libgomp/config/linux/futex.h

   1 /* Copyright (C) 2010-2013 Free Software Foundation, Inc.
   2    Contributed by ARM Ltd.
   3
   4    This file is part of the GNU OpenMP Library (libgomp).
   5
   6    Libgomp 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, or (at your option)
   9    any later version.
  10
  11    Libgomp 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 /* Provide target-specific access to the futex system call.  */
  26
  27 /* The include file hierachy above us (wait.h) has pushed visibility
  28    hidden, this will be applied to prototypes with headers we include
  29    with the effect that we cannot link against an external function
  30    (syscall). The solution here is to push default visibility, include
  31    our required headers then reinstante the original visibility.  */
  32
  33 #pragma GCC visibility push(default)
  34
  35 #define _GNU_SOURCE
  36 #include <unistd.h>
  37 #include <sys/syscall.h>
  38
  39 #pragma GCC visibility pop
  40
  41 static inline void
  42 futex_wait (int *addr, int val)
  43 {
  44   long err = syscall (SYS_futex, addr, gomp_futex_wait, val, NULL);
  45   if (__builtin_expect (err == -ENOSYS, 0))
  46     {
  47       gomp_futex_wait &= ~FUTEX_PRIVATE_FLAG;
  48       gomp_futex_wake &= ~FUTEX_PRIVATE_FLAG;
  49       syscall (SYS_futex, addr, gomp_futex_wait, val, NULL);
  50     }
  51 }
  52
  53 static inline void
  54 futex_wake (int *addr, int count)
  55 {
  56   long err = syscall (SYS_futex, addr, gomp_futex_wake, count);
  57   if (__builtin_expect (err == -ENOSYS, 0))
  58     {
  59       gomp_futex_wait &= ~FUTEX_PRIVATE_FLAG;
  60       gomp_futex_wake &= ~FUTEX_PRIVATE_FLAG;
  61       syscall (SYS_futex, addr, gomp_futex_wake, count);
  62     }
  63 }
  64
  65 static inline void
  66 cpu_relax (void)
  67 {
  68   __asm volatile ("" : : : "memory");
  69 }