:right-sidebar: True Task =================================================================== .. currentmodule:: gi.repository.Gio .. class:: Task(**properties: ~typing.Any) :no-contents-entry: Superclasses: :class:`~gi.repository.GObject.Object` Implemented Interfaces: :class:`~gi.repository.Gio.AsyncResult` :Constructors: :: Task(**properties) new(source_object:GObject.Object=None, cancellable:Gio.Cancellable=None, callback:Gio.AsyncReadyCallback=None, callback_data=None) -> Gio.Task Constructors ------------ .. rst-class:: interim-class .. class:: Task :no-index: .. classmethod:: new(source_object: ~gi.repository.GObject.Object | None = None, cancellable: ~gi.repository.Gio.Cancellable | None = None, callback: ~typing.Callable[[...], None] | None = None, *callback_data: ~typing.Any) -> ~gi.repository.Gio.Task Creates a :obj:`~gi.repository.Gio.Task` 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 :obj:`~gi.repository.Gio.Task` around throughout the asynchronous operation. You can use :func:`~gi.repository.Gio.Task.set_task_data` to attach task-specific data to the object, which you can retrieve later via :func:`~gi.repository.Gio.Task.get_task_data`. By default, if ``cancellable`` is cancelled, then the return value of the task will always be :const:`~gi.repository.Gio.IOErrorEnum.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 :func:`~gi.repository.Gio.Task.set_check_cancellable` to change it. .. versionadded:: 2.36 :param source_object: the :obj:`~gi.repository.GObject.Object` that owns this task, or :const:`None`. :param cancellable: optional :obj:`~gi.repository.Gio.Cancellable` object, :const:`None` to ignore. :param callback: a :obj:`~gi.repository.Gio.AsyncReadyCallback`. :param callback_data: user data passed to ``callback``. Methods ------- .. rst-class:: interim-class .. class:: Task :no-index: .. method:: get_cancellable() -> ~gi.repository.Gio.Cancellable | None Gets ``task``'s :obj:`~gi.repository.Gio.Cancellable` .. versionadded:: 2.36 .. method:: get_check_cancellable() -> bool Gets ``task``'s check-cancellable flag. See :func:`~gi.repository.Gio.Task.set_check_cancellable` for more details. .. versionadded:: 2.36 .. method:: get_completed() -> bool Gets the value of :obj:`~gi.repository.Gio.Task`:completed. This changes from :const:`False` to :const:`True` after the task’s callback is invoked, and will return :const:`False` if called from inside the callback. .. versionadded:: 2.44 .. method:: get_context() -> ~gi.repository.GLib.MainContext Gets the :obj:`~gi.repository.GLib.MainContext` 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-:const:`None` value, even if the task's context is the default :obj:`~gi.repository.GLib.MainContext`. .. versionadded:: 2.36 .. method:: get_name() -> str | None Gets ``task``’s name. See :func:`~gi.repository.Gio.Task.set_name`. .. versionadded:: 2.60 .. method:: get_priority() -> int Gets ``task``'s priority .. versionadded:: 2.36 .. method:: get_return_on_cancel() -> bool Gets ``task``'s return-on-cancel flag. See :func:`~gi.repository.Gio.Task.set_return_on_cancel` for more details. .. versionadded:: 2.36 .. method:: get_source_object() -> ~gi.repository.GObject.Object | None Gets the source object from ``task``. Like :func:`~gi.repository.Gio.AsyncResult.get_source_object`, but does not ref the object. .. versionadded:: 2.36 .. method:: get_source_tag() -> None Gets ``task``'s source tag. See :func:`~gi.repository.Gio.Task.set_source_tag`. .. versionadded:: 2.36 .. method:: get_task_data() -> None Gets ``task``'s ``task_data``. .. versionadded:: 2.36 .. method:: had_error() -> bool Tests if ``task`` resulted in an error. .. versionadded:: 2.36 .. method:: is_valid(result: ~gi.repository.Gio.AsyncResult, source_object: ~gi.repository.GObject.Object | None = None) -> bool Checks that ``result`` is a :obj:`~gi.repository.Gio.Task`, and that ``source_object`` is its source object (or that ``source_object`` is :const:`None` and ``result`` has no source object). This can be used in :func:`~gi.repository.GLib.return_if_fail` checks. .. versionadded:: 2.36 :param result: A :obj:`~gi.repository.Gio.AsyncResult` :param source_object: the source object expected to be associated with the task .. method:: propagate_boolean() -> bool Gets the result of ``task`` as a :obj:`~gi.repository.gboolean`. If the task resulted in an error, or was cancelled, then this will instead return :const:`False` and set ``error``. Since this method transfers ownership of the return value (or error) to the caller, you may only call it once. .. versionadded:: 2.36 .. method:: propagate_int() -> int Gets the result of ``task`` as an integer (:obj:`~gi.repository.