:right-sidebar: True Cancellable =================================================================== .. currentmodule:: gi.repository.Gio .. class:: Cancellable(**properties: ~typing.Any) :no-contents-entry: Superclasses: :class:`~gi.repository.GObject.Object` ``GCancellable`` allows operations to be cancelled. ``GCancellable`` is a thread-safe operation cancellation stack used throughout GIO to allow for cancellation of synchronous and asynchronous operations. Constructors ------------ .. rst-class:: interim-class .. class:: Cancellable :no-index: .. classmethod:: new() -> ~gi.repository.Gio.Cancellable Creates a new :obj:`~gi.repository.Gio.Cancellable` object. Applications that want to start one or more operations that should be cancellable should create a :obj:`~gi.repository.Gio.Cancellable` and pass it to the operations. One :obj:`~gi.repository.Gio.Cancellable` can be used in multiple consecutive operations or in multiple concurrent operations. Methods ------- .. rst-class:: interim-class .. class:: Cancellable :no-index: .. method:: cancel() -> None Will set ``cancellable`` to cancelled, and will emit the :obj:`~gi.repository.Gio.Cancellable`\::cancelled signal. (However, see the warning about race conditions in the documentation for that signal if you are planning to connect to it.) This function is thread-safe. In other words, you can safely call it from a thread other than the one running the operation that was passed the ``cancellable``\. If ``cancellable`` is :const:`None`, this function returns immediately for convenience. The convention within GIO is that cancelling an asynchronous operation causes it to complete asynchronously. That is, if you cancel the operation from the same thread in which it is running, then the operation's :obj:`~gi.repository.Gio.AsyncReadyCallback` will not be invoked until the application returns to the main loop. .. method:: connect(callback: ~typing.Callable[[], None], data: ~typing.Any = None) -> int Convenience function to connect to the :obj:`~gi.repository.Gio.Cancellable`\::cancelled signal. Also handles the race condition that may happen if the cancellable is cancelled right before connecting. ``callback`` is called at most once, either directly at the time of the connect if ``cancellable`` is already cancelled, or when ``cancellable`` is cancelled in some thread. ``data_destroy_func`` will be called when the handler is disconnected, or immediately if the cancellable is already cancelled. See :obj:`~gi.repository.Gio.Cancellable`\::cancelled for details on how to use this. Since GLib 2.40, the lock protecting ``cancellable`` is not held when ``callback`` is invoked. This lifts a restriction in place for earlier GLib versions which now makes it easier to write cleanup code that unconditionally invokes e.g. :func:`~gi.repository.Gio.Cancellable.cancel`. .. versionadded:: 2.22 :param callback: The :obj:`~gi.repository.GObject.Callback` to connect. :param data: Data to pass to ``callback``\. .. method:: disconnect(handler_id: int) -> None Disconnects a handler from a cancellable instance similar to :func:`~gi.repository.GObject.signal_handler_disconnect`. Additionally, in the event that a signal handler is currently running, this call will block until the handler has finished. Calling this function from a :obj:`~gi.repository.Gio.Cancellable`\::cancelled signal handler will therefore result in a deadlock. This avoids a race condition where a thread cancels at the same time as the cancellable operation is finished and the signal handler is removed. See :obj:`~gi.repository.Gio.Cancellable`\::cancelled for details on how to use this. If ``cancellable`` is :const:`None` or ``handler_id`` is ``0`` this function does nothing. .. versionadded:: 2.22 :param handler_id: Handler id of the handler to be disconnected, or ``0``\. .. method:: do_cancelled(self) -> None .. classmethod:: get_current() -> ~gi.repository.Gio.Cancellable | None Gets the top cancellable from the stack. .. method:: get_fd() -> int Gets the file descriptor for a cancellable job. This can be used to implement cancellable operations on Unix systems. The returned fd will turn readable when ``cancellable`` is cancelled. You are not supposed to read from the fd yourself, just check for readable status. Reading to unset the readable status is done with :func:`~gi.repository.Gio.Cancellable.reset`. After a successful return from this function, you