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glib/gio/gtask.c
Zander Brown d33752b5ce
gtask: Add g_task_return_prefixed_error() 
An equivalent to g_propagate_prefixed_error, but for errors sent though
GTask, allowing tasks to easily provide extra context to callers.
2023-11-02 02:55:55 +00:00

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/* GIO - GLib Input, Output and Streaming Library
*
* Copyright 2011-2018 Red Hat, Inc.
*
* SPDX-License-Identifier: LGPL-2.1-or-later
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General
* Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
*/
#include "config.h"
#include "gio_trace.h"
#include "gtask.h"
#include "gasyncresult.h"
#include "gcancellable.h"
#include "glib-private.h"
#include "gtrace-private.h"
#include "glibintl.h"
#include <string.h>
/**
* SECTION:gtask
* @short_description: Cancellable synchronous or asynchronous task
* and result
* @include: gio/gio.h
* @see_also: #GAsyncResult
*
* 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][g-main-context-push-thread-default]
* 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
* use g_task_propagate_pointer() or the like to extract the
* return value.
*
* Using #GTask requires the thread-default #GMainContext 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 GAsyncResult:
* |[<!-- language="C" -->
* 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][io-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:
* |[<!-- language="C" -->
* 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][g-main-context-push-thread-default]
* where the #GTask was created.
*
* Running a task in a thread:
* |[<!-- language="C" -->
* 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:
* |[<!-- language="C" -->
* 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 with g_task_get_task_data(). This replaces the
* abuse of g_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][io-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 use g_task_set_check_cancellable() to turn off that
* behavior.) On the other hand, g_task_run_in_thread()
* guarantees that it will always run your
* `task_func`, even if the task's #GCancellable
* is already cancelled before the task gets a chance to run;
* you can start your `task_func` with a
* g_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.
* Since g_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
* `_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
* g_async_result_legacy_propagate_error() to do old-style
* #GSimpleAsyncResult error-returning behavior, and
* g_async_result_is_tagged() 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 g_input_stream_read_async()).
*
* ## 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
*/
/**
* GTask:
*
* The opaque object representing a synchronous or asynchronous task
* and its result.
*/
struct _GTask {
GObject parent_instance;
gpointer source_object;
gpointer source_tag;
gchar *name; /* (owned); may only be modified before the #GTask is threaded */
gpointer task_data;
GDestroyNotify task_data_destroy;
GMainContext *context;
gint64 creation_time;
gint priority;
GCancellable *cancellable;
GAsyncReadyCallback callback;
gpointer callback_data;
GTaskThreadFunc task_func;
GMutex lock;
GCond cond;
/* This can’t be in the bit field because we access it from TRACE(). */
gboolean thread_cancelled;
/* Protected by the lock when task is threaded: */
guint thread_complete : 1;
guint return_on_cancel : 1;
guint : 0;
/* Unprotected, but written to when task runs in thread: */
guint completed : 1;
guint had_error : 1;
guint result_set : 1;
guint ever_returned : 1;
guint : 0;
/* Read-only once task runs in thread: */
guint check_cancellable : 1;
guint synchronous : 1;
guint blocking_other_task : 1;
guint name_is_static : 1;
GError *error;
union {
gpointer pointer;
gssize size;
gboolean boolean;
} result;
GDestroyNotify result_destroy;
};
#define G_TASK_IS_THREADED(task) ((task)->task_func != NULL)
struct _GTaskClass
{
GObjectClass parent_class;
};
typedef enum
{
PROP_COMPLETED = 1,
} GTaskProperty;
static void g_task_async_result_iface_init (GAsyncResultIface *iface);
static void g_task_thread_pool_init (void);
G_DEFINE_TYPE_WITH_CODE (GTask, g_task, G_TYPE_OBJECT,
G_IMPLEMENT_INTERFACE (G_TYPE_ASYNC_RESULT,
g_task_async_result_iface_init);
g_task_thread_pool_init ();)
static GThreadPool *task_pool;
static GMutex task_pool_mutex;
static GPrivate task_private = G_PRIVATE_INIT (NULL);
static GSource *task_pool_manager;
static guint64 task_wait_time;
static gint tasks_running;
static guint task_pool_max_counter;
static guint tasks_running_counter;
/* When the task pool fills up and blocks, and the program keeps
* queueing more tasks, we will slowly add more threads to the pool
* (in case the existing tasks are trying to queue subtasks of their
* own) until tasks start completing again. These "overflow" threads
* will only run one task apiece, and then exit, so the pool will
* eventually get back down to its base size.
*
* The base and multiplier below gives us 10 extra threads after about
* a second of blocking, 30 after 5 seconds, 100 after a minute, and
* 200 after 20 minutes.
*
* We specify maximum pool size of 330 to increase the waiting time up
* to around 30 minutes.
