Ubuntu Manpage: sd_bus_slot_set_floating, sd_bus_slot_get_floating - Control whether a bus slot object is "floating"

Provided by: libsystemd-dev_256.5-2ubuntu3.1_amd64

NAME

       sd_bus_slot_set_floating, sd_bus_slot_get_floating - Control whether a bus slot object is "floating"

SYNOPSIS

       #include <systemd/sd-bus.h>

       int sd_bus_slot_set_floating(sd_bus_slot *slot, int b);

       int sd_bus_slot_get_floating(sd_bus_slot *slot);

DESCRIPTION

sd_bus_slot_set_floating() controls whether the specified bus slot object slot shall be "floating" or
not. A floating bus slot object's lifetime is bound to the lifetime of the bus object it is associated
with, meaning that it remains allocated as long as the bus object itself and is freed automatically when
the bus object is freed. Regular (i.e. non-floating) bus slot objects keep the bus referenced, hence the
bus object remains allocated at least as long as there remains at least one referenced bus slot object
around. The floating state hence controls the direction of referencing between the bus object and the bus
slot objects: if floating the bus pins the bus slot, and otherwise the bus slot pins the bus objects. Use
sd_bus_slot_set_floating() to switch between both modes: if the b parameter is zero, the slot object is
considered floating, otherwise it is made a regular (non-floating) slot object.

Bus slot objects may be allocated with calls such as sd_bus_add_match(3). If the slot of these functions
is non-NULL the slot object will be of the regular kind (i.e. non-floating), otherwise it will be created
floating. With sd_bus_slot_set_floating() a bus slot object allocated as regular can be converted into a
floating object and back. This is particularly useful for creating a bus slot object, then changing
parameters of it, and then turning it into a floating object, whose lifecycle is managed by the bus
object.

sd_bus_slot_get_floating() returns the current floating state of the specified bus slot object. It
returns negative on error, zero if the bus slot object is a regular (non-floating) object and positive
otherwise.

RETURN VALUE

       On success, these functions return 0 or a positive integer. On failure, they return a negative
       errno-style error code.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           The slot parameter is NULL.

       -ECHILD
           The bus connection has been created in a different process, library or module instance.

       -ESTALE
           The bus object the specified bus slot object is associated with has already been freed, and hence no
           change in the floating state can be made anymore.

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