---
name: "sd_bus_slot_ref"
section: "3"
platform: "linux"
package: "systemd-libs"
version: "262.1-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/sd_bus_slot_ref"
---

# sd\_bus\_slot\_ref(3)

Create and destroy references to a bus slot object

## NAME

sd\_bus\_slot\_ref, sd\_bus\_slot\_unref, sd\_bus\_slot\_unrefp - Create and destroy references to a bus slot object

## SYNOPSIS

```
#include <systemd/sd-bus.h>
```

**sd\_bus\_slot \*sd\_bus\_slot\_ref(sd\_bus\_slot \****slot***);**

**sd\_bus\_slot \*sd\_bus\_slot\_unref(sd\_bus\_slot \****slot***);**

**void sd\_bus\_slot\_unrefp(sd\_bus\_slot \*\****slotp***);**

## DESCRIPTION

**sd\_bus\_slot\_ref()** increases the internal reference counter of *slot* by one.

**sd\_bus\_slot\_unref()** decreases the internal reference counter of *slot* by one. Once the reference count has dropped to zero, slot object is destroyed and cannot be used anymore, so further calls to **sd\_bus\_slot\_ref()** or **sd\_bus\_slot\_unref()** are illegal.

**sd\_bus\_slot\_unrefp()** is similar to **sd\_bus\_slot\_unref()** but takes a pointer to a pointer to an **sd\_bus\_slot** object. This call is useful in conjunction with GCC's and LLVM's **Clean-up Variable Attribute**\[1\]. See [**sd\_bus\_new**(3)](/sd_bus_new/3.md) for an example how to use the cleanup attribute.

**sd\_bus\_slot\_ref()** and **sd\_bus\_slot\_unref()** execute no operation if the passed in bus object address is **NULL**. **sd\_bus\_slot\_unrefp()** will first dereference its argument, which must not be **NULL**, and will execute no operation if *that* is **NULL**.

## RETURN VALUE

**sd\_bus\_slot\_ref()** always returns the argument.

**sd\_bus\_slot\_unref()** always returns **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)](/pkg-config/1.md) 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)](/getenv/3.md), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call [**setenv**(3)](/setenv/3.md) 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\_slot\_ref()**, **sd\_bus\_slot\_unref()**, and **sd\_bus\_slot\_unrefp()** were added in version 240.

## SEE ALSO

[**systemd**(1)](/systemd/1.md), [**sd-bus**(3)](/sd-bus/3.md), [**sd\_bus\_new**(3)](/sd_bus_new/3.md), [**sd\_bus\_message\_new**(3)](/sd_bus_message_new/3.md), [**sd\_bus\_call\_method\_async**(3)](/sd_bus_call_method_async/3.md)

## NOTES

- 1\.

  Clean-up Variable Attribute

  https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html