Content-type: text/html Man page of sem_wait

sem_wait

Section: C Library Functions (3)
Index Return to Main Contents
 

NAME

sem_wait, sem_trywait - Perform (or conditionally perform) a semaphore lock (P1003.1b)  

SYNOPSIS

#include <semaphore.h>

int sem_wait (
sem_t *sem);

int sem_trywait (
sem_t *sem);  

PARAMETERS

sem
Pointer to the semaphore to be locked.
 

DESCRIPTION

The sem_wait function locks the semaphore referenced by sem by performing a semaphore lock operation on it. If the semaphore value is zero, the sem_wait function blocks until it either locks the semaphore or is interrupted by a signal.

The sem_trywait function locks a semaphore only if the semaphore is currently not locked. If the semaphore value is zero, the sem_trywait function returns without locking the semaphore.

These functions help ensure that the resource associated with the semaphore cannot be accessed by other processes. The semaphore remains locked until the process unlocks it with a call to the sem_post function.

Use the sem_wait function instead of the sem_trywait function if the process should wait for access to the semaphore.  

RETURN VALUES

If the sem_wait or sem_trywait function returns successfully, a value of 0 is returned and the function executes the semaphore lock operation.

On an unsuccessful call, a value of -1 is returned and errno is set to indicate that an error occurred. The state of the semaphore remains unchanged.  

ERRORS

The sem_wait and sem_trywait functions fail under the following conditions:

[EAGAIN]
The semaphore was already locked, so it can not be immediately locked by the sem_trywait operation (sem_trywait only).
[EINTR]
A signal interrupted this function.
[EINVAL]
The sem argument does not refer to a valid semaphore.
 

RELATED INFORMATION

Functions: sem_post(3) delim off


 

Index

NAME
SYNOPSIS
PARAMETERS
DESCRIPTION
RETURN VALUES
ERRORS
RELATED INFORMATION

This document was created by man2html, using the manual pages.
Time: 02:42:18 GMT, October 02, 2010