Top |
Functions
Description
A GTask represents and manages a cancellable "task".
Asynchronous operations
The most common usage of GTask is as a GAsyncResult, to
manage data during an asynchronous operation. You call
g_task_new()
in the "start" method, followed by
g_task_set_task_data()
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
g_task_return_pointer()
or g_task_return_error()
, which will
save the value you give it and then invoke the task's callback
function in the
thread-default main context
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 GAsyncResult), and you can
can use g_task_propagate_pointer()
or the like to extract the
return value.
Here is an example for using GTask as a GAsyncResult:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 |
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. g_task_get_cancellable()
, g_task_get_context()
,
and g_task_get_priority()
allow you to get back the task's
GCancellable, GMainContext, and I/O priority
when starting a new subtask, so you don't have to keep track
of them yourself. g_task_attach_source()
simplifies the case
of waiting for a source to fire (automatically using the correct
GMainContext and priority).
Here is an example for chained asynchronous operations:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 |
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 g_task_run_in_thread()
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
where the GTask was created.
Running a task in a thread:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 |
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, g_task_run_in_thread()
and g_task_run_in_thread_sync()
can be used to turn an uncancellable operation into a
cancellable one. If you call g_task_set_return_on_cancel()
,
passing TRUE
, then if the task's GCancellable 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:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 |
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 GSimpleAsyncResult
GTask's API attempts to be simpler than GSimpleAsyncResult's in several ways:
You can save task-specific data with
g_task_set_task_data()
, and retrieve it later withg_task_get_task_data()
. This replaces the abuse ofg_simple_async_result_set_op_res_gpointer()
for the same purpose with GSimpleAsyncResult.In addition to the task data, GTask also keeps track of the priority, GCancellable, and GMainContext 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.
g_task_return_error_if_cancelled() provides simplified handling for cancellation. In addition, cancellation overrides any other GTask return value by default, like GSimpleAsyncResult does when
g_simple_async_result_set_check_cancellable()
is called. (You can useg_task_set_check_cancellable()
to turn off that behavior.) On the other hand,g_task_run_in_thread()
guarantees that it will always run yourtask_func
, even if the task's GCancellable is already cancelled before the task gets a chance to run; you can start yourtask_func
with ag_task_return_error_if_cancelled()
check if you need the old behavior.The "return" methods (eg,
g_task_return_pointer()
) 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 GMainContext, or delayed until the next iteration of the current GMainContext.)The "finish" functions for GTask based operations are generally much simpler than GSimpleAsyncResult ones, normally consisting of only a single call to
g_task_propagate_pointer()
or the like. Sinceg_task_propagate_pointer()
"steals" the return value from the GTask, it is not necessary to juggle pointers around to prevent it from being freed twice.With GSimpleAsyncResult, it was common to call
g_simple_async_result_propagate_error()
from the
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_finish()
g_task_propagate_
function. Note that wrapper methods can now useg_async_result_legacy_propagate_error()
to do old-style GSimpleAsyncResult error-returning behavior, andg_async_result_is_tagged()
to check if a result is tagged as having come from the
wrapper function (for "short-circuit" results, such as when passing 0 to_async()
g_input_stream_read_async()
).
Functions
g_task_new ()
GTask * g_task_new (gpointer source_object
,GCancellable *cancellable
,GAsyncReadyCallback callback
,gpointer callback_data
);
Creates a GTask acting on source_object
, which will eventually be
used to invoke callback
in the current
thread-default main context.
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 G_IO_ERROR_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
source_object |
[nullable][type GObject] | |
cancellable |
optional GCancellable object, |
[nullable] |
callback |
[scope async] | |
callback_data |
user data passed to |
[closure] |
Since: 2.36
g_task_set_task_data ()
void g_task_set_task_data (GTask *task
,gpointer task_data
,GDestroyNotify task_data_destroy
);
Sets task
's task data (freeing the existing task data, if any).
Parameters
task |
the GTask |
|
task_data |
task-specific data. |
[nullable] |
task_data_destroy |
GDestroyNotify for |
[nullable] |
Since: 2.36
g_task_set_priority ()
void g_task_set_priority (GTask *task
,gint 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()
.