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. .. versionadded:: 2.36 .. method:: propagate_pointer() -> None 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 :const:`None` and set ``error``. Since this method transfers ownership of the return value (or error) to the caller, you may only call it once. .. versionadded:: 2.36 .. method:: propagate_value() -> tuple[bool, ~typing.Any] Gets the result of ``task`` as a :obj:`~gi.repository.GObject.Value`, and transfers ownership of that value to the caller. As with :func:`~gi.repository.Gio.Task.return_value`, this is a generic low-level method; :func:`~gi.repository.Gio.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 :const:`False`. Since this method transfers ownership of the return value (or error) to the caller, you may only call it once. .. versionadded:: 2.64 .. method:: report_error(source_object: ~gi.repository.GObject.Object | None, callback: ~typing.Callable[[...], None] | None, source_tag: None, error: ~gi.repository.GLib.GError, *callback_data: ~typing.Any) -> None Creates a :obj:`~gi.repository.Gio.Task` and then immediately calls :func:`~gi.repository.Gio.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 :func:`~gi.repository.Gio.AsyncResult.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 :func:`~gi.repository.Gio.Task.report_new_error`. .. versionadded:: 2.36 :param source_object: the :obj:`~gi.repository.GObject.Object` that owns this task, or :const:`None`. :param callback: a :obj:`~gi.repository.Gio.AsyncReadyCallback`. :param source_tag: an opaque pointer indicating the source of this task :param error: error to report :param callback_data: user data passed to ``callback``. .. method:: return_boolean(result: bool) -> None Sets ``task``'s result to ``result`` and completes the task (see :func:`~gi.repository.Gio.Task.return_pointer` for more discussion of exactly what this means). .. versionadded:: 2.36 :param result: the :obj:`~gi.repository.gboolean` result of a task function. .. method:: return_error(error: ~gi.repository.GLib.GError) -> None Sets ``task``'s result to ``error`` (which ``task`` assumes ownership of) and completes the task (see :func:`~gi.repository.Gio.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 :func:`~gi.repository.Gio.Task.return_error`, you cannot assume that ``error`` is still valid after calling this. Call :func:`~gi.repository.GLib.Error.copy` on the error if you need to keep a local copy as well. See also :obj:`~gi.repository.Gio.Task.return_new_error`, :obj:`~gi.repository.Gio.Task.return_new_error_literal`. .. versionadded:: 2.36 :param error: the :obj:`~gi.repository.GLib.Error` result of a task function. .. method:: return_error_if_cancelled() -> bool Checks if ``task``'s :obj:`~gi.repository.Gio.Cancellable` has been cancelled, and if so, sets ``task``'s error accordingly and completes the task (see :func:`~gi.repository.Gio.Task.return_pointer` for more discussion of exactly what this means). .. versionadded:: 2.36 .. method:: return_int(result: int) -> None Sets ``task``'s result to ``result`` and completes the task (see :func:`~gi.repository.Gio.Task.return_pointer` for more discussion of exactly what this means). .. versionadded:: 2.36 :param result: the integer (:obj:`~gi.repository.gssize`) result of a task function. .. method:: return_new_error_literal(domain: int, code: int, message: str) -> None Sets ``task``’s result to a new :obj:`~gi.repository.GLib.Error` created from ``domain``, ``code``, ``message`` and completes the task. See :obj:`~gi.repository.Gio.Task.return_pointer` for more discussion of exactly what ‘completing the task’ means. See also :obj:`~gi.repository.Gio.Task.return_new_error`. .. versionadded:: 2.80 :param domain: a :obj:`~gi.repository.GLib.Quark`. :param code: an error code. :param message: an error message .. method:: return_pointer(result: None, result_destroy: ~typing.Callable[[None], None] | None = None) -> None Sets ``task``'s result to ``result`` and completes the task. If ``result`` is not :const:`None`, then ``result_destroy`` will be used to free ``result`` if the caller does not take ownership of it with :func:`~gi.repository.Gio.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 :obj:`~gi.repository.GLib.MainContext`, or in the next iteration of the current :obj:`~gi.repository.GLib.MainContext`. For a task run via :func:`~gi.repository.Gio.Task.run_in_thread` or :func:`~gi.repository.Gio.