+typedef enum /*< flags >*/
+{
+ G_IO_IN GLIB_SYSDEF_POLLIN,
+ G_IO_OUT GLIB_SYSDEF_POLLOUT,
+ G_IO_PRI GLIB_SYSDEF_POLLPRI,
+ G_IO_ERR GLIB_SYSDEF_POLLERR,
+ G_IO_HUP GLIB_SYSDEF_POLLHUP,
+ G_IO_NVAL GLIB_SYSDEF_POLLNVAL
+} GIOCondition;
+
+
+/**
+ * GMainContext:
+ *
+ * The `GMainContext` struct is an opaque data
+ * type representing a set of sources to be handled in a main loop.
+ */
+typedef struct _GMainContext GMainContext;
+
+/**
+ * GMainLoop:
+ *
+ * The `GMainLoop` struct is an opaque data type
+ * representing the main event loop of a GLib or GTK+ application.
+ */
+typedef struct _GMainLoop GMainLoop;
+
+/**
+ * GSource:
+ *
+ * The `GSource` struct is an opaque data type
+ * representing an event source.
+ */
+typedef struct _GSource GSource;
+typedef struct _GSourcePrivate GSourcePrivate;
+
+/**
+ * GSourceCallbackFuncs:
+ * @ref: Called when a reference is added to the callback object
+ * @unref: Called when a reference to the callback object is dropped
+ * @get: Called to extract the callback function and data from the
+ * callback object.
+
+ * The `GSourceCallbackFuncs` struct contains
+ * functions for managing callback objects.
+ */
+typedef struct _GSourceCallbackFuncs GSourceCallbackFuncs;
+
+/**
+ * GSourceFuncs:
+ * @prepare: Called before all the file descriptors are polled. If the
+ * source can determine that it is ready here (without waiting for the
+ * results of the poll() call) it should return %TRUE. It can also return
+ * a @timeout_ value which should be the maximum timeout (in milliseconds)
+ * which should be passed to the poll() call. The actual timeout used will
+ * be -1 if all sources returned -1, or it will be the minimum of all
+ * the @timeout_ values returned which were >= 0. Since 2.36 this may
+ * be %NULL, in which case the effect is as if the function always returns
+ * %FALSE with a timeout of -1. If @prepare returns a
+ * timeout and the source also has a 'ready time' set then the
+ * nearer of the two will be used.
+ * @check: Called after all the file descriptors are polled. The source
+ * should return %TRUE if it is ready to be dispatched. Note that some
+ * time may have passed since the previous prepare function was called,
+ * so the source should be checked again here. Since 2.36 this may
+ * be %NULL, in which case the effect is as if the function always returns
+ * %FALSE.
+ * @dispatch: Called to dispatch the event source, after it has returned
+ * %TRUE in either its @prepare or its @check function. The @dispatch
+ * function is passed in a callback function and data. The callback
+ * function may be %NULL if the source was never connected to a callback
+ * using g_source_set_callback(). The @dispatch function should call the
+ * callback function with @user_data and whatever additional parameters
+ * are needed for this type of event source.
+ * @finalize: Called when the source is finalized.
+ *
+ * The `GSourceFuncs` struct contains a table of
+ * functions used to handle event sources in a generic manner.
+ *
+ * For idle sources, the prepare and check functions always return %TRUE
+ * to indicate that the source is always ready to be processed. The prepare
+ * function also returns a timeout value of 0 to ensure that the poll() call
+ * doesn't block (since that would be time wasted which could have been spent
+ * running the idle function).
+ *
+ * For timeout sources, the prepare and check functions both return %TRUE
+ * if the timeout interval has expired. The prepare function also returns
+ * a timeout value to ensure that the poll() call doesn't block too long
+ * and miss the next timeout.
+ *
+ * For file descriptor sources, the prepare function typically returns %FALSE,
+ * since it must wait until poll() has been called before it knows whether
+ * any events need to be processed. It sets the returned timeout to -1 to
+ * indicate that it doesn't mind how long the poll() call blocks. In the
+ * check function, it tests the results of the poll() call to see if the
+ * required condition has been met, and returns %TRUE if so.
+ */
+typedef struct _GSourceFuncs GSourceFuncs;
+
+/**
+ * GPid:
+ *
+ * A type which is used to hold a process identification.
+ *
+ * On UNIX, processes are identified by a process id (an integer),
+ * while Windows uses process handles (which are pointers).
+ *
+ * GPid is used in GLib only for descendant processes spawned with
+ * the g_spawn functions.
+ */