Manpages - sd_event_source_set_prepare.3

sd_event_source_set_prepare - Set a preparation callback for event sources

  #include <systemd/sd-event.h>

int sd_event_source_set_prepare(sd_event_source **/source/, sd_event_handler_t callback);*

typedef int (*sd_event_handler_t)(sd_event_source **/s/, void */userdata/);*

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 sources 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 invoked.

On success, sd_event_source_set_prepare() returns a non-negative integer. On failure, it returns a negative errno-style error code.

These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd *pkg-config*(1) file.

*sd-event*(3), *sd_event_add_io*(3), *sd_event_add_time*(3), *sd_event_add_signal*(3), *sd_event_add_child*(3), *sd_event_add_inotify*(3), *sd_event_add_defer*(3), *sd_event_source_set_enabled*(3), *sd_event_source_set_priority*(3), *sd_event_source_set_userdata*(3)