Since: 2.36
g_task_set_check_cancellable ()
void g_task_set_check_cancellable (GTask *task
,gboolean check_cancellable
);
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
(G_IO_ERROR_CANCELLED
), regardless of any other error or return
value the task may have had.
If check_cancellable
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
task |
the GTask |
|
check_cancellable |
whether GTask will check the state of its GCancellable for you. |
Since: 2.36
g_task_set_return_on_cancel ()
gboolean g_task_set_return_on_cancel (GTask *task
,gboolean return_on_cancel
);
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 return_on_cancel
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
uninterruptable 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
task |
the GTask |
|
return_on_cancel |
whether the task returns automatically when it is cancelled. |
Returns
TRUE
if task
's return-on-cancel flag was changed to
match return_on_cancel
. FALSE
if task
has already been
cancelled.
Since: 2.36
g_task_set_source_tag ()
void g_task_set_source_tag (GTask *task
,gpointer source_tag
);
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.
Since: 2.36
g_task_report_error ()
void g_task_report_error (gpointer source_object
,GAsyncReadyCallback callback
,gpointer callback_data
,gpointer source_tag
,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
source_object |
[nullable][type GObject] | |
callback |
[scope async] | |
callback_data |
user data passed to |
[closure] |
source_tag |
an opaque pointer indicating the source of this task |
|
error |
error to report. |
[transfer full] |
Since: 2.36
g_task_report_new_error ()
void g_task_report_new_error (gpointer source_object
,GAsyncReadyCallback callback
,gpointer callback_data
,gpointer source_tag
,GQuark domain
,gint code
,const char *format
,...
);
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
source_object |
[nullable][type GObject] | |
callback |
[scope async] | |
callback_data |
user data passed to |
[closure] |
source_tag |
an opaque pointer indicating the source of this task |
|
domain |
a GQuark. |
|
code |
an error code. |
|
format |
a string with format characters. |
|
... |
a list of values to insert into |
Since: 2.36
g_task_get_task_data ()
gpointer
g_task_get_task_data (GTask *task
);
Gets task
's task_data
.
Since: 2.36
g_task_get_cancellable ()
GCancellable *
g_task_get_cancellable (GTask *task
);
Gets task
's GCancellable
Since: 2.36
g_task_get_check_cancellable ()
gboolean
g_task_get_check_cancellable (GTask *task
);
Gets task
's check-cancellable flag. See
g_task_set_check_cancellable()
for more details.
Since: 2.36
g_task_get_return_on_cancel ()
gboolean
g_task_get_return_on_cancel (GTask *task
);
Gets task
's return-on-cancel flag. See
g_task_set_return_on_cancel()
for more details.
Since: 2.36
g_task_get_context ()
GMainContext *
g_task_get_context (GTask *task
);
Gets the GMainContext that task
will return its result in (that
is, the context that was the
thread-default main context
at the point when task
was created).
This will always return a non-NULL
value, even if the task's
context is the default GMainContext.
Since: 2.36
g_task_get_source_object ()
gpointer
g_task_get_source_object (GTask *task
);
Gets the source object from task
. Like
g_async_result_get_source_object()
, but does not ref the object.
Since: 2.36
g_task_get_source_tag ()
gpointer
g_task_get_source_tag (GTask *task
);
Gets task
's source tag. See g_task_set_source_tag()
.
Since: 2.36
g_task_return_boolean ()
void g_task_return_boolean (GTask *task
,gboolean result
);
Sets task
's result to result
and completes the task (see
g_task_return_pointer()
for more discussion of exactly what this
means).
Since: 2.36
g_task_return_int ()
void g_task_return_int (GTask *task
,gssize result
);
Sets task
's result to result
and completes the task (see
g_task_return_pointer()
for more discussion of exactly what this
means).
