125 lines
3.5 KiB
C
125 lines
3.5 KiB
C
/* Copyright (C) 2012-2020 Free Software Foundation, Inc.
|
|
Contributed by Richard Henderson <rth@redhat.com>.
|
|
|
|
This file is part of the GNU Atomic Library (libatomic).
|
|
|
|
Libatomic 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.
|
|
|
|
Libatomic 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/>. */
|
|
|
|
#include "libatomic_i.h"
|
|
|
|
|
|
/* If we support the builtin, just use it. */
|
|
#if !DONE && defined(atomic_compare_exchange_n)
|
|
bool
|
|
SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval,
|
|
int smodel, int fmodel UNUSED)
|
|
{
|
|
if (maybe_specialcase_relaxed(smodel))
|
|
return atomic_compare_exchange_n (mptr, eptr, newval, false,
|
|
__ATOMIC_RELAXED, __ATOMIC_RELAXED);
|
|
else if (maybe_specialcase_acqrel(smodel))
|
|
return atomic_compare_exchange_n (mptr, eptr, newval, false,
|
|
__ATOMIC_ACQ_REL, __ATOMIC_RELAXED);
|
|
else
|
|
return atomic_compare_exchange_n (mptr, eptr, newval, false,
|
|
__ATOMIC_SEQ_CST, __ATOMIC_RELAXED);
|
|
}
|
|
|
|
#define DONE 1
|
|
#endif /* HAVE_ATOMIC_CAS */
|
|
|
|
|
|
/* If this type is not larger than word-sized, fall back to a word-sized
|
|
compare-and-swap loop, possibly assisted by the OS. */
|
|
#if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w)
|
|
bool
|
|
SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval,
|
|
int smodel, int fmodel)
|
|
{
|
|
UWORD mask, shift, weval, woldval, wnewval, t, *wptr;
|
|
|
|
pre_barrier (smodel);
|
|
|
|
if (N < WORDSIZE)
|
|
{
|
|
wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
|
|
shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK);
|
|
mask = SIZE(MASK) << shift;
|
|
}
|
|
else
|
|
{
|
|
wptr = (UWORD *)mptr;
|
|
shift = 0;
|
|
mask = -1;
|
|
}
|
|
|
|
weval = (UWORD)*eptr << shift;
|
|
wnewval = (UWORD)newval << shift;
|
|
woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
|
|
do
|
|
{
|
|
if ((woldval & mask) != weval)
|
|
goto failure;
|
|
t = (woldval & ~mask) | wnewval;
|
|
}
|
|
while (!atomic_compare_exchange_w (wptr, &woldval, t, true,
|
|
__ATOMIC_RELAXED, __ATOMIC_RELAXED));
|
|
post_barrier (smodel);
|
|
return true;
|
|
|
|
failure:
|
|
*eptr = woldval >> shift;
|
|
post_barrier (fmodel);
|
|
return false;
|
|
}
|
|
|
|
#define DONE 1
|
|
#endif /* HAVE_ATOMIC_CAS && N <= WORDSIZE */
|
|
|
|
|
|
/* Otherwise, fall back to some sort of protection mechanism. */
|
|
#if !DONE
|
|
bool
|
|
SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval,
|
|
int smodel, int fmodel UNUSED)
|
|
{
|
|
UTYPE oldval;
|
|
UWORD magic;
|
|
bool ret;
|
|
|
|
pre_seq_barrier (smodel);
|
|
magic = protect_start (mptr);
|
|
|
|
oldval = *mptr;
|
|
ret = (oldval == *eptr);
|
|
if (ret)
|
|
*mptr = newval;
|
|
else
|
|
*eptr = oldval;
|
|
|
|
protect_end (mptr, magic);
|
|
post_seq_barrier (smodel);
|
|
|
|
return ret;
|
|
}
|
|
#endif
|
|
|
|
EXPORT_ALIAS (SIZE(compare_exchange));
|