---
name: "rt_sem_wait"
section: "2"
platform: "linux"
package: "rtlinux"
version: "2.0rel-1"
release: "Debian 2.2 (Potato)"
platforms: ["linux"]
url: "https://new.carta.tech/rt_sem_wait"
---

# rt\_sem\_wait(2)

semaphore 'wait' operation (with blocking)

## NAME

rt\_sem\_wait - semaphore 'wait' operation (with blocking)

## SYNOPSIS

```
#define MODULE
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/version.h>
#include <linux/errno.h>
#include rt_ipc.h
```

**int rt\_sem\_wait(rt\_sem\_t \****sem***, RTIME** *timeout***);**

## DESCRIPTION

**rt\_sem\_wait** is the semaphore wait (sometimes known as 'take' or 'P') operation. Unlike with **rt\_sem\_trywait**, if the semaphore is not available, the calling task blocks until it is. *sem* points to the structure used in the call to **rt\_sem\_create**. An optional *timeout* can be specified.  If  *timeout* is RT\_WAIT\_FOREVER, the function does not time out.  If *timeout* is RT\_NO\_WAIT and the semaphore is not available, **rt\_sem\_wait** returns immediately.  If *timeout* is any other value, it represent a time at which the call to **rt\_sem\_wait** should time out.  If that time is reached, **rt\_sem\_wait** returns with -ETIME.

## RETURN VALUE

On success, 0 is returned.  On failure, a negative value is returned as described below.

## ERRORS

- **-ETIME**

  The timeout period expired.

- **-EINVAL**

  *sem* does not point to a valid rt\_sem\_t.

## AUTHOR

Jerry Epplin \<JerryEpplin@worldnet.att.net\>

## SEE ALSO

[**rt\_task\_ipc\_delete**(2)](/rt_task_ipc_delete/2.md), [**rt\_task\_ipc\_init**(2)](/rt_task_ipc_init/2.md), [**rt\_sem\_destroy**(2)](/rt_sem_destroy/2.md), [**rt\_sem\_init**(2)](/rt_sem_init/2.md), [**rt\_sem\_post**(2)](/rt_sem_post/2.md), [**rt\_sem\_trywait**(2)](/rt_sem_trywait/2.md)