*/
#define G_TASK_POOL_SIZE 10
#define G_TASK_WAIT_TIME_BASE 100000
#define G_TASK_WAIT_TIME_MULTIPLIER 1.03
#define G_TASK_WAIT_TIME_MAX_POOL_SIZE 330
static void
g_task_init (GTask *task)
{
task->check_cancellable = TRUE;
}
#ifdef G_ENABLE_DEBUG
G_LOCK_DEFINE_STATIC (task_list);
static GPtrArray *task_list = NULL;
void
g_task_print_alive_tasks (void)
{
GString *message_str = g_string_new ("");
G_LOCK (task_list);
if (task_list != NULL)
{
g_string_append_printf (message_str, "%u GTasks still alive:", task_list->len);
for (guint i = 0; i < task_list->len; i++)
{
GTask *task = g_ptr_array_index (task_list, i);
const gchar *name = g_task_get_name (task);
g_string_append_printf (message_str,
"\n • GTask %p, %s, ref count: %u, ever_returned: %u, completed: %u",
task, (name != NULL) ? name : "(no name set)",
((GObject *) task)->ref_count,
task->ever_returned, task->completed);
}
}
else
{
g_string_append (message_str, "No GTasks still alive");
}
G_UNLOCK (task_list);
g_message ("%s", message_str->str);
g_string_free (message_str, TRUE);
}
static void
g_task_constructed (GObject *object)
{
GTask *task = G_TASK (object);
G_OBJECT_CLASS (g_task_parent_class)->constructed (object);
/* Track pending tasks for debugging purposes */
G_LOCK (task_list);
if (G_UNLIKELY (task_list == NULL))
task_list = g_ptr_array_new ();
g_ptr_array_add (task_list, task);
G_UNLOCK (task_list);
}
#endif /* G_ENABLE_DEBUG */
static void
g_task_finalize (GObject *object)
{
GTask *task = G_TASK (object);
/* Warn if a #GTask is finalised without g_task_return() ever having been
* called on it.
*
* Tasks without a callback or which are run in g_task_run_in_thread{,_sync}()
* only trigger a debug message as that’s sometimes used as a pattern for
* running work in a worker thread without caring about the result. */
if (!task->ever_returned)
{
gchar *owned_task_name = NULL;
const gchar *task_name = g_task_get_name (task);
if (task_name == NULL)
task_name = owned_task_name = g_strdup_printf ("%p", task);
if (task->callback != NULL && !G_TASK_IS_THREADED (task))
g_critical ("GTask %s (source object: %p, source tag: %p) finalized without "
"ever returning (using g_task_return_*()). This potentially "
"indicates a bug in the program.",
task_name, task->source_object, task->source_tag);
else
g_debug ("GTask %s (source object: %p, source tag: %p) finalized without "
"ever returning (using g_task_return_*()). This potentially "
"indicates a bug in the program.",
task_name, task->source_object, task->source_tag);
g_free (owned_task_name);
}
g_clear_object (&task->source_object);
g_clear_object (&task->cancellable);
if (!task->name_is_static)
g_free (task->name);
if (task->context)
g_main_context_unref (task->context);
if (task->task_data_destroy)
task->task_data_destroy (task->task_data);
if (task->result_destroy && task->result.pointer)
task->result_destroy (task->result.pointer);
if (task->error)
g_error_free (task->error);
if (G_TASK_IS_THREADED (task))
{
g_mutex_clear (&task->lock);
g_cond_clear (&task->cond);
}
/* Track pending tasks for debugging purposes */
#ifdef G_ENABLE_DEBUG
G_LOCK (task_list);
g_assert (task_list != NULL);
g_ptr_array_remove_fast (task_list, task);
if (G_UNLIKELY (task_list->len == 0))
g_clear_pointer (&task_list, g_ptr_array_unref);
G_UNLOCK (task_list);
#endif /* G_ENABLE_DEBUG */
G_OBJECT_CLASS (g_task_parent_class)->finalize (object);
}
/**
* g_task_new:
* @source_object: (nullable) (type GObject): the #GObject that owns
* this task, or %NULL.
* @cancellable: (nullable): optional #GCancellable object, %NULL to ignore.
* @callback: (scope async): a #GAsyncReadyCallback.
* @callback_data: user data passed to @callback.
*
* Creates a #GTask acting on @source_object, which will eventually be
* used to invoke @callback in the current
* [thread-default main context][g-main-context-push-thread-default].
*
* Call this in the "start" method of your asynchronous method, and
* pass the #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.
*
* Returns: a #GTask.
*
* Since: 2.36
*/
GTask *
g_task_new (gpointer source_object,
GCancellable *cancellable,
GAsyncReadyCallback callback,
gpointer callback_data)
{
GTask *task;
GSource *source;
task = g_object_new (G_TYPE_TASK, NULL);
task->source_object = source_object ? g_object_ref (source_object) : NULL;
task->cancellable = cancellable ? g_object_ref (cancellable) : NULL;
task->callback = callback;
task->callback_data = callback_data;
task->context = g_main_context_ref_thread_default ();
source = g_main_current_source ();
if (source)
task->creation_time = g_source_get_time (source);
TRACE (GIO_TASK_NEW (task, source_object, cancellable,
callback, callback_data));
return task;
}
/**
* g_task_report_error:
* @source_object: (nullable) (type GObject): the #GObject that owns
* this task, or %NULL.
* @callback: (scope async) (closure callback_data): a #GAsyncReadyCallback.
* @callback_data: user data passed to @callback.
* @source_tag: an opaque pointer indicating the source of this task
* @error: (transfer full): error to report
*
* 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().
*
* Since: 2.36
*/
void
g_task_report_error (gpointer source_object,
GAsyncReadyCallback callback,
gpointer callback_data,
gpointer source_tag,
GError *error)
{
GTask *task;
task = g_task_new (source_object, NULL, callback, callback_data);
g_task_set_source_tag (task, source_tag);
g_task_set_static_name (task, G_STRFUNC);
g_task_return_error (task, error);
g_object_unref (task);
}
/**
* g_task_report_new_error:
* @source_object: (nullable) (type GObject): the #GObject that owns
* this task, or %NULL.
