Sets this'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
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 MainContext, or in the next iteration of the
current MainContext. 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 TaskThreadFunc exits.
Note that since the task may be completed before returning from return_pointer, you cannot assume that
result is still valid after calling this, unless you are still holding another reference on it.
| this |
a Task |
| result |
the pointer result of a task function |
| result_destroy |
a DestroyNotify function. |