1 /* Copyright (C) 2005-2013 Free Software Foundation, Inc.
2 Contributed by Richard Henderson <rth@redhat.com>.
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 a Linux specific implementation of a barrier synchronization
26 mechanism for libgomp. This type is private to the library. This
27 implementation uses atomic instructions and the futex syscall. */
28
29 #include <limits.h>
30 #include "wait.h"
31
32
33 void
gomp_barrier_wait_end(gomp_barrier_t * bar,gomp_barrier_state_t state)34 gomp_barrier_wait_end (gomp_barrier_t *bar, gomp_barrier_state_t state)
35 {
36 if (__builtin_expect ((state & 1) != 0, 0))
37 {
38 /* Next time we'll be awaiting TOTAL threads again. */
39 bar->awaited = bar->total;
40 __atomic_store_n (&bar->generation, bar->generation + 4,
41 MEMMODEL_RELEASE);
42 futex_wake ((int *) &bar->generation, INT_MAX);
43 }
44 else
45 {
46 do
47 do_wait ((int *) &bar->generation, state);
48 while (__atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE) == state);
49 }
50 }
51
52 void
gomp_barrier_wait(gomp_barrier_t * bar)53 gomp_barrier_wait (gomp_barrier_t *bar)
54 {
55 gomp_barrier_wait_end (bar, gomp_barrier_wait_start (bar));
56 }
57
58 /* Like gomp_barrier_wait, except that if the encountering thread
59 is not the last one to hit the barrier, it returns immediately.
60 The intended usage is that a thread which intends to gomp_barrier_destroy
61 this barrier calls gomp_barrier_wait, while all other threads
62 call gomp_barrier_wait_last. When gomp_barrier_wait returns,
63 the barrier can be safely destroyed. */
64
65 void
gomp_barrier_wait_last(gomp_barrier_t * bar)66 gomp_barrier_wait_last (gomp_barrier_t *bar)
67 {
68 gomp_barrier_state_t state = gomp_barrier_wait_start (bar);
69 if (state & 1)
70 gomp_barrier_wait_end (bar, state);
71 }
72
73 void
gomp_team_barrier_wake(gomp_barrier_t * bar,int count)74 gomp_team_barrier_wake (gomp_barrier_t *bar, int count)
75 {
76 futex_wake ((int *) &bar->generation, count == 0 ? INT_MAX : count);
77 }
78
79 void
gomp_team_barrier_wait_end(gomp_barrier_t * bar,gomp_barrier_state_t state)80 gomp_team_barrier_wait_end (gomp_barrier_t *bar, gomp_barrier_state_t state)
81 {
82 unsigned int generation, gen;
83
84 if (__builtin_expect ((state & 1) != 0, 0))
85 {
86 /* Next time we'll be awaiting TOTAL threads again. */
87 struct gomp_thread *thr = gomp_thread ();
88 struct gomp_team *team = thr->ts.team;
89
90 bar->awaited = bar->total;
91 if (__builtin_expect (team->task_count, 0))
92 {
93 gomp_barrier_handle_tasks (state);
94 state &= ~1;
95 }
96 else
97 {
98 __atomic_store_n (&bar->generation, state + 3, MEMMODEL_RELEASE);
99 futex_wake ((int *) &bar->generation, INT_MAX);
100 return;
101 }
102 }
103
104 generation = state;
105 do
106 {
107 do_wait ((int *) &bar->generation, generation);
108 gen = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
109 if (__builtin_expect (gen & 1, 0))
110 {
111 gomp_barrier_handle_tasks (state);
112 gen = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
113 }
114 if ((gen & 2) != 0)
115 generation |= 2;
116 }
117 while (gen != state + 4);
118 }
119
120 void
gomp_team_barrier_wait(gomp_barrier_t * bar)121 gomp_team_barrier_wait (gomp_barrier_t *bar)
122 {
123 gomp_team_barrier_wait_end (bar, gomp_barrier_wait_start (bar));
124 }
125