1/* Copyright (C) 2005-2015 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 file handles the ORDERED construct.  */
27
28#include "libgomp.h"
29
30
31/* This function is called when first allocating an iteration block.  That
32   is, the thread is not currently on the queue.  The work-share lock must
33   be held on entry.  */
34
35void
36gomp_ordered_first (void)
37{
38  struct gomp_thread *thr = gomp_thread ();
39  struct gomp_team *team = thr->ts.team;
40  struct gomp_work_share *ws = thr->ts.work_share;
41  unsigned index;
42
43  /* Work share constructs can be orphaned.  */
44  if (team == NULL || team->nthreads == 1)
45    return;
46
47  index = ws->ordered_cur + ws->ordered_num_used;
48  if (index >= team->nthreads)
49    index -= team->nthreads;
50  ws->ordered_team_ids[index] = thr->ts.team_id;
51
52  /* If this is the first and only thread in the queue, then there is
53     no one to release us when we get to our ordered section.  Post to
54     our own release queue now so that we won't block later.  */
55  if (ws->ordered_num_used++ == 0)
56    gomp_sem_post (team->ordered_release[thr->ts.team_id]);
57}
58
59/* This function is called when completing the last iteration block.  That
60   is, there are no more iterations to perform and so the thread should be
61   removed from the queue entirely.  Because of the way ORDERED blocks are
62   managed, it follows that we currently own access to the ORDERED block,
63   and should now pass it on to the next thread.  The work-share lock must
64   be held on entry.  */
65
66void
67gomp_ordered_last (void)
68{
69  struct gomp_thread *thr = gomp_thread ();
70  struct gomp_team *team = thr->ts.team;
71  struct gomp_work_share *ws = thr->ts.work_share;
72  unsigned next_id;
73
74  /* Work share constructs can be orphaned.  */
75  if (team == NULL || team->nthreads == 1)
76    return;
77
78  /* We're no longer the owner.  */
79  ws->ordered_owner = -1;
80
81  /* If we're not the last thread in the queue, then wake the next.  */
82  if (--ws->ordered_num_used > 0)
83    {
84      unsigned next = ws->ordered_cur + 1;
85      if (next == team->nthreads)
86	next = 0;
87      ws->ordered_cur = next;
88
89      next_id = ws->ordered_team_ids[next];
90      gomp_sem_post (team->ordered_release[next_id]);
91    }
92}
93
94
95/* This function is called when allocating a subsequent allocation block.
96   That is, we're done with the current iteration block and we're allocating
97   another.  This is the logical combination of a call to gomp_ordered_last
98   followed by a call to gomp_ordered_first.  The work-share lock must be
99   held on entry. */
100
101void
102gomp_ordered_next (void)
103{
104  struct gomp_thread *thr = gomp_thread ();
105  struct gomp_team *team = thr->ts.team;
106  struct gomp_work_share *ws = thr->ts.work_share;
107  unsigned index, next_id;
108
109  /* Work share constructs can be orphaned.  */
110  if (team == NULL || team->nthreads == 1)
111    return;
112
113  /* We're no longer the owner.  */
114  ws->ordered_owner = -1;
115
116  /* If there's only one thread in the queue, that must be us.  */
117  if (ws->ordered_num_used == 1)
118    {
119      /* We have a similar situation as in gomp_ordered_first
120	 where we need to post to our own release semaphore.  */
121      gomp_sem_post (team->ordered_release[thr->ts.team_id]);
122      return;
123    }
124
125  /* If the queue is entirely full, then we move ourself to the end of
126     the queue merely by incrementing ordered_cur.  Only if it's not
127     full do we have to write our id.  */
128  if (ws->ordered_num_used < team->nthreads)
129    {
130      index = ws->ordered_cur + ws->ordered_num_used;
131      if (index >= team->nthreads)
132	index -= team->nthreads;
133      ws->ordered_team_ids[index] = thr->ts.team_id;
134    }
135
136  index = ws->ordered_cur + 1;
137  if (index == team->nthreads)
138    index = 0;
139  ws->ordered_cur = index;
140
141  next_id = ws->ordered_team_ids[index];
