Provides a base class for implementing asynchronous function results. Asynchronous operations are broken up into two separate operations
which are chained together by a GAsyncReadyCallback. To begin
an asynchronous operation, provide a GAsyncReadyCallback to the
asynchronous function. This callback will be triggered when the
operation has completed, and will be passed a GAsyncResult instance
filled with the details of the operation's success or failure, the
object the asynchronous function was started for and any error codes
returned. The asynchronous callback function is then expected to call
the corresponding "finish()" function with the object the function
was called for, and the GAsyncResult instance, and optionally,
an error to grab any error conditions that may have occurred. The purpose of the "finish()" function is to take the generic
result of type GAsyncResult and return the specific result
that the operation in question yields (e.g. a GFileEnumerator for
a "enumerate children" operation). If the result or error status
of the operation is not needed, there is no need to call the
"finish()" function, GIO will take care of cleaning up the
result and error information after the GAsyncReadyCallback
returns. It is also allowed to take a reference to the GAsyncResult and
call "finish()" later. Example of a typical asynchronous operation flow:
frobnitz_result_func <- function(source_object, res, user_data)
{
success <- _theoretical_frobnitz_finish (source_object, res, NULL) if (success)
message("Hurray!")
else
message("Uh oh!") ## ....
} _theoretical_frobnitz_async (theoretical_data,
NULL,
frobnitz_result_func,
NULL)
The callback for an asynchronous operation is called only once, and is
always called, even in the case of a cancelled operation. On cancellation
the result is a G_IO_ERROR_CANCELLED error. Some ascynchronous operations are implemented using synchronous calls. These
are run in a separate thread, if GThread has been initialized, but otherwise they
are sent to the Main Event Loop and processed in an idle function. So, if you
truly need asynchronous operations, make sure to initialize GThread.