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/* GIO - GLib Input, Output and Streaming Library
 *
 * Copyright 2011 Red Hat, Inc.
 *
 * 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
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 * version 2.1 of the License, or (at your option) any later version.
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 *
 * 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
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 * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
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 */

#include "config.h"
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#include "gio_trace.h"
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#include "gtask.h"

#include "gasyncresult.h"
#include "gcancellable.h"
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#include "glib-private.h"
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#include "glibintl.h"

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/**
 * SECTION:gtask
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 * @short_description: Cancellable synchronous or asynchronous task
 *     and result
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 * @include: gio/gio.h
 * @see_also: #GAsyncResult
 *
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 * 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
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 * 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
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 * use g_task_propagate_pointer() or the like to extract the
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 * return value.
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 *
 * Here is an example for using GTask as a GAsyncResult:
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 * |[<!-- language="C" -->
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 *     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);
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 *           // g_task_return_error() takes ownership of error
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 *           g_task_return_error (task, error);
 *           g_object_unref (task);
 *           return;
 *         }
 *
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 *       g_task_return_pointer (task, cake, g_object_unref);
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 *       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)
 *         {
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 *           // _baker_get_cached_cake() returns a reffed cake
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 *           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);
 *     }
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 * ]|
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 *
 * ## Chained asynchronous operations
 *
 * #GTask also tries to simplify asynchronous operations that
 * internally chain together several smaller asynchronous
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 * 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).
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 *
 * Here is an example for chained asynchronous operations:
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 *   |[<!-- language="C" -->
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 *     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;
 *         }
 *
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 *       // baking_data_free() will drop its ref on the cake, so we have to
 *       // take another here to give to the caller.
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 *       g_task_return_pointer (task, g_object_ref (cake), g_object_unref);
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 *       g_object_unref (task);
 *     }
 *
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 *     static gboolean
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 *     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);
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 *
 *       return G_SOURCE_REMOVE;
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 *     }
 *
 *     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;
 *
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 *       // Bail out now if the user has already cancelled
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 *       if (g_task_return_error_if_cancelled (task))
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 *         {
 *           g_object_unref (task);
 *           return;
 *         }
 *
 *       if (cake_decorator_available (cake))
 *         decorator_ready (task);
 *       else
 *         {
 *           GSource *source;
 *
 *           source = cake_decorator_wait_source_new (cake);
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 *           // Attach @source to @task's GMainContext and have it call
 *           // decorator_ready() when it is ready.
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 *           g_task_attach_source (task, source, decorator_ready);
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 *           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);
 *     }
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 * ]|
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 *
 * ## Asynchronous operations from synchronous ones
 *
 * You can use g_task_run_in_thread() to turn a synchronous
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 * 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.
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 *
 * Running a task in a thread:
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 *   |[<!-- language="C" -->
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 *     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);
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 *       g_object_unref (task);
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 *     }
 *
 *     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);
 *     }
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 * ]|
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 *
 * ## 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:
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 *   |[<!-- language="C" -->
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 *     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;
 *         }
 *
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 *       // 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.
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 *       if (g_task_set_return_on_cancel (task, FALSE))
 *         {
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 *           // 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.
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 *           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)
 *     {
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 *       CakeData *cake_data;
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 *       GTask *task;
 *
 *       cake_data = g_slice_new (CakeData);
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 *
 *       ...
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 *
 *       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);
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 *
 *       ...
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 *
 *       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;
 *     }
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 * ]|
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 *
 * ## 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
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 *   [priority][io-priority], #GCancellable, and
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 *   #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
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 *   `task_func`, even if the task's #GCancellable
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 *   is already cancelled before the task gets a chance to run;
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 *   you can start your `task_func` with a
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 *   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.)
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 * - The "finish" functions for #GTask based operations are generally
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 *   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
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 *   `_finish()` wrapper function, and have
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 *   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
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 *   appropriate `g_task_propagate_` function.
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 *   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
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 *   having come from the `_async()` wrapper
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 *   function (for "short-circuit" results, such as when passing
 *   0 to g_input_stream_read_async()).
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 */

