Class Task

java.lang.Object
org.javagi.base.ProxyInstance
org.gnome.gobject.TypeInstance
org.gnome.gobject.GObject
org.gnome.gio.Task
All Implemented Interfaces:
AsyncResult, Proxy
@Generated("org.javagi.JavaGI") public class Task extends GObject implements AsyncResult

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 Task() in the ‘start’ method, followed by setTaskData(MemorySegment) 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 returnPointer(MemorySegment) or returnError(GError), which will save the value you give it and then invoke the task’s callback function in the thread-default main context (see MainContext#pushThreadDefault) 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 propagatePointer() or the like to extract the return value.

Using GTask requires the thread-default 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:

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. getCancellable(), getContext(), and getPriority() allow you to get back the task’s Cancellable, GLib.MainContext, and I/O priority when starting a new subtask, so you don’t have to keep track of them yourself. attachSource(Source, SourceFunc) simplifies the case of waiting for a source to fire (automatically using the correct GLib.MainContext and priority).

Here is an example for chained asynchronous operations:

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 runInThread(TaskThreadFunc) 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 MainContext#pushThreadDefault) where the GTask was created.

Running a task in a thread:

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, runInThread(TaskThreadFunc) and runInThreadSync(TaskThreadFunc) can be used to turn an uncancellable operation into a cancellable one. If you call setReturnOnCancel(boolean), 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:

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:

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

  • Constructor Details

    • Task

      public Task(MemorySegment address)
      Create a Task instance for the provided memory address.
      Parameters:
      address - the memory address of the native object

    • Task

      public Task(@Nullable GObject sourceObject, @Nullable Cancellable cancellable, @Nullable AsyncReadyCallback callback)

      Creates a GTask acting on sourceObject, which will eventually be used to invoke callback in the current thread-default main context (see MainContext#pushThreadDefault).

      Call this in the "start" method of your asynchronous method, and pass the GTask around throughout the asynchronous operation. You can use g_task_set_task_data() to attach task-specific data to the object, which you can retrieve later via g_task_get_task_data().

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

      Parameters:
      sourceObject - the GObject that owns this task, or null.
      cancellable - optional GCancellable object, null to ignore.
      callback - a GAsyncReadyCallback.
      Since:
      2.36

    • Task

      public Task()
      Create a new Task.

  • Method Details

    • getType

      public static @Nullable Type getType()
      Get the GType of the Task class.
      Returns:
      the GType

    • getMemoryLayout

      public static MemoryLayout getMemoryLayout()
      The memory layout of the native struct.
      Returns:
      the memory layout

    • asParent

      protected Task asParent()
      Return this instance as if it were its parent type. Comparable to the Java super keyword, but ensures the parent typeclass is also used in native code.
      Overrides:
      asParent in class GObject
      Returns:
      the instance as if it were its parent type

    • isValid

      public static boolean isValid(AsyncResult result, @Nullable GObject sourceObject)
      Checks that result is a GTask, and that sourceObject is its source object (or that sourceObject is null and result has no source object). This can be used in g_return_if_fail() checks.
      Parameters:
      result - A GAsyncResult
      sourceObject - the source object expected to be associated with the task
      Returns:
      true if result and sourceObject are valid, false if not
      Since:
      2.36

    • reportError

      public static void reportError(@Nullable GObject sourceObject, @Nullable AsyncReadyCallback callback, @Nullable MemorySegment sourceTag, GError error)

      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.

      See also g_task_report_new_error().

      Parameters:
      sourceObject - the GObject that owns this task, or null.
      callback - a GAsyncReadyCallback.
      sourceTag - an opaque pointer indicating the source of this task
      error - error to report
      Since:
      2.36

    • reportNewError

      public static void reportNewError(@Nullable GObject sourceObject, @Nullable AsyncReadyCallback callback, @Nullable MemorySegment sourceTag, Quark domain, int code, String format, Object... varargs)

      Creates a GTask and then immediately calls g_task_return_new_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.

      See also g_task_report_error().

      Parameters:
      sourceObject - the GObject that owns this task, or null.
      callback - a GAsyncReadyCallback.
      sourceTag - an opaque pointer indicating the source of this task
      domain - a GQuark.
      code - an error code.
      format - a string with format characters.
      varargs - a list of values to insert into format.
      Since:
      2.36

    • attachSource

      public void attachSource(Source source, @Nullable SourceFunc callback)

      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, and sets source's callback to callback, with this Task as the callback's user_data.

      It will set the source’s name to the task’s name (as set with g_task_set_name()), if one has been set on the task and the source doesn’t yet have a name.

      This takes a reference on this Task until source is destroyed.

