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A #GTask represents and manages a cancellable "task".

Asynchronous operations

The most common usage of #GTask is as a #GAsyncResult, to manage data during an asynchronous operation. You call g_task_new() in the "start" method, followed by g_task_set_task_data() and the like if you need to keep some additional data associated with the task, and then pass the task object around through your asynchronous operation. Eventually, you will call a method such as g_task_return_pointer() or g_task_return_error(), which will save the value you give it and then invoke the task's callback function in the [thread-default main context][g-main-context-push-thread-default] where it was created (waiting until the next iteration of the main loop first, if necessary). The caller will pass the #GTask back to the operation's finish function (as a #GAsyncResult), and you can use g_task_propagate_pointer() or the like to extract the return value.

Using #GTask requires the thread-default #GMainContext from when the #GTask was constructed to be running at least until the task has completed and its data has been freed.

Here is an example for using GTask as a GAsyncResult:

    typedef struct {
CakeFrostingType frosting;
char *message;
} DecorationData;

static void
decoration_data_free (DecorationData *decoration)
{
g_free (decoration->message);
g_slice_free (DecorationData, decoration);
}

static void
baked_cb (Cake *cake,
gpointer user_data)
{
GTask *task = user_data;
DecorationData *decoration = g_task_get_task_data (task);
GError *error = NULL;

if (cake == NULL)
{
g_task_return_new_error (task, BAKER_ERROR, BAKER_ERROR_NO_FLOUR,
"Go to the supermarket");
g_object_unref (task);
return;
}

if (!cake_decorate (cake, decoration->frosting, decoration->message, &error))
{
g_object_unref (cake);
// g_task_return_error() takes ownership of error
g_task_return_error (task, error);
g_object_unref (task);
return;
}

g_task_return_pointer (task, cake, g_object_unref);
g_object_unref (task);
}

void
baker_bake_cake_async (Baker *self,
guint radius,
CakeFlavor flavor,
CakeFrostingType frosting,
const char *message,
GCancellable *cancellable,
GAsyncReadyCallback callback,
gpointer user_data)
{
GTask *task;
DecorationData *decoration;
Cake *cake;

task = g_task_new (self, cancellable, callback, user_data);
if (radius < 3)
{
g_task_return_new_error (task, BAKER_ERROR, BAKER_ERROR_TOO_SMALL,
"%ucm radius cakes are silly",
radius);
g_object_unref (task);
return;
}

cake = _baker_get_cached_cake (self, radius, flavor, frosting, message);
if (cake != NULL)
{
// _baker_get_cached_cake() returns a reffed cake
g_task_return_pointer (task, cake, g_object_unref);
g_object_unref (task);
return;
}

decoration = g_slice_new (DecorationData);
decoration->frosting = frosting;
decoration->message = g_strdup (message);
g_task_set_task_data (task, decoration, (GDestroyNotify) decoration_data_free);

_baker_begin_cake (self, radius, flavor, cancellable, baked_cb, task);
}

Cake *
baker_bake_cake_finish (Baker *self,
GAsyncResult *result,
GError **error)
{
g_return_val_if_fail (g_task_is_valid (result, self), NULL);

return g_task_propagate_pointer (G_TASK (result), error);
}

Chained asynchronous operations

#GTask also tries to simplify asynchronous operations that internally chain together several smaller asynchronous operations. g_task_get_cancellable(), g_task_get_context(), and g_task_get_priority() allow you to get back the task's #GCancellable, #GMainContext, and [I/O priority][io-priority] when starting a new subtask, so you don't have to keep track of them yourself. g_task_attach_source() simplifies the case of waiting for a source to fire (automatically using the correct #GMainContext and priority).

Here is an example for chained asynchronous operations:

    typedef struct {
Cake *cake;
CakeFrostingType frosting;
char *message;
} BakingData;

static void
decoration_data_free (BakingData *bd)
{
if (bd->cake)
g_object_unref (bd->cake);
g_free (bd->message);
g_slice_free (BakingData, bd);
}

static void
decorated_cb (Cake *cake,
GAsyncResult *result,
gpointer user_data)
{
GTask *task = user_data;
GError *error = NULL;

if (!cake_decorate_finish (cake, result, &error))
{
g_object_unref (cake);
g_task_return_error (task, error);
g_object_unref (task);
return;
}

// baking_data_free() will drop its ref on the cake, so we have to
// take another here to give to the caller.
g_task_return_pointer (task, g_object_ref (cake), g_object_unref);
g_object_unref (task);
}

static gboolean
decorator_ready (gpointer user_data)
{
GTask *task = user_data;
BakingData *bd = g_task_get_task_data (task);

cake_decorate_async (bd->cake, bd->frosting, bd->message,
g_task_get_cancellable (task),
decorated_cb, task);

return G_SOURCE_REMOVE;
}

static void
baked_cb (Cake *cake,
gpointer user_data)
{
GTask *task = user_data;
BakingData *bd = g_task_get_task_data (task);
GError *error = NULL;

if (cake == NULL)
{
g_task_return_new_error (task, BAKER_ERROR, BAKER_ERROR_NO_FLOUR,
"Go to the supermarket");
g_object_unref (task);
return;
}

bd->cake = cake;