/**
 * GTask:
 *
 * The opaque object representing a synchronous or asynchronous task
 * and its result.
 */

struct _GTask {
  GObject parent_instance;

  gpointer source_object;
  gpointer source_tag;
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  gchar *name;  /* (owned); may only be modified before the #GTask is threaded */
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  gpointer task_data;
  GDestroyNotify task_data_destroy;

  GMainContext *context;
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  gint64 creation_time;
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  gint priority;
  GCancellable *cancellable;

  GAsyncReadyCallback callback;
  gpointer callback_data;

  GTaskThreadFunc task_func;
  GMutex lock;
  GCond cond;
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  /* This can’t be in the bit field because we access it from TRACE(). */
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  gboolean thread_cancelled;
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  gboolean check_cancellable : 1;
  gboolean completed : 1;
  gboolean return_on_cancel : 1;
  gboolean synchronous : 1;
  gboolean thread_complete : 1;
  gboolean blocking_other_task : 1;
  gboolean had_error : 1;
  gboolean result_set : 1;
  gboolean ever_returned : 1;
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  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;
};

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typedef enum
{
  PROP_COMPLETED = 1,
} GTaskProperty;

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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;
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static GMutex task_pool_mutex;
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static GPrivate task_private = G_PRIVATE_INIT (NULL);
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static GSource *task_pool_manager;
static guint64 task_wait_time;
static gint tasks_running;

/* 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.
 */
#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 (30 * 60 * 1000000)
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static void
g_task_init (GTask *task)
{
  task->check_cancellable = TRUE;
}

static void
g_task_finalize (GObject *object)
{
  GTask *task = G_TASK (object);

  g_clear_object (&task->source_object);
  g_clear_object (&task->cancellable);
641
  g_free (task->name);
642 643 644 645 646 647 648 649 650 651

  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);

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  if (task->error)
      g_error_free (task->error);

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  if (G_TASK_IS_THREADED (task))
    {
      g_mutex_clear (&task->lock);
      g_cond_clear (&task->cond);
    }

  G_OBJECT_CLASS (g_task_parent_class)->finalize (object);
}

/**
 * g_task_new:
666
 * @source_object: (nullable) (type GObject): the #GObject that owns
667
 *   this task, or %NULL.
668
 * @cancellable: (nullable): optional #GCancellable object, %NULL to ignore.
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 * @callback: (scope async): a #GAsyncReadyCallback.
 * @callback_data: (closure): user data passed to @callback.
 *
 * Creates a #GTask acting on @source_object, which will eventually be
673 674
 * used to invoke @callback in the current
 * [thread-default main context][g-main-context-push-thread-default].
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 *
 * 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);

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  TRACE (GIO_TASK_NEW (task, source_object, cancellable,
                       callback, callback_data));

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  return task;
}

/**
 * g_task_report_error:
721
 * @source_object: (nullable) (type GObject): the #GObject that owns
722
 *   this task, or %NULL.
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 * @callback: (scope async): a #GAsyncReadyCallback.
 * @callback_data: (closure): 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_return_error (task, error);
  g_object_unref (task);
}

/**
 * g_task_report_new_error:
756
 * @source_object: (nullable) (type GObject): the #GObject that owns
757
 *   this task, or %NULL.
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 * @callback: (scope async): a #GAsyncReadyCallback.
 * @callback_data: (closure): 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
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 * @task_data: (nullable): task-specific data
 * @task_data_destroy: (nullable): #GDestroyNotify for @task_data
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 *
 * 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)
{
814 815
  g_return_if_fail (G_IS_TASK (task));

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  if (task->task_data_destroy)
    task->task_data_destroy (task->task_data);

  task->task_data = task_data;
  task->task_data_destroy = task_data_destroy;
821 822

  TRACE (GIO_TASK_SET_TASK_DATA (task, task_data, task_data_destroy));
823 824 825 826 827
}

/**
 * g_task_set_priority:
 * @task: the #GTask
828
 * @priority: the [priority][io-priority] of the request
829 830 831 832 833 834 835 836 837 838 839 840 841 842 843
 *
 * 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)
{
844 845
  g_return_if_fail (G_IS_TASK (task));

846
  task->priority = priority;
847 848

  TRACE (GIO_TASK_SET_PRIORITY (task, priority));
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}

