gi-gio-2.0.32: Gio bindings

Copyright | Will Thompson and Iñaki García Etxebarria
License | LGPL-2.1
Maintainer | Iñaki García Etxebarria
Safe Haskell | Safe-Inferred
Language | Haskell2010

GI.Gio.Objects.Task

Contents

- Exported types
- Methods
  - getCancellable
  - getCheckCancellable
  - getCompleted
  - getContext
  - getName
  - getPriority
  - getReturnOnCancel
  - getSourceObject
  - getSourceTag
  - getTaskData
  - hadError
  - isValid
  - new
  - propagateBoolean
  - propagateInt
  - propagatePointer
  - propagateValue
  - reportError
  - returnBoolean
  - returnError
  - returnErrorIfCancelled
  - returnInt
  - returnNewErrorLiteral
  - returnPointer
  - returnValue
  - runInThread
  - runInThreadSync
  - setCheckCancellable
  - setName
  - setPriority
  - setReturnOnCancel
  - setSourceTag
  - setStaticName
  - setTaskData
- Properties
  - completed

Description

A `GTask` represents and manages a cancellable ‘task’.

## Asynchronous operations

The most common usage of `GTask` is as a `AsyncResult`, to manage data during an asynchronous operation. You call `taskNew` in the ‘start’ method, followed by `taskSetTaskData` 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 `taskReturnPointer` or `taskReturnError`, which will save the value you give it and then invoke the task’s callback function in the thread-default main context (see `mainContextPushThreadDefault`) 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 `AsyncResult`), and you can use `taskPropagatePointer` or the like to extract the return value.

Using `GTask` requires the thread-default [struct`gLib`.MainContext] from when the `GTask` was constructed to be running at least until the task has completed and its data has been freed.

If a `GTask` has been constructed and its callback set, it is an error to not call `g_task_return_*()` on it. GLib will warn at runtime if this happens (since 2.76).

Here is an example for using `GTask` as a `AsyncResult`:

### c code

    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. `taskGetCancellable`, `taskGetContext`, and `taskGetPriority` allow you to get back the task’s `Cancellable`, [struct`gLib`.MainContext], and I/O priority when starting a new subtask, so you don’t have to keep track of them yourself. `Task`.`attach_source`() simplifies the case of waiting for a source to fire (automatically using the correct [struct`gLib`.MainContext] and priority).

Here is an example for chained asynchronous operations:

### c code

    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 `taskRunInThread` 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 (see `mainContextPushThreadDefault`) where the `GTask` was created.

Running a task in a thread:

### c code

    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, `taskRunInThread` and `taskRunInThreadSync` can be used to turn an uncancellable operation into a cancellable one. If you call `taskSetReturnOnCancel`, passing `TRUE`, then if the task’s `Cancellable` 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:

### c code

    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 `SimpleAsyncResult`

`GTask`’s API attempts to be simpler than `SimpleAsyncResult`’s in several ways:

- You can save task-specific data with `taskSetTaskData`, and retrieve it later with `taskGetTaskData`. This replaces the abuse of `SimpleAsyncResult`.`set_op_res_gpointer`() for the same purpose with `SimpleAsyncResult`.
- In addition to the task data, `GTask` also keeps track of the priority, `Cancellable`, and [struct`gLib`.MainContext] 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.
- `taskReturnErrorIfCancelled` provides simplified handling for cancellation. In addition, cancellation overrides any other `GTask` return value by default, like `SimpleAsyncResult` does when `simpleAsyncResultSetCheckCancellable` is called. (You can use `taskSetCheckCancellable` to turn off that behavior.) On the other hand, `taskRunInThread` guarantees that it will always run your `task_func`, even if the task’s `Cancellable` is already cancelled before the task gets a chance to run; you can start your `task_func` with a `taskReturnErrorIfCancelled` check if you need the old behavior.
- The ‘return’ methods (eg, `taskReturnPointer`) 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 [struct`gLib`.MainContext], or delayed until the next iteration of the current [struct`gLib`.MainContext].)
- The ‘finish’ functions for `GTask` based operations are generally much simpler than `SimpleAsyncResult` ones, normally consisting of only a single call to `taskPropagatePointer` or the like. Since `taskPropagatePointer` ‘steals’ the return value from the `GTask`, it is not necessary to juggle pointers around to prevent it from being freed twice.
- With `SimpleAsyncResult`, it was common to call `simpleAsyncResultPropagateError` 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 `asyncResultLegacyPropagateError` to do old-style `SimpleAsyncResult` error-returning behavior, and `asyncResultIsTagged` 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 `inputStreamReadAsync`).

