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Functions
Description
As of GLib 2.36, GSimpleAsyncResult is deprecated in favor of GTask, which provides a simpler API.
GSimpleAsyncResult implements GAsyncResult.
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.
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:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 |
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); } |
Functions
GSimpleAsyncThreadFunc ()
void (*GSimpleAsyncThreadFunc) (GSimpleAsyncResult *res,GObject *object,GCancellable *cancellable);
Simple thread function that runs an asynchronous operation and checks for cancellation.
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.
The common convention is to create the GSimpleAsyncResult in the
function that starts the asynchronous operation and use that same
function as the source_tag
.
If your operation supports cancellation with GCancellable (which it
probably should) then you should provide the user's cancellable to
g_simple_async_result_set_check_cancellable() immediately after
this function returns.
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.
Parameters
source_object |
[allow-none] | |
callback |
[scope async] | |
user_data |
user data passed to |
[closure] |
domain |
a GQuark. |
|
code |
an error code. |
|
format |
a string with format characters. |
|
... |
a list of values to insert into |
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.
Parameters
source_object |
[allow-none] | |
callback |
[scope async] | |
user_data |
user data passed to |
[closure] |
error |
a GError |
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.
Parameters
source_object |
[allow-none] | |
callback |
[scope async] | |
user_data |
user data passed to |
[closure] |
error |
a GError |
Since 2.28
g_simple_async_result_set_check_cancellable ()
void g_simple_async_result_set_check_cancellable (GSimpleAsyncResult *simple,GCancellable *check_cancellable);
Sets a GCancellable to check before dispatching results.
This function has one very specific purpose: the provided cancellable
is checked at the time of g_simple_async_result_propagate_error() If
it is cancelled, these functions will return an "Operation was
cancelled" error (G_IO_ERROR_CANCELLED).
Implementors of cancellable asynchronous functions should use this in order to provide a guarantee to their callers that cancelling an async operation will reliably result in an error being returned for that operation (even if a positive result for the operation has already been sent as an idle to the main context to be dispatched).
The checking described above is done regardless of any call to the
unrelated g_simple_async_result_set_handle_cancellation() function.
Since 2.32
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.
Parameters
simple |
||
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.
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
.
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.
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.
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.
g_simple_async_result_get_source_tag ()
gpointer
g_simple_async_result_get_source_tag (GSimpleAsyncResult *simple);
Gets the source tag 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 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). (Alternatively, if either
source_tag
or result
's source tag is NULL, then the source tag
check is skipped.)
Parameters
result |
the GAsyncResult passed to the _finish function. |
|
source |
the GObject passed to the _finish function. |
[allow-none] |
source_tag |
the asynchronous function. |
[allow-none] |
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.
This function has nothing to do with
g_simple_async_result_set_check_cancellable(). It only refers to the
GCancellable passed to g_simple_async_result_run_in_thread().
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.
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 context
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.
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.
Parameters
simple |
||
func |
||
io_priority |
the io priority of the request. |
|
cancellable |
optional GCancellable object, |
[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.
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.
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.
If the GCancellable given to a prior call to
g_simple_async_result_set_check_cancellable() is cancelled then this
function will return TRUE with dest
set appropriately.
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.
Parameters
simple |
||
domain |
a GQuark (usually G_IO_ERROR). |
|
code |
an error code. |
|
format |
a formatted error reporting string. |
|
... |
a list of variables to fill in |
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().
Parameters
simple |
||
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.
Parameters
object |
[allow-none] | |
callback |
||
user_data |
user data passed to |
|
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 |
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.
Parameters
object |
[allow-none] | |
callback |
[scope async] | |
user_data |
user data passed to |
[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.
Parameters
object |
[allow-none] | |
callback |
||
user_data |
user data passed to |
|
error |
the GError to report |
Since 2.28
Types and Values
GSimpleAsyncResult
typedef struct _GSimpleAsyncResult GSimpleAsyncResult;
A simple implementation of GAsyncResult.