* @callback: (scope async) (closure callback_data): a #GAsyncReadyCallback.
* @callback_data: user data passed to @callback.
* @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 @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().
*
* Since: 2.36
*/
void
g_task_report_new_error (gpointer source_object,
GAsyncReadyCallback callback,
gpointer callback_data,
gpointer source_tag,
GQuark domain,
gint code,
const char *format,
...)
{
GError *error;
va_list ap;
va_start (ap, format);
error = g_error_new_valist (domain, code, format, ap);
va_end (ap);
g_task_report_error (source_object, callback, callback_data,
source_tag, error);
}
/**
* g_task_set_task_data:
* @task: the #GTask
* @task_data: (nullable): task-specific data
* @task_data_destroy: (nullable): #GDestroyNotify for @task_data
*
* Sets @task's task data (freeing the existing task data, if any).
*
* Since: 2.36
*/
void
g_task_set_task_data (GTask *task,
gpointer task_data,
GDestroyNotify task_data_destroy)
{
g_return_if_fail (G_IS_TASK (task));
if (task->task_data_destroy)
task->task_data_destroy (task->task_data);
task->task_data = task_data;
task->task_data_destroy = task_data_destroy;
TRACE (GIO_TASK_SET_TASK_DATA (task, task_data, task_data_destroy));
}
/**
* g_task_set_priority:
* @task: the #GTask
* @priority: the [priority][io-priority] of the request
*
* 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
*/
void
g_task_set_priority (GTask *task,
gint priority)
{
g_return_if_fail (G_IS_TASK (task));
task->priority = priority;
TRACE (GIO_TASK_SET_PRIORITY (task, priority));
}
/**
* g_task_set_check_cancellable:
* @task: the #GTask
* @check_cancellable: whether #GTask will check the state of
* its #GCancellable for you.
*
* 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.
*
* Since: 2.36
*/
void
g_task_set_check_cancellable (GTask *task,
gboolean check_cancellable)
{
g_return_if_fail (G_IS_TASK (task));
g_return_if_fail (check_cancellable || !task->return_on_cancel);
task->check_cancellable = check_cancellable;
}
static void g_task_thread_complete (GTask *task);
/**
* g_task_set_return_on_cancel:
* @task: the #GTask
* @return_on_cancel: whether the task returns automatically when
* it is cancelled.
*
* 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
* 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.
*
* 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
*/
gboolean
g_task_set_return_on_cancel (GTask *task,
gboolean return_on_cancel)
{
g_return_val_if_fail (G_IS_TASK (task), FALSE);
g_return_val_if_fail (task->check_cancellable || !return_on_cancel, FALSE);
if (!G_TASK_IS_THREADED (task))
{
task->return_on_cancel = return_on_cancel;
return TRUE;
}
g_mutex_lock (&task->lock);
if (task->thread_cancelled)
{
if (return_on_cancel && !task->return_on_cancel)
{
g_mutex_unlock (&task->lock);
g_task_thread_complete (task);
}
else
g_mutex_unlock (&task->lock);
return FALSE;
}
task->return_on_cancel = return_on_cancel;
g_mutex_unlock (&task->lock);
return TRUE;
}
/**
* g_task_set_source_tag:
* @task: the #GTask
* @source_tag: an opaque pointer indicating the source of this task
*
* 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 @source_tag if it’s not already
* set, for convenience.
*
* Since: 2.36
*/
void
(g_task_set_source_tag) (GTask *task,
gpointer source_tag)
{
g_return_if_fail (G_IS_TASK (task));
task->source_tag = source_tag;
TRACE (GIO_TASK_SET_SOURCE_TAG (task, source_tag));
}
/**
* g_task_set_name:
* @task: a #GTask
* @name: (nullable): a human readable name for the task, or %NULL to unset it
*
* 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 @task is first used in a thread
* other than the one it was constructed in. It is called automatically by
* g_task_set_source_tag() if not called already.
*
* Since: 2.60
*/
void
(g_task_set_name) (GTask *task,
const char *name)
{
char *new_name;
g_return_if_fail (G_IS_TASK (task));
new_name = g_strdup (name);
if (!task->name_is_static)
g_free (task->name);
task->name = g_steal_pointer (&new_name);
task->name_is_static = FALSE;
}
/**
* g_task_set_static_name:
* @task: a #GTask
* @name: (nullable): a human readable name for the task. Must be a string literal
*
* Sets @task’s name, used in debugging and profiling.
*
* This is a variant of g_task_set_name() that avoids copying @name.
*
* Since: 2.76
*/
void
g_task_set_static_name (GTask *task,
const char *name)
{
g_return_if_fail (G_IS_TASK (task));
if (!task->name_is_static)
g_free (task->name);
task->name = (char *) name;
task->name_is_static = TRUE;
}
/**
* g_task_get_source_object:
* @task: a #GTask
*
* Gets the source object from @task. Like
* g_async_result_get_source_object(), but does not ref the object.
*
* Returns: (transfer none) (nullable) (type GObject): @task's source object, or %NULL
*
* Since: 2.36
*/
gpointer
g_task_get_source_object (GTask *task)
{
g_return_val_if_fail (G_IS_TASK (task), NULL);
return task->source_object;
}
static GObject *
g_task_ref_source_object (GAsyncResult *res)
{
GTask *task = G_TASK (res);
if (task->source_object)
return g_object_ref (task->source_object);
else
return NULL;
}
/**
* g_task_get_task_data:
* @task: a #GTask
*
* Gets @task's `task_data`.