## Thread-safety considerations

Due to some infelicities in the API design, there is a thread-safety concern that users of `GTask` have to be aware of:

If the `main` thread drops its last reference to the source object or the task data before the task is finalized, then the finalizers of these objects may be called on the worker thread.

This is a problem if the finalizers use non-threadsafe API, and can lead to hard-to-debug crashes. Possible workarounds include:

- Clear task data in a signal handler for `notify::completed`
- Keep iterating a main context in the main thread and defer dropping the reference to the source object to that main context when the task is finalized

Synopsis

- newtype Task = Task (ManagedPtr Task)
- class (GObject o, IsDescendantOf Task o) => IsTask o
- toTask :: (MonadIO m, IsTask o) => o -> m Task
- taskGetCancellable :: (HasCallStack, MonadIO m, IsTask a) => a -> m (Maybe Cancellable)
- taskGetCheckCancellable :: (HasCallStack, MonadIO m, IsTask a) => a -> m Bool
- taskGetCompleted :: (HasCallStack, MonadIO m, IsTask a) => a -> m Bool
- taskGetContext :: (HasCallStack, MonadIO m, IsTask a) => a -> m MainContext
- taskGetName :: (HasCallStack, MonadIO m, IsTask a) => a -> m (Maybe Text)
- taskGetPriority :: (HasCallStack, MonadIO m, IsTask a) => a -> m Int32
- taskGetReturnOnCancel :: (HasCallStack, MonadIO m, IsTask a) => a -> m Bool
- taskGetSourceObject :: (HasCallStack, MonadIO m, IsTask a) => a -> m (Maybe Object)
- taskGetSourceTag :: (HasCallStack, MonadIO m, IsTask a) => a -> m (Ptr ())
- taskGetTaskData :: (HasCallStack, MonadIO m, IsTask a) => a -> m (Ptr ())
- taskHadError :: (HasCallStack, MonadIO m, IsTask a) => a -> m Bool
- taskIsValid :: (HasCallStack, MonadIO m, IsAsyncResult a, IsObject b) => a -> Maybe b -> m Bool
- taskNew :: (HasCallStack, MonadIO m, IsObject a, IsCancellable b) => Maybe a -> Maybe b -> Maybe AsyncReadyCallback -> m Task
- taskPropagateBoolean :: (HasCallStack, MonadIO m, IsTask a) => a -> m ()
- taskPropagateInt :: (HasCallStack, MonadIO m, IsTask a) => a -> m Int64
- taskPropagatePointer :: (HasCallStack, MonadIO m, IsTask a) => a -> m (Ptr ())
- taskPropagateValue :: (HasCallStack, MonadIO m, IsTask a) => a -> m GValue
- taskReportError :: (HasCallStack, MonadIO m, IsObject a) => Maybe a -> Maybe AsyncReadyCallback -> Ptr () -> GError -> m ()
- taskReturnBoolean :: (HasCallStack, MonadIO m, IsTask a) => a -> Bool -> m ()
- taskReturnError :: (HasCallStack, MonadIO m, IsTask a) => a -> GError -> m ()
- taskReturnErrorIfCancelled :: (HasCallStack, MonadIO m, IsTask a) => a -> m Bool
- taskReturnInt :: (HasCallStack, MonadIO m, IsTask a) => a -> Int64 -> m ()
- taskReturnNewErrorLiteral :: (HasCallStack, MonadIO m, IsTask a) => a -> Word32 -> Int32 -> Text -> m ()
- taskReturnPointer :: (HasCallStack, MonadIO m, IsTask a) => a -> Ptr () -> Maybe DestroyNotify -> m ()
- taskReturnValue :: (HasCallStack, MonadIO m, IsTask a) => a -> Maybe GValue -> m ()
- taskRunInThread :: (HasCallStack, MonadIO m, IsTask a) => a -> TaskThreadFunc -> m ()
- taskRunInThreadSync :: (HasCallStack, MonadIO m, IsTask a) => a -> TaskThreadFunc -> m ()
- taskSetCheckCancellable :: (HasCallStack, MonadIO m, IsTask a) => a -> Bool -> m ()
- taskSetName :: (HasCallStack, MonadIO m, IsTask a) => a -> Maybe Text -> m ()
- taskSetPriority :: (HasCallStack, MonadIO m, IsTask a) => a -> Int32 -> m ()
- taskSetReturnOnCancel :: (HasCallStack, MonadIO m, IsTask a) => a -> Bool -> m Bool
- taskSetSourceTag :: (HasCallStack, MonadIO m, IsTask a) => a -> Ptr () -> m ()
- taskSetStaticName :: (HasCallStack, MonadIO m, IsTask a) => a -> Maybe Text -> m ()
- taskSetTaskData :: (HasCallStack, MonadIO m, IsTask a) => a -> Ptr () -> Maybe DestroyNotify -> m ()
- getTaskCompleted :: (MonadIO m, IsTask o) => o -> m Bool

