pthread_once(3)

pthread_once3

Once-only initialization

Usage

#include <pthread.h>

pthread_once_t once_control = PTHREAD_ONCE_INIT;

int pthread_once(pthread_once_t *once_control, typeof(void (void)) *init_routine;

Overview

The purpose of pthread_once() is to ensure that a piece of initialization code is executed at most once. The once_control argument points to a static or extern variable statically initialized to PTHREAD_ONCE_INIT.

The first time pthread_once() is called with a given once_control argument, it calls init_routine with no argument and changes the value of the once_control variable to record that initialization has been performed. Subsequent calls to pthread_once() with the same once_control argument do nothing.

Return value

pthread_once() always returns 0.

Errors

None.

Releases

12 releases since Debian 3.1 (Sarge); the text changed 4 times.

  1. 3.1
  2. 4.0–5.0
  3. 6.0–12
  4. 13
  5. Arch

From man-pages 6.19-1 in Arch Linux 2026-11-01. Parsed by carta from the page's man source.