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 :obj:`~gi.repository.Gio.TaskThreadFunc` exits. Note that since the task may be completed before returning from :func:`~gi.repository.Gio.Task.return_pointer`, you cannot assume that ``result`` is still valid after calling this, unless you are still holding another reference on it. .. versionadded:: 2.36 :param result: the pointer result of a task function :param result_destroy: a :obj:`~gi.repository.GLib.DestroyNotify` function. .. method:: return_value(result: ~typing.Any | None = None) -> None Sets ``task``'s result to ``result`` (by copying it) and completes the task. If ``result`` is :const:`None` then a :obj:`~gi.repository.GObject.Value` of type ``%G_TYPE_POINTER`` with a value of :const:`None` will be used for the result. This is a very generic low-level method intended primarily for use by language bindings; for C code, :func:`~gi.repository.Gio.Task.return_pointer` and the like will normally be much easier to use. .. versionadded:: 2.64 :param result: the :obj:`~gi.repository.GObject.Value` result of a task function .. method:: run_in_thread(task_func: ~typing.Callable[[~gi.repository.Gio.Task, ~gi.repository.GObject.Object, None, ~gi.repository.Gio.Cancellable | None], None]) -> None Runs ``task_func`` in another thread. When ``task_func`` returns, ``task``'s :obj:`~gi.repository.Gio.AsyncReadyCallback` will be invoked in ``task``'s :obj:`~gi.repository.GLib.MainContext`. This takes a ref on ``task`` until the task completes. See :obj:`~gi.repository.Gio.TaskThreadFunc` for more details about how ``task_func`` is handled. Although GLib currently rate-limits the tasks queued via :func:`~gi.repository.Gio.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. Be aware that if your task depends on other tasks to complete, use of this function could lead to a livelock if the other tasks also use this function and enough of them (around 10) execute in a dependency chain, as that will exhaust the thread pool. If this situation is possible, consider using a separate worker thread or thread pool explicitly, rather than using :func:`~gi.repository.Gio.Task.run_in_thread`. .. versionadded:: 2.36 :param task_func: a :obj:`~gi.repository.Gio.TaskThreadFunc` .. method:: run_in_thread_sync(task_func: ~typing.Callable[[~gi.repository.Gio.Task, ~gi.repository.GObject.Object, None, ~gi.repository.Gio.Cancellable | None], None]) -> None Runs ``task_func`` in another thread, and waits for it to return or be cancelled. You can use :func:`~gi.repository.Gio.Task.propagate_pointer`, etc, afterward to get the result of ``task_func``. See :obj:`~gi.repository.Gio.TaskThreadFunc` for more details about how ``task_func`` is handled. Normally this is used with tasks created with a :const:`None` ``callback``, but note that even if the task does have a callback, it will not be invoked when ``task_func`` returns. :obj:`~gi.repository.Gio.Task`:completed will be set to :const:`True` just before this function returns. Although GLib currently rate-limits the tasks queued via :func:`~gi.repository.Gio.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. .. versionadded:: 2.36 :param task_func: a :obj:`~gi.repository.Gio.TaskThreadFunc` .. method:: set_check_cancellable(check_cancellable: bool) -> None Sets or clears ``task``'s check-cancellable flag. If this is :const:`True` (the default), then :func:`~gi.repository.Gio.Task.propagate_pointer`, etc, and :func:`~gi.repository.Gio.Task.had_error` will check the task's :obj:`~gi.repository.Gio.Cancellable` first, and if it has been cancelled, then they will consider the task to have returned an "Operation was cancelled" error (:const:`~gi.repository.Gio.IOErrorEnum.CANCELLED`), regardless of any other error or return value the task may have had. If ``check_cancellable`` is :const:`False`, then the :obj:`~gi.repository.Gio.Task` will not check the cancellable itself, and it is up to ``task``'s owner to do this (eg, via :func:`~gi.repository.Gio.Task.return_error_if_cancelled`). If you are using :func:`~gi.repository.Gio.Task.set_return_on_cancel` as well, then you must leave check-cancellable set :const:`True`. .. versionadded:: 2.36 :param check_cancellable: whether :obj:`~gi.repository.Gio.Task` will check the state of its :obj:`~gi.repository.Gio.Cancellable` for you. .. method:: set_name(name: str | None = None) -> None Sets ``task``’s name, used in debugging and profiling. The name defaults to :const:`None`. 