systemd sd_event_source_set_destroy_callback 3 sd_event_source_set_destroy_callback sd_event_source_get_destroy_callback sd_event_destroy_t Define the callback function for resource cleanup #include <systemd/sd-event.h> typedef int (*sd_event_destroy_t) void *userdata int sd_event_source_set_destroy_callback sd_event_source *source sd_event_destroy_t callback int sd_event_source_get_destroy_callback sd_event_source *source sd_event_destroy_t *callback sd_event_source_set_destroy_callback() sets callback as the callback function to be called right before the event source object source is deallocated. The userdata pointer from the event source object will be passed as the userdata parameter. This pointer can be set by an argument to the constructor functions, see sd_event_add_io3, or directly, see sd_event_source_set_userdata3. This callback function is called even if userdata is NULL. Note that this callback is invoked at a time where the event source object itself is already invalidated, and executing operations or taking new references to the event source object is not permissible. sd_event_source_get_destroy_callback() returns the current callback for source in the callback parameter. On success, sd_event_source_set_destroy_callback() returns 0 or a positive integer. On failure, it returns a negative errno-style error code. sd_event_source_get_destroy_callback() returns positive if the destroy callback function is set, 0 if not. On failure, returns a negative errno-style error code. Returned errors may indicate the following problems: -EINVAL The source parameter is NULL. sd_event_destroy_t(), sd_event_source_set_destroy_callback(), and sd_event_source_get_destroy_callback() were added in version 239. systemd1, sd-event3, sd_event_add_io3, sd_event_add_time3, sd_event_add_signal3, sd_event_add_child3, sd_event_add_inotify3, sd_event_add_defer3, sd_event_source_set_userdata3