1/* Copyright (C) 2005-2022 Free Software Foundation, Inc.
2   Contributed by Sebastian Huber <sebastian.huber@embedded-brains.de>.
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/* This is the RTEMS implementation of a barrier synchronization
26   mechanism for libgomp.  It is identical to the Linux implementation, except
27   that the futex API is slightly different.  This type is private to the
28   library.  */
29
30#ifndef GOMP_BARRIER_H
31#define GOMP_BARRIER_H 1
32
33#include <sys/lock.h>
34
35typedef struct
36{
37  /* Make sure total/generation is in a mostly read cacheline, while
38     awaited in a separate cacheline.  */
39  unsigned total __attribute__((aligned (64)));
40  unsigned generation;
41  struct _Futex_Control futex;
42  unsigned awaited __attribute__((aligned (64)));
43  unsigned awaited_final;
44} gomp_barrier_t;
45
46typedef unsigned int gomp_barrier_state_t;
47
48/* The generation field contains a counter in the high bits, with a few
49   low bits dedicated to flags.  Note that TASK_PENDING and WAS_LAST can
50   share space because WAS_LAST is never stored back to generation.  */
51#define BAR_TASK_PENDING	1
52#define BAR_WAS_LAST		1
53#define BAR_WAITING_FOR_TASK	2
54#define BAR_CANCELLED		4
55#define BAR_INCR		8
56
57static inline void gomp_barrier_init (gomp_barrier_t *bar, unsigned count)
58{
59  bar->total = count;
60  bar->awaited = count;
61  bar->awaited_final = count;
62  bar->generation = 0;
63  _Futex_Initialize (&bar->futex);
64}
65
66static inline void gomp_barrier_reinit (gomp_barrier_t *bar, unsigned count)
67{
68  __atomic_add_fetch (&bar->awaited, count - bar->total, MEMMODEL_ACQ_REL);
69  bar->total = count;
70}
71
72static inline void gomp_barrier_destroy (gomp_barrier_t *bar)
73{
74}
75
76extern void gomp_barrier_wait (gomp_barrier_t *);
77extern void gomp_barrier_wait_last (gomp_barrier_t *);
78extern void gomp_barrier_wait_end (gomp_barrier_t *, gomp_barrier_state_t);
79extern void gomp_team_barrier_wait (gomp_barrier_t *);
80extern void gomp_team_barrier_wait_final (gomp_barrier_t *);
81extern void gomp_team_barrier_wait_end (gomp_barrier_t *,
82					gomp_barrier_state_t);
83extern bool gomp_team_barrier_wait_cancel (gomp_barrier_t *);
84extern bool gomp_team_barrier_wait_cancel_end (gomp_barrier_t *,
85					       gomp_barrier_state_t);
86extern void gomp_team_barrier_wake (gomp_barrier_t *, int);
87struct gomp_team;
88extern void gomp_team_barrier_cancel (struct gomp_team *);
89
90static inline gomp_barrier_state_t
91gomp_barrier_wait_start (gomp_barrier_t *bar)
92{
93  unsigned int ret = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
94  ret &= -BAR_INCR | BAR_CANCELLED;
95  /* A memory barrier is needed before exiting from the various forms
96     of gomp_barrier_wait, to satisfy OpenMP API version 3.1 section
97     2.8.6 flush Construct, which says there is an implicit flush during
98     a barrier region.  This is a convenient place to add the barrier,
99     so we use MEMMODEL_ACQ_REL here rather than MEMMODEL_ACQUIRE.  */
100  if (__atomic_add_fetch (&bar->awaited, -1, MEMMODEL_ACQ_REL) == 0)
101    ret |= BAR_WAS_LAST;
102  return ret;
103}
104
105static inline gomp_barrier_state_t
106gomp_barrier_wait_cancel_start (gomp_barrier_t *bar)
107{
108  return gomp_barrier_wait_start (bar);
109}
110
111/* This is like gomp_barrier_wait_start, except it decrements
112   bar->awaited_final rather than bar->awaited and should be used
113   for the gomp_team_end barrier only.  */
114static inline gomp_barrier_state_t
115gomp_barrier_wait_final_start (gomp_barrier_t *bar)
116{
117  unsigned int ret = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
118  ret &= -BAR_INCR | BAR_CANCELLED;
119  /* See above gomp_barrier_wait_start comment.  */
120  if (__atomic_add_fetch (&bar->awaited_final, -1, MEMMODEL_ACQ_REL) == 0)
121    ret |= BAR_WAS_LAST;
122  return ret;
123}
124
125static inline bool
126gomp_barrier_last_thread (gomp_barrier_state_t state)
127{
128  return state & BAR_WAS_LAST;
129}
130
131/* All the inlines below must be called with team->task_lock
132   held.  */
133
134static inline void
135gomp_team_barrier_set_task_pending (gomp_barrier_t *bar)
136{
137  bar->generation |= BAR_TASK_PENDING;
138}
139
140static inline void
141gomp_team_barrier_clear_task_pending (gomp_barrier_t *bar)
142{
143  bar->generation &= ~BAR_TASK_PENDING;
144}
145
146static inline void
147gomp_team_barrier_set_waiting_for_tasks (gomp_barrier_t *bar)
148{
149  bar->generation |= BAR_WAITING_FOR_TASK;
150}
151
152static inline bool
153gomp_team_barrier_waiting_for_tasks (gomp_barrier_t *bar)
154{
155  return (bar->generation & BAR_WAITING_FOR_TASK) != 0;
156}
157
158static inline bool
159gomp_team_barrier_cancelled (gomp_barrier_t *bar)
160{
161  return __builtin_expect ((bar->generation & BAR_CANCELLED) != 0, 0);
162}
163
164static inline void
165gomp_team_barrier_done (gomp_barrier_t *bar, gomp_barrier_state_t state)
166{
167  bar->generation = (state & -BAR_INCR) + BAR_INCR;
168}
169
170#endif /* GOMP_BARRIER_H */
171