/*
 * Copyright © 2024 Nick Bowler
 *
 * Helpers for hosts using POSIX threading (pthreads) API.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * The pthread_in_use detection is based on Gnulib code written by Bruno
 * Haible, distributed with the following copyright and permission notice:
 *
 *      Copyright (C) 2005-2022 Free Software Foundation, Inc.
 *
 *      This file is free software: you can redistribute it and/or modify
 *      it under the terms of the GNU Lesser General Public License as
 *      published by the Free Software Foundation; either version 2.1 of
 *      the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <pthread.h>

extern int glthread_in_use();

#if !defined c11_threads_in_use
#  if HAVE_THREADS_H && USE_POSIX_THREADS_FROM_LIBC
#    define c11_threads_in_use 1
#  elif HAVE_THREADS_H && USE_POSIX_THREADS_WEAK
#    include <threads.h>
#    pragma weak thrd_exit
#    define c11_threads_in_use (thrd_exit != NULL)
#  else
#    define c11_threads_in_use 0
#  endif
#endif

#if PTHREAD_IN_USE_DETECTION_HARD
#  define pthread_in_use glthread_in_use()
#elif USE_POSIX_THREADS_WEAK
#  pragma weak pthread_mutexattr_gettype
#  define pthread_in_use (pthread_mutexattr_gettype || c11_threads_in_use)
#else
#  define pthread_in_use 1
#endif

#if USE_POSIX_THREADS_WEAK
#  pragma weak pthread_key_create
#  pragma weak pthread_getspecific
#  pragma weak pthread_setspecific
#  pragma weak pthread_once
#endif

static struct {
	union {
		pthread_key_t mt;
#if USE_POSIX_THREADS_WEAK
		void *st;
#endif
	} u;

#if USE_POSIX_THREADS_WEAK
	signed char valid;
#else
	bool valid;
#endif
} tls_key;
#define tls_key_valid (tls_key.valid != 0)

static void init_once_cb(void);

static void *tls_get(void)
{
#if USE_POSIX_THREADS_WEAK
	if (tls_key.valid < 0)
		return tls_key.u.st;
#endif
	return pthread_getspecific(tls_key.u.mt);
}

static int tls_set(void *p)
{
#if USE_POSIX_THREADS_WEAK
	if (tls_key.valid < 0)
		return (tls_key.u.st = p, 1);
#endif
	return !pthread_setspecific(tls_key.u.mt, p);
}

static void init_once_with_tls(void)
{
	tls_key.valid = !pthread_key_create(&tls_key.u.mt, free);
	init_once_cb();
}

static int init_once(void)
{
	if (pthread_in_use) {
		static pthread_once_t ctrl = PTHREAD_ONCE_INIT;
		return !pthread_once(&ctrl, init_once_with_tls);
	} else if (!tls_key_valid) {
		tls_key.valid = -1;
		init_once_cb();
	}

	return 1;
}