1 /* Copyright (C) 2005-2023 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
35 typedef 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
46 typedef 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
57 static 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
66 static 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
72 static inline void gomp_barrier_destroy (gomp_barrier_t *bar)
73 {
74 }
75
76 extern void gomp_barrier_wait (gomp_barrier_t *);
77 extern void gomp_barrier_wait_last (gomp_barrier_t *);
78 extern void gomp_barrier_wait_end (gomp_barrier_t *, gomp_barrier_state_t);
79 extern void gomp_team_barrier_wait (gomp_barrier_t *);
80 extern void gomp_team_barrier_wait_final (gomp_barrier_t *);
81 extern void gomp_team_barrier_wait_end (gomp_barrier_t *,
82 gomp_barrier_state_t);
83 extern bool gomp_team_barrier_wait_cancel (gomp_barrier_t *);
84 extern bool gomp_team_barrier_wait_cancel_end (gomp_barrier_t *,
85 gomp_barrier_state_t);
86 extern void gomp_team_barrier_wake (gomp_barrier_t *, int);
87 struct gomp_team;
88 extern void gomp_team_barrier_cancel (struct gomp_team *);
89
90 static inline gomp_barrier_state_t
91 gomp_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
105 static inline gomp_barrier_state_t
106 gomp_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. */
114 static inline gomp_barrier_state_t
115 gomp_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
125 static inline bool
126 gomp_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
134 static inline void
135 gomp_team_barrier_set_task_pending (gomp_barrier_t *bar)
136 {
137 bar->generation |= BAR_TASK_PENDING;
138 }
139
140 static inline void
141 gomp_team_barrier_clear_task_pending (gomp_barrier_t *bar)
142 {
143 bar->generation &= ~BAR_TASK_PENDING;
144 }
145
146 static inline void
147 gomp_team_barrier_set_waiting_for_tasks (gomp_barrier_t *bar)
148 {
149 bar->generation |= BAR_WAITING_FOR_TASK;
150 }
151
152 static inline bool
153 gomp_team_barrier_waiting_for_tasks (gomp_barrier_t *bar)
154 {
155 return (bar->generation & BAR_WAITING_FOR_TASK) != 0;
156 }
157
158 static inline bool
159 gomp_team_barrier_cancelled (gomp_barrier_t *bar)
160 {
161 return __builtin_expect ((bar->generation & BAR_CANCELLED) != 0, 0);
162 }
163
164 static inline void
165 gomp_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 */