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 :obj:`~gi.repository.GLib.Source` 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 :func:`~gi.repository.Gio.Task.set_source_tag` if not called already. .. versionadded:: 2.60 :param name: a human readable name for the task, or :const:`None` to unset it .. method:: set_priority(priority: int) -> None Sets ``task``'s priority. If you do not call this, it will default to ``%G_PRIORITY_DEFAULT``. This will affect the priority of :obj:`~gi.repository.GLib.Source` created with :func:`~gi.repository.Gio.Task.attach_source` and the scheduling of tasks run in threads, and can also be explicitly retrieved later via :func:`~gi.repository.Gio.Task.get_priority`. .. versionadded:: 2.36 :param priority: the `priority `_ of the request .. method:: set_return_on_cancel(return_on_cancel: bool) -> bool Sets or clears ``task``'s return-on-cancel flag. This is only meaningful for tasks run via :func:`~gi.repository.Gio.Task.run_in_thread` or :func:`~gi.repository.Gio.Task.run_in_thread_sync`. If ``return_on_cancel`` is :const:`True`, then cancelling ``task``'s :obj:`~gi.repository.Gio.Cancellable` will immediately cause it to return, as though the task's :obj:`~gi.repository.Gio.TaskThreadFunc` had called :func:`~gi.repository.Gio.Task.return_error_if_cancelled` and then returned. This allows you to create a cancellable wrapper around an uninterruptible function. The :obj:`~gi.repository.Gio.TaskThreadFunc` 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 :func:`~gi.repository.Gio.Task.set_return_on_cancel` again to (atomically) set return-on-cancel :const:`False` before making externally-visible changes; if the task gets cancelled before the return-on-cancel flag could be changed, :func:`~gi.repository.Gio.Task.set_return_on_cancel` will indicate this by returning :const:`False`. You can disable and re-enable this flag multiple times if you wish. If the task's :obj:`~gi.repository.Gio.Cancellable` is cancelled while return-on-cancel is :const:`False`, then calling :func:`~gi.repository.Gio.Task.set_return_on_cancel` to set it :const:`True` again will cause the task to be cancelled at that point. If the task's :obj:`~gi.repository.Gio.Cancellable` is already cancelled before you call :func:`~gi.repository.Gio.Task.run_in_thread`/:func:`~gi.repository.Gio.Task.run_in_thread_sync`, then the :obj:`~gi.repository.Gio.TaskThreadFunc` will still be run (for consistency), but the task will also be completed right away. .. versionadded:: 2.36 :param return_on_cancel: whether the task returns automatically when it is cancelled. .. method:: set_source_tag(source_tag: None) -> None 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 :func:`~gi.repository.Gio.Task.get_source_tag` (or :func:`~gi.repository.Gio.AsyncResult.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. .. versionadded:: 2.36 :param source_tag: an opaque pointer indicating the source of this task .. method:: set_static_name(name: str | None = None) -> None Sets ``task``’s name, used in debugging and profiling. This is a variant of :func:`~gi.repository.Gio.Task.set_name` that avoids copying ``name``. .. versionadded:: 2.76 :param name: a human readable name for the task. Must be a string literal .. method:: set_task_data(task_data: None, task_data_destroy: ~typing.Callable[[None], None] | None = None) -> None Sets ``task``'s task data (freeing the existing task data, if any). .. versionadded:: 2.36 :param task_data: task-specific data :param task_data_destroy: :obj:`~gi.repository.GLib.DestroyNotify` for ``task_data`` Properties ---------- .. rst-class:: interim-class .. class:: Task :no-index: .. attribute:: props.completed :type: bool Whether the task has completed, meaning its callback (if set) has been invoked. This can only happen after :func:`~gi.repository.Gio.Task.return_pointer`, :func:`~gi.repository.Gio.Task.return_error` or one of the other return functions have been called on the task. However, it is not guaranteed to happen immediately after those functions are called, as the task’s callback may need to be scheduled to run in a different thread. That means it is **not safe** to use this property to track whether a return function has been called on the :obj:`~gi.repository.Gio.Task`. Callers must do that tracking themselves, typically by linking the lifetime of the :obj:`~gi.repository.Gio.Task` to the control flow of their code. This property is guaranteed to change from :const:`False` to :const:`True` exactly once. The :obj:`~gi.repository.GObject.Object`::notify signal for this change is emitted in the same main context as the task’s callback, immediately after that callback is invoked. .. versionadded:: 2.44