Class

GioSimpleAsyncResult

Description [src]

final class Gio.SimpleAsyncResult : GObject.Object {
  /* No available fields */
}

As of GLib 2.46, GSimpleAsyncResult is deprecated in favor of GTask, which provides a simpler API.

GSimpleAsyncResult implements GAsyncResult.

GSimpleAsyncResult handles GAsyncReadyCallbacks, error reporting, operation cancellation and the final state of an operation, completely transparent to the application. Results can be returned as a pointer e.g. for functions that return data that is collected asynchronously, a boolean value for checking the success or failure of an operation, or a #gssize for operations which return the number of bytes modified by the operation; all of the simple return cases are covered.

Most of the time, an application will not need to know of the details of this API; it is handled transparently, and any necessary operations are handled by GAsyncResults interface. However, if implementing a new GIO module, for writing language bindings, or for complex applications that need better control of how asynchronous operations are completed, it is important to understand this functionality.

GSimpleAsyncResults are tagged with the calling function to ensure that asynchronous functions and their finishing functions are used together correctly.

To create a new GSimpleAsyncResult, call g_simple_async_result_new(). If the result needs to be created for a GError, use g_simple_async_result_new_from_error() or g_simple_async_result_new_take_error(). If a GError is not available (e.g. the asynchronous operation’s doesn’t take a GError argument), but the result still needs to be created for an error condition, use g_simple_async_result_new_error() (or g_simple_async_result_set_error_va() if your application or binding requires passing a variable argument list directly), and the error can then be propagated through the use of g_simple_async_result_propagate_error().

An asynchronous operation can be made to ignore a cancellation event by calling g_simple_async_result_set_handle_cancellation() with a GSimpleAsyncResult for the operation and FALSE. This is useful for operations that are dangerous to cancel, such as close (which would cause a leak if cancelled before being run).

GSimpleAsyncResult can integrate into GLib’s event loop, GMainLoop, or it can use GThreads. g_simple_async_result_complete() will finish an I/O task directly from the point where it is called. g_simple_async_result_complete_in_idle() will finish it from an idle handler in the [thread-default main context][g-main-context-push-thread-default] where the GSimpleAsyncResult was created. g_simple_async_result_run_in_thread() will run the job in a separate thread and then use g_simple_async_result_complete_in_idle() to deliver the result.

To set the results of an asynchronous function, g_simple_async_result_set_op_res_gpointer(), g_simple_async_result_set_op_res_gboolean(), and g_simple_async_result_set_op_res_gssize() are provided, setting the operation’s result to a gpointer, gboolean, or gssize, respectively.

Likewise, to get the result of an asynchronous function, g_simple_async_result_get_op_res_gpointer(), g_simple_async_result_get_op_res_gboolean(), and g_simple_async_result_get_op_res_gssize() are provided, getting the operation’s result as a gpointer, gboolean, and gssize, respectively.

For the details of the requirements implementations must respect, see GAsyncResult. A typical implementation of an asynchronous operation using GSimpleAsyncResult looks something like this:

static void
baked_cb (Cake    *cake,
          gpointer user_data)
{
  // In this example, this callback is not given a reference to the cake,
  // so the GSimpleAsyncResult has to take a reference to it.
  GSimpleAsyncResult *result = user_data;

  if (cake == NULL)
    g_simple_async_result_set_error (result,
                                     BAKER_ERRORS,
                                     BAKER_ERROR_NO_FLOUR,
                                     "Go to the supermarket");
  else
    g_simple_async_result_set_op_res_gpointer (result,
                                               g_object_ref (cake),
                                               g_object_unref);


  // In this example, we assume that baked_cb is called as a callback from
  // the mainloop, so it's safe to complete the operation synchronously here.
  // If, however, _baker_prepare_cake () might call its callback without
  // first returning to the mainloop — inadvisable, but some APIs do so —
  // we would need to use `g_simple_async_result_complete_in_idle()`.
  g_simple_async_result_complete (result);
  g_object_unref (result);
}

void
baker_bake_cake_async (Baker              *self,
                       guint               radius,
                       GAsyncReadyCallback callback,
                       gpointer            user_data)
{
  GSimpleAsyncResult *simple;
  Cake               *cake;

  if (radius < 3)
    {
      g_simple_async_report_error_in_idle (G_OBJECT (self),
                                           callback,
                                           user_data,
                                           BAKER_ERRORS,
                                           BAKER_ERROR_TOO_SMALL,
                                           "%ucm radius cakes are silly",
                                           radius);
      return;
    }

  simple = g_simple_async_result_new (G_OBJECT (self),
                                      callback,
                                      user_data,
                                      baker_bake_cake_async);
  cake = _baker_get_cached_cake (self, radius);

  if (cake != NULL)
    {
      g_simple_async_result_set_op_res_gpointer (simple,
                                                 g_object_ref (cake),
                                                 g_object_unref);
      g_simple_async_result_complete_in_idle (simple);
      g_object_unref (simple);
      // Drop the reference returned by _baker_get_cached_cake();
      // the GSimpleAsyncResult has taken its own reference.
      g_object_unref (cake);
      return;
    }