Since: 2.36
g_task_return_pointer ()
void g_task_return_pointer (GTask *task
,gpointer result
,GDestroyNotify result_destroy
);
Sets task
's result to result
and completes the task. If result
is not NULL
, then result_destroy
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
task |
a GTask |
|
result |
the pointer result of a task function. |
[nullable][transfer full] |
result_destroy |
a GDestroyNotify function. |
[nullable] |
Since: 2.36
g_task_return_error ()
void g_task_return_error (GTask *task
,GError *error
);
Sets task
's result to error
(which 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 g_task_return_new_error()
.
Since: 2.36
g_task_return_new_error ()
void g_task_return_new_error (GTask *task
,GQuark domain
,gint code
,const char *format
,...
);
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()
.
Since: 2.36
g_task_return_error_if_cancelled ()
gboolean
g_task_return_error_if_cancelled (GTask *task
);
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).
Since: 2.36
g_task_propagate_boolean ()
gboolean g_task_propagate_boolean (GTask *task
,GError **error
);
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.
Since: 2.36
g_task_propagate_int ()
gssize g_task_propagate_int (GTask *task
,GError **error
);
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
g_task_propagate_pointer ()
gpointer g_task_propagate_pointer (GTask *task
,GError **error
);
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 NULL
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
g_task_had_error ()
gboolean
g_task_had_error (GTask *task
);
Tests if task
resulted in an error.
Since: 2.36
g_task_get_completed ()
gboolean
g_task_get_completed (GTask *task
);
Gets the value of “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
g_task_run_in_thread ()
void g_task_run_in_thread (GTask *task
,GTaskThreadFunc task_func
);
Runs task_func
in another thread. When task_func
returns, task
's
GAsyncReadyCallback will be invoked in task
's GMainContext.
This takes a ref on task
until the task completes.
See GTaskThreadFunc for more details about how task_func
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, 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
g_task_run_in_thread_sync ()
void g_task_run_in_thread_sync (GTask *task
,GTaskThreadFunc task_func
);
Runs task_func
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 task_func
.
See GTaskThreadFunc for more details about how task_func
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 task_func
returns.
“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.
Since: 2.36
GTaskThreadFunc ()
void (*GTaskThreadFunc) (GTask *task
,gpointer source_object
,gpointer task_data
,GCancellable *cancellable
);
The prototype for a task function to be run in a thread via
g_task_run_in_thread()
or g_task_run_in_thread_sync()
.
If the return-on-cancel flag is set on task
, and cancellable
gets
cancelled, then the GTask will be completed immediately (as though
g_task_return_error_if_cancelled()
had been called), without
waiting for the task function to complete. However, the task
function will continue running in its thread in the background. The
function therefore needs to be careful about how it uses
externally-visible state in this case. See
g_task_set_return_on_cancel()
for more details.
Other than in that case, task
will be completed when the
GTaskThreadFunc returns, not when it calls a
g_task_return_
function.
Parameters
task |
the GTask |
|
source_object |
|
[type GObject] |
task_data |
|
|
cancellable |
|
Since: 2.36
g_task_attach_source ()
void g_task_attach_source (GTask *task
,GSource *source
,GSourceFunc 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 task
as the callback's user_data
.
This takes a reference on task
until source
is destroyed.
Parameters
task |
a GTask |
|
source |
the source to attach |
|
callback |
the callback to invoke when |
Since: 2.36
g_task_is_valid ()
gboolean g_task_is_valid (gpointer result
,gpointer source_object
);
Checks that result
is a GTask, and that source_object
is its
source object (or that source_object
is NULL
and result
has no
source object). This can be used in g_return_if_fail()
checks.
Parameters
result |
A GAsyncResult. |
[type Gio.AsyncResult] |
source_object |
the source object expected to be associated with the task. |
[nullable][type GObject] |
Since: 2.36
Property Details
The “completed”
property
“completed” gboolean
Whether the task has completed, meaning its callback (if set) has been
invoked. This can only happen after g_task_return_pointer()
,
g_task_return_error()
or one of the other return functions have been called
on the task.
This property is guaranteed to change from FALSE
to TRUE
exactly once.
The “notify” signal for this change is emitted in the same main context as the task’s callback, immediately after that callback is invoked.
Flags: Read
Default value: FALSE
Since: 2.44