libgomp/config/linux/ptrlock.c

   1 /* Copyright (C) 2008-2018 Free Software Foundation, Inc.
   2    Contributed by Jakub Jelinek <jakub@redhat.com>.
   3
   4    This file is part of the GNU Offloading and Multi Processing Library
   5    (libgomp).
   6
   7    Libgomp is free software; you can redistribute it and/or modify it
   8    under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3, or (at your option)
  10    any later version.
  11
  12    Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
  13    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  14    FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  15    more details.
  16
  17    Under Section 7 of GPL version 3, you are granted additional
  18    permissions described in the GCC Runtime Library Exception, version
  19    3.1, as published by the Free Software Foundation.
  20
  21    You should have received a copy of the GNU General Public License and
  22    a copy of the GCC Runtime Library Exception along with this program;
  23    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  24    <http://www.gnu.org/licenses/>.  */
  25
  26 /* This is a Linux specific implementation of a mutex synchronization
  27    mechanism for libgomp.  This type is private to the library.  This
  28    implementation uses atomic instructions and the futex syscall.  */
  29
  30 #include <endian.h>
  31 #include <limits.h>
  32 #include "wait.h"
  33
  34 void *
  35 gomp_ptrlock_get_slow (gomp_ptrlock_t *ptrlock)
  36 {
  37   int *intptr;
  38   uintptr_t oldval = 1;
  39
  40   __atomic_compare_exchange_n (ptrlock, &oldval, 2, false,
  41                                MEMMODEL_RELAXED, MEMMODEL_RELAXED);
  42
  43   /* futex works on ints, not pointers.
  44      But a valid work share pointer will be at least
  45      8 byte aligned, so it is safe to assume the low
  46      32-bits of the pointer won't contain values 1 or 2.  */
  47   __asm volatile ("" : "=r" (intptr) : "0" (ptrlock));
  48 #if __BYTE_ORDER == __BIG_ENDIAN
  49   if (sizeof (*ptrlock) > sizeof (int))
  50     intptr += (sizeof (*ptrlock) / sizeof (int)) - 1;
  51 #endif
  52   do
  53     do_wait (intptr, 2);
  54   while (__atomic_load_n (intptr, MEMMODEL_RELAXED) == 2);
  55   __asm volatile ("" : : : "memory");
  56   return (void *) __atomic_load_n (ptrlock, MEMMODEL_ACQUIRE);
  57 }
  58
  59 void
  60 gomp_ptrlock_set_slow (gomp_ptrlock_t *ptrlock)
  61 {
  62   int *intptr;
  63
  64   __asm volatile ("" : "=r" (intptr) : "0" (ptrlock));
  65 #if __BYTE_ORDER == __BIG_ENDIAN
  66   if (sizeof (*ptrlock) > sizeof (int))
  67     intptr += (sizeof (*ptrlock) / sizeof (int)) - 1;
  68 #endif
  69   futex_wake (intptr, INT_MAX);
  70 }