      Parameters:
      source - the source to attach
      callback - the callback to invoke when source triggers
      Since:
      2.36

    • getCancellable

      public @Nullable Cancellable getCancellable()
      Gets task's GCancellable
      Returns:
      task's GCancellable
      Since:
      2.36

    • getCheckCancellable

      public boolean getCheckCancellable()
      Gets task's check-cancellable flag. See g_task_set_check_cancellable() for more details.
      Since:
      2.36

    • getCompleted

      public boolean getCompleted()
      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.
      Returns:
      true if the task has completed, false otherwise.
      Since:
      2.44

    • getContext

      public MainContext getContext()

      Gets the GMainContext that this Task will return its result in (that is, the context that was the thread-default main context (see MainContext#pushThreadDefault) at the point when this Task was created).

      This will always return a non-null value, even if the task's context is the default GMainContext.

      Returns:
      task's GMainContext
      Since:
      2.36

    • getName

      public @Nullable String getName()
      Gets task’s name. See g_task_set_name().
      Returns:
      task’s name, or null
      Since:
      2.60

    • getPriority

      public int getPriority()
      Gets task's priority
      Returns:
      task's priority
      Since:
      2.36

    • getReturnOnCancel

      public boolean getReturnOnCancel()
      Gets task's return-on-cancel flag. See g_task_set_return_on_cancel() for more details.
      Since:
      2.36

    • getSourceObject

      public @Nullable GObject getSourceObject()
      Gets the source object from task. Like g_async_result_get_source_object(), but does not ref the object.
      Specified by:
      getSourceObject in interface AsyncResult
      Returns:
      task's source object, or null
      Since:
      2.36

    • getSourceTag

      public @Nullable MemorySegment getSourceTag()
      Gets task's source tag. See g_task_set_source_tag().
      Returns:
      task's source tag
      Since:
      2.36

    • getTaskData

      public @Nullable MemorySegment getTaskData()
      Gets task's task_data.
      Returns:
      task's task_data.
      Since:
      2.36

    • hadError

      public boolean hadError()
      Tests if this Task resulted in an error.
      Returns:
      true if the task resulted in an error, false otherwise.
      Since:
      2.36

    • propagateBoolean

      public boolean propagateBoolean() throws GErrorException

      Gets the result of this 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.

      Returns:
      the task result, or false on error
      Throws:
      GErrorException - see GError
      Since:
      2.36

    • propagateInt

      public long propagateInt() throws GErrorException

      Gets the result of this 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.

      Returns:
      the task result, or -1 on error
      Throws:
      GErrorException - see GError
      Since:
      2.36

    • propagatePointer

      public @Nullable MemorySegment propagatePointer() throws GErrorException

      Gets the result of this 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 null and set error.

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

      Returns:
      the task result, or null on error
      Throws:
      GErrorException - see GError
      Since:
      2.36

    • propagateValue

      public boolean propagateValue(Value value) throws GErrorException

      Gets the result of this Task as a GValue, and transfers ownership of that value to the caller. As with g_task_return_value(), this is a generic low-level method; g_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 false.

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

      Parameters:
      value - return location for the GValue
      Returns:
      true if this Task succeeded, false on error.
      Throws:
      GErrorException - see GError
      Since:
      2.64

    • returnBoolean

      public void returnBoolean(boolean result)
      Sets task's result to result and completes the task (see g_task_return_pointer() for more discussion of exactly what this means).
      Parameters:
      result - the gboolean result of a task function.
      Since:
      2.36

    • returnError

      public void returnError(GError error)

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

      See also returnNewError(Quark, int, String, Object...), returnNewErrorLiteral(Quark, int, String).

      Parameters:
      error - the GError result of a task function.
      Since:
      2.36

    • returnErrorIfCancelled

      public boolean returnErrorIfCancelled()
      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).
      Returns:
      true if this Task has been cancelled, false if not
      Since:
      2.36

    • returnInt

      public void returnInt(long result)
      Sets task's result to result and completes the task (see g_task_return_pointer() for more discussion of exactly what this means).
      Parameters:
      result - the integer (gssize) result of a task function.
      Since:
      2.36

    • returnNewError

      public void returnNewError(Quark domain, int code, String format, Object... varargs)

      Sets task's result to a new GError created from domain, code, format, and the remaining arguments, and completes the task (see g_task_return_pointer() for more discussion of exactly what this means).

      See also g_task_return_error().

      Parameters:
      domain - a GQuark.
      code - an error code.
      format - a string with format characters.
      varargs - a list of values to insert into format.
      Since:
      2.36

    • returnNewErrorLiteral

      public void returnNewErrorLiteral(Quark domain, int code, String message)

      Sets task’s result to a new GLib.Error created from domain, code, message and completes the task.

      See returnPointer(MemorySegment) for more discussion of exactly what ‘completing the task’ means.

      See also returnNewError(Quark, int, String, Object...).

      Parameters:
      domain - a GQuark.
      code - an error code.
      message - an error message
      Since:
      2.80

    • returnPointer

      public void returnPointer(@Nullable MemorySegment result)

      Sets task's result to result and completes the task. If result is not null, then resultDestroy will be used to free result if the caller does not take ownership of it with g_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 GMainContext, or in the next iteration of the current GMainContext. For a task run via g_task_run_in_thread() or g_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 GTaskThreadFunc exits.

