sd_event_source_set_prepare - Set a preparation callback for event sources
sd_event_source_set_prepare() may be used to set a preparation callback
for the event source object specified as source. The callback function
specified as callback will be invoked immediately before the event loop
goes to sleep to wait for incoming events. It is invoked with the user data
pointer passed when the event source was created. The event source will be
disabled if the callback function returns a negative error code. The callback
function may be used to reconfigure the precise events to wait for. If the
callback parameter is passed as NULL the callback function is reset.
Event source objects have no preparation callback associated when
they are first created with calls such as sd_event_add_io(3),
sd_event_add_time(3). Preparation callback functions are supported
for all event source types with the exception of those created with
sd_event_add_exit(3). Preparation callback functions are dispatched
in the order indicated by the event source's priority field, as set with
sd_event_source_set_priority(3). Preparation callbacks of disabled
event sources (see sd_event_source_set_enabled(3)) are not
On success, sd_event_source_set_prepare() returns a non-negative integer.
On failure, it returns a negative errno-style error code.
Returned errors may indicate the following problems:
source is not a valid pointer to an
The event loop is already terminated.
Not enough memory.
The event loop has been created in a different
These APIs are implemented as a shared library, which can be compiled and linked
to with the libsystemd pkg-config(1) file.