# Exported types

newtype Task Source #

Memory-managed wrapper type.

Constructors

Task (ManagedPtr Task) |

#### Instances

Instances details

Eq Task Source # |
Instance details Defined in GI.Gio.Objects.Task Methods (==) :: Task -> Task -> Bool Source # (/=) :: Task -> Task -> Bool Source #
GObject Task Source # |
Instance details Defined in GI.Gio.Objects.Task
ManagedPtrNewtype Task Source # |
Instance details Defined in GI.Gio.Objects.Task Methods toManagedPtr :: Task -> ManagedPtr Task Source #
TypedObject Task Source # |
Instance details Defined in GI.Gio.Objects.Task Methods glibType :: IO GType Source #
HasParentTypes Task Source # |
Instance details Defined in GI.Gio.Objects.Task
IsGValue (Maybe Task) Source # | Convert `Task` to and from `GValue`. See `toGValue` and `fromGValue`.
Instance details Defined in GI.Gio.Objects.Task Methods gvalueGType_ :: IO GType Source # gvalueSet_ :: Ptr GValue -> Maybe Task -> IO () Source # gvalueGet_ :: Ptr GValue -> IO (Maybe Task) Source #
type ParentTypes Task Source # |
Instance details Defined in GI.Gio.Objects.Task type ParentTypes Task = '[Object, AsyncResult]

class (GObject o, IsDescendantOf Task o) => IsTask o Source #

Type class for types which can be safely cast to `Task`, for instance with `toTask`.

#### Instances

Instances details

(GObject o, IsDescendantOf Task o) => IsTask o Source # |
Instance details Defined in GI.Gio.Objects.Task

toTask :: (MonadIO m, IsTask o) => o -> m Task Source #

Cast to `Task`, for types for which this is known to be safe. For general casts, use `castTo`.

# Methods

### Click to display all available methods, including inherited ones

Expand

#### Methods

bindProperty, bindPropertyFull, forceFloating, freezeNotify, getv, hadError, isFloating, isTagged, legacyPropagateError, notify, notifyByPspec, propagateBoolean, propagateInt, propagatePointer, propagateValue, ref, refSink, returnBoolean, returnError, returnErrorIfCancelled, returnInt, returnNewErrorLiteral, returnPointer, returnValue, runDispose, runInThread, runInThreadSync, stealData, stealQdata, thawNotify, unref, watchClosure.

#### Getters

getCancellable, getCheckCancellable, getCompleted, getContext, getData, getName, getPriority, getProperty, getQdata, getReturnOnCancel, getSourceObject, getSourceTag, getTaskData, getUserData.

