readAsync
Asynchronously opens @file for reading.
For more details, see g_file_read() which is the synchronous version of this call.
When the operation is finished, @callback will be called. You can then call g_file_read_finish() to get the result of the operation.
Parameters
ioPriority
the io-priority of the request
cancellable
optional #GCancellable object, null to ignore
callback
a #GAsyncReadyCallback to call when the request is satisfied