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125 lines
3.5 KiB
C
125 lines
3.5 KiB
C
/* Copyright (C) 2012-2020 Free Software Foundation, Inc.
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Contributed by Richard Henderson <rth@redhat.com>.
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This file is part of the GNU Atomic Library (libatomic).
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Libatomic is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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#include "libatomic_i.h"
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/* If we support the builtin, just use it. */
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#if !DONE && defined(atomic_compare_exchange_n)
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bool
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SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval,
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int smodel, int fmodel UNUSED)
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{
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if (maybe_specialcase_relaxed(smodel))
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return atomic_compare_exchange_n (mptr, eptr, newval, false,
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__ATOMIC_RELAXED, __ATOMIC_RELAXED);
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else if (maybe_specialcase_acqrel(smodel))
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return atomic_compare_exchange_n (mptr, eptr, newval, false,
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__ATOMIC_ACQ_REL, __ATOMIC_RELAXED);
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else
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return atomic_compare_exchange_n (mptr, eptr, newval, false,
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__ATOMIC_SEQ_CST, __ATOMIC_RELAXED);
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}
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#define DONE 1
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#endif /* HAVE_ATOMIC_CAS */
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/* If this type is not larger than word-sized, fall back to a word-sized
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compare-and-swap loop, possibly assisted by the OS. */
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#if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w)
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bool
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SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval,
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int smodel, int fmodel)
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{
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UWORD mask, shift, weval, woldval, wnewval, t, *wptr;
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pre_barrier (smodel);
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if (N < WORDSIZE)
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{
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wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
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shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK);
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mask = SIZE(MASK) << shift;
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}
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else
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{
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wptr = (UWORD *)mptr;
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shift = 0;
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mask = -1;
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}
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weval = (UWORD)*eptr << shift;
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wnewval = (UWORD)newval << shift;
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woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
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do
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{
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if ((woldval & mask) != weval)
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goto failure;
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t = (woldval & ~mask) | wnewval;
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}
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while (!atomic_compare_exchange_w (wptr, &woldval, t, true,
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__ATOMIC_RELAXED, __ATOMIC_RELAXED));
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post_barrier (smodel);
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return true;
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failure:
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*eptr = woldval >> shift;
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post_barrier (fmodel);
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return false;
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}
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#define DONE 1
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#endif /* HAVE_ATOMIC_CAS && N <= WORDSIZE */
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/* Otherwise, fall back to some sort of protection mechanism. */
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#if !DONE
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bool
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SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval,
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int smodel, int fmodel UNUSED)
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{
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UTYPE oldval;
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UWORD magic;
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bool ret;
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pre_seq_barrier (smodel);
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magic = protect_start (mptr);
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oldval = *mptr;
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ret = (oldval == *eptr);
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if (ret)
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*mptr = newval;
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else
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*eptr = oldval;
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protect_end (mptr, magic);
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post_seq_barrier (smodel);
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return ret;
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}
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#endif
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EXPORT_ALIAS (SIZE(compare_exchange));
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