Index · Directives systemd 239


sd_bus_slot_set_destroy_callback, sd_bus_slot_get_destroy_callback, sd_bus_track_set_destroy_callback, sd_bus_track_get_destroy_callback, sd_bus_destroy_t — Define the callback function for resource cleanup.


#include <systemd/sd-bus.h>
typedef int (*sd_bus_destroy_t)(void *userdata);
int sd_bus_slot_set_destroy_callback(sd_bus_slot *slot,
 sd_bus_destroy_t callback);
int sd_bus_slot_get_destroy_callback(sd_bus_slot *slot,
 sd_bus_destroy_t *callback);
int sd_bus_track_set_destroy_callback(sd_bus_track *track,
 sd_bus_destroy_t callback);
int sd_bus_track_get_destroy_callback(sd_bus_track *track,
 sd_bus_destroy_t *callback);


sd_bus_slot_set_destroy_callback() sets callback as the callback function to be called right before the bus slot object slot is deallocated. The userdata pointer from the slot object will be passed as the userdata parameter. This pointer can be set by an argument to the constructor functions, see sd_bus_add_match(3), or directly, see sd_bus_slot_set_userdata(3). This callback function is called even if userdata is NULL. Note that this callback is invoked at a time where the bus slot object itself is already invalidated, and executing operations or taking new references to the bus slot object is not permissible.

sd_bus_slot_get_destroy_callback() returns the current callback for slot in the callback parameter.

sd_bus_track_set_destroy_callback() and sd_bus_track_get_destroy_callback provide equivalent functionality for the userdata pointer associated with bus peer tracking objects. For details about bus peer tracking objects, see sd_bus_track_new(3).

Return Value

On success, sd_bus_slot_set_destroy_callback() and sd_bus_track_set_destroy_callback() return 0 or a positive integer. On failure, they return a negative errno-style error code.

sd_bus_slot_get_destroy_callback() and sd_bus_track_get_destroy_callback return positive if the destroy callback function is set, 0 if not. On failure, they return a negative errno-style error code.


Returned errors may indicate the following problems:


The slot or track parameter is NULL.


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

See Also

systemd(1), sd-bus(3), sd_bus_slot_set_floating(3), sd_bus_add_match(3), sd_bus_track_new(3), sd_bus_slot_set_userdata(3), sd_bus_track_set_userdata(3)