### Interface

# Gio AsyncResult

#### Description [src]

    interface Gio.AsyncResult : GObject.Object

`GAsyncResult` 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 must be run in a later iteration of the thread-default main context (see `g_main_context_push_thread_default()`) from where the operation was initiated. It 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. You can pass `NULL` for the `GAsyncReadyCallback` if you don’t need to take any action at all after the operation completes. 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.

## I/O Priority

Many I/O-related asynchronous operations have a priority parameter, which is used in certain cases to determine the order in which operations are executed. They are not used to determine system-wide I/O scheduling. Priorities are integers, with lower numbers indicating higher priority. It is recommended to choose priorities between `G_PRIORITY_LOW` and `G_PRIORITY_HIGH`, with `G_PRIORITY_DEFAULT` as a default.

#### Prerequisite

In order to implement AsyncResult, your type must inherit from`GObject`.

#### Implementations

- GSimpleAsyncResult
- GTask

#### Instance methods

###### 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).

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`.

since: 2.34

#### Interface structure

    struct GioAsyncResultIface {
      GTypeInterface g_iface;
      gpointer (* get_user_data) (
        GAsyncResult* res
      );
      GObject* (* get_source_object) (
        GAsyncResult* res
      );
      gboolean (* is_tagged) (
        GAsyncResult* res,
        gpointer source_tag
      );

    }

Interface definition for `GAsyncResult`.

###### Interface members

`g_iface` |
    GTypeInterface
| The parent interface.
`get_user_data` |
    gpointer (* get_user_data) (
        GAsyncResult* res
      )
| Gets the user data passed to the callback.
`get_source_object` |
    GObject* (* get_source_object) (
        GAsyncResult* res
      )
| Gets the source object that issued the asynchronous operation.
`is_tagged` |
    gboolean (* is_tagged) (
        GAsyncResult* res,
        gpointer source_tag
      )
| Checks if a result is tagged with a particular source.

#### Virtual methods

###### Gio.AsyncResult.get_source_object

Gets the source object from a `GAsyncResult`.

###### Gio.AsyncResult.get_user_data

Gets the user data from a `GAsyncResult`.

###### Gio.AsyncResult.is_tagged

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

since: 2.34