Sets our main struct and passes it to the parent class.
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].
A utility function for dealing with async operations where you need to wait for a #GSource to trigger. Attaches @source to @task's #GMainContext with @task's priority[io-priority], and sets @source's callback to @callback, with @task as the callback's user_data.
Gets @task's #GCancellable
Gets @task's check-cancellable flag. See g_task_set_check_cancellable() for more details.
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.
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).
Gets @task's priority
Gets @task's return-on-cancel flag. See g_task_set_return_on_cancel() for more details.
Gets the source object from @task. Like g_async_result_get_source_object(), but does not ref the object.
Gets @task's source tag. See g_task_set_source_tag().
the main Gtk struct as a void*
Gets @task's task_data.
Get the main Gtk struct
Tests if @task resulted in an error.
Gets the result of @task as a #gboolean.
Gets the result of @task as an integer (#gssize).
Gets the result of @task as a pointer, and transfers ownership of that value to the caller.
Sets @task's result to @result and completes the task (see g_task_return_pointer() for more discussion of exactly what this means).
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).
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).
Sets @task's result to @result and completes the task (see g_task_return_pointer() for more discussion of exactly what this means).
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().
Runs @task_func in another thread. When @task_func returns, @task's #GAsyncReadyCallback will be invoked in @task's #GMainContext.
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.
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.
Sets @task's priority. If you do not call this, it will default to %G_PRIORITY_DEFAULT.
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().
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.
Sets @task's task data (freeing the existing task data, if any).
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.
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.
the main Gtk struct
the main Gtk struct
Get the main Gtk struct
the main Gtk struct as a void*
Gets a D Object from the objects table of associations.
The notify signal is emitted on an object when one of its properties has been changed. Note that getting this signal doesn't guarantee that the value of the property has actually changed, it may also be emitted when the setter for the property is called to reinstate the previous value.
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().
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.
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().
Increases the reference count of the object by one and sets a callback to be called when all other references to the object are dropped, or when this is already the last reference to the object and another reference is established.
Adds a weak reference from weak_pointer to @object to indicate that the pointer located at @weak_pointer_location is only valid during the lifetime of @object. When the @object is finalized, @weak_pointer will be set to %NULL.
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:
Complete version of g_object_bind_property().
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 is a variant of g_object_get_data() which returns a 'duplicate' of the value. @dup_func defines the meaning of 'duplicate' in this context, it could e.g. take a reference on a ref-counted object.
This is a variant of g_object_get_qdata() which returns a 'duplicate' of the value. @dup_func defines the meaning of 'duplicate' in this context, it could e.g. take a reference on a ref-counted object.
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().
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.
Gets a named field from the objects table of associations (see g_object_set_data()).
Gets a property of an object. @value must have been initialized to the expected type of the property (or a type to which the expected type can be transformed) using g_value_init().
This function gets back user data pointers stored via g_object_set_qdata().
Gets properties of an object.
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.
Checks whether @object has a floating[floating-ref] reference.
Emits a "notify" signal for the property @property_name on @object.
Emits a "notify" signal for the property specified by @pspec on @object.
Increases the reference count of @object.
Increase the reference count of @object, and possibly remove the floating[floating-ref] reference, if @object has a floating reference.
Removes a reference added with g_object_add_toggle_ref(). The reference count of the object is decreased by one.
Removes a weak reference from @object that was previously added using g_object_add_weak_pointer(). The @weak_pointer_location has to match the one used with g_object_add_weak_pointer().
Compares the user data for the key @key on @object with @oldval, and if they are the same, replaces @oldval with @newval.
Compares the user data for the key @quark on @object with @oldval, and if they are the same, replaces @oldval with @newval.
Releases all references to other objects. This can be used to break reference cycles.
Each object carries around a table of associations from strings to pointers. This function lets you set an association.
Like g_object_set_data() except it adds notification for when the association is destroyed, either by setting it to a different value or when the object is destroyed.
Sets a property on an object.
This sets an opaque, named pointer on an object. The name is specified through a #GQuark (retrived e.g. via g_quark_from_static_string()), and the pointer can be gotten back from the @object with g_object_get_qdata() until the @object is finalized. Setting a previously set user data pointer, overrides (frees) the old pointer set, using #NULL as pointer essentially removes the data stored.
This function works like g_object_set_qdata(), but in addition, a void (*destroy) (gpointer) function may be specified which is called with @data as argument when the @object is finalized, or the data is being overwritten by a call to g_object_set_qdata() with the same @quark.
Sets properties on an object.
Sets @n_properties properties for an @object. Properties to be set will be taken from @values. All properties must be valid. Warnings will be emitted and undefined behaviour may result if invalid properties are passed in.
Remove a specified datum from the object's data associations, without invoking the association's destroy handler.
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: |[<!-- language="C" --> 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"); // retrive the old string list GList *list = g_object_steal_qdata (object, quark_string_list);
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.
Decreases the reference count of @object. When its reference count drops to 0, the object is finalized (i.e. its memory is freed).
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.
Adds a weak reference callback to an object. Weak references are used for notification when an object is finalized. They are called "weak references" because they allow you to safely hold a pointer to an object without calling g_object_ref() (g_object_ref() adds a strong reference, that is, forces the object to stay alive).
Removes a weak reference callback to an object.
Clears a reference to a #GObject.
Get the main Gtk struct
the main Gtk struct as a void*
Gets the source object from a #GAsyncResult.
Gets the user data from a #GAsyncResult.
Checks if @res has the given @source_tag (generally a function pointer indicating the function @res was created by).
If @res is a #GSimpleAsyncResult, this is equivalent to g_simple_async_result_propagate_error(). Otherwise it returns %FALSE.
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 can use g_task_propagate_pointer() or the like to extract the return value.
Here is an example for using GTask as a GAsyncResult: |[<!-- language="C" --> 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: |[<!-- language="C" --> 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: |[<!-- language="C" --> 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: |[<!-- language="C" --> 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()).