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)