// Bail out now if the user has already cancelled
if (g_task_return_error_if_cancelled (task))
{
g_object_unref (task);
return;
}

if (cake_decorator_available (cake))
decorator_ready (task);
else
{
GSource *source;

source = cake_decorator_wait_source_new (cake);
// Attach `source` to `task'`s GMainContext and have it call
// decorator_ready() when it is ready.
g_task_attach_source (task, source, decorator_ready);
g_source_unref (source);
}
}

void
baker_bake_cake_async (Baker *self,
guint radius,
CakeFlavor flavor,
CakeFrostingType frosting,
const char *message,
gint priority,
GCancellable *cancellable,
GAsyncReadyCallback callback,
gpointer user_data)
{
GTask *task;
BakingData *bd;

task = g_task_new (self, cancellable, callback, user_data);
g_task_set_priority (task, priority);

bd = g_slice_new0 (BakingData);
bd->frosting = frosting;
bd->message = g_strdup (message);
g_task_set_task_data (task, bd, (GDestroyNotify) baking_data_free);

_baker_begin_cake (self, radius, flavor, cancellable, baked_cb, task);
}

Cake *
baker_bake_cake_finish (Baker *self,
GAsyncResult *result,
GError **error)
{
g_return_val_if_fail (g_task_is_valid (result, self), NULL);

return g_task_propagate_pointer (G_TASK (result), error);
}

Asynchronous operations from synchronous ones

You can use g_task_run_in_thread() to turn a synchronous operation into an asynchronous one, by running it in a thread. When it completes, the result will be dispatched to the [thread-default main context][g-main-context-push-thread-default] where the #GTask was created.

Running a task in a thread:

    typedef struct {
guint radius;
CakeFlavor flavor;
CakeFrostingType frosting;
char *message;
} CakeData;

static void
cake_data_free (CakeData *cake_data)
{
g_free (cake_data->message);
g_slice_free (CakeData, cake_data);
}

static void
bake_cake_thread (GTask *task,
gpointer source_object,
gpointer task_data,
GCancellable *cancellable)
{
Baker *self = source_object;
CakeData *cake_data = task_data;
Cake *cake;
GError *error = NULL;

cake = bake_cake (baker, cake_data->radius, cake_data->flavor,
cake_data->frosting, cake_data->message,
cancellable, &error);
if (cake)
g_task_return_pointer (task, cake, g_object_unref);
else
g_task_return_error (task, error);
}

void
baker_bake_cake_async (Baker *self,
guint radius,
CakeFlavor flavor,
CakeFrostingType frosting,
const char *message,
GCancellable *cancellable,
GAsyncReadyCallback callback,
gpointer user_data)
{
CakeData *cake_data;
GTask *task;

cake_data = g_slice_new (CakeData);
cake_data->radius = radius;
cake_data->flavor = flavor;
cake_data->frosting = frosting;
cake_data->message = g_strdup (message);
task = g_task_new (self, cancellable, callback, user_data);
g_task_set_task_data (task, cake_data, (GDestroyNotify) cake_data_free);
g_task_run_in_thread (task, bake_cake_thread);
g_object_unref (task);
}

Cake *
baker_bake_cake_finish (Baker *self,
GAsyncResult *result,
GError **error)
{
g_return_val_if_fail (g_task_is_valid (result, self), NULL);

return g_task_propagate_pointer (G_TASK (result), error);
}

Adding cancellability to uncancellable tasks

Finally, g_task_run_in_thread() and g_task_run_in_thread_sync() can be used to turn an uncancellable operation into a cancellable one. If you call g_task_set_return_on_cancel(), passing %TRUE, then if the task's #GCancellable is cancelled, it will return control back to the caller immediately, while allowing the task thread to continue running in the background (and simply discarding its result when it finally does finish). Provided that the task thread is careful about how it uses locks and other externally-visible resources, this allows you to make "GLib-friendly" asynchronous and cancellable synchronous variants of blocking APIs.

Cancelling a task:

    static void
bake_cake_thread (GTask *task,
gpointer source_object,
gpointer task_data,
GCancellable *cancellable)
{
Baker *self = source_object;
CakeData *cake_data = task_data;
Cake *cake;
GError *error = NULL;

cake = bake_cake (baker, cake_data->radius, cake_data->flavor,
cake_data->frosting, cake_data->message,
&error);
if (error)
{
g_task_return_error (task, error);
return;
}