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

      Parameters:
      result - the pointer result of a task function
      Since:
      2.36

    • returnPrefixedError

      public void returnPrefixedError(GError error, String format, Object... varargs)

      Sets task's result to error (which this Task assumes ownership of), with the message prefixed according to format, and completes the task (see g_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 g_task_return_prefixed_error(), you cannot assume that error is still valid after calling this. Call g_error_copy() on the error if you need to keep a local copy as well.

      See also g_task_return_error(), g_prefix_error().

      Parameters:
      error - the GError result of a task function.
      format - a string with format characters.
      varargs - a list of values to insert into format.
      Since:
      2.80

    • returnValue

      public void returnValue(@Nullable Value result)

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

      If result is null then a GValue of type G_TYPE_POINTER with a value of null will be used for the result.

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

      Parameters:
      result - the GValue result of a task function
      Since:
      2.64

    • runInThread

      public void runInThread(@Nullable TaskThreadFunc taskFunc)

      Runs taskFunc in another thread. When taskFunc returns, task's GAsyncReadyCallback will be invoked in task's GMainContext.

      This takes a ref on this Task until the task completes.

      See GTaskThreadFunc for more details about how taskFunc is handled.

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

      Parameters:
      taskFunc - a GTaskThreadFunc
      Since:
      2.36

    • runInThreadSync

      public void runInThreadSync(@Nullable TaskThreadFunc taskFunc)

      Runs taskFunc 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 taskFunc.

      See GTaskThreadFunc for more details about how taskFunc is handled.

      Normally this is used with tasks created with a null callback, but note that even if the task does have a callback, it will not be invoked when taskFunc returns. GTask:completed will be set to true just before this function returns.

      Although GLib currently rate-limits the tasks queued via g_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.

      Parameters:
      taskFunc - a GTaskThreadFunc
      Since:
      2.36

    • setCheckCancellable

      public void setCheckCancellable(boolean checkCancellable)

      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 (IOErrorEnum.CANCELLED), regardless of any other error or return value the task may have had.

      If checkCancellable is false, then the GTask will not check the cancellable itself, and it is up to task's owner to do this (eg, via g_task_return_error_if_cancelled()).

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

      Parameters:
      checkCancellable - whether GTask will check the state of its GCancellable for you.
      Since:
      2.36

    • setName

      public void setName(@Nullable String name)

      Sets task’s name, used in debugging and profiling. The name defaults to null.

      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 GSource used for idle completion of the task.

      This function may only be called before the this Task is first used in a thread other than the one it was constructed in.

      Parameters:
      name - a human readable name for the task, or null to unset it
      Since:
      2.60

    • setPriority

      public void setPriority(int priority)

      Sets task's priority. If you do not call this, it will default to G_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 g_task_get_priority().

      Parameters:
      priority - the priority of the request
      Since:
      2.36

    • setReturnOnCancel

      public boolean setReturnOnCancel(boolean returnOnCancel)

      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().

      If returnOnCancel is true, then cancelling task's GCancellable will immediately cause it to return, as though the task's GTaskThreadFunc had called g_task_return_error_if_cancelled() and then returned.

      This allows you to create a cancellable wrapper around an uninterruptible function. The GTaskThreadFunc 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 g_task_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, g_task_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 GCancellable is cancelled while return-on-cancel is false, then calling g_task_set_return_on_cancel() to set it true again will cause the task to be cancelled at that point.

      If the task's GCancellable is already cancelled before you call g_task_run_in_thread()/g_task_run_in_thread_sync(), then the GTaskThreadFunc will still be run (for consistency), but the task will also be completed right away.

      Parameters:
      returnOnCancel - whether the task returns automatically when it is cancelled.
      Returns:
      true if task's return-on-cancel flag was changed to match returnOnCancel. false if this Task has already been cancelled.
      Since:
      2.36

    • setSourceTag

      public void setSourceTag(@Nullable MemorySegment sourceTag)

      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.

      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.

      Parameters:
      sourceTag - an opaque pointer indicating the source of this task
      Since:
      2.36

    • setStaticName

      public void setStaticName(@Nullable String name)

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

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

      This function is called automatically by setSourceTag(MemorySegment) unless a name is set.

      Parameters:
      name - a human readable name for the task. Must be a string literal
      Since:
      2.76

    • setTaskData

      public void setTaskData(@Nullable MemorySegment taskData)
      Sets task's task data (freeing the existing task data, if any).
      Parameters:
      taskData - task-specific data
      Since:
      2.36

    • builder

      public static Task.Builder<? extends Task.Builder> builder()
      A Task.Builder object constructs a Task with the specified properties. Use the various set...() methods to set properties, and finish construction with Task.Builder.build().
      Returns:
      the builder object