#### Setters

setCheckCancellable, setData, setDataFull, setName, setPriority, setProperty, setReturnOnCancel, setSourceTag, setStaticName, setTaskData.

## getCancellable

taskGetCancellable Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> m (Maybe Cancellable) | Returns: `task`'s `Cancellable`

Gets `task`'s `Cancellable`

Since: 2.36

## getCheckCancellable

taskGetCheckCancellable Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: the `Task`
-> m Bool |

Gets `task`'s check-cancellable flag. See `taskSetCheckCancellable` for more details.

Since: 2.36

## getCompleted

taskGetCompleted Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`.
-> m Bool | Returns: `True` if the task has completed, `False` otherwise.

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.

Since: 2.44

## getContext

taskGetContext Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> m MainContext | Returns: `task`'s `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-`Nothing` value, even if the task's context is the default `MainContext`.

Since: 2.36

## getName

taskGetName Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> m (Maybe Text) | Returns: `task`’s name, or `Nothing`

Gets `task`’s name. See `taskSetName`.

Since: 2.60

## getPriority

taskGetPriority Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> m Int32 | Returns: `task`'s priority

Gets `task`'s priority

Since: 2.36

## getReturnOnCancel

taskGetReturnOnCancel Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: the `Task`
-> m Bool |

Gets `task`'s return-on-cancel flag. See `taskSetReturnOnCancel` for more details.

Since: 2.36

## getSourceObject

taskGetSourceObject Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> m (Maybe Object) | Returns: `task`'s source object, or `Nothing`

Gets the source object from `task`. Like `asyncResultGetSourceObject`, but does not ref the object.

Since: 2.36

## getSourceTag

taskGetSourceTag Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> m (Ptr ()) | Returns: `task`'s source tag

Gets `task`'s source tag. See `taskSetSourceTag`.

Since: 2.36

## getTaskData

taskGetTaskData Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> m (Ptr ()) | Returns: `task`'s `task_data`.

Gets `task`'s `task_data`.

Since: 2.36

## hadError

taskHadError Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`.
-> m Bool | Returns: `True` if the task resulted in an error, `False` otherwise.

Tests if `task` resulted in an error.

Since: 2.36

## isValid

taskIsValid Source #

Arguments

:: (HasCallStack, MonadIO m, IsAsyncResult a, IsObject b) |
=> a | `result`: A `AsyncResult`
-> Maybe b | `sourceObject`: the source object expected to be associated with the task
-> m Bool | Returns: `True` if `result` and `sourceObject` are valid, `False` if not

Checks that `result` is a `Task`, and that `sourceObject` is its source object (or that `sourceObject` is `Nothing` and `result` has no source object). This can be used in `g_return_if_fail()` checks.

Since: 2.36

## new

taskNew Source #

Arguments

:: (HasCallStack, MonadIO m, IsObject a, IsCancellable b) |
=> Maybe a | `sourceObject`: the `Object` that owns this task, or `Nothing`.
-> Maybe b | `cancellable`: optional `Cancellable` object, `Nothing` to ignore.
-> Maybe AsyncReadyCallback | `callback`: a `AsyncReadyCallback`.
-> m Task | Returns: a `Task`.

Creates a `Task` acting on `sourceObject`, 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 `taskSetTaskData` to attach task-specific data to the object, which you can retrieve later via `taskGetTaskData`.

By default, if `cancellable` is cancelled, then the return value of the task will always be `IOErrorEnumCancelled`, 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 `taskSetCheckCancellable` to change it.

Since: 2.36

## propagateBoolean

taskPropagateBoolean Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`.
-> m () | (Can throw `GError`)

Gets the result of `task` as a `Bool`.

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.

Since: 2.36

## propagateInt

taskPropagateInt Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`.
-> m Int64 | Returns: the task result, or -1 on error (Can throw `GError`)

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.

Since: 2.36

## propagatePointer

taskPropagatePointer Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> m (Ptr ()) | Returns: the task result, or `Nothing` on error (Can throw `GError`)

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 `Nothing` and set `error`.

