NAME

       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

SYNOPSIS

       #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);

DESCRIPTION

       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.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           The slot or track parameter is NULL.

NOTES

       Functions described here are available as a shared library, which can be compiled against and linked to
       with the libsystemd pkg-config(1) file.

       The code described here uses getenv(3), which is declared to be not multi-thread-safe. This means that
       the code calling the functions described here must not call setenv(3) from a parallel thread. It is
       recommended to only do calls to setenv() from an early phase of the program when no other threads have
       been started.

HISTORY

       sd_bus_destroy_t(), sd_bus_slot_set_destroy_callback(), sd_bus_slot_get_destroy_callback(),
       sd_bus_track_set_destroy_callback(), and sd_bus_track_get_destroy_callback() were added in version 239.

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)