*
* Returns: (transfer none): @task's `task_data`.
*
* Since: 2.36
*/
gpointer
g_task_get_task_data (GTask *task)
{
g_return_val_if_fail (G_IS_TASK (task), NULL);
return task->task_data;
}
/**
* g_task_get_priority:
* @task: a #GTask
*
* Gets @task's priority
*
* Returns: @task's priority
*
* Since: 2.36
*/
gint
g_task_get_priority (GTask *task)
{
g_return_val_if_fail (G_IS_TASK (task), G_PRIORITY_DEFAULT);
return task->priority;
}
/**
* g_task_get_context:
* @task: a #GTask
*
* Gets the #GMainContext 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-%NULL value, even if the task's
* context is the default #GMainContext.
*
* Returns: (transfer none): @task's #GMainContext
*
* Since: 2.36
*/
GMainContext *
g_task_get_context (GTask *task)
{
g_return_val_if_fail (G_IS_TASK (task), NULL);
return task->context;
}
/**
* g_task_get_cancellable:
* @task: a #GTask
*
* Gets @task's #GCancellable
*
* Returns: (nullable) (transfer none): @task's #GCancellable
*
* Since: 2.36
*/
GCancellable *
g_task_get_cancellable (GTask *task)
{
g_return_val_if_fail (G_IS_TASK (task), NULL);
return task->cancellable;
}
/**
* g_task_get_check_cancellable:
* @task: the #GTask
*
* Gets @task's check-cancellable flag. See
* g_task_set_check_cancellable() for more details.
*
* Since: 2.36
*/
gboolean
g_task_get_check_cancellable (GTask *task)
{
g_return_val_if_fail (G_IS_TASK (task), FALSE);
/* Convert from a bit field to a boolean. */
return task->check_cancellable ? TRUE : FALSE;
}
/**
* g_task_get_return_on_cancel:
* @task: the #GTask
*
* Gets @task's return-on-cancel flag. See
* g_task_set_return_on_cancel() for more details.
*
* Since: 2.36
*/
gboolean
g_task_get_return_on_cancel (GTask *task)
{
g_return_val_if_fail (G_IS_TASK (task), FALSE);
/* Convert from a bit field to a boolean. */
return task->return_on_cancel ? TRUE : FALSE;
}
/**
* g_task_get_source_tag:
* @task: a #GTask
*
* Gets @task's source tag. See g_task_set_source_tag().
*
* Returns: (transfer none): @task's source tag
*
* Since: 2.36
*/
gpointer
g_task_get_source_tag (GTask *task)
{
g_return_val_if_fail (G_IS_TASK (task), NULL);
return task->source_tag;
}
/**
* g_task_get_name:
* @task: a #GTask
*
* Gets @task’s name. See g_task_set_name().
*
* Returns: (nullable) (transfer none): @task’s name, or %NULL
* Since: 2.60
*/
const gchar *
g_task_get_name (GTask *task)
{
g_return_val_if_fail (G_IS_TASK (task), NULL);
return task->name;
}
static void
g_task_return_now (GTask *task)
{
TRACE (GIO_TASK_BEFORE_RETURN (task, task->source_object, task->callback,
task->callback_data));
g_main_context_push_thread_default (task->context);
if (task->callback != NULL)
{
task->callback (task->source_object,
G_ASYNC_RESULT (task),
task->callback_data);
}
task->completed = TRUE;
g_object_notify (G_OBJECT (task), "completed");
g_main_context_pop_thread_default (task->context);
}
static gboolean
complete_in_idle_cb (gpointer task)
{
g_task_return_now (task);
g_object_unref (task);
return FALSE;
}
typedef enum {
G_TASK_RETURN_SUCCESS,
G_TASK_RETURN_ERROR,
G_TASK_RETURN_FROM_THREAD
} GTaskReturnType;
static void
g_task_return (GTask *task,
GTaskReturnType type)
{
GSource *source;
if (type != G_TASK_RETURN_FROM_THREAD)
task->ever_returned = TRUE;
if (type == G_TASK_RETURN_SUCCESS)
task->result_set = TRUE;
if (task->synchronous)
return;
/* Normally we want to invoke the task's callback when its return
* value is set. But if the task is running in a thread, then we
* want to wait until after the task_func returns, to simplify
* locking/refcounting/etc.
*/
if (G_TASK_IS_THREADED (task) && type != G_TASK_RETURN_FROM_THREAD)
return;
g_object_ref (task);
/* See if we can complete the task immediately. First, we have to be
* running inside the task's thread/GMainContext.
*/
source = g_main_current_source ();
if (source && g_source_get_context (source) == task->context)
{
/* Second, we can only complete immediately if this is not the
* same iteration of the main loop that the task was created in.
*/
if (g_source_get_time (source) > task->creation_time)
{
/* Finally, if the task has been cancelled, we shouldn't
* return synchronously from inside the
* GCancellable::cancelled handler. It's easier to run
* another iteration of the main loop than tracking how the
* cancellation was handled.