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

Since: 2.36

## propagateValue

taskPropagateValue Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> m GValue | (Can throw `GError`)

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

Since: 2.64

## reportError

taskReportError Source #

Arguments

:: (HasCallStack, MonadIO m, IsObject a) |
=> Maybe a | `sourceObject`: the `Object` that owns this task, or `Nothing`.
-> Maybe AsyncReadyCallback | `callback`: a `AsyncReadyCallback`.
-> Ptr () | `sourceTag`: an opaque pointer indicating the source of this task
-> GError | `error`: error to report
-> m () |

Creates a `Task` and then immediately calls `taskReturnError` 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 `asyncResultIsTagged` 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()`.

Since: 2.36

## returnBoolean

taskReturnBoolean Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`.
-> Bool | `result`: the `Bool` result of a task function.
-> m () |

Sets `task`'s result to `result` and completes the task (see `taskReturnPointer` for more discussion of exactly what this means).

Since: 2.36

## returnError

taskReturnError Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`.
-> GError | `error`: the `GError` result of a task function.
-> m () |

Sets `task`'s result to `error` (which `task` assumes ownership of) and completes the task (see `taskReturnPointer` 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 `taskReturnError`, you cannot assume that `error` is still valid after calling this. Call `errorCopy` on the error if you need to keep a local copy as well.

See also `Task`.`return_new_error`(), `taskReturnNewErrorLiteral`.

Since: 2.36

## returnErrorIfCancelled

taskReturnErrorIfCancelled Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> m Bool | Returns: `True` if `task` has been cancelled, `False` if not

Checks if `task`'s `Cancellable` has been cancelled, and if so, sets `task`'s error accordingly and completes the task (see `taskReturnPointer` for more discussion of exactly what this means).

Since: 2.36

## returnInt

taskReturnInt Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`.
-> Int64 | `result`: the integer (`gssize`) result of a task function.
-> m () |

Sets `task`'s result to `result` and completes the task (see `taskReturnPointer` for more discussion of exactly what this means).

Since: 2.36

## returnNewErrorLiteral

taskReturnNewErrorLiteral Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`.
-> Word32 | `domain`: a `GQuark`.
-> Int32 | `code`: an error code.
-> Text | `message`: an error message
-> m () |

Sets `task`’s result to a new [type`gLib`.Error] created from `domain`, `code`, `message` and completes the task.

See `taskReturnPointer` for more discussion of exactly what ‘completing the task’ means.

See also `Task`.`return_new_error`().

Since: 2.80

## returnPointer

taskReturnPointer Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> Ptr () | `result`: the pointer result of a task function
-> Maybe DestroyNotify | `resultDestroy`: a `DestroyNotify` function.
-> m () |

Sets `task`'s result to `result` and completes the task. If `result` is not `Nothing`, then `resultDestroy` will be used to free `result` if the caller does not take ownership of it with `taskPropagatePointer`.

"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 `taskRunInThread` or `taskRunInThreadSync`, 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 `taskReturnPointer`, you cannot assume that `result` is still valid after calling this, unless you are still holding another reference on it.

Since: 2.36

## returnValue

taskReturnValue Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> Maybe GValue | `result`: the `Value` result of a task function
-> m () |

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

If `result` is `Nothing` then a `Value` of type `G_TYPE_POINTER` with a value of `Nothing` will be used for the result.

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

Since: 2.64

## runInThread

taskRunInThread Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> TaskThreadFunc | `taskFunc`: a `TaskThreadFunc`
-> m () |

Runs `taskFunc` in another thread. When `taskFunc` 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 `taskFunc` is handled.

Although GLib currently rate-limits the tasks queued via `taskRunInThread`, 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 `taskRunInThread`.

Since: 2.36

## runInThreadSync

taskRunInThreadSync Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> TaskThreadFunc | `taskFunc`: a `TaskThreadFunc`
-> m () |

Runs `taskFunc` in another thread, and waits for it to return or be cancelled. You can use `taskPropagatePointer`, etc, afterward to get the result of `taskFunc`.

