uclibc-ng/libpthread/nptl/sysdeps/unix/sysv/linux/kvx/pthread_once.c

/*
 * This file is subject to the terms and conditions of the LGPL V2.1
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (C) 2019 Kalray Inc.
 */

#include "pthreadP.h"
#include <lowlevellock.h>

unsigned long int __fork_generation attribute_hidden;

static void
clear_once_control (void *arg)
{
	pthread_once_t *once_control = (pthread_once_t *) arg;

	*once_control = 0;
	lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
}


int
__pthread_once (once_control, init_routine)
	pthread_once_t *once_control;
	void (*init_routine) (void);
{
	while (1)
	{
		int oldval, val, newval;

		val = *once_control;
		do
		{
			/* Check if the initialized has already been done. */
			if ((val & 2) != 0)
				return 0;

			oldval = val;
			newval = (oldval & 3) | __fork_generation | 1;
			val = atomic_compare_and_exchange_val_acq (once_control, newval, oldval);
		} while (__builtin_expect (val != oldval, 0));

		/* Check if another thread already runs the initializer. */
		if ((oldval & 1) != 0)
		{
		/* Check whether the initializer execution was interrupted
		 * by a fork. */
			if (((oldval ^ newval) & -4) == 0)
			{
				/* Same generation, some other thread was faster. Wait. */
				lll_futex_wait (once_control, newval, LLL_PRIVATE);
				continue;
			}
		}
		/* This thread is the first here.  Do the initialization.
		 * Register a cleanup handler so that in case the thread gets
		 * interrupted the initialization can be restarted. */
		pthread_cleanup_push (clear_once_control, once_control);

		init_routine ();

		pthread_cleanup_pop (0);

		/* Add one to *once_control. */
		atomic_increment (once_control);

		/* Wake up all other threads. */
		lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
		break;
	}

	return 0;
}
weak_alias (__pthread_once, pthread_once)
strong_alias (__pthread_once, __pthread_once_internal)