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GSimpleAsyncResult

GSimpleAsyncResult — Simple asynchronous results implementation

Synopsis

#include <gio/gio.h>

                    GSimpleAsyncResult;
void                (*GSimpleAsyncThreadFunc)           (GSimpleAsyncResult *res,
                                                         GObject *object,
                                                         GCancellable *cancellable);
GSimpleAsyncResult * g_simple_async_result_new          (GObject *source_object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         gpointer source_tag);
GSimpleAsyncResult * g_simple_async_result_new_error    (GObject *source_object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         GQuark domain,
                                                         gint code,
                                                         const char *format,
                                                         ...);
GSimpleAsyncResult * g_simple_async_result_new_from_error
                                                        (GObject *source_object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         const GError *error);
GSimpleAsyncResult * g_simple_async_result_new_take_error
                                                        (GObject *source_object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         GError *error);
void                g_simple_async_result_set_op_res_gpointer
                                                        (GSimpleAsyncResult *simple,
                                                         gpointer op_res,
                                                         GDestroyNotify destroy_op_res);
gpointer            g_simple_async_result_get_op_res_gpointer
                                                        (GSimpleAsyncResult *simple);
void                g_simple_async_result_set_op_res_gssize
                                                        (GSimpleAsyncResult *simple,
                                                         gssize op_res);
gssize              g_simple_async_result_get_op_res_gssize
                                                        (GSimpleAsyncResult *simple);
void                g_simple_async_result_set_op_res_gboolean
                                                        (GSimpleAsyncResult *simple,
                                                         gboolean op_res);
gboolean            g_simple_async_result_get_op_res_gboolean
                                                        (GSimpleAsyncResult *simple);
gpointer            g_simple_async_result_get_source_tag
                                                        (GSimpleAsyncResult *simple);
gboolean            g_simple_async_result_is_valid      (GAsyncResult *result,
                                                         GObject *source,
                                                         gpointer source_tag);
void                g_simple_async_result_set_handle_cancellation
                                                        (GSimpleAsyncResult *simple,
                                                         gboolean handle_cancellation);
void                g_simple_async_result_complete      (GSimpleAsyncResult *simple);
void                g_simple_async_result_complete_in_idle
                                                        (GSimpleAsyncResult *simple);
void                g_simple_async_result_run_in_thread (GSimpleAsyncResult *simple,
                                                         GSimpleAsyncThreadFunc func,
                                                         int io_priority,
                                                         GCancellable *cancellable);
void                g_simple_async_result_set_from_error
                                                        (GSimpleAsyncResult *simple,
                                                         const GError *error);
void                g_simple_async_result_take_error    (GSimpleAsyncResult *simple,
                                                         GError *error);
gboolean            g_simple_async_result_propagate_error
                                                        (GSimpleAsyncResult *simple,
                                                         GError **dest);
void                g_simple_async_result_set_error     (GSimpleAsyncResult *simple,
                                                         GQuark domain,
                                                         gint code,
                                                         const char *format,
                                                         ...);
void                g_simple_async_result_set_error_va  (GSimpleAsyncResult *simple,
                                                         GQuark domain,
                                                         gint code,
                                                         const char *format,
                                                         va_list args);
void                g_simple_async_report_error_in_idle (GObject *object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         GQuark domain,
                                                         gint code,
                                                         const char *format,
                                                         ...);
void                g_simple_async_report_gerror_in_idle
                                                        (GObject *object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         const GError *error);
void                g_simple_async_report_take_gerror_in_idle
                                                        (GObject *object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         GError *error);

Object Hierarchy

  GObject
   +----GSimpleAsyncResult

Implemented Interfaces

GSimpleAsyncResult implements GAsyncResult.

Description

Implements GAsyncResult for simple cases. Most of the time, this will be all an application needs, and will be used transparently. Because of this, GSimpleAsyncResult is used throughout GIO for handling asynchronous functions.

GSimpleAsyncResult handles GAsyncReadyCallbacks, error reporting, operation cancellation and the final state of an operation, completely transparent to the application. Results can be returned as a pointer e.g. for functions that return data that is collected asynchronously, a boolean value for checking the success or failure of an operation, or a gssize for operations which return the number of bytes modified by the operation; all of the simple return cases are covered.