// If the task has already been cancelled, then we don't want to add
// the cake to the cake cache. Likewise, we don't want to have the
// task get cancelled in the middle of updating the cache.
// g_task_set_return_on_cancel() will return %TRUE here if it managed
// to disable return-on-cancel, or %FALSE if the task was cancelled
// before it could.
if (g_task_set_return_on_cancel (task, FALSE))
{
// If the caller cancels at this point, their
// GAsyncReadyCallback won't be invoked until we return,
// so we don't have to worry that this code will run at
// the same time as that code does. But if there were
// other functions that might look at the cake cache,
// then we'd probably need a GMutex here as well.
baker_add_cake_to_cache (baker, cake);
g_task_return_pointer (task, cake, g_object_unref);
}
}

void
baker_bake_cake_async (Baker *self,
guint radius,
CakeFlavor flavor,
CakeFrostingType frosting,
const char *message,
GCancellable *cancellable,
GAsyncReadyCallback callback,
gpointer user_data)
{
CakeData *cake_data;
GTask *task;

cake_data = g_slice_new (CakeData);

...

task = g_task_new (self, cancellable, callback, user_data);
g_task_set_task_data (task, cake_data, (GDestroyNotify) cake_data_free);
g_task_set_return_on_cancel (task, TRUE);
g_task_run_in_thread (task, bake_cake_thread);
}

Cake *
baker_bake_cake_sync (Baker *self,
guint radius,
CakeFlavor flavor,
CakeFrostingType frosting,
const char *message,
GCancellable *cancellable,
GError **error)
{
CakeData *cake_data;
GTask *task;
Cake *cake;

cake_data = g_slice_new (CakeData);

...

task = g_task_new (self, cancellable, NULL, NULL);
g_task_set_task_data (task, cake_data, (GDestroyNotify) cake_data_free);
g_task_set_return_on_cancel (task, TRUE);
g_task_run_in_thread_sync (task, bake_cake_thread);

cake = g_task_propagate_pointer (task, error);
g_object_unref (task);
return cake;
}

Porting from GSimpleAsyncResult

#GTask's API attempts to be simpler than #GSimpleAsyncResult's in several ways:

  • You can save task-specific data with g_task_set_task_data(), and retrieve it later with g_task_get_task_data(). This replaces the abuse of g_simple_async_result_set_op_res_gpointer() for the same purpose with #GSimpleAsyncResult.
  • In addition to the task data, #GTask also keeps track of the [priority][io-priority], #GCancellable, and #GMainContext associated with the task, so tasks that consist of a chain of simpler asynchronous operations will have easy access to those values when starting each sub-task.
  • g_task_return_error_if_cancelled() provides simplified handling for cancellation. In addition, cancellation overrides any other #GTask return value by default, like #GSimpleAsyncResult does when g_simple_async_result_set_check_cancellable() is called. (You can use g_task_set_check_cancellable() to turn off that behavior.) On the other hand, g_task_run_in_thread() guarantees that it will always run your task_func, even if the task's #GCancellable is already cancelled before the task gets a chance to run; you can start your task_func with a g_task_return_error_if_cancelled() check if you need the old behavior.
  • The "return" methods (eg, g_task_return_pointer()) automatically cause the task to be "completed" as well, and there is no need to worry about the "complete" vs "complete in idle" distinction. (#GTask automatically figures out whether the task's callback can be invoked directly, or if it needs to be sent to another #GMainContext, or delayed until the next iteration of the current #GMainContext.)
  • The "finish" functions for #GTask based operations are generally much simpler than #GSimpleAsyncResult ones, normally consisting of only a single call to g_task_propagate_pointer() or the like. Since g_task_propagate_pointer() "steals" the return value from the #GTask, it is not necessary to juggle pointers around to prevent it from being freed twice.
  • With #GSimpleAsyncResult, it was common to call g_simple_async_result_propagate_error() from the _finish() wrapper function, and have virtual method implementations only deal with successful returns. This behavior is deprecated, because it makes it difficult for a subclass to chain to a parent class's async methods. Instead, the wrapper function should just be a simple wrapper, and the virtual method should call an appropriate g_task_propagate_ function. Note that wrapper methods can now use g_async_result_legacy_propagate_error() to do old-style #GSimpleAsyncResult error-returning behavior, and g_async_result_is_tagged() to check if a result is tagged as having come from the _async() wrapper function (for "short-circuit" results, such as when passing 0 to g_input_stream_read_async()).

Hierarchy

Index

Constructors

  • Parameters

    Returns Gio.Task

  • Creates a #GTask acting on source_object, which will eventually be used to invoke callback in the current [thread-default main context][g-main-context-push-thread-default].

    Call this in the "start" method of your asynchronous method, and pass the #GTask around throughout the asynchronous operation. You can use g_task_set_task_data() to attach task-specific data to the object, which you can retrieve later via g_task_get_task_data().

    By default, if cancellable is cancelled, then the return value of the task will always be %G_IO_ERROR_CANCELLED, even if the task had already completed before the cancellation. This allows for simplified handling in cases where cancellation may imply that other objects that the task depends on have been destroyed. If you do not want this behavior, you can use g_task_set_check_cancellable() to change it.

    Parameters

    Returns Gio.Task

Properties

completed: boolean

Whether the task has completed, meaning its callback (if set) has been invoked. This can only happen after g_task_return_pointer(), g_task_return_error() or one of the other return functions have been called on the task.

This property is guaranteed to change from %FALSE to %TRUE exactly once.

