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comparison libgomp/ordered.c @ 0:a06113de4d67

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author kent <kent@cr.ie.u-ryukyu.ac.jp>
date Fri, 17 Jul 2009 14:47:48 +0900
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-1:000000000000 0:a06113de4d67
1 /* Copyright (C) 2005, 2009 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 file handles the ORDERED construct. */
26
27 #include "libgomp.h"
28
29
30 /* This function is called when first allocating an iteration block. That
31 is, the thread is not currently on the queue. The work-share lock must
32 be held on entry. */
33
34 void
35 gomp_ordered_first (void)
36 {
37 struct gomp_thread *thr = gomp_thread ();
38 struct gomp_team *team = thr->ts.team;
39 struct gomp_work_share *ws = thr->ts.work_share;
40 unsigned index;
41
42 /* Work share constructs can be orphaned. */
43 if (team == NULL || team->nthreads == 1)
44 return;
45
46 index = ws->ordered_cur + ws->ordered_num_used;
47 if (index >= team->nthreads)
48 index -= team->nthreads;
49 ws->ordered_team_ids[index] = thr->ts.team_id;
50
51 /* If this is the first and only thread in the queue, then there is
52 no one to release us when we get to our ordered section. Post to
53 our own release queue now so that we won't block later. */
54 if (ws->ordered_num_used++ == 0)
55 gomp_sem_post (team->ordered_release[thr->ts.team_id]);
56 }
57
58 /* This function is called when completing the last iteration block. That
59 is, there are no more iterations to perform and so the thread should be
60 removed from the queue entirely. Because of the way ORDERED blocks are
61 managed, it follows that we currently own access to the ORDERED block,
62 and should now pass it on to the next thread. The work-share lock must
63 be held on entry. */
64
65 void
66 gomp_ordered_last (void)
67 {
68 struct gomp_thread *thr = gomp_thread ();
69 struct gomp_team *team = thr->ts.team;
70 struct gomp_work_share *ws = thr->ts.work_share;
71 unsigned next_id;
72
73 /* Work share constructs can be orphaned. */
74 if (team == NULL || team->nthreads == 1)
75 return;
76
77 /* We're no longer the owner. */
78 ws->ordered_owner = -1;
79
80 /* If we're not the last thread in the queue, then wake the next. */
81 if (--ws->ordered_num_used > 0)
82 {
83 unsigned next = ws->ordered_cur + 1;
84 if (next == team->nthreads)
85 next = 0;
86 ws->ordered_cur = next;
87
88 next_id = ws->ordered_team_ids[next];
89 gomp_sem_post (team->ordered_release[next_id]);
90 }
91 }
92
93
94 /* This function is called when allocating a subsequent allocation block.
95 That is, we're done with the current iteration block and we're allocating
96 another. This is the logical combination of a call to gomp_ordered_last
97 followed by a call to gomp_ordered_first. The work-share lock must be
98 held on entry. */
99
100 void
101 gomp_ordered_next (void)
102 {
103 struct gomp_thread *thr = gomp_thread ();
104 struct gomp_team *team = thr->ts.team;
105 struct gomp_work_share *ws = thr->ts.work_share;
106 unsigned index, next_id;
107
108 /* Work share constructs can be orphaned. */
109 if (team == NULL || team->nthreads == 1)
110 return;
111
112 /* We're no longer the owner. */
113 ws->ordered_owner = -1;
114
115 /* If there's only one thread in the queue, that must be us. */
116 if (ws->ordered_num_used == 1)
117 {
118 /* We have a similar situation as in gomp_ordered_first
119 where we need to post to our own release semaphore. */
120 gomp_sem_post (team->ordered_release[thr->ts.team_id]);
121 return;
122 }
123
124 /* If the queue is entirely full, then we move ourself to the end of
125 the queue merely by incrementing ordered_cur. Only if it's not
126 full do we have to write our id. */
127 if (ws->ordered_num_used < team->nthreads)
128 {
129 index = ws->ordered_cur + ws->ordered_num_used;
