gtk2/gtk/gtkprintbackend.c
2010-07-13 19:40:47 +02:00

841 lines
24 KiB
C

/* GTK - The GIMP Toolkit
* gtkprintbackend.h: Abstract printer backend interfaces
* Copyright (C) 2003, Red Hat, Inc.
*
* 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 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, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
#include "config.h"
#include <string.h>
#include <gmodule.h>
#include "gtkintl.h"
#include "gtkmodules.h"
#include "gtkmarshalers.h"
#include "gtkprivate.h"
#include "gtkprintbackend.h"
#define GTK_PRINT_BACKEND_GET_PRIVATE(o) \
(G_TYPE_INSTANCE_GET_PRIVATE ((o), GTK_TYPE_PRINT_BACKEND, GtkPrintBackendPrivate))
static void gtk_print_backend_dispose (GObject *object);
static void gtk_print_backend_set_property (GObject *object,
guint prop_id,
const GValue *value,
GParamSpec *pspec);
static void gtk_print_backend_get_property (GObject *object,
guint prop_id,
GValue *value,
GParamSpec *pspec);
struct _GtkPrintBackendPrivate
{
GHashTable *printers;
guint printer_list_requested : 1;
guint printer_list_done : 1;
GtkPrintBackendStatus status;
char **auth_info_required;
char **auth_info;
};
enum {
PRINTER_LIST_CHANGED,
PRINTER_LIST_DONE,
PRINTER_ADDED,
PRINTER_REMOVED,
PRINTER_STATUS_CHANGED,
REQUEST_PASSWORD,
LAST_SIGNAL
};
static guint signals[LAST_SIGNAL] = { 0 };
enum
{
PROP_ZERO,
PROP_STATUS
};
static GObjectClass *backend_parent_class;
GQuark
gtk_print_backend_error_quark (void)
{
static GQuark quark = 0;
if (quark == 0)
quark = g_quark_from_static_string ("gtk-print-backend-error-quark");
return quark;
}
/*****************************************
* GtkPrintBackendModule modules *
*****************************************/
typedef struct _GtkPrintBackendModule GtkPrintBackendModule;
typedef struct _GtkPrintBackendModuleClass GtkPrintBackendModuleClass;
struct _GtkPrintBackendModule
{
GTypeModule parent_instance;
GModule *library;
void (*init) (GTypeModule *module);
void (*exit) (void);
GtkPrintBackend* (*create) (void);
gchar *path;
};
struct _GtkPrintBackendModuleClass
{
GTypeModuleClass parent_class;
};
G_DEFINE_TYPE (GtkPrintBackendModule, _gtk_print_backend_module, G_TYPE_TYPE_MODULE)
#define GTK_TYPE_PRINT_BACKEND_MODULE (_gtk_print_backend_module_get_type ())
#define GTK_PRINT_BACKEND_MODULE(module) (G_TYPE_CHECK_INSTANCE_CAST ((module), GTK_TYPE_PRINT_BACKEND_MODULE, GtkPrintBackendModule))
static GSList *loaded_backends;
static gboolean
gtk_print_backend_module_load (GTypeModule *module)
{
GtkPrintBackendModule *pb_module = GTK_PRINT_BACKEND_MODULE (module);
gpointer initp, exitp, createp;
pb_module->library = g_module_open (pb_module->path, G_MODULE_BIND_LAZY | G_MODULE_BIND_LOCAL);
if (!pb_module->library)
{
g_warning ("%s", g_module_error());
return FALSE;
}
/* extract symbols from the lib */
if (!g_module_symbol (pb_module->library, "pb_module_init",
&initp) ||
!g_module_symbol (pb_module->library, "pb_module_exit",
&exitp) ||
!g_module_symbol (pb_module->library, "pb_module_create",
&createp))
{
g_warning ("%s", g_module_error());
g_module_close (pb_module->library);
return FALSE;
}
pb_module->init = initp;
pb_module->exit = exitp;
pb_module->create = createp;
/* call the printbackend's init function to let it */