*/
if (!g_cancellable_is_cancelled (task->cancellable))
{
g_task_return_now (task);
g_object_unref (task);
return;
}
}
}
/* Otherwise, complete in the next iteration */
source = g_idle_source_new ();
/* Note: in case the task name is NULL we set it as a const string instead
* of going through the concat path which is more expensive and may show in the
* profiler if g_task_return is called very often
*/
if (task->name == NULL)
g_source_set_static_name (source, "[gio] (unnamed) complete_in_idle_cb");
else
{
gchar *source_name;
source_name = g_strconcat ("[gio] ", task->name, " complete_in_idle_cb", NULL);
g_source_set_name (source, source_name);
g_free (source_name);
}
g_task_attach_source (task, source, complete_in_idle_cb);
g_source_unref (source);
}
/**
* GTaskThreadFunc:
* @task: the #GTask
* @source_object: (type GObject): @task's source object
* @task_data: @task's task data
* @cancellable: @task's #GCancellable, or %NULL
*
* 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.
*
* Since: 2.36
*/
static void task_thread_cancelled (GCancellable *cancellable,
gpointer user_data);
static void
g_task_thread_complete (GTask *task)
{
g_mutex_lock (&task->lock);
if (task->thread_complete)
{
/* The task belatedly completed after having been cancelled
* (or was cancelled in the midst of being completed).
*/
g_mutex_unlock (&task->lock);
return;
}
TRACE (GIO_TASK_AFTER_RUN_IN_THREAD (task, task->thread_cancelled));
task->thread_complete = TRUE;
g_mutex_unlock (&task->lock);
if (task->cancellable)
g_signal_handlers_disconnect_by_func (task->cancellable, task_thread_cancelled, task);
if (task->synchronous)
g_cond_signal (&task->cond);
else
g_task_return (task, G_TASK_RETURN_FROM_THREAD);
}
static gboolean
task_pool_manager_timeout (gpointer user_data)
{
g_mutex_lock (&task_pool_mutex);
g_thread_pool_set_max_threads (task_pool, tasks_running + 1, NULL);
g_trace_set_int64_counter (task_pool_max_counter, tasks_running + 1);
g_source_set_ready_time (task_pool_manager, -1);
g_mutex_unlock (&task_pool_mutex);
return TRUE;
}
static void
g_task_thread_setup (void)
{
g_private_set (&task_private, GUINT_TO_POINTER (TRUE));
g_mutex_lock (&task_pool_mutex);
tasks_running++;
g_trace_set_int64_counter (tasks_running_counter, tasks_running);
if (tasks_running == G_TASK_POOL_SIZE)
task_wait_time = G_TASK_WAIT_TIME_BASE;
else if (tasks_running > G_TASK_POOL_SIZE && tasks_running < G_TASK_WAIT_TIME_MAX_POOL_SIZE)
task_wait_time *= G_TASK_WAIT_TIME_MULTIPLIER;
if (tasks_running >= G_TASK_POOL_SIZE)
g_source_set_ready_time (task_pool_manager, g_get_monotonic_time () + task_wait_time);
g_mutex_unlock (&task_pool_mutex);
}
static void
g_task_thread_cleanup (void)
{
gint tasks_pending;
g_mutex_lock (&task_pool_mutex);
tasks_pending = g_thread_pool_unprocessed (task_pool);
if (tasks_running > G_TASK_POOL_SIZE)
{
g_thread_pool_set_max_threads (task_pool, tasks_running - 1, NULL);
g_trace_set_int64_counter (task_pool_max_counter, tasks_running - 1);
}
else if (tasks_running + tasks_pending < G_TASK_POOL_SIZE)
g_source_set_ready_time (task_pool_manager, -1);
if (tasks_running > G_TASK_POOL_SIZE && tasks_running < G_TASK_WAIT_TIME_MAX_POOL_SIZE)
task_wait_time /= G_TASK_WAIT_TIME_MULTIPLIER;
tasks_running--;
g_trace_set_int64_counter (tasks_running_counter, tasks_running);
g_mutex_unlock (&task_pool_mutex);
g_private_set (&task_private, GUINT_TO_POINTER (FALSE));
}
static void
g_task_thread_pool_thread (gpointer thread_data,
gpointer pool_data)
{
GTask *task = thread_data;
g_task_thread_setup ();
task->task_func (task, task->source_object, task->task_data,
task->cancellable);
g_task_thread_complete (task);
g_object_unref (task);
g_task_thread_cleanup ();
}
static void
task_thread_cancelled (GCancellable *cancellable,
gpointer user_data)
{
GTask *task = user_data;
/* Move this task to the front of the queue - no need for
* a complete resorting of the queue.
*/
g_thread_pool_move_to_front (task_pool, task);
g_mutex_lock (&task->lock);
task->thread_cancelled = TRUE;
if (!task->return_on_cancel)
{
g_mutex_unlock (&task->lock);
return;
}
/* We don't actually set task->error; g_task_return_error() doesn't
* use a lock, and g_task_propagate_error() will call
* g_cancellable_set_error_if_cancelled() anyway.