The #GObject::notify signal for this change is emitted in the same main context as the task’s callback, immediately after that callback is invoked.

gTypeInstance: TypeInstance
$gtype: GType<Gio.Task>
name: string

Methods

  • Creates a binding between source_property on source and target_property on target.

    Whenever the source_property is changed the target_property is updated using the same value. For instance:

      g_object_bind_property (action, "active", widget, "sensitive", 0);
    

    Will result in the "sensitive" property of the widget #GObject instance to be updated with the same value of the "active" property of the action #GObject instance.

    If flags contains %G_BINDING_BIDIRECTIONAL then the binding will be mutual: if target_property on target changes then the source_property on source will be updated as well.

    The binding will automatically be removed when either the source or the target instances are finalized. To remove the binding without affecting the source and the target you can just call g_object_unref() on the returned #GBinding instance.

    Removing the binding by calling g_object_unref() on it must only be done if the binding, source and target are only used from a single thread and it is clear that both source and target outlive the binding. Especially it is not safe to rely on this if the binding, source or target can be finalized from different threads. Keep another reference to the binding and use g_binding_unbind() instead to be on the safe side.

    A #GObject can have multiple bindings.

    Parameters

    • sourceProperty: string

      the property on source to bind

    • target: GObject.Object

      the target #GObject

    • targetProperty: string

      the property on target to bind

    • flags: BindingFlags

      flags to pass to #GBinding

    Returns Binding

  • Creates a binding between source_property on source and target_property on target, allowing you to set the transformation functions to be used by the binding.

    This function is the language bindings friendly version of g_object_bind_property_full(), using #GClosures instead of function pointers.

    Parameters

    • sourceProperty: string

      the property on source to bind

    • target: GObject.Object

      the target #GObject

    • targetProperty: string

      the property on target to bind

    • flags: BindingFlags

      flags to pass to #GBinding

    • transformTo: TClosure<any, any>

      a #GClosure wrapping the transformation function from the source to the target, or %NULL to use the default

    • transformFrom: TClosure<any, any>

      a #GClosure wrapping the transformation function from the target to the source, or %NULL to use the default

    Returns Binding

  • connect(sigName: "notify::completed", callback: ((...args: any[]) => void)): number
  • connect(sigName: string, callback: ((...args: any[]) => void)): number
  • Parameters

    • sigName: "notify::completed"
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns number

  • Parameters

    • sigName: string
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns number

  • emit(sigName: "notify::completed", ...args: any[]): void
  • emit(sigName: string, ...args: any[]): void
  • forceFloating(): void
  • This function is intended for #GObject implementations to re-enforce a [floating][floating-ref] object reference. Doing this is seldom required: all #GInitiallyUnowneds are created with a floating reference which usually just needs to be sunken by calling g_object_ref_sink().

    Returns void

  • freezeNotify(): void
  • Increases the freeze count on object. If the freeze count is non-zero, the emission of "notify" signals on object is stopped. The signals are queued until the freeze count is decreased to zero. Duplicate notifications are squashed so that at most one #GObject::notify signal is emitted for each property modified while the object is frozen.

    This is necessary for accessors that modify multiple properties to prevent premature notification while the object is still being modified.

    Returns void

  • getCheckCancellable(): boolean
  • Gets task's check-cancellable flag. See g_task_set_check_cancellable() for more details.

    Returns boolean

  • getCompleted(): boolean
  • Gets the value of #GTask:completed. This changes from %FALSE to %TRUE after the task’s callback is invoked, and will return %FALSE if called from inside the callback.

    Returns boolean

  • Gets the #GMainContext that task will return its result in (that is, the context that was the [thread-default main context][g-main-context-push-thread-default] at the point when task was created).

    This will always return a non-%NULL value, even if the task's context is the default #GMainContext.

    Returns MainContext

  • getData(key?: string): object
  • Gets a named field from the objects table of associations (see g_object_set_data()).

    Parameters

    • Optional key: string

      name of the key for that association

    Returns object

  • getName(): string
  • Gets task’s name. See g_task_set_name().

    Returns string

  • getPriority(): number
  • getProperty(propertyName?: string, value?: any): void
  • Gets a property of an object.

    The value can be:

    • an empty #GValue initialized by %G_VALUE_INIT, which will be automatically initialized with the expected type of the property (since GLib 2.60)
    • a #GValue initialized with the expected type of the property
    • a #GValue initialized with a type to which the expected type of the property can be transformed

    In general, a copy is made of the property contents and the caller is responsible for freeing the memory by calling g_value_unset().

    Note that g_object_get_property() is really intended for language bindings, g_object_get() is much more convenient for C programming.

    Parameters

    • Optional propertyName: string

      the name of the property to get

    • Optional value: any

      return location for the property value

    Returns void

  • getQdata(quark: number): object
  • This function gets back user data pointers stored via g_object_set_qdata().

    Parameters

    • quark: number

      A #GQuark, naming the user data pointer

    Returns object

  • getReturnOnCancel(): boolean
  • Gets task's return-on-cancel flag. See g_task_set_return_on_cancel() for more details.

