x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_BUS_SLOT_SET_USERDATA(3)sd_bus_slot_set_userdataSD_BUS_SLOT_SET_USERDATA(3)
NAME
sd_bus_slot_set_userdata, sd_bus_slot_get_userdata - Set and query the
value in the "userdata" field
SYNOPSIS
#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);
DESCRIPTION
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.
RETURN VALUE
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.
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.
SEE ALSO
systemd(1), sd-bus(3), sd_bus_slot_set_destroy_callback(3),
sd_bus_add_match(3), sd_bus_slot_get_current_userdata(3)
systemd 254 SD_BUS_SLOT_SET_USERDATA(3)
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