*/
g_mutex_unlock (&task->lock);
g_task_thread_complete (task);
}
static void
task_thread_cancelled_disconnect_notify (gpointer task,
GClosure *closure)
{
g_object_unref (task);
}
static void
g_task_start_task_thread (GTask *task,
GTaskThreadFunc task_func)
{
g_mutex_init (&task->lock);
g_cond_init (&task->cond);
g_mutex_lock (&task->lock);
TRACE (GIO_TASK_BEFORE_RUN_IN_THREAD (task, task_func));
task->task_func = task_func;
if (task->cancellable)
{
if (task->return_on_cancel &&
g_cancellable_set_error_if_cancelled (task->cancellable,
&task->error))
{
task->thread_cancelled = task->thread_complete = TRUE;
TRACE (GIO_TASK_AFTER_RUN_IN_THREAD (task, task->thread_cancelled));
g_thread_pool_push (task_pool, g_object_ref (task), NULL);
return;
}
/* This introduces a reference count loop between the GTask and
* GCancellable, but is necessary to avoid a race on finalising the GTask
* between task_thread_cancelled() (in one thread) and
* g_task_thread_complete() (in another).
*
* Accordingly, the signal handler *must* be removed once the task has
* completed.
*/
g_signal_connect_data (task->cancellable, "cancelled",
G_CALLBACK (task_thread_cancelled),
g_object_ref (task),
task_thread_cancelled_disconnect_notify,
G_CONNECT_DEFAULT);
}
if (g_private_get (&task_private))
task->blocking_other_task = TRUE;
g_thread_pool_push (task_pool, g_object_ref (task), NULL);
}
/**
* g_task_run_in_thread:
* @task: a #GTask
* @task_func: (scope async): a #GTaskThreadFunc
*
* 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 (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().
*
* Since: 2.36
*/
void
g_task_run_in_thread (GTask *task,
GTaskThreadFunc task_func)
{
g_return_if_fail (G_IS_TASK (task));
g_object_ref (task);
g_task_start_task_thread (task, task_func);
/* The task may already be cancelled, or g_thread_pool_push() may
* have failed.
*/
if (task->thread_complete)
{
g_mutex_unlock (&task->lock);
g_task_return (task, G_TASK_RETURN_FROM_THREAD);
}
else
g_mutex_unlock (&task->lock);
g_object_unref (task);
}
/**
* g_task_run_in_thread_sync:
* @task: a #GTask
* @task_func: (scope async): a #GTaskThreadFunc
*
* 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.
* #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.
*
* Since: 2.36
*/
void
g_task_run_in_thread_sync (GTask *task,
GTaskThreadFunc task_func)
{
g_return_if_fail (G_IS_TASK (task));
g_object_ref (task);
task->synchronous = TRUE;
g_task_start_task_thread (task, task_func);
while (!task->thread_complete)
g_cond_wait (&task->cond, &task->lock);
g_mutex_unlock (&task->lock);
TRACE (GIO_TASK_BEFORE_RETURN (task, task->source_object,
NULL /* callback */,
NULL /* callback data */));
/* Notify of completion in this thread. */
task->completed = TRUE;
g_object_notify (G_OBJECT (task), "completed");
g_object_unref (task);
}
/**
* g_task_attach_source:
* @task: a #GTask
* @source: the source to attach
* @callback: the callback to invoke when @source triggers
*
* 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][io-priority], and sets @source's
* callback to @callback, with @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 @task until @source is destroyed.
*
* Since: 2.36
*/
void
g_task_attach_source (GTask *task,
GSource *source,
GSourceFunc callback)
{
g_return_if_fail (G_IS_TASK (task));
g_source_set_callback (source, callback,
g_object_ref (task), g_object_unref);
g_source_set_priority (source, task->priority);
if (task->name != NULL && g_source_get_name (source) == NULL)
g_source_set_name (source, task->name);
g_source_attach (source, task->context);
}
static gboolean
g_task_propagate_error (GTask *task,
GError **error)
{
gboolean error_set;
if (task->check_cancellable &&
g_cancellable_set_error_if_cancelled (task->cancellable, error))
error_set = TRUE;
else if (task->error)
{
g_propagate_error (error, task->error);
task->error = NULL;
task->had_error = TRUE;
error_set = TRUE;
}
else
error_set = FALSE;
TRACE (GIO_TASK_PROPAGATE (task, error_set));
return error_set;
}
/**
* g_task_return_pointer:
* @task: a #GTask
* @result: (nullable) (transfer full): the pointer result of a task
* function
* @result_destroy: (nullable): a #GDestroyNotify function.
*
* 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.
*
* Since: 2.36
*/
void
g_task_return_pointer (GTask *task,
gpointer result,
GDestroyNotify result_destroy)
{
g_return_if_fail (G_IS_TASK (task));
g_return_if_fail (!task->ever_returned);
task->result.pointer = result;
task->result_destroy = result_destroy;
g_task_return (task, G_TASK_RETURN_SUCCESS);
}
/**
* g_task_propagate_pointer:
* @task: a #GTask
* @error: return location for a #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 %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: (transfer full): the task result, or %NULL on error
*
* Since: 2.36
*/
gpointer
g_task_propagate_pointer (GTask *task,
GError **error)
{
g_return_val_if_fail (G_IS_TASK (task), NULL);
if (g_task_propagate_error (task, error))
return NULL;
g_return_val_if_fail (task->result_set, NULL);
task->result_destroy = NULL;
task->result_set = FALSE;
return task->result.pointer;
}
/**
* g_task_return_int:
* @task: a #GTask.
* @result: the integer (#gssize) result of a task function.
*
* 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
*/
void
g_task_return_int (GTask *task,
gssize result)
{
g_return_if_fail (G_IS_TASK (task));
g_return_if_fail (!task->ever_returned);
task->result.size = result;
g_task_return (task, G_TASK_RETURN_SUCCESS);
}
/**
* g_task_propagate_int:
* @task: a #GTask.