    Returns boolean

  • getSourceTag(): object
  • Gets task's source tag. See g_task_set_source_tag().

    Returns object

  • getTaskData(): object
  • getUserData(): object
  • getv(names: string[], values: any[]): void
  • Gets n_properties properties for an object. Obtained properties will be set to values. All properties must be valid. Warnings will be emitted and undefined behaviour may result if invalid properties are passed in.

    Parameters

    • names: string[]

      the names of each property to get

    • values: any[]

      the values of each property to get

    Returns void

  • hadError(): boolean
  • isFloating(): boolean
  • isTagged(sourceTag: object): boolean
  • Checks if res has the given source_tag (generally a function pointer indicating the function res was created by).

    Parameters

    • sourceTag: object

      an application-defined tag

    Returns boolean

  • legacyPropagateError(): boolean
  • If res is a #GSimpleAsyncResult, this is equivalent to g_simple_async_result_propagate_error(). Otherwise it returns %FALSE.

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

    Returns boolean

  • notify(propertyName: string): void
  • Emits a "notify" signal for the property property_name on object.

    When possible, eg. when signaling a property change from within the class that registered the property, you should use g_object_notify_by_pspec() instead.

    Note that emission of the notify signal may be blocked with g_object_freeze_notify(). In this case, the signal emissions are queued and will be emitted (in reverse order) when g_object_thaw_notify() is called.

    Parameters

    • propertyName: string

      the name of a property installed on the class of object.

    Returns void

  • Emits a "notify" signal for the property specified by pspec on object.

    This function omits the property name lookup, hence it is faster than g_object_notify().

    One way to avoid using g_object_notify() from within the class that registered the properties, and using g_object_notify_by_pspec() instead, is to store the GParamSpec used with g_object_class_install_property() inside a static array, e.g.:

      enum
    {
    PROP_0,
    PROP_FOO,
    PROP_LAST
    };

    static GParamSpec *properties[PROP_LAST];

    static void
    my_object_class_init (MyObjectClass *klass)
    {
    properties[PROP_FOO] = g_param_spec_int ("foo", "Foo", "The foo",
    0, 100,
    50,
    G_PARAM_READWRITE);
    g_object_class_install_property (gobject_class,
    PROP_FOO,
    properties[PROP_FOO]);
    }

    and then notify a change on the "foo" property with:

      g_object_notify_by_pspec (self, properties[PROP_FOO]);
    

    Parameters

    • pspec: ParamSpec

      the #GParamSpec of a property installed on the class of object.

    Returns void

  • off(sigName: "notify::completed", callback: ((...args: any[]) => void)): EventEmitter
  • off(sigName: string, callback: ((...args: any[]) => void)): EventEmitter
  • Parameters

    • sigName: "notify::completed"
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns EventEmitter

  • Parameters

    • sigName: string
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns EventEmitter

  • on(sigName: "notify::completed", callback: ((...args: any[]) => void), after?: boolean): EventEmitter
  • on(sigName: string, callback: ((...args: any[]) => void), after?: boolean): EventEmitter
  • Parameters

    • sigName: "notify::completed"
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    • Optional after: boolean

    Returns EventEmitter

  • Parameters

    • sigName: string
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    • Optional after: boolean

    Returns EventEmitter

  • once(sigName: "notify::completed", callback: ((...args: any[]) => void), after?: boolean): EventEmitter
  • once(sigName: string, callback: ((...args: any[]) => void), after?: boolean): EventEmitter
  • Parameters

    • sigName: "notify::completed"
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    • Optional after: boolean

    Returns EventEmitter

  • Parameters

    • sigName: string
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    • Optional after: boolean

    Returns EventEmitter

  • propagateBoolean(): boolean
  • Gets the result of task as a #gboolean.

    If the task resulted in an error, or was cancelled, then this will instead return %FALSE and set error.

    Since this method transfers ownership of the return value (or error) to the caller, you may only call it once.

    Returns boolean

  • propagateInt(): number
  • Gets the result of task as an integer (#gssize).

    If the task resulted in an error, or was cancelled, then this will instead return -1 and set error.

    Since this method transfers ownership of the return value (or error) to the caller, you may only call it once.

    Returns number

  • propagatePointer(): object
  • Gets the result of task as a pointer, and transfers ownership of that value to the caller.

    If the task resulted in an error, or was cancelled, then this will instead return %NULL and set error.

    Since this method transfers ownership of the return value (or error) to the caller, you may only call it once.

    Returns object

  • propagateValue(): [boolean, any]
  • Gets the result of task as a #GValue, and transfers ownership of that value to the caller. As with g_task_return_value(), this is a generic low-level method; g_task_propagate_pointer() and the like will usually be more useful for C code.

    If the task resulted in an error, or was cancelled, then this will instead set error and return %FALSE.

    Since this method transfers ownership of the return value (or error) to the caller, you may only call it once.

    Returns [boolean, any]

  • Increases the reference count of object.

