  53   if (handle) {
  54     destroy(handle);
  55     handle = 0;
  56   }
  57 }
  58
  59 #endif  // nsGtkUtils_h__