class Gio::SimpleAsyncResult

Overview

As of GLib 2.46, #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-main-context-push-thread-default] where the #GSimpleAsyncResult was created. g_simple_async_result_run_in_thread() will run the job in a separate thread and then use g_simple_async_result_complete_in_idle() to deliver the result.

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:

|[ 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); } ]|

Included Modules

Defined in:

auto/gio-2.0/simple_async_result.cr

Constructors

Class Method Summary

Instance Method Summary

Instance methods inherited from module Gio::AsyncResult

is_tagged(source_tag : Pointer(Void)?) : Bool is_tagged, legacy_propagate_error : Bool legacy_propagate_error, source_object : GObject::Object? source_object, to_unsafe to_unsafe, user_data : Pointer(Void)? user_data

Instance methods inherited from class GObject::Object

bind_property(source_property : String, target : GObject::Object, target_property : String, flags : GObject::BindingFlags) : GObject::Binding bind_property, bind_property_full(source_property : String, target : GObject::Object, target_property : String, flags : GObject::BindingFlags, transform_to : GObject::Closure, transform_from : GObject::Closure) : GObject::Binding bind_property_full, data(key : String) : Pointer(Void)? data, finalize finalize, freeze_notify : Nil freeze_notify, getv(names : Enumerable(String), values : Enumerable(_)) : Nil getv, notify(property_name : String) : Nil notify, notify_by_pspec(pspec : GObject::ParamSpec) : Nil notify_by_pspec, notify_signal notify_signal, property(property_name : String, value : _) : Nil property, qdata(quark : UInt32) : Pointer(Void)? qdata, ref_count ref_count, run_dispose : Nil run_dispose, set_data(key : String, data : Pointer(Void)?) : Nil set_data, set_property(property_name : String, value : _) : Nil set_property, steal_data(key : String) : Pointer(Void)? steal_data, steal_qdata(quark : UInt32) : Pointer(Void)? steal_qdata, thaw_notify : Nil thaw_notify, to_unsafe : Pointer(Void) to_unsafe, watch_closure(closure : GObject::Closure) : Nil watch_closure

Constructor methods inherited from class GObject::Object

cast(obj : GObject::Object) : self cast, cast?(obj : GObject::Object) : self? cast?, new new, newv(object_type : UInt64, parameters : Enumerable(GObject::Parameter)) : self newv

Class methods inherited from class GObject::Object

compat_control(what : UInt64, data : Pointer(Void)?) : UInt64 compat_control, g_type : UInt64 g_type, interface_find_property(g_iface : GObject::TypeInterface, property_name : String) : GObject::ParamSpec interface_find_property, interface_list_properties(g_iface : GObject::TypeInterface) : Enumerable(GObject::ParamSpec) interface_list_properties

Constructor Detail

def self.new(source_object : GObject::Object?, callback : Gio::AsyncReadyCallback?, user_data : Pointer(Void)?, source_tag : Pointer(Void)?) #

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.


def self.new #

Initialize a new SimpleAsyncResult.


def self.new_from_error(source_object : GObject::Object?, callback : Gio::AsyncReadyCallback?, user_data : Pointer(Void)?, error : GLib::Error) : self #

Creates a #GSimpleAsyncResult from an error condition.


Class Method Detail

def self.g_type : UInt64 #

Returns the type id (GType) registered in GLib type system.


def self.is_valid(result : Gio::AsyncResult, source : GObject::Object?, source_tag : Pointer(Void)?) : Bool #

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.)


Instance Method Detail

def check_cancellable=(check_cancellable : Gio::Cancellable?) : Nil #

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.


def complete : Nil #

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.


def complete_in_idle : Nil #

Completes an asynchronous function in an idle handler in the [thread-default main context][g-main-context-push-thread-default] 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.


def from_error=(error : GLib::Error) : Nil #

Sets the result from a #GError.


def handle_cancellation=(handle_cancellation : Bool) : Nil #

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().


def op_res_gboolean : Bool #

Gets the operation result boolean from within the asynchronous result.


def op_res_gboolean=(op_res : Bool) : Nil #

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


def op_res_gssize : Int64 #

Gets a gssize from the asynchronous result.


def op_res_gssize=(op_res : Int64) : Nil #

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


def propagate_error : Bool #

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.