glib/glibmm/wrap.cc

/* wrap.cc
 *
 * Copyright (C) 1998-2002 The gtkmm Development Team
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <glibmmconfig.h>
#include <glibmm/object.h>
#include <glibmm/quark.h>
#include <glibmm/wrap.h>
#include <vector>
#include <glib.h>
#include <glib-object.h>

namespace
{

// Although the new g_type_set_qdata() interface is used now, we still need
// a table because we cannot assume that a function pointer fits into void*
// on any platform.  Nevertheless, indexing a vector costs almost nothing
// compared to a map lookup.

using WrapFuncTable = std::vector<Glib::WrapNewFunction>;

static WrapFuncTable* wrap_func_table = nullptr;

} // anonymous namespace

namespace Glib
{

void
wrap_register_init()
{
  // g_type_init() is deprecated as of 2.36.
  // g_type_init();

  if (!Glib::quark_)
  {
    Glib::quark_ = g_quark_from_static_string("glibmm__Glib::quark_");
    Glib::quark_cpp_wrapper_deleted_ =
      g_quark_from_static_string("glibmm__Glib::quark_cpp_wrapper_deleted_");
  }

  if (!wrap_func_table)
  {
    // Make the first element a dummy so we can detect unregistered types.
    // g_type_get_qdata() returns NULL if no data has been set up.
    wrap_func_table = new WrapFuncTable(1);
  }
}

void
wrap_register_cleanup()
{
  if (wrap_func_table)
  {
    delete wrap_func_table;
    wrap_func_table = nullptr;
  }
}

// Register the unique wrap_new() function of a new C++ wrapper type.
// The GType argument specifies the parent C type to wrap from.
//
void
wrap_register(GType type, WrapNewFunction func)
{
  // 0 is not a valid GType.
  // It would lead to a critical warning in g_type_set_qdata().
  // We allow this, failing silently, to make life easier for gstreamermm.
  if (type == 0)
    return;

  const guint idx = wrap_func_table->size();
  wrap_func_table->emplace_back(func);

  // Store the table index in the type's static data.
  g_type_set_qdata(type, Glib::quark_, GUINT_TO_POINTER(idx));
}

static Glib::ObjectBase*
wrap_create_new_wrapper(GObject* object)
{
  g_return_val_if_fail(wrap_func_table != nullptr, nullptr);

  const bool gtkmm_wrapper_already_deleted =
    (bool)g_object_get_qdata((GObject*)object, Glib::quark_cpp_wrapper_deleted_);
  if (gtkmm_wrapper_already_deleted)
  {
    g_warning("Glib::wrap_create_new_wrapper: Attempted to create a 2nd C++ wrapper for a C "
              "instance whose C++ wrapper has been deleted.");
    return nullptr;
  }

  // Traverse upwards through the inheritance hierarchy
  // to find the most-specialized wrap_new() for this GType.
  //
  for (GType type = G_OBJECT_TYPE(object); type != 0; type = g_type_parent(type))
  {
    // Look up the wrap table index stored in the type's static data.
    // If a wrap_new() has been registered for the type then call it.
    //
    if (const gpointer idx = g_type_get_qdata(type, Glib::quark_))
    {
      const Glib::WrapNewFunction func = (*wrap_func_table)[GPOINTER_TO_UINT(idx)];
      return (*func)(object);
    }
  }

  return nullptr;
}

static gboolean
gtype_wraps_interface(GType implementer_type, GType interface_type)
{
  guint n_ifaces = 0;
  GType* ifaces = g_type_interfaces(implementer_type, &n_ifaces);

  gboolean found = FALSE;
  while (n_ifaces-- && !found)
  {
    found = (ifaces[n_ifaces] == interface_type);
  }

  g_free(ifaces);

  return found;
}

Glib::ObjectBase*
wrap_create_new_wrapper_for_interface(GObject* object, GType interface_gtype)
{
  g_return_val_if_fail(wrap_func_table != nullptr, nullptr);

  const bool gtkmm_wrapper_already_deleted =
    (bool)g_object_get_qdata((GObject*)object, Glib::quark_cpp_wrapper_deleted_);
  if (gtkmm_wrapper_already_deleted)
  {
    g_warning("Glib::wrap_create_new_wrapper: Attempted to create a 2nd C++ wrapper for a C "
              "instance whose C++ wrapper has been deleted.");
    return nullptr;
  }

  // Traverse upwards through the inheritance hierarchy
  // to find the most-specialized wrap_new() for this GType.
  //
  for (GType type = G_OBJECT_TYPE(object); type != 0; type = g_type_parent(type))
  {
    // Look up the wrap table index stored in the type's static data.
    // If a wrap_new() has been registered for the type then call it.
    // But only if the type implements the interface,
    // so that the C++ instance is likely to inherit from the appropriate class too.
    //
    const gpointer idx = g_type_get_qdata(type, Glib::quark_);
    if (idx && gtype_wraps_interface(type, interface_gtype))
    {
      const Glib::WrapNewFunction func = (*wrap_func_table)[GPOINTER_TO_UINT(idx)];
      return (*func)(object);
    }
  }

  return nullptr;
}

// This is a factory function that converts any type to
// its C++ wrapper instance by looking up a wrap_new() function in a map.
//
ObjectBase*
wrap_auto(GObject* object, bool take_copy)
{
  if (!object)
    return nullptr;

  // Look up current C++ wrapper instance:
  ObjectBase* pCppObject = ObjectBase::_get_current_wrapper(object);

  if (!pCppObject)
  {
    // There's not already a wrapper: generate a new C++ instance.
    pCppObject = wrap_create_new_wrapper(object);

    if (!pCppObject)
    {
      g_warning("Failed to wrap object of type '%s'. Hint: this error is commonly caused by "
                "failing to call a library init() function.",
        G_OBJECT_TYPE_NAME(object));
      return nullptr;
    }
  }

  // take_copy=true is used where the GTK+ function doesn't do
  // an extra ref for us, and always for plain struct members.
  if (take_copy)
    pCppObject->reference();

  return pCppObject;
}

Glib::RefPtr<Object>
wrap(GObject* object, bool take_copy /* = false */)
{
  return Glib::RefPtr<Object>(dynamic_cast<Object*>(wrap_auto(object, take_copy)));
}

} /* namespace Glib */