Creating a new GSource in GLib

Question

I'm trying to understand what it means when I call g_source_new. The latest API documentation (at this time its 2.38.2) on the call just says:

Creates a new GSource structure. The size is specified to allow creating structures derived from GSource that contain additional data. The size passed in must be at least sizeof (GSource).

I'm trying to understand if invoking this API means that I'm instantiating a new instance of my GSource or if it's intended as a registration of a new GSource type.

The underlying question is this: Am I allowed to create one new GSource using g_source_new and then apply that to any number of contexts (via g_source_attach)? Or must I utilize both functions even when attempting to apply the same GSource I've defined to multiple contexts?

Answer 1

From the source definition it looks like you can attach a GSource only to one GMainContext

struct _GSource
{
  /*< private >*/
  gpointer callback_data;
  GSourceCallbackFuncs *callback_funcs;

  const GSourceFuncs *source_funcs;
  guint ref_count;

  GMainContext *context;    // <<<<<

  gint priority;
  guint flags;
  guint source_id;

  GSList *poll_fds;

  GSource *prev;
  GSource *next;

  char    *name;

  GSourcePrivate *priv;
};

Have a look at

static guint
g_source_attach_unlocked (GSource      *source,
                      GMainContext *context,
                      gboolean      do_wakeup)

which will tell you that only the associated GMainContext will be woken.

Example of derived GSource usage: https://github.com/chergert/iris/blob/master/iris/iris-gsource.c