/**
 * 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)
{
878
  g_return_if_fail (G_IS_TASK (task));
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  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
 * 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.
 *
 * 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)
{
931
  g_return_val_if_fail (G_IS_TASK (task), FALSE);
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  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.
 *
 * Since: 2.36
 */
void
g_task_set_source_tag (GTask    *task,
                       gpointer  source_tag)
{
976 977
  g_return_if_fail (G_IS_TASK (task));

978
  task->source_tag = source_tag;
979 980

  TRACE (GIO_TASK_SET_SOURCE_TAG (task, source_tag));
981 982
}

983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012
/**
 * 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.
 *
 * Since: 2.60
 */
void
g_task_set_name (GTask       *task,
                 const gchar *name)
{
  gchar *new_name;

  g_return_if_fail (G_IS_TASK (task));

  new_name = g_strdup (name);
  g_free (task->name);
  task->name = g_steal_pointer (&new_name);
}

1013 1014 1015 1016 1017 1018 1019
/**
 * 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.
 *
1020
 * Returns: (transfer none) (nullable) (type GObject): @task's source object, or %NULL
1021 1022 1023 1024 1025 1026
 *
 * Since: 2.36
 */
gpointer
g_task_get_source_object (GTask *task)
{
1027 1028
  g_return_val_if_fail (G_IS_TASK (task), NULL);

1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046
  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
 *
1047
 * Gets @task's `task_data`.
1048
 *
1049
 * Returns: (transfer none): @task's `task_data`.
1050 1051 1052 1053 1054 1055
 *
 * Since: 2.36
 */
gpointer
g_task_get_task_data (GTask *task)
{
1056 1057
  g_return_val_if_fail (G_IS_TASK (task), NULL);

1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073
  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)
{
1074 1075
  g_return_val_if_fail (G_IS_TASK (task), G_PRIORITY_DEFAULT);

1076 1077 1078 1079 1080 1081 1082 1083
  return task->priority;
}

/**
 * g_task_get_context:
 * @task: a #GTask
 *
 * Gets the #GMainContext that @task will return its result in (that
1084 1085 1086
 * is, the context that was the
 * [thread-default main context][g-main-context-push-thread-default]
 * at the point when @task was created).
1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097
 *
 * 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)
{
1098 1099
  g_return_val_if_fail (G_IS_TASK (task), NULL);

1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115
  return task->context;
}

/**
 * g_task_get_cancellable:
 * @task: a #GTask
 *
 * Gets @task's #GCancellable
 *
 * Returns: (transfer none): @task's #GCancellable
 *
 * Since: 2.36
 */
GCancellable *
g_task_get_cancellable (GTask *task)
{
1116 1117
  g_return_val_if_fail (G_IS_TASK (task), NULL);

1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132
  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)
{
1133 1134
  g_return_val_if_fail (G_IS_TASK (task), FALSE);

1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149
  return task->check_cancellable;
}

/**
 * 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)
{
1150 1151
  g_return_val_if_fail (G_IS_TASK (task), FALSE);

1152 1153 1154 1155 1156 1157 1158 1159 1160
  return task->return_on_cancel;
}

/**
 * g_task_get_source_tag:
 * @task: a #GTask
 *
 * Gets @task's source tag. See g_task_set_source_tag().
 *
1161
 * Returns: (transfer none): @task's source tag
1162 1163 1164 1165 1166 1167
 *
 * Since: 2.36
 */
gpointer
g_task_get_source_tag (GTask *task)
{
1168 1169
  g_return_val_if_fail (G_IS_TASK (task), NULL);

1170 1171 1172
  return task->source_tag;
}

1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188
/**
 * 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;
}
1189 1190 1191 1192

static void
g_task_return_now (GTask *task)
{
1193 1194 1195
  TRACE (GIO_TASK_BEFORE_RETURN (task, task->source_object, task->callback,
                                 task->callback_data));

1196
  g_main_context_push_thread_default (task->context);
1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207

  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");

1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230
  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;

1231 1232 1233
  if (type != G_TASK_RETURN_FROM_THREAD)
    task->ever_returned = TRUE;

1234 1235 1236
  if (type == G_TASK_RETURN_SUCCESS)
    task->result_set = TRUE;

