---
name: "sd_event_source_set_destroy_callback"
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_set_destroy_callback"
---

# sd\_event\_source\_set\_destroy\_callback(3)

Define the callback function for resource cleanup

## NAME

sd\_event\_source\_set\_destroy\_callback, sd\_event\_source\_get\_destroy\_callback, sd\_event\_destroy\_t - Define the callback function for resource cleanup

## SYNOPSIS

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

**typedef int (\*sd\_event\_destroy\_t)(void \****userdata***);**

**int sd\_event\_source\_set\_destroy\_callback(sd\_event\_source \****source***, sd\_event\_destroy\_t** *callback***);**

**int sd\_event\_source\_get\_destroy\_callback(sd\_event\_source \****source***, sd\_event\_destroy\_t \****callback***);**

## DESCRIPTION

**sd\_event\_source\_set\_destroy\_callback()** sets *callback* as the callback function to be called right before the event source object *source* is deallocated. The *userdata* pointer from the event source object will be passed as the *userdata* parameter. This pointer can be set by an argument to the constructor functions, see [**sd\_event\_add\_io**(3)](/sd_event_add_io/3.md), or directly, see [**sd\_event\_source\_set\_userdata**(3)](/sd_event_source_set_userdata/3.md). This callback function is called even if *userdata* is **NULL**. Note that this callback is invoked at a time where the event source object itself is already invalidated, and executing operations or taking new references to the event source object is not permissible.

**sd\_event\_source\_get\_destroy\_callback()** returns the current callback for *source* in the *callback* parameter.

## RETURN VALUE

On success, **sd\_event\_source\_set\_destroy\_callback()** returns 0 or a positive integer. On failure, it returns a negative errno-style error code.

**sd\_event\_source\_get\_destroy\_callback()** returns positive if the destroy callback function is set, 0 if not. On failure, returns a negative errno-style error code.

### Errors

Returned errors may indicate the following problems:

**-EINVAL**

The *source* parameter is **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\_event\_destroy\_t()**, **sd\_event\_source\_set\_destroy\_callback()**, and **sd\_event\_source\_get\_destroy\_callback()** were added in version 239.

## SEE ALSO

[**systemd**(1)](/systemd/1.md), [**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\_userdata**(3)](/sd_event_source_set_userdata/3.md)