1  /* Copyright (C) 2008-2023 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 */