/* setup anything it needs to set up. */
pb_module->init (module);
return TRUE;
}
static void
gtk_print_backend_module_unload (GTypeModule *module)
{
GtkPrintBackendModule *pb_module = GTK_PRINT_BACKEND_MODULE (module);
pb_module->exit();
g_module_close (pb_module->library);
pb_module->library = NULL;
pb_module->init = NULL;
pb_module->exit = NULL;
pb_module->create = NULL;
}
/* This only will ever be called if an error occurs during
* initialization
*/
static void
gtk_print_backend_module_finalize (GObject *object)
{
GtkPrintBackendModule *module = GTK_PRINT_BACKEND_MODULE (object);
g_free (module->path);
G_OBJECT_CLASS (_gtk_print_backend_module_parent_class)->finalize (object);
}
static void
_gtk_print_backend_module_class_init (GtkPrintBackendModuleClass *class)
{
GTypeModuleClass *module_class = G_TYPE_MODULE_CLASS (class);
GObjectClass *gobject_class = G_OBJECT_CLASS (class);
module_class->load = gtk_print_backend_module_load;
module_class->unload = gtk_print_backend_module_unload;
gobject_class->finalize = gtk_print_backend_module_finalize;
}
static void
gtk_print_backend_set_property (GObject *object,
guint prop_id,
const GValue *value,
GParamSpec *pspec)
{
GtkPrintBackend *backend = GTK_PRINT_BACKEND (object);
GtkPrintBackendPrivate *priv;
priv = backend->priv = GTK_PRINT_BACKEND_GET_PRIVATE (backend);
switch (prop_id)
{
case PROP_STATUS:
priv->status = g_value_get_int (value);
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
break;
}
}
static void
gtk_print_backend_get_property (GObject *object,
guint prop_id,
GValue *value,
GParamSpec *pspec)
{
GtkPrintBackend *backend = GTK_PRINT_BACKEND (object);
GtkPrintBackendPrivate *priv;
priv = backend->priv = GTK_PRINT_BACKEND_GET_PRIVATE (backend);
switch (prop_id)
{
case PROP_STATUS:
g_value_set_int (value, priv->status);
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
break;
}
}
static void
_gtk_print_backend_module_init (GtkPrintBackendModule *pb_module)
{
}
static GtkPrintBackend *
_gtk_print_backend_module_create (GtkPrintBackendModule *pb_module)
{
GtkPrintBackend *pb;
if (g_type_module_use (G_TYPE_MODULE (pb_module)))
{
pb = pb_module->create ();
g_type_module_unuse (G_TYPE_MODULE (pb_module));
return pb;
}
return NULL;
}
static GtkPrintBackend *
_gtk_print_backend_create (const gchar *backend_name)
{
GSList *l;
gchar *module_path;
gchar *full_name;
GtkPrintBackendModule *pb_module;
GtkPrintBackend *pb;
for (l = loaded_backends; l != NULL; l = l->next)
{
pb_module = l->data;
if (strcmp (G_TYPE_MODULE (pb_module)->name, backend_name) == 0)
return _gtk_print_backend_module_create (pb_module);
}
pb = NULL;
if (g_module_supported ())
{
full_name = g_strconcat ("printbackend-", backend_name, NULL);
module_path = _gtk_find_module (full_name, "printbackends");
g_free (full_name);
if (module_path)
{
pb_module = g_object_new (GTK_TYPE_PRINT_BACKEND_MODULE, NULL);
g_type_module_set_name (G_TYPE_MODULE (pb_module), backend_name);
pb_module->path = g_strdup (module_path);
loaded_backends = g_slist_prepend (loaded_backends,
pb_module);
pb = _gtk_print_backend_module_create (pb_module);
/* Increase use-count so that we don't unload print backends.
* There is a problem with module unloading in the cups module,
* see cups_dispatch_watch_finalize for details.
