1/* Copyright (C) 2008-2015 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   A ptrlock has four states:
31   0/NULL Initial
32   1      Owned by me, I get to write a pointer to ptrlock.
33   2      Some thread is waiting on the ptrlock.
34   >2     Ptrlock contains a valid pointer.
35   It is not valid to gain the ptrlock and then write a NULL to it.  */
36
37#ifndef GOMP_PTRLOCK_H
38#define GOMP_PTRLOCK_H 1
39
40typedef void *gomp_ptrlock_t;
41
42static inline void gomp_ptrlock_init (gomp_ptrlock_t *ptrlock, void *ptr)
43{
44  *ptrlock = ptr;
45}
46
47extern void *gomp_ptrlock_get_slow (gomp_ptrlock_t *ptrlock);
48static inline void *gomp_ptrlock_get (gomp_ptrlock_t *ptrlock)
49{
50  uintptr_t oldval;
51
52  uintptr_t v = (uintptr_t) __atomic_load_n (ptrlock, MEMMODEL_ACQUIRE);
53  if (v > 2)
54    return (void *) v;
55
56  oldval = 0;
57  if (__atomic_compare_exchange_n (ptrlock, &oldval, 1, false,
58				   MEMMODEL_ACQUIRE, MEMMODEL_ACQUIRE))
59    return NULL;
60
61  return gomp_ptrlock_get_slow (ptrlock);
62}
63
64extern void gomp_ptrlock_set_slow (gomp_ptrlock_t *ptrlock);
65static inline void gomp_ptrlock_set (gomp_ptrlock_t *ptrlock, void *ptr)
66{
67  void *wait = __atomic_exchange_n (ptrlock, ptr, MEMMODEL_RELEASE);
68  if ((uintptr_t) wait != 1)
69    gomp_ptrlock_set_slow (ptrlock);
70}
71
72static inline void gomp_ptrlock_destroy (gomp_ptrlock_t *ptrlock)
73{
74}
75
76#endif /* GOMP_PTRLOCK_H */
77