Most of the time, an application will not need to know of the details of this API; it is handled transparently, and any necessary operations are handled by GAsyncResult's interface. However, if implementing a new GIO module, for writing language bindings, or for complex applications that need better control of how asynchronous operations are completed, it is important to understand this functionality.

GSimpleAsyncResults are tagged with the calling function to ensure that asynchronous functions and their finishing functions are used together correctly.

To create a new GSimpleAsyncResult, call g_simple_async_result_new(). If the result needs to be created for a GError, use g_simple_async_result_new_from_error() or g_simple_async_result_new_take_error(). If a GError is not available (e.g. the asynchronous operation's doesn't take a GError argument), but the result still needs to be created for an error condition, use g_simple_async_result_new_error() (or g_simple_async_result_set_error_va() if your application or binding requires passing a variable argument list directly), and the error can then be propagated through the use of g_simple_async_result_propagate_error().

An asynchronous operation can be made to ignore a cancellation event by calling g_simple_async_result_set_handle_cancellation() with a GSimpleAsyncResult for the operation and FALSE. This is useful for operations that are dangerous to cancel, such as close (which would cause a leak if cancelled before being run).

GSimpleAsyncResult can integrate into GLib's event loop, GMainLoop, or it can use GThreads if available. g_simple_async_result_complete() will finish an I/O task directly from the point where it is called. g_simple_async_result_complete_in_idle() will finish it from an idle handler in the thread-default main context. g_simple_async_result_run_in_thread() will run the job in a separate thread and then deliver the result to the thread-default main context.

To set the results of an asynchronous function, g_simple_async_result_set_op_res_gpointer(), g_simple_async_result_set_op_res_gboolean(), and g_simple_async_result_set_op_res_gssize() are provided, setting the operation's result to a gpointer, gboolean, or gssize, respectively.

Likewise, to get the result of an asynchronous function, g_simple_async_result_get_op_res_gpointer(), g_simple_async_result_get_op_res_gboolean(), and g_simple_async_result_get_op_res_gssize() are provided, getting the operation's result as a gpointer, gboolean, and gssize, respectively.

For the details of the requirements implementations must respect, see GAsyncResult. A typical implementation of an asynchronous operation using GSimpleAsyncResult looks something like this: 

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static void
baked_cb (Cake    *cake,
          gpointer user_data)
{
  /* In this example, this callback is not given a reference to the cake, so
   * the GSimpleAsyncResult has to take a reference to it.
   */
  GSimpleAsyncResult *result = user_data;

  if (cake == NULL)
    g_simple_async_result_set_error (result,
                                     BAKER_ERRORS,
                                     BAKER_ERROR_NO_FLOUR,
                                     "Go to the supermarket");
  else
    g_simple_async_result_set_op_res_gpointer (result,
                                               g_object_ref (cake),
                                               g_object_unref);


  /* In this example, we assume that baked_cb is called as a callback from
   * the mainloop, so it's safe to complete the operation synchronously here.
   * If, however, _baker_prepare_cake () might call its callback without
   * first returning to the mainloop — inadvisable, but some APIs do so —
   * we would need to use g_simple_async_result_complete_in_idle().
   */
  g_simple_async_result_complete (result);
  g_object_unref (result);
}

void
baker_bake_cake_async (Baker              *self,
                       guint               radius,
                       GAsyncReadyCallback callback,
                       gpointer            user_data)
{
  GSimpleAsyncResult *simple;
  Cake               *cake;

  if (radius < 3)
    {
      g_simple_async_report_error_in_idle (G_OBJECT (self),
                                           callback,
                                           user_data,
                                           BAKER_ERRORS,
                                           BAKER_ERROR_TOO_SMALL,
                                           "%ucm radius cakes are silly",
                                           radius);
      return;
    }

  simple = g_simple_async_result_new (G_OBJECT (self),
                                      callback,
                                      user_data,
                                      baker_bake_cake_async);
  cake = _baker_get_cached_cake (self, radius);

  if (cake != NULL)
    {
      g_simple_async_result_set_op_res_gpointer (simple,
                                                 g_object_ref (cake),
                                                 g_object_unref);
      g_simple_async_result_complete_in_idle (simple);
      g_object_unref (simple);
      /* Drop the reference returned by _baker_get_cached_cake(); the
       * GSimpleAsyncResult has taken its own reference.
       */
      g_object_unref (cake);
      return;
    }