*/
g_type_module_use (G_TYPE_MODULE (pb_module));
}
g_free (module_path);
}
return pb;
}
/**
* gtk_printer_backend_load_modules:
*
* Return value: (element-type GtkPrintBackend) (transfer container):
*/
GList *
gtk_print_backend_load_modules (void)
{
GList *result;
GtkPrintBackend *backend;
gchar *setting;
gchar **backends;
gint i;
GtkSettings *settings;
result = NULL;
settings = gtk_settings_get_default ();
if (settings)
g_object_get (settings, "gtk-print-backends", &setting, NULL);
else
setting = g_strdup (GTK_PRINT_BACKENDS);
backends = g_strsplit (setting, ",", -1);
for (i = 0; backends[i]; i++)
{
g_strchug (backends[i]);
g_strchomp (backends[i]);
backend = _gtk_print_backend_create (backends[i]);
if (backend)
result = g_list_append (result, backend);
}
g_strfreev (backends);
g_free (setting);
return result;
}
/*****************************************
* GtkPrintBackend *
*****************************************/
G_DEFINE_TYPE (GtkPrintBackend, gtk_print_backend, G_TYPE_OBJECT)
static void fallback_printer_request_details (GtkPrinter *printer);
static gboolean fallback_printer_mark_conflicts (GtkPrinter *printer,
GtkPrinterOptionSet *options);
static gboolean fallback_printer_get_hard_margins (GtkPrinter *printer,
gdouble *top,
gdouble *bottom,
gdouble *left,
gdouble *right);
static GList * fallback_printer_list_papers (GtkPrinter *printer);
static GtkPageSetup * fallback_printer_get_default_page_size (GtkPrinter *printer);
static GtkPrintCapabilities fallback_printer_get_capabilities (GtkPrinter *printer);
static void request_password (GtkPrintBackend *backend,
gpointer auth_info_required,
gpointer auth_info_default,
gpointer auth_info_display,
gpointer auth_info_visible,
const gchar *prompt);
static void
gtk_print_backend_class_init (GtkPrintBackendClass *class)
{
GObjectClass *object_class;
object_class = (GObjectClass *) class;
backend_parent_class = g_type_class_peek_parent (class);
object_class->dispose = gtk_print_backend_dispose;
object_class->set_property = gtk_print_backend_set_property;
object_class->get_property = gtk_print_backend_get_property;
class->printer_request_details = fallback_printer_request_details;
class->printer_mark_conflicts = fallback_printer_mark_conflicts;
class->printer_get_hard_margins = fallback_printer_get_hard_margins;
class->printer_list_papers = fallback_printer_list_papers;
class->printer_get_default_page_size = fallback_printer_get_default_page_size;
class->printer_get_capabilities = fallback_printer_get_capabilities;
class->request_password = request_password;
g_object_class_install_property (object_class,
PROP_STATUS,
g_param_spec_int ("status",
"Status",
"The status of the print backend",
GTK_PRINT_BACKEND_STATUS_UNKNOWN,
GTK_PRINT_BACKEND_STATUS_UNAVAILABLE,
GTK_PRINT_BACKEND_STATUS_UNKNOWN,
GTK_PARAM_READWRITE));
g_type_class_add_private (class, sizeof (GtkPrintBackendPrivate));
signals[PRINTER_LIST_CHANGED] =
g_signal_new (I_("printer-list-changed"),
G_TYPE_FROM_CLASS (class),
G_SIGNAL_RUN_LAST,
G_STRUCT_OFFSET (GtkPrintBackendClass, printer_list_changed),
NULL, NULL,
g_cclosure_marshal_VOID__VOID,
G_TYPE_NONE, 0);
signals[PRINTER_LIST_DONE] =
g_signal_new (I_("printer-list-done"),
G_TYPE_FROM_CLASS (class),
G_SIGNAL_RUN_LAST,
G_STRUCT_OFFSET (GtkPrintBackendClass, printer_list_done),
NULL, NULL,
g_cclosure_marshal_VOID__VOID,
