sd_bus_slot_set_userdata - Man Page

#include <systemd/sd-bus​.h>

void* sd_bus_slot_set_userdata(sd_bus_slot* slot, void* userdata);

void* sd_bus_slot_get_userdata(sd_bus_slot* slot);

The userdata pointer allows data to be passed between the point where a callback is registered, for example when a filter is added using sd_bus_add_filter(3) or an asynchronous function call is made using sd_bus_call_async(3), and the point where the callback is called, without having any global state​. The pointer has type void* and is not used by the sd-bus functions in any way, except to pass to the callback function​.

Usually, the userdata field is set when the slot object is initially registered​. sd_bus_slot_set_userdata() may be used to change it later for the bus slot object slot​. Previous value of the field is returned​. The argument and returned value may be NULL​. It will be passed as the userdata argument to the callback function attached to the slot​.

sd_bus_slot_set_userdata() gets the value of the userdata field in the bus slot object slot​.

On success, these functions return the value of the userdata field before the function call​. If the slot object is NULL, NULL will be returned to signify an error, but this is not distinguishable from the userdata field value being NULL​.

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

All functions listed here are thread-agnostic and only a single thread may operate on a given object at any given time​. Different threads may access the same object at different times​. Multiple independent objects may be used from different threads in parallel​.

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​.

sd_bus_slot_set_userdata() and sd_bus_slot_get_userdata() were added in version 240​.

systemd(1), sd-bus(3), sd_bus_slot_set_destroy_callback(3), sd_bus_add_match(3), sd_bus_slot_get_current_userdata(3)