  _baker_prepare_cake (self, radius, baked_cb, simple);
}

Cake *
baker_bake_cake_finish (Baker        *self,
                        GAsyncResult *result,
                        GError      **error)
{
  GSimpleAsyncResult *simple;
  Cake               *cake;

  g_return_val_if_fail (g_simple_async_result_is_valid (result,
                                                        G_OBJECT (self),
                                                        baker_bake_cake_async),
                        NULL);

  simple = (GSimpleAsyncResult *) result;

  if (g_simple_async_result_propagate_error (simple, error))
    return NULL;

  cake = CAKE (g_simple_async_result_get_op_res_gpointer (simple));
  return g_object_ref (cake);
}

Details

GSimpleAsyncResult

typedef struct _GSimpleAsyncResult GSimpleAsyncResult;

A simple implementation of GAsyncResult.

GSimpleAsyncThreadFunc ()

void                (*GSimpleAsyncThreadFunc)           (GSimpleAsyncResult *res,
                                                         GObject *object,
                                                         GCancellable *cancellable);

Simple thread function that runs an asynchronous operation and checks for cancellation.

res :

 a GSimpleAsyncResult.

object :

 a GObject.

cancellable :

 optional GCancellable object, NULL to ignore.

g_simple_async_result_new ()

GSimpleAsyncResult * g_simple_async_result_new          (GObject *source_object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         gpointer source_tag);

Creates a GSimpleAsyncResult.

source_object :

 a GObject, or NULL. [allow-none]

callback :

 a GAsyncReadyCallback. [scope async]

user_data :

 user data passed to callback. [closure]

source_tag :

 the asynchronous function.

Returns :

 a GSimpleAsyncResult.

g_simple_async_result_new_error ()

GSimpleAsyncResult * g_simple_async_result_new_error    (GObject *source_object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         GQuark domain,
                                                         gint code,
                                                         const char *format,
                                                         ...);

Creates a new GSimpleAsyncResult with a set error.

source_object :

 a GObject, or NULL. [allow-none]

callback :

 a GAsyncReadyCallback. [scope async]

user_data :

 user data passed to callback. [closure]

domain :

 a GQuark.

code :

 an error code.

format :

 a string with format characters.

... :

 a list of values to insert into format.

Returns :

 a GSimpleAsyncResult.

g_simple_async_result_new_from_error ()

GSimpleAsyncResult * g_simple_async_result_new_from_error
                                                        (GObject *source_object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         const GError *error);

Creates a GSimpleAsyncResult from an error condition.

source_object :

 a GObject, or NULL. [allow-none]

callback :

 a GAsyncReadyCallback. [scope async]

user_data :

 user data passed to callback. [closure]

error :

 a GError

Returns :

 a GSimpleAsyncResult.

g_simple_async_result_new_take_error ()

GSimpleAsyncResult * g_simple_async_result_new_take_error
                                                        (GObject *source_object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         GError *error);

Creates a GSimpleAsyncResult from an error condition, and takes over the caller's ownership of error, so the caller does not need to free it anymore.

source_object :

 a GObject, or NULL. [allow-none]

callback :

 a GAsyncReadyCallback. [scope async]

user_data :

 user data passed to callback. [closure]

error :

 a GError

Returns :

 a GSimpleAsyncResult

Since 2.28

g_simple_async_result_set_op_res_gpointer ()

void                g_simple_async_result_set_op_res_gpointer
                                                        (GSimpleAsyncResult *simple,
                                                         gpointer op_res,
                                                         GDestroyNotify destroy_op_res);

Sets the operation result within the asynchronous result to a pointer.

simple :

 a GSimpleAsyncResult.

op_res :

 a pointer result from an asynchronous function.

destroy_op_res :

 a GDestroyNotify function.

g_simple_async_result_get_op_res_gpointer ()

gpointer            g_simple_async_result_get_op_res_gpointer
                                                        (GSimpleAsyncResult *simple);

Gets a pointer result as returned by the asynchronous function.

simple :

 a GSimpleAsyncResult.