G_TYPE_NONE, 0);
signals[PRINTER_ADDED] =
g_signal_new (I_("printer-added"),
G_TYPE_FROM_CLASS (class),
G_SIGNAL_RUN_LAST,
G_STRUCT_OFFSET (GtkPrintBackendClass, printer_added),
NULL, NULL,
g_cclosure_marshal_VOID__OBJECT,
G_TYPE_NONE, 1, GTK_TYPE_PRINTER);
signals[PRINTER_REMOVED] =
g_signal_new (I_("printer-removed"),
G_TYPE_FROM_CLASS (class),
G_SIGNAL_RUN_LAST,
G_STRUCT_OFFSET (GtkPrintBackendClass, printer_removed),
NULL, NULL,
g_cclosure_marshal_VOID__OBJECT,
G_TYPE_NONE, 1, GTK_TYPE_PRINTER);
signals[PRINTER_STATUS_CHANGED] =
g_signal_new (I_("printer-status-changed"),
G_TYPE_FROM_CLASS (class),
G_SIGNAL_RUN_LAST,
G_STRUCT_OFFSET (GtkPrintBackendClass, printer_status_changed),
NULL, NULL,
g_cclosure_marshal_VOID__OBJECT,
G_TYPE_NONE, 1, GTK_TYPE_PRINTER);
signals[REQUEST_PASSWORD] =
g_signal_new (I_("request-password"),
G_TYPE_FROM_CLASS (class),
G_SIGNAL_RUN_LAST,
G_STRUCT_OFFSET (GtkPrintBackendClass, request_password),
NULL, NULL,
_gtk_marshal_VOID__POINTER_POINTER_POINTER_POINTER_STRING,
G_TYPE_NONE, 5, G_TYPE_POINTER, G_TYPE_POINTER, G_TYPE_POINTER, G_TYPE_POINTER, G_TYPE_STRING);
}
static void
gtk_print_backend_init (GtkPrintBackend *backend)
{
GtkPrintBackendPrivate *priv;
priv = backend->priv = GTK_PRINT_BACKEND_GET_PRIVATE (backend);
priv->printers = g_hash_table_new_full (g_str_hash, g_str_equal,
(GDestroyNotify) g_free,
(GDestroyNotify) g_object_unref);
priv->auth_info_required = NULL;
priv->auth_info = NULL;
}
static void
gtk_print_backend_dispose (GObject *object)
{
GtkPrintBackend *backend;
GtkPrintBackendPrivate *priv;
backend = GTK_PRINT_BACKEND (object);
priv = backend->priv;
/* We unref the printers in dispose, not in finalize so that
* we can break refcount cycles with gtk_print_backend_destroy
*/
if (priv->printers)
{
g_hash_table_destroy (priv->printers);
priv->printers = NULL;
}
backend_parent_class->dispose (object);
}
static void
fallback_printer_request_details (GtkPrinter *printer)
{
}
static gboolean
fallback_printer_mark_conflicts (GtkPrinter *printer,
GtkPrinterOptionSet *options)
{
return FALSE;
}
static gboolean
fallback_printer_get_hard_margins (GtkPrinter *printer,
gdouble *top,
gdouble *bottom,
gdouble *left,
gdouble *right)
{
return FALSE;
}
static GList *
fallback_printer_list_papers (GtkPrinter *printer)
{
return NULL;
}
static GtkPageSetup *
fallback_printer_get_default_page_size (GtkPrinter *printer)
{
return NULL;
}
static GtkPrintCapabilities
fallback_printer_get_capabilities (GtkPrinter *printer)
{
return 0;
}
static void
printer_hash_to_sorted_active_list (const gchar *key,
gpointer value,
GList **out_list)
{
GtkPrinter *printer;
printer = GTK_PRINTER (value);
if (gtk_printer_get_name (printer) == NULL)
return;
if (!gtk_printer_is_active (printer))
return;
*out_list = g_list_insert_sorted (*out_list, value, (GCompareFunc) gtk_printer_compare);
}
void
gtk_print_backend_add_printer (GtkPrintBackend *backend,
GtkPrinter *printer)
{
GtkPrintBackendPrivate *priv;
g_return_if_fail (GTK_IS_PRINT_BACKEND (backend));
priv = backend->priv;
if (!priv->printers)
return;
g_hash_table_insert (priv->printers,
g_strdup (gtk_printer_get_name (printer)),
g_object_ref (printer));
}
void
gtk_print_backend_remove_printer (GtkPrintBackend *backend,
GtkPrinter *printer)
{
GtkPrintBackendPrivate *priv;
g_return_if_fail (GTK_IS_PRINT_BACKEND (backend));
