---
name: "sd_event_loop"
section: "3"
platform: "linux"
package: "libsystemd-dev"
version: "257.13-1~deb13u1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/sd_event_run"
---

# sd\_event\_loop(3)

Run an event loop

Part of [sd\_event\_run(3)](/sd_event_run/3.md).

## NAME

sd\_event\_run, sd\_event\_loop - Run an event loop

## SYNOPSIS

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

**int sd\_event\_run(sd\_event \****event***, uint64\_t** *usec***);**

**int sd\_event\_loop(sd\_event \****event***);**

## DESCRIPTION

**sd\_event\_run()** may be used to run a single iteration of the event loop specified in the *event* parameter. The function waits until an event to process is available, and dispatches the registered handler for it. The *usec* parameter specifies the maximum time (in microseconds) to wait for an event. Use **(uint64\_t) -1** to specify an infinite timeout.

**sd\_event\_loop()** invokes **sd\_event\_run()** in a loop, thus implementing the actual event loop. The call returns as soon as exiting was requested using [**sd\_event\_exit**(3)](/sd_event_exit/3.md).

The event loop object *event* is created with [**sd\_event\_new**(3)](/sd_event_new/3.md). Events sources to wait for and their handlers may be registered with [**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\_defer**(3)](/sd_event_add_defer/3.md), [**sd\_event\_add\_post**(3)](/sd_event_add_post/3.md) and [**sd\_event\_add\_exit**(3)](/sd_event_add_exit/3.md).

For low-level control of event loop execution, use [**sd\_event\_prepare**(3)](/sd_event_prepare/3.md), [**sd\_event\_wait**(3)](/sd_event_wait/3.md) and [**sd\_event\_dispatch**(3)](/sd_event_dispatch/3.md) which are wrapped by **sd\_event\_run()**. Along with [**sd\_event\_get\_fd**(3)](/sd_event_get_fd/3.md), these functions allow integration of an [**sd-event**(3)](/sd-event/3.md) event loop into foreign event loop implementations.

## RETURN VALUE

On failure, these functions return a negative errno-style error code. **sd\_event\_run()** returns a positive, non-zero integer if an event source was dispatched, and zero when the specified timeout hit before an event source has seen any event, and hence no event source was dispatched. **sd\_event\_loop()** returns the exit code specified when invoking **sd\_event\_exit()**.

### Errors

Returned errors may indicate the following problems:

**-EINVAL**

The *event* parameter is invalid or **NULL**.

**-EBUSY**

The event loop object is not in the right state (see [**sd\_event\_prepare**(3)](/sd_event_prepare/3.md) for an explanation of possible states).

**-ESTALE**

The event loop is already terminated.

**-ECHILD**

The event loop has been created in a different process, library or module instance.

Other errors are possible, too.

## 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.

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\_run()** and **sd\_event\_loop()** were added in version 220.

## SEE ALSO

[**systemd**(1)](/systemd/1.md), [**sd-event**(3)](/sd-event/3.md), [**sd\_event\_new**(3)](/sd_event_new/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\_exit**(3)](/sd_event_exit/3.md), [**sd\_event\_get\_fd**(3)](/sd_event_get_fd/3.md), [**sd\_event\_wait**(3)](/sd_event_wait/3.md), **GLib Main Event Loop**\[1\]

## NOTES

- 1\.

  GLib Main Event Loop

  https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html