Struct gio::AsyncResult

#[repr(transparent)]
pub struct AsyncResult { /* private fields */ }

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][g-main-context-push-thread-default] from where the operation was initiated. It will be passed a 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 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 AsyncResult) 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 None 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 AsyncResult and call “_finish()” later; however, the “_finish()” function may be called at most once.

Example of a typical asynchronous operation flow:

⚠️ The following code is in C ⚠️

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 IOErrorEnum::Cancelled error.

I/O Priority # {io-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.

Implements

AsyncResultExt

Implementations

impl AsyncResult

pub const NONE: Option<&'static AsyncResult> = None

Trait Implementations

impl Clone for AsyncResult

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for AsyncResult

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for AsyncResult

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Hash for AsyncResult

fn hash<H>(&self, state: &mut H)where H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for AsyncResult

fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Selfwhere Self: Sized + PartialOrd<Self>,

Restrict a value to a certain interval.

impl<OT: ObjectType> PartialEq<OT> for AsyncResult

fn eq(&self, other: &OT) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<OT: ObjectType> PartialOrd<OT> for AsyncResult

fn partial_cmp(&self, other: &OT) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl StaticType for AsyncResult

fn static_type() -> Type

Returns the type identifier of Self.

impl Eq for AsyncResult

impl<V: ValueType> IsA<AsyncResult> for LocalTask<V>

impl<V: ValueType + Send> IsA<AsyncResult> for Task<V>