protected Source ()
Creates a new SignalSource structure.
The size is specified to allow creating structures derived from SignalSource that contain additional data. The size passed in must be at least `sizeof (GSource)`.
The source will not initially be associated with any MainContext and must be added to one with attach before it will be executed.
structure containing functions that implement the sources behavior.
size of the SignalSource structure to create.
the newly-created SignalSource.