  _baker_prepare_cake (self, radius, baked_cb, simple);
}

Cake *
baker_bake_cake_finish (Baker        *self,
                        GAsyncResult *result,
                        GError      **error)
{
  GSimpleAsyncResult *simple;
  Cake               *cake;

  g_return_val_if_fail (g_simple_async_result_is_valid (result,
                                                        G_OBJECT (self),
                                                        baker_bake_cake_async),
                        NULL);

  simple = (GSimpleAsyncResult *) result;

  if (g_simple_async_result_propagate_error (simple, error))
    return NULL;

  cake = CAKE (g_simple_async_result_get_op_res_gpointer (simple));
  return g_object_ref (cake);
}

Hierarchy

hierarchy this GSimpleAsyncResult implements_0 GAsyncResult this--implements_0 ancestor_0 GObject ancestor_0--this

Ancestors

Implements

Constructors

g_simple_async_result_new

Creates a GSimpleAsyncResult.

Deprecated since: 2.46

g_simple_async_result_new_error

Creates a new GSimpleAsyncResult with a set error.

Deprecated since: 2.46

g_simple_async_result_new_from_error

Creates a GSimpleAsyncResult from an error condition.

Deprecated since: 2.46

g_simple_async_result_new_take_error

Creates a GSimpleAsyncResult from an error condition, and takes over the caller’s ownership of error, so the caller does not need to free it anymore.

Available since: 2.28

Deprecated since: 2.46

Functions

g_simple_async_result_is_valid

Ensures that the data passed to the _finish function of an async operation is consistent. Three checks are performed.

Available since: 2.20

Deprecated since: 2.46

Instance methods

g_simple_async_result_complete

Completes an asynchronous I/O job immediately. Must be called in the thread where the asynchronous result was to be delivered, as it invokes the callback directly. If you are in a different thread use g_simple_async_result_complete_in_idle().

Deprecated since: 2.46

g_simple_async_result_complete_in_idle

Completes an asynchronous function in an idle handler in the [thread-default main context][g-main-context-push-thread-default] of the thread that simple was initially created in (and re-pushes that context around the invocation of the callback).

Deprecated since: 2.46

g_simple_async_result_get_op_res_gboolean

Gets the operation result boolean from within the asynchronous result.

Deprecated since: 2.46

g_simple_async_result_get_op_res_gpointer

Gets a pointer result as returned by the asynchronous function.

Deprecated since: 2.46

g_simple_async_result_get_op_res_gssize

Gets a gssize from the asynchronous result.

Deprecated since: 2.46

g_simple_async_result_get_source_tag

Gets the source tag for the GSimpleAsyncResult.

Deprecated since: 2.46.

g_simple_async_result_propagate_error

Propagates an error from within the simple asynchronous result to a given destination.

Deprecated since: 2.46

g_simple_async_result_run_in_thread

Runs the asynchronous job in a separate thread and then calls g_simple_async_result_complete_in_idle() on simple to return the result to the appropriate main loop.

Deprecated since: 2.46

g_simple_async_result_set_check_cancellable

Sets a GCancellable to check before dispatching results.

Available since: 2.32

Deprecated since: 2.46

g_simple_async_result_set_error

Sets an error within the asynchronous result without a GError.

Deprecated since: 2.46

g_simple_async_result_set_error_va

Sets an error within the asynchronous result without a GError. Unless writing a binding, see g_simple_async_result_set_error().

Deprecated since: 2.46

g_simple_async_result_set_from_error

Sets the result from a GError.

Deprecated since: 2.46

g_simple_async_result_set_handle_cancellation

Sets whether to handle cancellation within the asynchronous operation.

g_simple_async_result_set_op_res_gboolean

Sets the operation result to a boolean within the asynchronous result.

Deprecated since: 2.46

g_simple_async_result_set_op_res_gpointer

Sets the operation result within the asynchronous result to a pointer.

Deprecated since: 2.46

g_simple_async_result_set_op_res_gssize

Sets the operation result within the asynchronous result to the given op_res.

Deprecated since: 2.46

g_simple_async_result_take_error

Sets the result from error, and takes over the caller’s ownership of error, so the caller does not need to free it any more.

Available since: 2.28

Deprecated since: 2.46

Methods inherited from GObject (43)
Methods inherited from GAsyncResult (4)
g_async_result_get_source_object

Gets the source object from a GAsyncResult.

g_async_result_get_user_data

Gets the user data from a GAsyncResult.

g_async_result_is_tagged

Checks if res has the given source_tag (generally a function pointer indicating the function res was created by).

Available since: 2.34

g_async_result_legacy_propagate_error

If res is a GSimpleAsyncResult, this is equivalent to g_simple_async_result_propagate_error(). Otherwise it returns FALSE.

Available since: 2.34

Signals

Signals inherited from GObject (1)

Class structure

struct GioSimpleAsyncResultClass {
  /* no available fields */
}