1237
  if (task->synchronous)
1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268
    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)
        {
          g_task_return_now (task);
          g_object_unref (task);
          return;
        }
    }

  /* Otherwise, complete in the next iteration */
  source = g_idle_source_new ();
1269
  g_source_set_name (source, "[gio] complete_in_idle_cb");
1270
  g_task_attach_source (task, source, complete_in_idle_cb);
1271 1272 1273 1274 1275 1276 1277
  g_source_unref (source);
}


/**
 * GTaskThreadFunc:
 * @task: the #GTask
1278
 * @source_object: (type GObject): @task's source object
1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294
 * @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
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 * #GTaskThreadFunc returns, not when it calls a
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 * `g_task_return_` function.
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 *
 * 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;
    }

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  TRACE (GIO_TASK_AFTER_RUN_IN_THREAD (task, task->thread_cancelled));

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  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);
}

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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_source_set_ready_time (task_pool_manager, -1);
  g_mutex_unlock (&task_pool_mutex);

  return TRUE;
}

static void
g_task_thread_setup (void)
{
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  g_private_set (&task_private, GUINT_TO_POINTER (TRUE));
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  g_mutex_lock (&task_pool_mutex);
  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 && task_wait_time < G_TASK_WAIT_TIME_MAX)
    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);
  else if (tasks_running + tasks_pending < G_TASK_POOL_SIZE)
    g_source_set_ready_time (task_pool_manager, -1);

  tasks_running--;
  g_mutex_unlock (&task_pool_mutex);
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  g_private_set (&task_private, GUINT_TO_POINTER (FALSE));
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}

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static void
g_task_thread_pool_thread (gpointer thread_data,
                           gpointer pool_data)
{
  GTask *task = thread_data;

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  g_task_thread_setup ();
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  task->task_func (task, task->source_object, task->task_data,
                   task->cancellable);
  g_task_thread_complete (task);
  g_object_unref (task);
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  g_task_thread_cleanup ();
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}

static void
task_thread_cancelled (GCancellable *cancellable,
                       gpointer      user_data)
{
  GTask *task = user_data;

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Matthias Clasen committed
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  /* 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);
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  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);

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  TRACE (GIO_TASK_BEFORE_RUN_IN_THREAD (task, task_func));

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  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;
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          TRACE (GIO_TASK_AFTER_RUN_IN_THREAD (task, task->thread_cancelled));
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          g_thread_pool_push (task_pool, g_object_ref (task), NULL);
          return;
        }

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      /* 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.
       */
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      g_signal_connect_data (task->cancellable, "cancelled",
                             G_CALLBACK (task_thread_cancelled),
                             g_object_ref (task),
                             task_thread_cancelled_disconnect_notify, 0);
    }

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  if (g_private_get (&task_private))
    task->blocking_other_task = TRUE;
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  g_thread_pool_push (task_pool, g_object_ref (task), NULL);
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}

/**
 * g_task_run_in_thread:
 * @task: a #GTask
 * @task_func: 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.
 *
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 * 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.
 *
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 * 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: 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
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 * `callback`, but note that even if the task does
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 * have a callback, it will not be invoked when @task_func returns.
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 * #GTask:completed will be set to %TRUE just before this function returns.
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 *
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 * 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.
 *
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 * 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);
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  TRACE (GIO_TASK_BEFORE_RETURN (task, task->source_object,
                                 NULL  /* callback */,
                                 NULL  /* callback data */));

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  /* Notify of completion in this thread. */
  task->completed = TRUE;
  g_object_notify (G_OBJECT (task), "completed");

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  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
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 * #GMainContext with @task's [priority][io-priority], and sets @source's
 * callback to @callback, with @task as the callback's `user_data`.
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 *
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 * It will set the @source’s name to the task’s name (as set with
 * g_task_set_name()), if one has been set.
 *
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 * This takes a reference on @task until @source is destroyed.
 *
 * Since: 2.36
 */
void
g_task_attach_source (GTask       *task,
                      GSource     *source,
                      GSourceFunc  callback)
{
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  g_return_if_fail (G_IS_TASK (task));

