1 /* Copyright (C) 2005-2020 Free Software Foundation, Inc.
2 Contributed by Richard Henderson <rth@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 barrier 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_BARRIER_H
31 #define GOMP_BARRIER_H 1
32
33 #include "mutex.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 unsigned awaited __attribute__((aligned (64)));
42 unsigned awaited_final;
43 } gomp_barrier_t;
44
45 typedef unsigned int gomp_barrier_state_t;
46
47 /* The generation field contains a counter in the high bits, with a few
48 low bits dedicated to flags. Note that TASK_PENDING and WAS_LAST can
49 share space because WAS_LAST is never stored back to generation. */
50 #define BAR_TASK_PENDING 1
51 #define BAR_WAS_LAST 1
52 #define BAR_WAITING_FOR_TASK 2
53 #define BAR_CANCELLED 4
54 #define BAR_INCR 8
55
gomp_barrier_init(gomp_barrier_t * bar,unsigned count)56 static inline void gomp_barrier_init (gomp_barrier_t *bar, unsigned count)
57 {
58 bar->total = count;
59 bar->awaited = count;
60 bar->awaited_final = count;
61 bar->generation = 0;
62 }
63
gomp_barrier_reinit(gomp_barrier_t * bar,unsigned count)64 static inline void gomp_barrier_reinit (gomp_barrier_t *bar, unsigned count)
65 {
66 __atomic_add_fetch (&bar->awaited, count - bar->total, MEMMODEL_ACQ_REL);
67 bar->total = count;
68 }
69
gomp_barrier_destroy(gomp_barrier_t * bar)70 static inline void gomp_barrier_destroy (gomp_barrier_t *bar)
71 {
72 }
73
74 extern void gomp_barrier_wait (gomp_barrier_t *);
75 extern void gomp_barrier_wait_last (gomp_barrier_t *);
76 extern void gomp_barrier_wait_end (gomp_barrier_t *, gomp_barrier_state_t);
77 extern void gomp_team_barrier_wait (gomp_barrier_t *);
78 extern void gomp_team_barrier_wait_final (gomp_barrier_t *);
79 extern void gomp_team_barrier_wait_end (gomp_barrier_t *,
80 gomp_barrier_state_t);
81 extern bool gomp_team_barrier_wait_cancel (gomp_barrier_t *);
82 extern bool gomp_team_barrier_wait_cancel_end (gomp_barrier_t *,
83 gomp_barrier_state_t);
84 extern void gomp_team_barrier_wake (gomp_barrier_t *, int);
85 struct gomp_team;
86 extern void gomp_team_barrier_cancel (struct gomp_team *);
87
88 static inline gomp_barrier_state_t
gomp_barrier_wait_start(gomp_barrier_t * bar)89 gomp_barrier_wait_start (gomp_barrier_t *bar)
90 {
91 unsigned int ret = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
92 ret &= -BAR_INCR | BAR_CANCELLED;
93 /* A memory barrier is needed before exiting from the various forms
94 of gomp_barrier_wait, to satisfy OpenMP API version 3.1 section
95 2.8.6 flush Construct, which says there is an implicit flush during
96 a barrier region. This is a convenient place to add the barrier,
97 so we use MEMMODEL_ACQ_REL here rather than MEMMODEL_ACQUIRE. */
98 if (__atomic_add_fetch (&bar->awaited, -1, MEMMODEL_ACQ_REL) == 0)
99 ret |= BAR_WAS_LAST;
100 return ret;
101 }
102
103 static inline gomp_barrier_state_t
gomp_barrier_wait_cancel_start(gomp_barrier_t * bar)104 gomp_barrier_wait_cancel_start (gomp_barrier_t *bar)
105 {
106 return gomp_barrier_wait_start (bar);
107 }
108
109 /* This is like gomp_barrier_wait_start, except it decrements
110 bar->awaited_final rather than bar->awaited and should be used
111 for the gomp_team_end barrier only. */
112 static inline gomp_barrier_state_t
gomp_barrier_wait_final_start(gomp_barrier_t * bar)113 gomp_barrier_wait_final_start (gomp_barrier_t *bar)
114 {
115 unsigned int ret = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
116 ret &= -BAR_INCR | BAR_CANCELLED;
117 /* See above gomp_barrier_wait_start comment. */
118 if (__atomic_add_fetch (&bar->awaited_final, -1, MEMMODEL_ACQ_REL) == 0)
119 ret |= BAR_WAS_LAST;
120 return ret;
121 }
122
123 static inline bool
gomp_barrier_last_thread(gomp_barrier_state_t state)124 gomp_barrier_last_thread (gomp_barrier_state_t state)
125 {
126 return state & BAR_WAS_LAST;
127 }
128
129 /* All the inlines below must be called with team->task_lock
130 held. */
131
132 static inline void
gomp_team_barrier_set_task_pending(gomp_barrier_t * bar)133 gomp_team_barrier_set_task_pending (gomp_barrier_t *bar)
134 {
135 bar->generation |= BAR_TASK_PENDING;
136 }
137
138 static inline void
gomp_team_barrier_clear_task_pending(gomp_barrier_t * bar)139 gomp_team_barrier_clear_task_pending (gomp_barrier_t *bar)
140 {
141 bar->generation &= ~BAR_TASK_PENDING;
142 }
143
144 static inline void
gomp_team_barrier_set_waiting_for_tasks(gomp_barrier_t * bar)145 gomp_team_barrier_set_waiting_for_tasks (gomp_barrier_t *bar)
146 {
147 bar->generation |= BAR_WAITING_FOR_TASK;
148 }
149
150 static inline bool
gomp_team_barrier_waiting_for_tasks(gomp_barrier_t * bar)151 gomp_team_barrier_waiting_for_tasks (gomp_barrier_t *bar)
152 {
153 return (bar->generation & BAR_WAITING_FOR_TASK) != 0;
154 }
155
156 static inline bool
gomp_team_barrier_cancelled(gomp_barrier_t * bar)157 gomp_team_barrier_cancelled (gomp_barrier_t *bar)
158 {
159 return __builtin_expect ((bar->generation & BAR_CANCELLED) != 0, 0);
160 }
161
162 static inline void
gomp_team_barrier_done(gomp_barrier_t * bar,gomp_barrier_state_t state)163 gomp_team_barrier_done (gomp_barrier_t *bar, gomp_barrier_state_t state)
164 {
165 bar->generation = (state & -BAR_INCR) + BAR_INCR;
166 }
167
168 #endif /* GOMP_BARRIER_H */
169