    Since GLib 2.56, if GLIB_VERSION_MAX_ALLOWED is 2.56 or greater, the type of object will be propagated to the return type (using the GCC typeof() extension), so any casting the caller needs to do on the return type must be explicit.

    Returns GObject.Object

  • Increase the reference count of object, and possibly remove the [floating][floating-ref] reference, if object has a floating reference.

    In other words, if the object is floating, then this call "assumes ownership" of the floating reference, converting it to a normal reference by clearing the floating flag while leaving the reference count unchanged. If the object is not floating, then this call adds a new normal reference increasing the reference count by one.

    Since GLib 2.56, the type of object will be propagated to the return type under the same conditions as for g_object_ref().

    Returns GObject.Object

  • returnBoolean(result: boolean): void
  • Sets task's result to result and completes the task (see g_task_return_pointer() for more discussion of exactly what this means).

    Parameters

    • result: boolean

      the #gboolean result of a task function.

    Returns void

  • Sets task's result to error (which task assumes ownership of) and completes the task (see g_task_return_pointer() for more discussion of exactly what this means).

    Note that since the task takes ownership of error, and since the task may be completed before returning from g_task_return_error(), you cannot assume that error is still valid after calling this. Call g_error_copy() on the error if you need to keep a local copy as well.

    See also g_task_return_new_error().

    Parameters

    • error: GLib.Error

      the #GError result of a task function.

    Returns void

  • returnErrorIfCancelled(): boolean
  • Checks if task's #GCancellable has been cancelled, and if so, sets task's error accordingly and completes the task (see g_task_return_pointer() for more discussion of exactly what this means).

    Returns boolean

  • returnInt(result: number): void
  • Sets task's result to result and completes the task (see g_task_return_pointer() for more discussion of exactly what this means).

    Parameters

    • result: number

      the integer (#gssize) result of a task function.

    Returns void

  • Sets task's result to result and completes the task. If result is not %NULL, then result_destroy will be used to free result if the caller does not take ownership of it with g_task_propagate_pointer().

    "Completes the task" means that for an ordinary asynchronous task it will either invoke the task's callback, or else queue that callback to be invoked in the proper #GMainContext, or in the next iteration of the current #GMainContext. For a task run via g_task_run_in_thread() or g_task_run_in_thread_sync(), calling this method will save result to be returned to the caller later, but the task will not actually be completed until the #GTaskThreadFunc exits.

    Note that since the task may be completed before returning from g_task_return_pointer(), you cannot assume that result is still valid after calling this, unless you are still holding another reference on it.

    Parameters

    • result: object

      the pointer result of a task function

    • resultDestroy: GLib.DestroyNotify

      a #GDestroyNotify function.

    Returns void

  • returnValue(result: any): void
  • Sets task's result to result (by copying it) and completes the task.

    If result is %NULL then a #GValue of type %G_TYPE_POINTER with a value of %NULL will be used for the result.

    This is a very generic low-level method intended primarily for use by language bindings; for C code, g_task_return_pointer() and the like will normally be much easier to use.

    Parameters

    • result: any

      the #GValue result of a task function

    Returns void

  • runDispose(): void
  • Releases all references to other objects. This can be used to break reference cycles.

    This function should only be called from object system implementations.

    Returns void

  • Runs task_func in another thread. When task_func returns, task's #GAsyncReadyCallback will be invoked in task's #GMainContext.

    This takes a ref on task until the task completes.

    See #GTaskThreadFunc for more details about how task_func is handled.

    Although GLib currently rate-limits the tasks queued via g_task_run_in_thread(), you should not assume that it will always do this. If you have a very large number of tasks to run (several tens of tasks), but don't want them to all run at once, you should only queue a limited number of them (around ten) at a time.

    Parameters

    Returns void

  • Runs task_func in another thread, and waits for it to return or be cancelled. You can use g_task_propagate_pointer(), etc, afterward to get the result of task_func.

    See #GTaskThreadFunc for more details about how task_func is handled.

    Normally this is used with tasks created with a %NULL callback, but note that even if the task does have a callback, it will not be invoked when task_func returns. #GTask:completed will be set to %TRUE just before this function returns.

    Although GLib currently rate-limits the tasks queued via g_task_run_in_thread_sync(), you should not assume that it will always do this. If you have a very large number of tasks to run, but don't want them to all run at once, you should only queue a limited number of them at a time.

    Parameters

    Returns void

  • setCheckCancellable(checkCancellable: boolean): void
  • Sets or clears task's check-cancellable flag. If this is %TRUE (the default), then g_task_propagate_pointer(), etc, and g_task_had_error() will check the task's #GCancellable first, and if it has been cancelled, then they will consider the task to have returned an "Operation was cancelled" error (%G_IO_ERROR_CANCELLED), regardless of any other error or return value the task may have had.

    If check_cancellable is %FALSE, then the #GTask will not check the cancellable itself, and it is up to task's owner to do this (eg, via g_task_return_error_if_cancelled()).

    If you are using g_task_set_return_on_cancel() as well, then you must leave check-cancellable set %TRUE.

    Parameters

    • checkCancellable: boolean

      whether #GTask will check the state of its #GCancellable for you.