See `TaskThreadFunc` for more details about how `taskFunc` is handled.

Normally this is used with tasks created with a `Nothing` `callback`, but note that even if the task does have a callback, it will not be invoked when `taskFunc` returns. Task:completed will be set to `True` just before this function returns.

Although GLib currently rate-limits the tasks queued via `taskRunInThreadSync`, 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.

Since: 2.36

## setCheckCancellable

taskSetCheckCancellable Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: the `Task`
-> Bool | `checkCancellable`: whether `Task` will check the state of its `Cancellable` for you.
-> m () |

Sets or clears `task`'s check-cancellable flag. If this is `True` (the default), then `taskPropagatePointer`, etc, and `taskHadError` 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 (`IOErrorEnumCancelled`), regardless of any other error or return value the task may have had.

If `checkCancellable` is `False`, then the `Task` will not check the cancellable itself, and it is up to `task`'s owner to do this (eg, via `taskReturnErrorIfCancelled`).

If you are using `taskSetReturnOnCancel` as well, then you must leave check-cancellable set `True`.

Since: 2.36

## setName

taskSetName Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> Maybe Text | `name`: a human readable name for the task, or `Nothing` to unset it
-> m () |

Sets `task`’s name, used in debugging and profiling. The name defaults to `Nothing`.

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 `taskSetSourceTag` if not called already.

Since: 2.60

## setPriority

taskSetPriority Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: the `Task`
-> Int32 | `priority`: the priority of the request
-> m () |

Sets `task`'s priority. If you do not call this, it will default to `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 `taskGetPriority`.

Since: 2.36

## setReturnOnCancel

taskSetReturnOnCancel Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: the `Task`
-> Bool | `returnOnCancel`: whether the task returns automatically when it is cancelled.
-> m Bool | Returns: `True` if `task`'s return-on-cancel flag was changed to match `returnOnCancel`. `False` if `task` has already been cancelled.

Sets or clears `task`'s return-on-cancel flag. This is only meaningful for tasks run via `taskRunInThread` or `taskRunInThreadSync`.

If `returnOnCancel` is `True`, then cancelling `task`'s `Cancellable` will immediately cause it to return, as though the task's `TaskThreadFunc` had called `taskReturnErrorIfCancelled` 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 `taskSetReturnOnCancel` 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, `taskSetReturnOnCancel` 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 `taskSetReturnOnCancel` 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 `taskRunInThread`/`taskRunInThreadSync`, then the `TaskThreadFunc` will still be run (for consistency), but the task will also be completed right away.

Since: 2.36

## setSourceTag

taskSetSourceTag Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: the `Task`
-> Ptr () | `sourceTag`: an opaque pointer indicating the source of this task
-> m () |

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 `taskGetSourceTag` (or `asyncResultIsTagged`) 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 `sourceTag` if it’s not already set, for convenience.

Since: 2.36

## setStaticName

taskSetStaticName Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: a `Task`
-> Maybe Text | `name`: a human readable name for the task. Must be a string literal
-> m () |

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

This is a variant of `taskSetName` that avoids copying `name`.

Since: 2.76

## setTaskData

taskSetTaskData Source #

Arguments

:: (HasCallStack, MonadIO m, IsTask a) |
=> a | `task`: the `Task`
-> Ptr () | `taskData`: task-specific data
-> Maybe DestroyNotify | `taskDataDestroy`: `DestroyNotify` for `taskData`
-> m () |

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

Since: 2.36

# Properties

## completed

Whether the task has completed, meaning its callback (if set) has been invoked.

This can only happen after `taskReturnPointer`, `taskReturnError` 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 `Task`. Callers must do that tracking themselves, typically by linking the lifetime of the `Task` to the control flow of their code.

This property is guaranteed to change from `False` to `True` exactly once.

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

Since: 2.44

getTaskCompleted :: (MonadIO m, IsTask o) => o -> m Bool Source #

Get the value of the “`completed`” property. When overloading is enabled, this is equivalent to

    get task #completed