glib/gio/gasyncresult.c

/* GIO - GLib Input, Output and Streaming Library
 *
 * Copyright (C) 2006-2007 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.
 *
 * Author: Alexander Larsson <alexl@redhat.com>
 */

#include "config.h"
#include "gasyncresult.h"
#include "glibintl.h"


/**
 * SECTION:gasyncresult
 * @short_description: Asynchronous Function Results
 * @include: gio/gio.h
 * @see_also: #GSimpleAsyncResult
 *
 * Provides a base class for implementing asynchronous function results.
 *
 * Asynchronous operations are broken up into two separate operations
 * which are chained together by a #GAsyncReadyCallback. To begin
 * an asynchronous operation, provide a #GAsyncReadyCallback to the
 * asynchronous function. This callback will be triggered when the
 * operation has completed, and will be passed a #GAsyncResult instance
 * filled with the details of the operation's success or failure, the
 * object the asynchronous function was started for and any error codes
 * returned. The asynchronous callback function is then expected to call
 * the corresponding "_finish()" function, passing the object the
 * function was called for, the #GAsyncResult instance, and (optionally)
 * an @error to grab any error conditions that may have occurred.
 *
 * The "_finish()" function for an operation takes the generic result
 * (of type #GAsyncResult) and returns the specific result that the
 * operation in question yields (e.g. a #GFileEnumerator for a
 * "enumerate children" operation). If the result or error status of the
 * operation is not needed, there is no need to call the "_finish()"
 * function; GIO will take care of cleaning up the result and error
 * information after the #GAsyncReadyCallback returns. Applications may
 * also take a reference to the #GAsyncResult and call "_finish()"
 * later; however, the "_finish()" function may be called at most once.
 *
 * Example of a typical asynchronous operation flow:
 * |[
 * void _theoretical_frobnitz_async (Theoretical         *t,
 *                                   GCancellable        *c,
 *                                   GAsyncReadyCallback *cb,
 *                                   gpointer             u);
 *
 * gboolean _theoretical_frobnitz_finish (Theoretical   *t,
 *                                        GAsyncResult  *res,
 *                                        GError       **e);
 *
 * static void
 * frobnitz_result_func (GObject      *source_object,
 *			 GAsyncResult *res,
 *			 gpointer      user_data)
 * {
 *   gboolean success = FALSE;
 *
 *   success = _theoretical_frobnitz_finish (source_object, res, NULL);
 *
 *   if (success)
 *     g_printf ("Hurray!\n");
 *   else
 *     g_printf ("Uh oh!\n");
 *
 *   /<!-- -->* ... *<!-- -->/
 *
 * }
 *
 * int main (int argc, void *argv[])
 * {
 *    /<!-- -->* ... *<!-- -->/
 *
 *    _theoretical_frobnitz_async (theoretical_data,
 *                                 NULL,
 *                                 frobnitz_result_func,
 *                                 NULL);
 *
 *    /<!-- -->* ... *<!-- -->/
 * }
 * ]|
 *
 * The callback for an asynchronous operation is called only once, and is
 * always called, even in the case of a cancelled operation. On cancellation
 * the result is a %G_IO_ERROR_CANCELLED error.
 *
 * Some asynchronous operations are implemented using synchronous calls.
 * These are run in a separate thread, if #GThread has been initialized, but
 * otherwise they are sent to the Main Event Loop and processed in an idle
 * function. So, if you truly need asynchronous operations, make sure to
 * initialize #GThread.
 **/

typedef GAsyncResultIface GAsyncResultInterface;
G_DEFINE_INTERFACE (GAsyncResult, g_async_result, G_TYPE_OBJECT)

static void
g_async_result_default_init (GAsyncResultInterface *iface)
{
}

/**
 * g_async_result_get_user_data:
 * @res: a #GAsyncResult.
 *
 * Gets the user data from a #GAsyncResult.
 *
 * Returns: (transfer full): the user data for @res.
 **/
gpointer
g_async_result_get_user_data (GAsyncResult *res)
{
  GAsyncResultIface *iface;

  g_return_val_if_fail (G_IS_ASYNC_RESULT (res), NULL);

  iface = G_ASYNC_RESULT_GET_IFACE (res);

  return (* iface->get_user_data) (res);
}

/**
 * g_async_result_get_source_object:
 * @res: a #GAsyncResult
 *
 * Gets the source object from a #GAsyncResult.
 *
 * Returns: (transfer full): a new reference to the source object for the @res,
 *    or %NULL if there is none.
 */
GObject *
g_async_result_get_source_object (GAsyncResult *res)
{
  GAsyncResultIface *iface;

  g_return_val_if_fail (G_IS_ASYNC_RESULT (res), NULL);

  iface = G_ASYNC_RESULT_GET_IFACE (res);

  return (* iface->get_source_object) (res);
}