    Returns void

  • setData(key: string, data?: object): void
  • Each object carries around a table of associations from strings to pointers. This function lets you set an association.

    If the object already had an association with that name, the old association will be destroyed.

    Internally, the key is converted to a #GQuark using g_quark_from_string(). This means a copy of key is kept permanently (even after object has been finalized) — so it is recommended to only use a small, bounded set of values for key in your program, to avoid the #GQuark storage growing unbounded.

    Parameters

    • key: string

      name of the key

    • Optional data: object

      data to associate with that key

    Returns void

  • setName(name: string): void
  • Sets task’s name, used in debugging and profiling. The name defaults to %NULL.

    The task name should describe in a human readable way what the task does. For example, ‘Open file’ or ‘Connect to network host’. It is used to set the name of the #GSource used for idle completion of the task.

    This function may only be called before the task is first used in a thread other than the one it was constructed in. It is called automatically by g_task_set_source_tag() if not called already.

    Parameters

    • name: string

      a human readable name for the task, or %NULL to unset it

    Returns void

  • setPriority(priority: number): void
  • Sets task's priority. If you do not call this, it will default to %G_PRIORITY_DEFAULT.

    This will affect the priority of #GSources created with g_task_attach_source() and the scheduling of tasks run in threads, and can also be explicitly retrieved later via g_task_get_priority().

    Parameters

    • priority: number

      the [priority][io-priority] of the request

    Returns void

  • setProperty(propertyName: string, value?: any): void
  • Sets a property on an object.

    Parameters

    • propertyName: string

      the name of the property to set

    • Optional value: any

      the value

    Returns void

  • setReturnOnCancel(returnOnCancel: boolean): boolean
  • Sets or clears task's return-on-cancel flag. This is only meaningful for tasks run via g_task_run_in_thread() or g_task_run_in_thread_sync().

    If return_on_cancel is %TRUE, then cancelling task's #GCancellable will immediately cause it to return, as though the task's #GTaskThreadFunc had called g_task_return_error_if_cancelled() and then returned.

    This allows you to create a cancellable wrapper around an uninterruptible function. The #GTaskThreadFunc just needs to be careful that it does not modify any externally-visible state after it has been cancelled. To do that, the thread should call g_task_set_return_on_cancel() again to (atomically) set return-on-cancel %FALSE before making externally-visible changes; if the task gets cancelled before the return-on-cancel flag could be changed, g_task_set_return_on_cancel() will indicate this by returning %FALSE.

    You can disable and re-enable this flag multiple times if you wish. If the task's #GCancellable is cancelled while return-on-cancel is %FALSE, then calling g_task_set_return_on_cancel() to set it %TRUE again will cause the task to be cancelled at that point.

    If the task's #GCancellable is already cancelled before you call g_task_run_in_thread()/g_task_run_in_thread_sync(), then the #GTaskThreadFunc will still be run (for consistency), but the task will also be completed right away.

    Parameters

    • returnOnCancel: boolean

      whether the task returns automatically when it is cancelled.

    Returns boolean

  • setSourceTag(sourceTag: object): void
  • Sets task's source tag.

    You can use this to tag a task return value with a particular pointer (usually a pointer to the function doing the tagging) and then later check it using g_task_get_source_tag() (or g_async_result_is_tagged()) in the task's "finish" function, to figure out if the response came from a particular place.

    A macro wrapper around this function will automatically set the task’s name to the string form of source_tag if it’s not already set, for convenience.

    Parameters

    • sourceTag: object

      an opaque pointer indicating the source of this task

    Returns void

  • Sets task's task data (freeing the existing task data, if any).

    Parameters

    • taskData: object

      task-specific data

    • taskDataDestroy: GLib.DestroyNotify

      #GDestroyNotify for task_data

    Returns void

  • stealData(key?: string): object
  • Remove a specified datum from the object's data associations, without invoking the association's destroy handler.

    Parameters

    • Optional key: string

      name of the key

    Returns object

  • stealQdata(quark: number): object
  • This function gets back user data pointers stored via g_object_set_qdata() and removes the data from object without invoking its destroy() function (if any was set). Usually, calling this function is only required to update user data pointers with a destroy notifier, for example:

    void
    object_add_to_user_list (GObject *object,
    const gchar *new_string)
    {
    // the quark, naming the object data
    GQuark quark_string_list = g_quark_from_static_string ("my-string-list");
    // retrieve the old string list
    GList *list = g_object_steal_qdata (object, quark_string_list);

    // prepend new string
    list = g_list_prepend (list, g_strdup (new_string));
    // this changed 'list', so we need to set it again
    g_object_set_qdata_full (object, quark_string_list, list, free_string_list);
    }
    static void
    free_string_list (gpointer data)
    {
    GList *node, *list = data;

    for (node = list; node; node = node->next)
    g_free (node->data);
    g_list_free (list);
    }

    Using g_object_get_qdata() in the above example, instead of g_object_steal_qdata() would have left the destroy function set, and thus the partial string list would have been freed upon g_object_set_qdata_full().