* @error: return location for a #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.
*
* Returns: the task result, or -1 on error
*
* Since: 2.36
*/
gssize
g_task_propagate_int (GTask *task,
GError **error)
{
g_return_val_if_fail (G_IS_TASK (task), -1);
if (g_task_propagate_error (task, error))
return -1;
g_return_val_if_fail (task->result_set, -1);
task->result_set = FALSE;
return task->result.size;
}
/**
* g_task_return_boolean:
* @task: a #GTask.
* @result: the #gboolean result of a task function.
*
* 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
*/
void
g_task_return_boolean (GTask *task,
gboolean result)
{
g_return_if_fail (G_IS_TASK (task));
g_return_if_fail (!task->ever_returned);
task->result.boolean = result;
g_task_return (task, G_TASK_RETURN_SUCCESS);
}
/**
* g_task_propagate_boolean:
* @task: a #GTask.
* @error: return location for a #GError
*
* 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.
*
* Returns: the task result, or %FALSE on error
*
* Since: 2.36
*/
gboolean
g_task_propagate_boolean (GTask *task,
GError **error)
{
g_return_val_if_fail (G_IS_TASK (task), FALSE);
if (g_task_propagate_error (task, error))
return FALSE;
g_return_val_if_fail (task->result_set, FALSE);
task->result_set = FALSE;
return task->result.boolean;
}
/**
* g_task_return_error:
* @task: a #GTask.
* @error: (transfer full): the #GError result of a task function.
*
* 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
*/
void
g_task_return_error (GTask *task,
GError *error)
{
g_return_if_fail (G_IS_TASK (task));
g_return_if_fail (!task->ever_returned);
g_return_if_fail (error != NULL);
task->error = error;
g_task_return (task, G_TASK_RETURN_ERROR);
}
/**
* g_task_return_prefixed_error:
* @task: a #GTask.
* @error: (transfer full): the #GError result of a task function.
* @format: a string with format characters.
* @...: a list of values to insert into @format.
*
* Sets @task's result to @error (which @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().
*
* Since: 2.80
*/
void
g_task_return_prefixed_error (GTask *task,
GError *error,
const char *format,
...)
{
char *prefix;
va_list ap;
g_return_if_fail (G_IS_TASK (task));
g_return_if_fail (!task->ever_returned);
g_return_if_fail (error != NULL);
task->error = error;
va_start (ap, format);
prefix = g_strdup_vprintf (format, ap);
va_end (ap);
g_prefix_error_literal (&task->error, prefix);
g_free (prefix);
g_task_return (task, G_TASK_RETURN_ERROR);
}
/**
* g_task_return_new_error:
* @task: a #GTask.
* @domain: a #GQuark.
* @code: an error code.
* @format: a string with format characters.
* @...: a list of values to insert into @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
*/
void
g_task_return_new_error (GTask *task,
GQuark domain,
gint code,
const char *format,
...)
{
GError *error;
va_list args;
va_start (args, format);
error = g_error_new_valist (domain, code, format, args);
va_end (args);
g_task_return_error (task, error);
}
/**
* g_task_return_error_if_cancelled:
* @task: a #GTask
*
* 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 @task has been cancelled, %FALSE if not
*
* Since: 2.36
*/
gboolean
g_task_return_error_if_cancelled (GTask *task)
{
GError *error = NULL;
g_return_val_if_fail (G_IS_TASK (task), FALSE);
g_return_val_if_fail (!task->ever_returned, FALSE);
if (g_cancellable_set_error_if_cancelled (task->cancellable, &error))
{
/* We explicitly set task->error so this works even when
* check-cancellable is not set.
*/
g_clear_error (&task->error);
task->error = error;
g_task_return (task, G_TASK_RETURN_ERROR);
return TRUE;
}
else
return FALSE;
}
/**
* g_task_had_error:
* @task: a #GTask.
*
* Tests if @task resulted in an error.
*
* Returns: %TRUE if the task resulted in an error, %FALSE otherwise.
*
* Since: 2.36
*/
gboolean
g_task_had_error (GTask *task)
{
g_return_val_if_fail (G_IS_TASK (task), FALSE);
if (task->error != NULL || task->had_error)
return TRUE;
if (task->check_cancellable && g_cancellable_is_cancelled (task->cancellable))
return TRUE;
return FALSE;
}
static void
value_free (gpointer value)
{
g_value_unset (value);
g_free (value);
}
/**
* g_task_return_value:
* @task: a #GTask
* @result: (nullable) (transfer none): the #GValue result of
* a task function
*
* 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.
*
* Since: 2.64
*/
void
g_task_return_value (GTask *task,
GValue *result)
{
GValue *value;
g_return_if_fail (G_IS_TASK (task));
g_return_if_fail (!task->ever_returned);
value = g_new0 (GValue, 1);
if (result == NULL)
{
g_value_init (value, G_TYPE_POINTER);
g_value_set_pointer (value, NULL);
}
else
{
g_value_init (value, G_VALUE_TYPE (result));
g_value_copy (result, value);
}
g_task_return_pointer (task, value, value_free);
}
/**
* g_task_propagate_value:
* @task: a #GTask
* @value: (out caller-allocates): return location for the #GValue
* @error: return location for a #GError
*
* Gets the result of @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.
*
* Returns: %TRUE if @task succeeded, %FALSE on error.