priv = backend->priv;
if (!priv->printers)
return;
g_hash_table_remove (priv->printers,
gtk_printer_get_name (printer));
}
void
gtk_print_backend_set_list_done (GtkPrintBackend *backend)
{
if (!backend->priv->printer_list_done)
{
backend->priv->printer_list_done = TRUE;
g_signal_emit (backend, signals[PRINTER_LIST_DONE], 0);
}
}
/**
* gtk_print_backend_get_printer_list:
*
* Return value: (element-type GtkPrinter) (transfer container):
*/
GList *
gtk_print_backend_get_printer_list (GtkPrintBackend *backend)
{
GtkPrintBackendPrivate *priv;
GList *result;
g_return_val_if_fail (GTK_IS_PRINT_BACKEND (backend), NULL);
priv = backend->priv;
result = NULL;
if (priv->printers != NULL)
g_hash_table_foreach (priv->printers,
(GHFunc) printer_hash_to_sorted_active_list,
&result);
if (!priv->printer_list_requested && priv->printers != NULL)
{
if (GTK_PRINT_BACKEND_GET_CLASS (backend)->request_printer_list)
GTK_PRINT_BACKEND_GET_CLASS (backend)->request_printer_list (backend);
priv->printer_list_requested = TRUE;
}
return result;
}
gboolean
gtk_print_backend_printer_list_is_done (GtkPrintBackend *print_backend)
{
g_return_val_if_fail (GTK_IS_PRINT_BACKEND (print_backend), TRUE);
return print_backend->priv->printer_list_done;
}
GtkPrinter *
gtk_print_backend_find_printer (GtkPrintBackend *backend,
const gchar *printer_name)
{
GtkPrintBackendPrivate *priv;
GtkPrinter *printer;
g_return_val_if_fail (GTK_IS_PRINT_BACKEND (backend), NULL);
priv = backend->priv;
if (priv->printers)
printer = g_hash_table_lookup (priv->printers, printer_name);
else
printer = NULL;
return printer;
}
void
gtk_print_backend_print_stream (GtkPrintBackend *backend,
GtkPrintJob *job,
GIOChannel *data_io,
GtkPrintJobCompleteFunc callback,
gpointer user_data,
GDestroyNotify dnotify)
{
g_return_if_fail (GTK_IS_PRINT_BACKEND (backend));
GTK_PRINT_BACKEND_GET_CLASS (backend)->print_stream (backend,
job,
data_io,
callback,
user_data,
dnotify);
}
void
gtk_print_backend_set_password (GtkPrintBackend *backend,
gchar **auth_info_required,
gchar **auth_info)
{
g_return_if_fail (GTK_IS_PRINT_BACKEND (backend));
if (GTK_PRINT_BACKEND_GET_CLASS (backend)->set_password)
GTK_PRINT_BACKEND_GET_CLASS (backend)->set_password (backend, auth_info_required, auth_info);
}
static void
store_entry (GtkEntry *entry,
gpointer user_data)
{
gchar **data = (gchar **) user_data;
if (*data != NULL)
{
memset (*data, 0, strlen (*data));
g_free (*data);
}
*data = g_strdup (gtk_entry_get_text (entry));
}
static void
password_dialog_response (GtkWidget *dialog,
gint response_id,
GtkPrintBackend *backend)
{
GtkPrintBackendPrivate *priv = backend->priv;
gint i;
if (response_id == GTK_RESPONSE_OK)
gtk_print_backend_set_password (backend, priv->auth_info_required, priv->auth_info);
else
gtk_print_backend_set_password (backend, priv->auth_info_required, NULL);
for (i = 0; i < g_strv_length (priv->auth_info_required); i++)
if (priv->auth_info[i] != NULL)
{
memset (priv->auth_info[i], 0, strlen (priv->auth_info[i]));
g_free (priv->auth_info[i]);
priv->auth_info[i] = NULL;
}
g_free (priv->auth_info);
priv->auth_info = NULL;
g_strfreev (priv->auth_info_required);
gtk_widget_destroy (dialog);
g_object_unref (backend);
}
static void
request_password (GtkPrintBackend *backend,
gpointer auth_info_required,
gpointer auth_info_default,
gpointer auth_info_display,