    Parameters

    • quark: number

      A #GQuark, naming the user data pointer

    Returns object

  • thawNotify(): void
  • Reverts the effect of a previous call to g_object_freeze_notify(). The freeze count is decreased on object and when it reaches zero, queued "notify" signals are emitted.

    Duplicate notifications for each property are squashed so that at most one #GObject::notify signal is emitted for each property, in the reverse order in which they have been queued.

    It is an error to call this function when the freeze count is zero.

    Returns void

  • unref(): void
  • Decreases the reference count of object. When its reference count drops to 0, the object is finalized (i.e. its memory is freed).

    If the pointer to the #GObject may be reused in future (for example, if it is an instance variable of another object), it is recommended to clear the pointer to %NULL rather than retain a dangling pointer to a potentially invalid #GObject instance. Use g_clear_object() for this.

    Returns void

  • watchClosure(closure: TClosure<any, any>): void
  • This function essentially limits the life time of the closure to the life time of the object. That is, when the object is finalized, the closure is invalidated by calling g_closure_invalidate() on it, in order to prevent invocations of the closure with a finalized (nonexisting) object. Also, g_object_ref() and g_object_unref() are added as marshal guards to the closure, to ensure that an extra reference count is held on object during invocation of the closure. Usually, this function will be called on closures that use this object as closure data.

    Parameters

    • closure: TClosure<any, any>

      #GClosure to watch

    Returns void

  • compatControl(what: number, data: object): number
  • Find the #GParamSpec with the given name for an interface. Generally, the interface vtable passed in as g_iface will be the default vtable from g_type_default_interface_ref(), or, if you know the interface has already been loaded, g_type_default_interface_peek().

    Parameters

    • gIface: TypeInterface

      any interface vtable for the interface, or the default vtable for the interface

    • propertyName: string

      name of a property to look up.

    Returns ParamSpec

  • Add a property to an interface; this is only useful for interfaces that are added to GObject-derived types. Adding a property to an interface forces all objects classes with that interface to have a compatible property. The compatible property could be a newly created #GParamSpec, but normally g_object_class_override_property() will be used so that the object class only needs to provide an implementation and inherits the property description, default value, bounds, and so forth from the interface property.

    This function is meant to be called from the interface's default vtable initialization function (the class_init member of #GTypeInfo.) It must not be called after after class_init has been called for any object types implementing this interface.

    If pspec is a floating reference, it will be consumed.

    Parameters

    • gIface: TypeInterface

      any interface vtable for the interface, or the default vtable for the interface.

    • pspec: ParamSpec

      the #GParamSpec for the new property

    Returns void

  • Lists the properties of an interface.Generally, the interface vtable passed in as g_iface will be the default vtable from g_type_default_interface_ref(), or, if you know the interface has already been loaded, g_type_default_interface_peek().

    Parameters

    • gIface: TypeInterface

      any interface vtable for the interface, or the default vtable for the interface

    Returns ParamSpec[]

  • Checks that result is a #GTask, and that source_object is its source object (or that source_object is %NULL and result has no source object). This can be used in g_return_if_fail() checks.

    Parameters

    • result: AsyncResult

      A #GAsyncResult

    • sourceObject: GObject.Object

      the source object expected to be associated with the task

    Returns boolean

  • Creates a #GTask acting on source_object, which will eventually be used to invoke callback in the current [thread-default main context][g-main-context-push-thread-default].

    Call this in the "start" method of your asynchronous method, and pass the #GTask around throughout the asynchronous operation. You can use g_task_set_task_data() to attach task-specific data to the object, which you can retrieve later via g_task_get_task_data().

    By default, if cancellable is cancelled, then the return value of the task will always be %G_IO_ERROR_CANCELLED, even if the task had already completed before the cancellation. This allows for simplified handling in cases where cancellation may imply that other objects that the task depends on have been destroyed. If you do not want this behavior, you can use g_task_set_check_cancellable() to change it.

    Parameters

    Returns Gio.Task

  • Creates a new instance of a #GObject subtype and sets its properties.

    Construction parameters (see %G_PARAM_CONSTRUCT, %G_PARAM_CONSTRUCT_ONLY) which are not explicitly specified are set to their default values.

    Parameters

    • objectType: GType<unknown>

      the type id of the #GObject subtype to instantiate

    • parameters: GObject.Parameter[]

      an array of #GParameter

    Returns GObject.Object

  • Creates a #GTask and then immediately calls g_task_return_error() on it. Use this in the wrapper function of an asynchronous method when you want to avoid even calling the virtual method. You can then use g_async_result_is_tagged() in the finish method wrapper to check if the result there is tagged as having been created by the wrapper method, and deal with it appropriately if so.

    See also g_task_report_new_error().

    Parameters

    • sourceObject: GObject.Object

      the #GObject that owns this task, or %NULL.

    • callback: AsyncReadyCallback

      a #GAsyncReadyCallback.

    • sourceTag: object

      an opaque pointer indicating the source of this task

    • error: GLib.Error

      error to report

    Returns void

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