*
* Since: 2.64
*/
gboolean
g_task_propagate_value (GTask *task,
GValue *value,
GError **error)
{
g_return_val_if_fail (G_IS_TASK (task), FALSE);
g_return_val_if_fail (value != NULL, FALSE);
g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
if (g_task_propagate_error (task, error))
return FALSE;
g_return_val_if_fail (task->result_set, FALSE);
g_return_val_if_fail (task->result_destroy == value_free, FALSE);
memcpy (value, task->result.pointer, sizeof (GValue));
g_free (task->result.pointer);
task->result_destroy = NULL;
task->result_set = FALSE;
return TRUE;
}
/**
* g_task_get_completed:
* @task: a #GTask.
*
* 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
*/
gboolean
g_task_get_completed (GTask *task)
{
g_return_val_if_fail (G_IS_TASK (task), FALSE);
/* Convert from a bit field to a boolean. */
return task->completed ? TRUE : FALSE;
}
/**
* g_task_is_valid:
* @result: (type Gio.AsyncResult): A #GAsyncResult
* @source_object: (nullable) (type GObject): the source object
* expected to be associated with the task
*
* 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.
*
* Returns: %TRUE if @result and @source_object are valid, %FALSE
* if not
*
* Since: 2.36
*/
gboolean
g_task_is_valid (gpointer result,
gpointer source_object)
{
if (!G_IS_TASK (result))
return FALSE;
return G_TASK (result)->source_object == source_object;
}
static gint
g_task_compare_priority (gconstpointer a,
gconstpointer b,
gpointer user_data)
{
const GTask *ta = a;
const GTask *tb = b;
gboolean a_cancelled, b_cancelled;
/* Tasks that are causing other tasks to block have higher
* priority.
*/
if (ta->blocking_other_task && !tb->blocking_other_task)
return -1;
else if (tb->blocking_other_task && !ta->blocking_other_task)
return 1;
/* Let already-cancelled tasks finish right away */
a_cancelled = (ta->check_cancellable &&
g_cancellable_is_cancelled (ta->cancellable));
b_cancelled = (tb->check_cancellable &&
g_cancellable_is_cancelled (tb->cancellable));
if (a_cancelled && !b_cancelled)
return -1;
else if (b_cancelled && !a_cancelled)
return 1;
/* Lower priority == run sooner == negative return value */
return ta->priority - tb->priority;
}
static gboolean
trivial_source_dispatch (GSource *source,
GSourceFunc callback,
gpointer user_data)
{
return callback (user_data);
}
GSourceFuncs trivial_source_funcs = {
NULL, /* prepare */
NULL, /* check */
trivial_source_dispatch,
NULL, /* finalize */
NULL, /* closure */
NULL /* marshal */
};
static void
g_task_thread_pool_init (void)
{
task_pool = g_thread_pool_new (g_task_thread_pool_thread, NULL,
G_TASK_POOL_SIZE, FALSE, NULL);
g_assert (task_pool != NULL);
g_thread_pool_set_sort_function (task_pool, g_task_compare_priority, NULL);
task_pool_manager = g_source_new (&trivial_source_funcs, sizeof (GSource));
g_source_set_static_name (task_pool_manager, "GTask thread pool manager");
g_source_set_callback (task_pool_manager, task_pool_manager_timeout, NULL, NULL);
g_source_set_ready_time (task_pool_manager, -1);
g_source_attach (task_pool_manager,
GLIB_PRIVATE_CALL (g_get_worker_context ()));
g_source_unref (task_pool_manager);
}
static void
g_task_get_property (GObject *object,
guint prop_id,
GValue *value,
GParamSpec *pspec)
{
GTask *task = G_TASK (object);
switch ((GTaskProperty) prop_id)
{
case PROP_COMPLETED:
g_value_set_boolean (value, g_task_get_completed (task));
break;
}
}
static void
g_task_class_init (GTaskClass *klass)
{
GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
#ifdef G_ENABLE_DEBUG
gobject_class->constructed = g_task_constructed;
#endif
gobject_class->get_property = g_task_get_property;
gobject_class->finalize = g_task_finalize;
/**
* GTask:completed:
*
* 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 #GObject::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
*/
g_object_class_install_property (gobject_class, PROP_COMPLETED,
g_param_spec_boolean ("completed",
P_("Task completed"),
P_("Whether the task has completed yet"),
FALSE, G_PARAM_READABLE | G_PARAM_STATIC_STRINGS));
if (G_UNLIKELY (task_pool_max_counter == 0))
{
/* We use two counters to track characteristics of the GTask thread pool.
* task pool max size - the value of g_thread_pool_set_max_threads()
* tasks running - the number of running threads
*/
task_pool_max_counter = g_trace_define_int64_counter ("GIO", "task pool max size", "Maximum number of threads allowed in the GTask thread pool; see g_thread_pool_set_max_threads()");
tasks_running_counter = g_trace_define_int64_counter ("GIO", "tasks running", "Number of currently running tasks in the GTask thread pool");
}
}
static gpointer
g_task_get_user_data (GAsyncResult *res)
{
return G_TASK (res)->callback_data;
}
static gboolean
g_task_is_tagged (GAsyncResult *res,
gpointer source_tag)
{
return G_TASK (res)->source_tag == source_tag;
}
static void
g_task_async_result_iface_init (GAsyncResultIface *iface)
{
iface->get_user_data = g_task_get_user_data;
iface->get_source_object = g_task_ref_source_object;
iface->is_tagged = g_task_is_tagged;
}
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