libgomp/plugin/mutex.c

/* Mutex implementation for libgomp plugins.

   Copyright (C) 2025-2026 Free Software Foundation, Inc.

   Contributed by BayLibre

   This file is part of the GNU Offloading and Multi Processing Library
   (libgomp).

   Libgomp 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, or (at your option)
   any later version.

   Libgomp 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.

   Under Section 7 of GPL version 3, you are granted additional
   permissions described in the GCC Runtime Library Exception, version
   3.1, as published by the Free Software Foundation.

   You should have received a copy of the GNU General Public License and
   a copy of the GCC Runtime Library Exception along with this program;
   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
   <http://www.gnu.org/licenses/>.  */

/* This is a minimal implementation of the gomp_mutex_t spinlocks, but
   without all the dependencies used by the config/linux/mutex implementation.

   At the time of writing, this is only used by simple_alloc which has
   short-lived locks and should be fine with these.  The actual locks are in
   a header file, so only the fallback "slow" functions are needed here.  */

#include "config.h"
#include <unistd.h>
#include "libgomp.h"

#ifndef HAVE_SYNC_BUILTINS
#error "HAVE_SYNC_BUILTINS is required to build this"
#endif

void
gomp_mutex_lock_slow (gomp_mutex_t *mutex, int oldval)
{
  while (oldval == 1)
    {
      usleep (1);
      oldval = __atomic_exchange_n (mutex, 1, __ATOMIC_ACQUIRE);
    }
}

void
gomp_mutex_unlock_slow (gomp_mutex_t *mutex)
{
  GOMP_PLUGIN_fatal ("gomp_mutex_unlock_slow should be unreachable");
}