Returns :

 a pointer from the result.

g_simple_async_result_set_op_res_gssize ()

void                g_simple_async_result_set_op_res_gssize
                                                        (GSimpleAsyncResult *simple,
                                                         gssize op_res);

Sets the operation result within the asynchronous result to the given op_res.

simple :

 a GSimpleAsyncResult.

op_res :

 a gssize.

g_simple_async_result_get_op_res_gssize ()

gssize              g_simple_async_result_get_op_res_gssize
                                                        (GSimpleAsyncResult *simple);

Gets a gssize from the asynchronous result.

simple :

 a GSimpleAsyncResult.

Returns :

 a gssize returned from the asynchronous function.

g_simple_async_result_set_op_res_gboolean ()

void                g_simple_async_result_set_op_res_gboolean
                                                        (GSimpleAsyncResult *simple,
                                                         gboolean op_res);

Sets the operation result to a boolean within the asynchronous result.

simple :

 a GSimpleAsyncResult.

op_res :

 a gboolean.

g_simple_async_result_get_op_res_gboolean ()

gboolean            g_simple_async_result_get_op_res_gboolean
                                                        (GSimpleAsyncResult *simple);

Gets the operation result boolean from within the asynchronous result.

simple :

 a GSimpleAsyncResult.

Returns :

 TRUE if the operation's result was TRUE, FALSE if the operation's result was FALSE.

g_simple_async_result_get_source_tag ()

gpointer            g_simple_async_result_get_source_tag
                                                        (GSimpleAsyncResult *simple);

Gets the source tag for the GSimpleAsyncResult.

simple :

 a GSimpleAsyncResult.

Returns :

 a gpointer to the source object for the GSimpleAsyncResult.

g_simple_async_result_is_valid ()

gboolean            g_simple_async_result_is_valid      (GAsyncResult *result,
                                                         GObject *source,
                                                         gpointer source_tag);

Ensures that the data passed to the _finish function of an async operation is consistent. Three checks are performed.

First, result is checked to ensure that it is really a GSimpleAsyncResult. Second, source is checked to ensure that it matches the source object of result. Third, source_tag is checked to ensure that it is either NULL (as it is when the result was created by g_simple_async_report_error_in_idle() or g_simple_async_report_gerror_in_idle()) or equal to the source_tag argument given to g_simple_async_result_new() (which, by convention, is a pointer to the _async function corresponding to the _finish function from which this function is called).

result :

 the GAsyncResult passed to the _finish function.

source :

 the GObject passed to the _finish function.

source_tag :

 the asynchronous function.

Returns :

 TRUE if all checks passed or FALSE if any failed.

Since 2.20

g_simple_async_result_set_handle_cancellation ()

void                g_simple_async_result_set_handle_cancellation
                                                        (GSimpleAsyncResult *simple,
                                                         gboolean handle_cancellation);

Sets whether to handle cancellation within the asynchronous operation.

simple :

 a GSimpleAsyncResult.

handle_cancellation :

 a gboolean.

g_simple_async_result_complete ()

void                g_simple_async_result_complete      (GSimpleAsyncResult *simple);

Completes an asynchronous I/O job immediately. Must be called in the thread where the asynchronous result was to be delivered, as it invokes the callback directly. If you are in a different thread use g_simple_async_result_complete_in_idle().

Calling this function takes a reference to simple for as long as is needed to complete the call.

simple :

 a GSimpleAsyncResult.

g_simple_async_result_complete_in_idle ()

void                g_simple_async_result_complete_in_idle
                                                        (GSimpleAsyncResult *simple);

Completes an asynchronous function in an idle handler in the thread-default main loop of the thread that simple was initially created in (and re-pushes that context around the invocation of the callback).

Calling this function takes a reference to simple for as long as is needed to complete the call.

simple :

 a GSimpleAsyncResult.

g_simple_async_result_run_in_thread ()

void                g_simple_async_result_run_in_thread (GSimpleAsyncResult *simple,
                                                         GSimpleAsyncThreadFunc func,
                                                         int io_priority,
                                                         GCancellable *cancellable);

Runs the asynchronous job in a separate thread and then calls g_simple_async_result_complete_in_idle() on simple to return the result to the appropriate main loop.