should use :func:`~gi.repository.Gio.Cancellable.release_fd` to free up resources allocated for the returned file descriptor. See also :func:`~gi.repository.Gio.Cancellable.make_pollfd`. .. method:: is_cancelled() -> bool Checks if a cancellable job has been cancelled. .. method:: make_pollfd(pollfd: ~gi.repository.GLib.PollFD) -> bool Creates a :obj:`~gi.repository.GLib.PollFD` corresponding to ``cancellable``\; this can be passed to :func:`~gi.repository.GLib.poll` and used to poll for cancellation. This is useful both for unix systems without a native poll and for portability to windows. When this function returns :const:`True`, you should use :func:`~gi.repository.Gio.Cancellable.release_fd` to free up resources allocated for the ``pollfd``\. After a :const:`False` return, do not call :func:`~gi.repository.Gio.Cancellable.release_fd`. If this function returns :const:`False`, either no ``cancellable`` was given or resource limits prevent this function from allocating the necessary structures for polling. (On Linux, you will likely have reached the maximum number of file descriptors.) The suggested way to handle these cases is to ignore the ``cancellable``\. You are not supposed to read from the fd yourself, just check for readable status. Reading to unset the readable status is done with :func:`~gi.repository.Gio.Cancellable.reset`. .. versionadded:: 2.22 :param pollfd: a pointer to a :obj:`~gi.repository.GLib.PollFD` .. method:: pop_current() -> None Pops ``cancellable`` off the cancellable stack (verifying that ``cancellable`` is on the top of the stack). .. method:: push_current() -> None Pushes ``cancellable`` onto the cancellable stack. The current cancellable can then be received using :func:`~gi.repository.Gio.Cancellable.get_current`. This is useful when implementing cancellable operations in code that does not allow you to pass down the cancellable object. This is typically called automatically by e.g. :obj:`~gi.repository.Gio.File` operations, so you rarely have to call this yourself. .. method:: release_fd() -> None Releases a resources previously allocated by :func:`~gi.repository.Gio.Cancellable.get_fd` or :func:`~gi.repository.Gio.Cancellable.make_pollfd`. For compatibility reasons with older releases, calling this function is not strictly required, the resources will be automatically freed when the ``cancellable`` is finalized. However, the ``cancellable`` will block scarce file descriptors until it is finalized if this function is not called. This can cause the application to run out of file descriptors when many :obj:`~gi.repository.Gio.Cancellable` are used at the same time. .. versionadded:: 2.22 .. method:: reset() -> None Resets ``cancellable`` to its uncancelled state. If cancellable is currently in use by any cancellable operation then the behavior of this function is undefined. Note that it is generally not a good idea to reuse an existing cancellable for more operations after it has been cancelled once, as this function might tempt you to do. The recommended practice is to drop the reference to a cancellable after cancelling it, and let it die with the outstanding async operations. You should create a fresh cancellable for further async operations. .. method:: set_error_if_cancelled() -> bool If the ``cancellable`` is cancelled, sets the error to notify that the operation was cancelled. .. method:: source_new() -> ~gi.repository.GLib.Source Creates a source that triggers if ``cancellable`` is cancelled and calls its callback of type ``GCancellableSourceFunc``. This is primarily useful for attaching to another (non-cancellable) source with :func:`~gi.repository.GLib.Source.add_child_source` to add cancellability to it. For convenience, you can call this with a :const:`None` :obj:`~gi.repository.Gio.Cancellable`\, in which case the source will never trigger. The new :obj:`~gi.repository.GLib.Source` will hold a reference to the :obj:`~gi.repository.Gio.Cancellable`\. .. versionadded:: 2.28 Signals ------- .. rst-class:: interim-class .. class:: Cancellable.signals :no-index: .. method:: cancelled() -> None The type of the None singleton. Virtual Methods --------------- .. rst-class:: interim-class .. class:: Cancellable :no-index: .. method:: do_cancelled() -> None The type of the None singleton. Fields ------ .. rst-class:: interim-class .. class:: Cancellable :no-index: .. attribute:: parent_instance .. attribute:: priv