OFOnce.m

/*
 * Copyright (c) 2008-2024 Jonathan Schleifer <js@nil.im>
 *
 * All rights reserved.
 *
 * This program is free software: you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License version 3.0 only,
 * as published by the Free Software Foundation.
 *
 * 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 Lesser General Public License
 * version 3.0 for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * version 3.0 along with this program. If not, see
 * <https://www.gnu.org/licenses/>.
 */
 
#include "config.h"
 
#include <stdbool.h>
 
#import "OFOnce.h"
#if defined(OF_HAVE_THREADS) && defined(OF_HAVE_ATOMIC_OPS)
# import "OFAtomic.h"
# import "OFPlainMutex.h"
#endif
 
#ifdef OF_AMIGAOS
# define Class IntuitionClass
# include <proto/exec.h>
# undef Class
#endif
 
void
OFOnce(OFOnceControl *control, void (*function)(void))
{
#if !defined(OF_HAVE_THREADS)
    if (*control == 0) {
        function();
        *control = 1;
    }
#elif defined(OF_HAVE_PTHREADS)
    pthread_once(control, function);
#elif defined(OF_HAVE_ATOMIC_OPS)
    /* Avoid atomic operations in case it's already done. */
    if (*control == 2)
        return;
 
    if (OFAtomicIntCompareAndSwap(control, 0, 1)) {
        OFAcquireMemoryBarrier();
 
        function();
        OFAtomicIntIncrease(control);
 
        OFReleaseMemoryBarrier();
    } else
        while (*control == 1)
            OFYieldThread();
#elif defined(OF_AMIGAOS)
    bool run = false;
 
    /* Avoid Forbid() in case it's already done. */
    if (*control == 2)
        return;
 
    Forbid();
 
    switch (*control) {
    case 0:
        *control = 1;
        run = true;
        break;
    case 1:
        while (*control == 1) {
            Permit();
            Forbid();
        }
    }
 
    Permit();
 
    if (run) {
        function();
        *control = 2;
    }
#else
# error No OFOnce available
#endif
}