Calling this function takes a reference to simple for as long as is needed to run the job and report its completion.

simple :

 a GSimpleAsyncResult.

func :

 a GSimpleAsyncThreadFunc.

io_priority :

 the io priority of the request.

cancellable :

 optional GCancellable object, NULL to ignore. [allow-none]

g_simple_async_result_set_from_error ()

void                g_simple_async_result_set_from_error
                                                        (GSimpleAsyncResult *simple,
                                                         const GError *error);

Sets the result from a GError.

simple :

 a GSimpleAsyncResult.

error :

 GError.

g_simple_async_result_take_error ()

void                g_simple_async_result_take_error    (GSimpleAsyncResult *simple,
                                                         GError *error);

Sets the result from error, and takes over the caller's ownership of error, so the caller does not need to free it any more.

simple :

 a GSimpleAsyncResult

error :

 a GError

Since 2.28

g_simple_async_result_propagate_error ()

gboolean            g_simple_async_result_propagate_error
                                                        (GSimpleAsyncResult *simple,
                                                         GError **dest);

Propagates an error from within the simple asynchronous result to a given destination.

simple :

 a GSimpleAsyncResult.

dest :

 a location to propagate the error to. [out]

Returns :

 TRUE if the error was propagated to dest. FALSE otherwise.

g_simple_async_result_set_error ()

void                g_simple_async_result_set_error     (GSimpleAsyncResult *simple,
                                                         GQuark domain,
                                                         gint code,
                                                         const char *format,
                                                         ...);

Sets an error within the asynchronous result without a GError.

simple :

 a GSimpleAsyncResult.

domain :

 a GQuark (usually G_IO_ERROR).

code :

 an error code.

format :

 a formatted error reporting string.

... :

 a list of variables to fill in format.

g_simple_async_result_set_error_va ()

void                g_simple_async_result_set_error_va  (GSimpleAsyncResult *simple,
                                                         GQuark domain,
                                                         gint code,
                                                         const char *format,
                                                         va_list args);

Sets an error within the asynchronous result without a GError. Unless writing a binding, see g_simple_async_result_set_error().

simple :

 a GSimpleAsyncResult.

domain :

 a GQuark (usually G_IO_ERROR).

code :

 an error code.

format :

 a formatted error reporting string.

args :

 va_list of arguments.

g_simple_async_report_error_in_idle ()

void                g_simple_async_report_error_in_idle (GObject *object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         GQuark domain,
                                                         gint code,
                                                         const char *format,
                                                         ...);

Reports an error in an asynchronous function in an idle function by directly setting the contents of the GAsyncResult with the given error information.

object :

 a GObject, or NULL. [allow-none]

callback :

 a GAsyncReadyCallback.

user_data :

 user data passed to callback.

domain :

 a GQuark containing the error domain (usually G_IO_ERROR).

code :

 a specific error code.

format :

 a formatted error reporting string.

... :

 a list of variables to fill in format.

g_simple_async_report_gerror_in_idle ()

void                g_simple_async_report_gerror_in_idle
                                                        (GObject *object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         const GError *error);

Reports an error in an idle function. Similar to g_simple_async_report_error_in_idle(), but takes a GError rather than building a new one.

object :

 a GObject, or NULL. [allow-none]

callback :

 a GAsyncReadyCallback. [scope async]

user_data :

 user data passed to callback. [closure]

error :

 the GError to report

g_simple_async_report_take_gerror_in_idle ()

void                g_simple_async_report_take_gerror_in_idle
                                                        (GObject *object,
                                                         GAsyncReadyCallback callback,
                                                         gpointer user_data,
                                                         GError *error);

Reports an error in an idle function. Similar to g_simple_async_report_gerror_in_idle(), but takes over the caller's ownership of error, so the caller does not have to free it any more.

object :

 a GObject, or NULL. [allow-none]

callback :

 a GAsyncReadyCallback.

user_data :

 user data passed to callback.

error :

 the GError to report

Since 2.28

See Also

GAsyncResult
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