AsyncResult#
- class AsyncResult(*args, **kwargs)#
Implementations: SimpleAsyncResult
, Task
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
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 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 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.
Methods#
- class AsyncResult
- get_source_object() Object | None #
Gets the source object from a
AsyncResult
.
- get_user_data() None #
Gets the user data from a
AsyncResult
.
- is_tagged(source_tag: None) bool #
Checks if
res
has the givensource_tag
(generally a function pointer indicating the functionres
was created by).Added in version 2.34.
- Parameters:
source_tag – an application-defined tag
- legacy_propagate_error() bool #
If
res
is aSimpleAsyncResult
, this is equivalent topropagate_error
. Otherwise it returnsFALSE
.This can be used for legacy error handling in async
*_finish()
wrapper functions that traditionally handledSimpleAsyncResult
error returns themselves rather than calling into the virtual method. This should not be used in new code;AsyncResult
errors that are set by virtual methods should also be extracted by virtual methods, to enable subclasses to chain up correctly.Added in version 2.34.
Virtual Methods#
- class AsyncResult
- do_get_source_object() Object | None #
Gets the source object from a
AsyncResult
.
- do_get_user_data() None #
Gets the user data from a
AsyncResult
.