libatomic/tas_n.c

   1 /* Copyright (C) 2012-2017 Free Software Foundation, Inc.
   2    Contributed by Richard Henderson <rth@redhat.com>.
   3
   4    This file is part of the GNU Atomic Library (libatomic).
   5
   6    Libatomic is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
  12    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  13    FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  14    more details.
  15
  16    Under Section 7 of GPL version 3, you are granted additional
  17    permissions described in the GCC Runtime Library Exception, version
  18    3.1, as published by the Free Software Foundation.
  19
  20    You should have received a copy of the GNU General Public License and
  21    a copy of the GCC Runtime Library Exception along with this program;
  22    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23    <http://www.gnu.org/licenses/>.  */
  24
  25 #include "libatomic_i.h"
  26
  27
  28 /* If we support the builtin, just use it.  */
  29 #if !DONE && SIZE(HAVE_ATOMIC_TAS)
  30 bool
  31 SIZE(libat_test_and_set) (UTYPE *mptr, int smodel)
  32 {
  33   if (maybe_specialcase_relaxed(smodel))
  34     return __atomic_test_and_set (mptr, __ATOMIC_RELAXED);
  35   else if (maybe_specialcase_acqrel(smodel))
  36     return __atomic_test_and_set (mptr, __ATOMIC_ACQ_REL);
  37   else
  38     return __atomic_test_and_set (mptr, __ATOMIC_SEQ_CST);
  39 }
  40
  41 #define DONE 1
  42 #endif /* HAVE_ATOMIC_TAS */
  43
  44
  45 /* If this type is smaller than word-sized, fall back to a word-sized
  46    compare-and-swap loop.  */
  47 #if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w)
  48 bool
  49 SIZE(libat_test_and_set) (UTYPE *mptr, int smodel)
  50 {
  51   UWORD wval, woldval, shift, *wptr, t;
  52
  53   pre_barrier (smodel);
  54
  55   if (N < WORDSIZE)
  56     {
  57       wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
  58       shift = SIZE(INVERT_MASK);
  59     }
  60   else
  61     {
  62       wptr = (UWORD *)mptr;
  63       shift = 0;
  64     }
  65
  66   wval = (UWORD)__GCC_ATOMIC_TEST_AND_SET_TRUEVAL << shift;
  67   woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
  68   do
  69     {
  70       t = woldval | wval;
  71     }
  72   while (!atomic_compare_exchange_w (wptr, &woldval, t, true,
  73                                      __ATOMIC_RELAXED, __ATOMIC_RELAXED));
  74
  75   post_barrier (smodel);
  76   return woldval != 0;
  77 }
  78
  79 #define DONE 1
  80 #endif /* HAVE_ATOMIC_CAS && N < WORDSIZE */
  81
  82
  83 /* Otherwise, fall back to some sort of protection mechanism.  */
  84 #if !DONE && N == 1
  85 bool
  86 SIZE(libat_test_and_set) (UTYPE *mptr, int smodel)
  87 {
  88   UTYPE oldval;
  89   UWORD magic;
  90
  91   pre_seq_barrier (smodel);
  92   magic = protect_start (mptr);
  93
  94   oldval = *mptr;
  95   *mptr = __GCC_ATOMIC_TEST_AND_SET_TRUEVAL;
  96
  97   protect_end (mptr, magic);
  98   post_seq_barrier (smodel);
  99
 100   return oldval != 0;
 101 }
 102
 103 #define DONE 1
 104 #endif /* N == 1 */
 105
 106
 107 #if !DONE
 108 bool
 109 SIZE(libat_test_and_set) (UTYPE *mptr, int smodel UNUSED)
 110 {
 111   return libat_test_and_set_1 ((U_1 *)mptr, smodel);
 112 }
 113 #endif
 114
 115 EXPORT_ALIAS (SIZE(test_and_set));