Task

class Task(**properties: Any)

Superclasses: Object

Implemented Interfaces: AsyncResult

Constructors:

Task(**properties)
new(source_object:GObject.Object=None, cancellable:Gio.Cancellable=None, callback:Gio.AsyncReadyCallback=None, callback_data=None) -> Gio.Task

Constructors

class Task

classmethod new(source_object: Object | None = None, cancellable: Cancellable | None = None, callback: Callable[[...], None] | None = None, *callback_data: Any) → Task

Creates a 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 Task around throughout the asynchronous operation. You can use set_task_data() to attach task-specific data to the object, which you can retrieve later via get_task_data().

By default, if cancellable is cancelled, then the return value of the task will always be 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 set_check_cancellable() to change it.

Added in version 2.36.

Parameters:

source_object – the Object that owns this task, or None.
cancellable – optional Cancellable object, None to ignore.
callback – a AsyncReadyCallback.
callback_data – user data passed to callback.

Methods

class Task

get_cancellable() → Cancellable | None: Gets task’s Cancellable

Added in version 2.36.

get_check_cancellable() → bool: Gets task’s check-cancellable flag. See set_check_cancellable() for more details.

Added in version 2.36.

get_completed() → bool: Gets the value of Task:completed. This changes from False to True after the task’s callback is invoked, and will return False if called from inside the callback.

Added in version 2.44.

get_context() → MainContext

Gets the 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-None value, even if the task’s context is the default MainContext.

Added in version 2.36.

get_name() → str | None: Gets task’s name. See set_name().

Added in version 2.60.

get_priority() → int: Gets task’s priority

Added in version 2.36.

get_return_on_cancel() → bool: Gets task’s return-on-cancel flag. See set_return_on_cancel() for more details.

Added in version 2.36.

get_source_object() → Object | None: Gets the source object from task. Like get_source_object(), but does not ref the object.

Added in version 2.36.

get_source_tag() → None: Gets task’s source tag. See set_source_tag().

Added in version 2.36.

get_task_data() → None: Gets task’s task_data.

Added in version 2.36.

had_error() → bool: Tests if task resulted in an error.

Added in version 2.36.

is_valid(result: AsyncResult, source_object: Object | None = None) → bool

Checks that result is a Task, and that source_object is its source object (or that source_object is None and result has no source object). This can be used in return_if_fail() checks.

Added in version 2.36.

Parameters:

result – A AsyncResult
source_object – the source object expected to be associated with the task

propagate_boolean() → bool

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.

Added in version 2.36.

propagate_int() → int

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.

Added in version 2.36.

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 None and set error.

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

Added in version 2.36.

propagate_value() → tuple[bool, Any]

Gets the result of task as a Value, and transfers ownership of that value to the caller. As with return_value(), this is a generic low-level method; 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.

Added in version 2.64.

report_error(source_object: Object | None, callback: Callable[[...], None] | None, source_tag: None, error: GError, *callback_data: Any) → None

Creates a Task and then immediately calls 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 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 return_new_error.

Added in version 2.80.

Parameters:

domain – a Quark.
code – an error code.
message – an error message

return_pointer(result: None, result_destroy: Callable[[None], None] | None = None) → None

Sets task’s result to result and completes the task. If result is not None, then result_destroy will be used to free result if the caller does not take ownership of it with 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 MainContext, or in the next iteration of the current MainContext. For a task run via run_in_thread() or 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 TaskThreadFunc exits.

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

Added in version 2.36.

Parameters:

result – the pointer result of a task function
result_destroy – a DestroyNotify function.

return_value(result: Any | None = None) → None

Sets task’s result to result (by copying it) and completes the task.

If result is None then a Value of type %G_TYPE_POINTER with a value of 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, return_pointer() and the like will normally be much easier to use.

Added in version 2.64.

Parameters:: result – the Value result of a task function

run_in_thread(task_func: Callable[[Task, Object, None, Cancellable | None], None]) → None

Runs task_func in another thread. When task_func returns, task’s AsyncReadyCallback will be invoked in task’s MainContext.

This takes a ref on task until the task completes.

See TaskThreadFunc for more details about how task_func is handled.

Although GLib currently rate-limits the tasks queued via 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 run_in_thread().

Added in version 2.36.

Parameters:: task_func – a TaskThreadFunc

run_in_thread_sync(task_func: Callable[[Task, Object, None, Cancellable | None], None]) → None

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

See TaskThreadFunc for more details about how task_func is handled.

Normally this is used with tasks created with a None callback, but note that even if the task does have a callback, it will not be invoked when task_func returns. Task:completed will be set to True just before this function returns.

Although GLib currently rate-limits the tasks queued via 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.

Added in version 2.36.

Parameters:: task_func – a TaskThreadFunc

set_check_cancellable(check_cancellable: bool) → None

Sets or clears task’s check-cancellable flag. If this is True (the default), then propagate_pointer(), etc, and had_error() will check the task’s Cancellable first, and if it has been cancelled, then they will consider the task to have returned an “Operation was cancelled” error (CANCELLED), regardless of any other error or return value the task may have had.

If check_cancellable is False, then the Task will not check the cancellable itself, and it is up to task’s owner to do this (eg, via return_error_if_cancelled()).

If you are using set_return_on_cancel() as well, then you must leave check-cancellable set True.

Added in version 2.36.

Parameters:: check_cancellable – whether Task will check the state of its Cancellable for you.

set_name(name: str | None = None) → None

Sets task’s name, used in debugging and profiling. The name defaults to 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 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 set_source_tag() if not called already.

Added in version 2.60.

Parameters:: name – a human readable name for the task, or None to unset it

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 Source created with attach_source() and the scheduling of tasks run in threads, and can also be explicitly retrieved later via get_priority().

Added in version 2.36.

Parameters:: priority – the priority of the request

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 run_in_thread() or run_in_thread_sync().

If return_on_cancel is True, then cancelling task’s Cancellable will immediately cause it to return, as though the task’s TaskThreadFunc had called return_error_if_cancelled() and then returned.

This allows you to create a cancellable wrapper around an uninterruptible function. The 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 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, 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 Cancellable is cancelled while return-on-cancel is False, then calling set_return_on_cancel() to set it True again will cause the task to be cancelled at that point.

If the task’s Cancellable is already cancelled before you call run_in_thread()/run_in_thread_sync(), then the TaskThreadFunc will still be run (for consistency), but the task will also be completed right away.

Added in version 2.36.

Parameters:: return_on_cancel – whether the task returns automatically when it is cancelled.

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 get_source_tag() (or 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.

Added in version 2.36.

Parameters:: source_tag – an opaque pointer indicating the source of this task

set_static_name(name: str | None = None) → None

Sets task’s name, used in debugging and profiling.

This is a variant of set_name() that avoids copying name.

Added in version 2.76.

Parameters:: name – a human readable name for the task. Must be a string literal

set_task_data(task_data: None, task_data_destroy: Callable[[None], None] | None = None) → None

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

Added in version 2.36.

Parameters:

task_data – task-specific data
task_data_destroy – DestroyNotify for task_data

Properties

class Task

props.completed: bool: The type of the None singleton.

Added in version 2.44.