142  gomp_sem_post (team->ordered_release[next_id]);
143}
144
145
146/* This function is called when a statically scheduled loop is first
147   being created.  */
148
149void
150gomp_ordered_static_init (void)
151{
152  struct gomp_thread *thr = gomp_thread ();
153  struct gomp_team *team = thr->ts.team;
154
155  if (team == NULL || team->nthreads == 1)
156    return;
157
158  gomp_sem_post (team->ordered_release[0]);
159}
160
161/* This function is called when a statically scheduled loop is moving to
162   the next allocation block.  Static schedules are not first come first
163   served like the others, so we're to move to the numerically next thread,
164   not the next thread on a list.  The work-share lock should *not* be held
165   on entry.  */
166
167void
168gomp_ordered_static_next (void)
169{
170  struct gomp_thread *thr = gomp_thread ();
171  struct gomp_team *team = thr->ts.team;
172  struct gomp_work_share *ws = thr->ts.work_share;
173  unsigned id = thr->ts.team_id;
174
175  if (team == NULL || team->nthreads == 1)
176    return;
177
178  ws->ordered_owner = -1;
179
180  /* This thread currently owns the lock.  Increment the owner.  */
181  if (++id == team->nthreads)
182    id = 0;
183  ws->ordered_team_ids[0] = id;
184  gomp_sem_post (team->ordered_release[id]);
185}
186
187/* This function is called when we need to assert that the thread owns the
188   ordered section.  Due to the problem of posted-but-not-waited semaphores,
189   this needs to happen before completing a loop iteration.  */
190
191void
192gomp_ordered_sync (void)
193{
194  struct gomp_thread *thr = gomp_thread ();
195  struct gomp_team *team = thr->ts.team;
196  struct gomp_work_share *ws = thr->ts.work_share;
197
198  /* Work share constructs can be orphaned.  But this clearly means that
199     we are the only thread, and so we automatically own the section.  */
200  if (team == NULL || team->nthreads == 1)
201    return;
202
203  /* ??? I believe it to be safe to access this data without taking the
204     ws->lock.  The only presumed race condition is with the previous
205     thread on the queue incrementing ordered_cur such that it points
206     to us, concurrently with our check below.  But our team_id is
207     already present in the queue, and the other thread will always
208     post to our release semaphore.  So the two cases are that we will
209     either win the race an momentarily block on the semaphore, or lose
210     the race and find the semaphore already unlocked and so not block.
211     Either way we get correct results.
212     However, there is an implicit flush on entry to an ordered region,
213     so we do need to have a barrier here.  If we were taking a lock
214     this could be MEMMODEL_RELEASE since the acquire would be coverd
215     by the lock.  */
216
217  __atomic_thread_fence (MEMMODEL_ACQ_REL);
218  if (ws->ordered_owner != thr->ts.team_id)
219    {
220      gomp_sem_wait (team->ordered_release[thr->ts.team_id]);
221      ws->ordered_owner = thr->ts.team_id;
222    }
223}
224
225/* This function is called by user code when encountering the start of an
226   ORDERED block.  We must check to see if the current thread is at the
227   head of the queue, and if not, block.  */
228
229#ifdef HAVE_ATTRIBUTE_ALIAS
230extern void GOMP_ordered_start (void)
231	__attribute__((alias ("gomp_ordered_sync")));
232#else
233void
234GOMP_ordered_start (void)
235{
236  gomp_ordered_sync ();
237}
238#endif
239
240/* This function is called by user code when encountering the end of an
241   ORDERED block.  With the current ORDERED implementation there's nothing
242   for us to do.
243
244   However, the current implementation has a flaw in that it does not allow
245   the next thread into the ORDERED section immediately after the current
246   thread exits the ORDERED section in its last iteration.  The existance
247   of this function allows the implementation to change.  */
248
249void
250GOMP_ordered_end (void)
251{
252}
253