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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | SEE ALSO | COLOPHON |
SD_BUS_SLOT_SET_USERDATA(3)d_bus_slot_set_userdataD_BUS_SLOT_SET_USERDATA(3)
sd_bus_slot_set_userdata, sd_bus_slot_get_userdata - Set and query
the value in the "userdata" field
#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.
These APIs are implemented as a shared library, which can be compiled
and linked to with the libsystemd pkg-config(1) file.
systemd(1), sd-bus(3), sd_bus_slot_set_destroy_callback(3),
sd_bus_add_match(3), sd_bus_slot_get_current_userdata(3)
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systemd 246 SD_BUS_SLOT_SET_USERDATA(3)
Pages that refer to this page: 30-systemd-environment-d-generator(7) , systemd.index(7)