gpointer auth_info_visible,
const gchar *prompt)
{
GtkPrintBackendPrivate *priv = backend->priv;
GtkWidget *dialog, *box, *main_box, *label, *icon, *vbox, *entry;
GtkWidget *focus = NULL;
GtkWidget *content_area;
gchar *markup;
gint length;
gint i;
gchar **ai_required = (gchar **) auth_info_required;
gchar **ai_default = (gchar **) auth_info_default;
gchar **ai_display = (gchar **) auth_info_display;
gboolean *ai_visible = (gboolean *) auth_info_visible;
priv->auth_info_required = g_strdupv (ai_required);
length = g_strv_length (ai_required);
priv->auth_info = g_new0 (gchar *, length);
dialog = gtk_dialog_new_with_buttons ( _("Authentication"), NULL, GTK_DIALOG_MODAL,
GTK_STOCK_CANCEL, GTK_RESPONSE_CANCEL,
GTK_STOCK_OK, GTK_RESPONSE_OK,
NULL);
gtk_dialog_set_default_response (GTK_DIALOG (dialog), GTK_RESPONSE_OK);
gtk_dialog_set_has_separator (GTK_DIALOG (dialog), FALSE);
main_box = gtk_hbox_new (FALSE, 0);
/* Left */
icon = gtk_image_new_from_stock (GTK_STOCK_DIALOG_AUTHENTICATION, GTK_ICON_SIZE_DIALOG);
gtk_misc_set_alignment (GTK_MISC (icon), 0.5, 0.0);
gtk_misc_set_padding (GTK_MISC (icon), 6, 6);
/* Right */
vbox = gtk_vbox_new (FALSE, 0);
gtk_widget_set_size_request (GTK_WIDGET (vbox), 320, -1);
/* Right - 1. */
label = gtk_label_new (NULL);
markup = g_markup_printf_escaped ("<span weight=\"bold\" size=\"large\">%s</span>", prompt);
gtk_label_set_markup (GTK_LABEL (label), markup);
gtk_label_set_line_wrap (GTK_LABEL (label), TRUE);
gtk_widget_set_size_request (GTK_WIDGET (label), 320, -1);
g_free (markup);
/* Packing */
content_area = gtk_dialog_get_content_area (GTK_DIALOG (dialog));
gtk_box_pack_start (GTK_BOX (content_area), main_box, TRUE, FALSE, 0);
gtk_box_pack_start (GTK_BOX (main_box), icon, FALSE, FALSE, 6);
gtk_box_pack_start (GTK_BOX (main_box), vbox, FALSE, FALSE, 6);
gtk_box_pack_start (GTK_BOX (vbox), label, FALSE, TRUE, 6);
/* Right - 2. */
for (i = 0; i < length; i++)
{
priv->auth_info[i] = g_strdup (ai_default[i]);
if (ai_display[i] != NULL)
{
box = gtk_hbox_new (TRUE, 0);
label = gtk_label_new (ai_display[i]);
gtk_misc_set_alignment (GTK_MISC (label), 0.0, 0.5);
entry = gtk_entry_new ();
focus = entry;
if (ai_default[i] != NULL)
gtk_entry_set_text (GTK_ENTRY (entry), ai_default[i]);
gtk_entry_set_visibility (GTK_ENTRY (entry), ai_visible[i]);
gtk_entry_set_activates_default (GTK_ENTRY (entry), TRUE);
gtk_box_pack_start (GTK_BOX (vbox), box, FALSE, TRUE, 6);
gtk_box_pack_start (GTK_BOX (box), label, TRUE, TRUE, 0);
gtk_box_pack_start (GTK_BOX (box), entry, TRUE, TRUE, 0);
g_signal_connect (entry, "changed",
G_CALLBACK (store_entry), &(priv->auth_info[i]));
}
}
if (focus != NULL)
{
gtk_widget_grab_focus (focus);
focus = NULL;
}
g_object_ref (backend);
g_signal_connect (G_OBJECT (dialog), "response",
G_CALLBACK (password_dialog_response), backend);
gtk_widget_show_all (dialog);
}
void
gtk_print_backend_destroy (GtkPrintBackend *print_backend)
{
/* The lifecycle of print backends and printers are tied, such that
* the backend owns the printers, but the printers also ref the backend.
* This is so that if the app has a reference to a printer its backend
* will be around. However, this results in a cycle, which we break
* with this call, which causes the print backend to release its printers.
*/
g_object_run_dispose (G_OBJECT (print_backend));
}