AsyncResult
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 method@GLib.MainContext.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 class@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 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.
Inheritors
Types
The AsyncResultImpl type represents a native instance of the AsyncResult interface.
Functions
Given @connection to communicate with a proxy (eg, a #GSocketConnection that is connected to the proxy server), this does the necessary handshake to connect to @proxy_address, and if required, wraps the #GIOStream to handle proxy payload.
Asynchronous version of g_proxy_connect().
See g_proxy_connect().
Gets the source object from a iface@Gio.AsyncResult.
Gets the user data from a iface@Gio.AsyncResult.
If @res is a class@Gio.SimpleAsyncResult, this is equivalent to method@Gio.SimpleAsyncResult.propagate_error. Otherwise it returns FALSE.
Some proxy protocols expect to be passed a hostname, which they will resolve to an IP address themselves. Others, like SOCKS4, do not allow this. This function will return false if @proxy is implementing such a protocol. When false is returned, the caller should resolve the destination hostname first, and then pass a #GProxyAddress containing the stringified IP address to g_proxy_connect() or g_proxy_connect_async().