130 if (index >= team->nthreads)
131 index -= team->nthreads;
132 ws->ordered_team_ids[index] = thr->ts.team_id;
133 }
134
135 index = ws->ordered_cur + 1;
136 if (index == team->nthreads)
137 index = 0;
138 ws->ordered_cur = index;
139
140 next_id = ws->ordered_team_ids[index];
141 gomp_sem_post (team->ordered_release[next_id]);
142 }
143
144
145 /* This function is called when a statically scheduled loop is first
146 being created. */
147
148 void
149 gomp_ordered_static_init (void)
150 {
151 struct gomp_thread *thr = gomp_thread ();
152 struct gomp_team *team = thr->ts.team;
153
154 if (team == NULL || team->nthreads == 1)
155 return;
156
157 gomp_sem_post (team->ordered_release[0]);
158 }
159
160 /* This function is called when a statically scheduled loop is moving to
161 the next allocation block. Static schedules are not first come first
162 served like the others, so we're to move to the numerically next thread,
163 not the next thread on a list. The work-share lock should *not* be held
164 on entry. */
165
166 void
167 gomp_ordered_static_next (void)
168 {
169 struct gomp_thread *thr = gomp_thread ();
170 struct gomp_team *team = thr->ts.team;
171 struct gomp_work_share *ws = thr->ts.work_share;
172 unsigned id = thr->ts.team_id;
173
174 if (team == NULL || team->nthreads == 1)
175 return;
176
177 ws->ordered_owner = -1;
178
179 /* This thread currently owns the lock. Increment the owner. */
180 if (++id == team->nthreads)
181 id = 0;
182 ws->ordered_team_ids[0] = id;
183 gomp_sem_post (team->ordered_release[id]);
184 }
185
186 /* This function is called when we need to assert that the thread owns the
187 ordered section. Due to the problem of posted-but-not-waited semaphores,
188 this needs to happen before completing a loop iteration. */
189
190 void
191 gomp_ordered_sync (void)
192 {
193 struct gomp_thread *thr = gomp_thread ();
194 struct gomp_team *team = thr->ts.team;
195 struct gomp_work_share *ws = thr->ts.work_share;
196
197 /* Work share constructs can be orphaned. But this clearly means that
198 we are the only thread, and so we automatically own the section. */
199 if (team == NULL || team->nthreads == 1)
200 return;
201
202 /* ??? I believe it to be safe to access this data without taking the
203 ws->lock. The only presumed race condition is with the previous
204 thread on the queue incrementing ordered_cur such that it points
205 to us, concurrently with our check below. But our team_id is
206 already present in the queue, and the other thread will always
207 post to our release semaphore. So the two cases are that we will
208 either win the race an momentarily block on the semaphore, or lose
209 the race and find the semaphore already unlocked and so not block.
210 Either way we get correct results. */
211
212 if (ws->ordered_owner != thr->ts.team_id)
213 {
214 gomp_sem_wait (team->ordered_release[thr->ts.team_id]);
215 ws->ordered_owner = thr->ts.team_id;
216 }
217 }
218
219 /* This function is called by user code when encountering the start of an
220 ORDERED block. We must check to see if the current thread is at the
221 head of the queue, and if not, block. */
222
223 #ifdef HAVE_ATTRIBUTE_ALIAS
224 extern void GOMP_ordered_start (void)
225 __attribute__((alias ("gomp_ordered_sync")));
226 #else
227 void
228 GOMP_ordered_start (void)
229 {
230 gomp_ordered_sync ();
231 }
232 #endif
233
234 /* This function is called by user code when encountering the end of an
235 ORDERED block. With the current ORDERED implementation there's nothing
236 for us to do.
237
238 However, the current implementation has a flaw in that it does not allow
239 the next thread into the ORDERED section immediately after the current
240 thread exits the ORDERED section in its last iteration. The existance
241 of this function allows the implementation to change. */
242
243 void
244 GOMP_ordered_end (void)
245 {
246 }