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  g_source_set_callback (source, callback,
                         g_object_ref (task), g_object_unref);
  g_source_set_priority (source, task->priority);
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  if (task->name != NULL)
    g_source_set_name (source, task->name);

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  g_source_attach (source, task->context);
}


static gboolean
g_task_propagate_error (GTask   *task,
                        GError **error)
{
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  gboolean error_set;

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  if (task->check_cancellable &&
      g_cancellable_set_error_if_cancelled (task->cancellable, error))
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    error_set = TRUE;
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  else if (task->error)
    {
      g_propagate_error (error, task->error);
      task->error = NULL;
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      task->had_error = TRUE;
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      error_set = TRUE;
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    }
  else
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    error_set = FALSE;

  TRACE (GIO_TASK_PROPAGATE (task, error_set));

  return error_set;
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}

/**
 * g_task_return_pointer:
 * @task: a #GTask
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 * @result: (nullable) (transfer full): the pointer result of a task
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 *     function
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 * @result_destroy: (nullable): a #GDestroyNotify function.
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 *
 * 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)
{
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  g_return_if_fail (G_IS_TASK (task));
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  g_return_if_fail (!task->ever_returned);
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  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)
{
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  g_return_val_if_fail (G_IS_TASK (task), NULL);

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  if (g_task_propagate_error (task, error))
    return NULL;

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  g_return_val_if_fail (task->result_set, NULL);
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  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)
{
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  g_return_if_fail (G_IS_TASK (task));
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  g_return_if_fail (!task->ever_returned);
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  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)
{
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  g_return_val_if_fail (G_IS_TASK (task), -1);

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  if (g_task_propagate_error (task, error))
    return -1;

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  g_return_val_if_fail (task->result_set, -1);
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  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)
{
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  g_return_if_fail (G_IS_TASK (task));
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  g_return_if_fail (!task->ever_returned);
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  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)
{
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  g_return_val_if_fail (G_IS_TASK (task), FALSE);

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  if (g_task_propagate_error (task, error))
    return FALSE;

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  g_return_val_if_fail (task->result_set, FALSE);
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  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)
{
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  g_return_if_fail (G_IS_TASK (task));
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  g_return_if_fail (!task->ever_returned);
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  g_return_if_fail (error != NULL);

  task->error = error;

  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).
 *
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 * Returns: %TRUE if @task has been cancelled, %FALSE if not
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 *
 * Since: 2.36
 */
gboolean
g_task_return_error_if_cancelled (GTask *task)
{
  GError *error = NULL;

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  g_return_val_if_fail (G_IS_TASK (task), FALSE);
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  g_return_val_if_fail (!task->ever_returned, FALSE);
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  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)
{
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  g_return_val_if_fail (G_IS_TASK (task), FALSE);

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  if (task->error != NULL || task->had_error)
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    return TRUE;

  if (task->check_cancellable && g_cancellable_is_cancelled (task->cancellable))
    return TRUE;

  return FALSE;
}

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/**
 * 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);

  return task->completed;
}

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/**
 * g_task_is_valid:
 * @result: (type Gio.AsyncResult): A #GAsyncResult
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 * @source_object: (nullable) (type GObject): the source object
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 *   expected to be associated with the task
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 *
 * 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.
 *
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 * Returns: %TRUE if @result and @source_object are valid, %FALSE
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 * 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;

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  /* 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;

2000
  /* Let already-cancelled tasks finish right away */
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  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;
}

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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
};

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static void
g_task_thread_pool_init (void)
{
  task_pool = g_thread_pool_new (g_task_thread_pool_thread, NULL,
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                                 G_TASK_POOL_SIZE, FALSE, NULL);
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  g_assert (task_pool != NULL);

  g_thread_pool_set_sort_function (task_pool, g_task_compare_priority, NULL);
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  task_pool_manager = g_source_new (&trivial_source_funcs, sizeof (GSource));
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  g_source_set_name (task_pool_manager, "GTask thread pool manager");
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  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);
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}

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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, task->completed);
      break;
    }
}

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static void
g_task_class_init (GTaskClass *klass)
{
  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);

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  gobject_class->get_property = g_task_get_property;
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  gobject_class->finalize = g_task_finalize;
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  /**
   * 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));
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}

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;
}