Gio.AsyncResult

Implementations:  Gio.SimpleAsyncResult, Gio.Task

Methods

	get_source_object ()
	get_user_data ()
	is_tagged (source_tag)
	legacy_propagate_error ()

Virtual Methods

	do_get_source_object ()
	do_get_user_data ()
	do_is_tagged (source_tag)

Properties

None

Signals

None

Fields

None

Class Details

class Gio.AsyncResult

Bases:GObject.GInterface Structure:Gio.AsyncResultIface

Provides a base class for implementing asynchronous function results.

Asynchronous operations are broken up into two separate operations which are chained together by a Gio.AsyncReadyCallback. To begin an asynchronous operation, provide a Gio.AsyncReadyCallback 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 from where the operation was initiated. It will be passed a Gio.AsyncResult 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 Gio.AsyncResult 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 Gio.AsyncResult) and returns the specific result that the operation in question yields (e.g. a Gio.FileEnumerator 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 Gio.AsyncReadyCallback returns. You can pass None for the Gio.AsyncReadyCallback if you don’t need to take any action at all after the operation completes. Applications may also take a reference to the Gio.AsyncResult 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 Gio.IOErrorEnum.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 GLib.PRIORITY_LOW and GLib.PRIORITY_HIGH, with GLib.PRIORITY_DEFAULT as a default.

get_source_object()

Returns:a new reference to the source object for the self, or None if there is none. Return type:GObject.Object or None

Gets the source object from a Gio.AsyncResult.

get_user_data()

Returns:the user data for self. Return type:object or None

Gets the user data from a Gio.AsyncResult.

is_tagged(source_tag)

Parameters:source_tag (object or None) – an application-defined tag Returns:True if self has the indicated source_tag, False if not. Return type:bool

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

New in version 2.34.

legacy_propagate_error()

Raises:GLib.Error Returns:True if error is has been filled in with an error from self, False if not. Return type:bool

If self is a Gio.SimpleAsyncResult, this is equivalent to Gio.SimpleAsyncResult.propagate_error(). Otherwise it returns False.

This can be used for legacy error handling in async *_finish() wrapper functions that traditionally handled Gio.SimpleAsyncResult error returns themselves rather than calling into the virtual method. This should not be used in new code; Gio.AsyncResult errors that are set by virtual methods should also be extracted by virtual methods, to enable subclasses to chain up correctly.

New in version 2.34.

do_get_source_object() virtual

Returns:a new reference to the source object for the res, or None if there is none. Return type:GObject.Object or None

Gets the source object from a Gio.AsyncResult.

do_get_user_data() virtual

Returns:the user data for res. Return type:object or None

Gets the user data from a Gio.AsyncResult.

do_is_tagged(source_tag) virtual

Parameters:source_tag (object or None) – an application-defined tag Returns:True if res has the indicated source_tag, False if not. Return type:bool

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

New in version 2.34.