libgomp/config/linux/wait.h

   1 /* Copyright (C) 2008-2019 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 #ifndef GOMP_WAIT_H
  31 #define GOMP_WAIT_H 1
  32
  33 #include "libgomp.h"
  34 #include <errno.h>
  35
  36 #define FUTEX_WAIT      0
  37 #define FUTEX_WAKE      1
  38 #define FUTEX_PRIVATE_FLAG      128
  39
  40 #ifdef HAVE_ATTRIBUTE_VISIBILITY
  41 # pragma GCC visibility push(hidden)
  42 #endif
  43
  44 extern int gomp_futex_wait, gomp_futex_wake;
  45
  46 #include <futex.h>
  47
  48 static inline int do_spin (int *addr, int val)
  49 {
  50   unsigned long long i, count = gomp_spin_count_var;
  51
  52   if (__builtin_expect (__atomic_load_n (&gomp_managed_threads,
  53                                          MEMMODEL_RELAXED)
  54                         > gomp_available_cpus, 0))
  55     count = gomp_throttled_spin_count_var;
  56   for (i = 0; i < count; i++)
  57     if (__builtin_expect (__atomic_load_n (addr, MEMMODEL_RELAXED) != val, 0))
  58       return 0;
  59     else
  60       cpu_relax ();
  61   return 1;
  62 }
  63
  64 static inline void do_wait (int *addr, int val)
  65 {
  66   if (do_spin (addr, val))
  67     futex_wait (addr, val);
  68 }
  69
  70 #ifdef HAVE_ATTRIBUTE_VISIBILITY
  71 # pragma GCC visibility pop
  72 #endif
  73
  74 #endif /* GOMP_WAIT_H */