---
name: "sd_event_source_unref"
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_event_source_unref"
---

# sd\_event\_source\_unref(3)

Increase or decrease event source reference counters

## NAME

sd\_event\_source\_unref, sd\_event\_source\_unrefp, sd\_event\_source\_ref, sd\_event\_source\_disable\_unref, sd\_event\_source\_disable\_unrefp - Increase or decrease event source reference counters

## SYNOPSIS

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

**sd\_event\_source\* sd\_event\_source\_unref(sd\_event\_source \****source***);**

**void sd\_event\_source\_unrefp(sd\_event\_source \*\****source***);**

**sd\_event\_source\* sd\_event\_source\_ref(sd\_event\_source \****source***);**

**sd\_event\_source\* sd\_event\_source\_disable\_unref(sd\_event\_source \****source***);**

**void sd\_event\_source\_disable\_unrefp(sd\_event\_source \*\****source***);**

## DESCRIPTION

**sd\_event\_source\_unref()** may be used to decrement by one the internal reference counter of the event source object specified as *source*. The reference counter is initially set to one, when the event source is created with calls such as [**sd\_event\_add\_io**(3)](/sd_event_add_io/3.md) or [**sd\_event\_add\_time**(3)](/sd_event_add_time/3.md). When the reference counter reaches zero, the object is detached from the event loop object and destroyed.

**sd\_event\_source\_unrefp()** is similar to **sd\_event\_source\_unref()** but takes a pointer to a pointer to an **sd\_event\_source** object. This call is useful in conjunction with GCC's and LLVM's **Clean-up Variable Attribute**\[1\]. Note that this function is defined as inline function.

**sd\_event\_source\_ref()** may be used to increase by one the internal reference counter of the event source object specified as *source*.

**sd\_event\_source\_ref()** and **sd\_event\_source\_unref()** execute no operation if the passed event source object is **NULL**. **sd\_event\_source\_unrefp()** will first dereference its argument, which must not be **NULL**, and will execute no operation if *that* is **NULL**.

Note that event source objects stay alive and may be dispatched as long as they have a reference counter greater than zero. In order to drop a reference of an event source and make sure the associated event source handler function is not called anymore it is recommended to combine a call of **sd\_event\_source\_unref()** with a prior call to **sd\_event\_source\_set\_enabled()** with **SD\_EVENT\_OFF** or call **sd\_event\_source\_disable\_unref()**, see below.

**sd\_event\_source\_disable\_unref()** combines a call to **sd\_event\_source\_set\_enabled()** with **SD\_EVENT\_OFF** with **sd\_event\_source\_unref()**. This ensures that the source is disabled before the local reference to it is lost. The *source* parameter is allowed to be **NULL**.

**sd\_event\_source\_disable\_unrefp()** is similar to **sd\_event\_source\_unrefp()**, but in addition disables the source first. This call is useful in conjunction with GCC's and LLVM's **Clean-up Variable Attribute**\[1\]. Note that this function is defined as inline function.

## RETURN VALUE

**sd\_event\_source\_unref()** and **sd\_event\_source\_disable\_unref()** always return **NULL**. **sd\_event\_source\_ref()** always returns the event source object passed in.

## 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\_event\_source\_unref()**, **sd\_event\_source\_unrefp()**, and **sd\_event\_source\_ref()** were added in version 229.

**sd\_event\_source\_disable\_unref()** and **sd\_event\_source\_disable\_unrefp()** were added in version 243.

## SEE ALSO

[**sd-event**(3)](/sd-event/3.md), [**sd\_event\_add\_io**(3)](/sd_event_add_io/3.md), [**sd\_event\_add\_time**(3)](/sd_event_add_time/3.md), [**sd\_event\_add\_signal**(3)](/sd_event_add_signal/3.md), [**sd\_event\_add\_child**(3)](/sd_event_add_child/3.md), [**sd\_event\_add\_inotify**(3)](/sd_event_add_inotify/3.md), [**sd\_event\_add\_defer**(3)](/sd_event_add_defer/3.md), [**sd\_event\_source\_set\_enabled**(3)](/sd_event_source_set_enabled/3.md)

## NOTES

- 1\.

  Clean-up Variable Attribute

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