libgomp/parallel.c

   1 /* Copyright (C) 2005-2014 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 (bare) PARALLEL construct.  */
  26
  27 #include "libgomp.h"
  28 #include <limits.h>
  29
  30
  31 /* Determine the number of threads to be launched for a PARALLEL construct.
  32    This algorithm is explicitly described in OpenMP 3.0 section 2.4.1.
  33    SPECIFIED is a combination of the NUM_THREADS clause and the IF clause.
  34    If the IF clause is false, SPECIFIED is forced to 1.  When NUM_THREADS
  35    is not present, SPECIFIED is 0.  */
  36
  37 unsigned
  38 gomp_resolve_num_threads (unsigned specified, unsigned count)
  39 {
  40   struct gomp_thread *thr = gomp_thread ();
  41   struct gomp_task_icv *icv;
  42   unsigned threads_requested, max_num_threads, num_threads;
  43   unsigned long busy;
  44   struct gomp_thread_pool *pool;
  45
  46   icv = gomp_icv (false);
  47
  48   if (specified == 1)
  49     return 1;
  50   else if (thr->ts.active_level >= 1 && !icv->nest_var)
  51     return 1;
  52   else if (thr->ts.active_level >= gomp_max_active_levels_var)
  53     return 1;
  54
  55   /* If NUM_THREADS not specified, use nthreads_var.  */
  56   if (specified == 0)
  57     threads_requested = icv->nthreads_var;
  58   else
  59     threads_requested = specified;
  60
  61   max_num_threads = threads_requested;
  62
  63   /* If dynamic threads are enabled, bound the number of threads
  64      that we launch.  */
  65   if (icv->dyn_var)
  66     {
  67       unsigned dyn = gomp_dynamic_max_threads ();
  68       if (dyn < max_num_threads)
  69         max_num_threads = dyn;
  70
  71       /* Optimization for parallel sections.  */
  72       if (count && count < max_num_threads)
  73         max_num_threads = count;
  74     }
  75
  76   /* UINT_MAX stands for infinity.  */
  77   if (__builtin_expect (icv->thread_limit_var == UINT_MAX, 1)
  78       || max_num_threads == 1)
  79     return max_num_threads;
  80
  81   /* The threads_busy counter lives in thread_pool, if there
  82      isn't a thread_pool yet, there must be just one thread
  83      in the contention group.  If thr->team is NULL, this isn't
  84      nested parallel, so there is just one thread in the
  85      contention group as well, no need to handle it atomically.  */
  86   pool = thr->thread_pool;
  87   if (thr->ts.team == NULL)
  88     {
  89       num_threads = max_num_threads;
  90       if (num_threads > icv->thread_limit_var)
  91         num_threads = icv->thread_limit_var;
  92       if (pool)
  93         pool->threads_busy = num_threads;
  94       return num_threads;
  95     }
  96
  97 #ifdef HAVE_SYNC_BUILTINS
  98   do
  99     {
 100       busy = pool->threads_busy;
 101       num_threads = max_num_threads;
 102       if (icv->thread_limit_var - busy + 1 < num_threads)
 103         num_threads = icv->thread_limit_var - busy + 1;
 104     }
 105   while (__sync_val_compare_and_swap (&pool->threads_busy,
 106                                       busy, busy + num_threads - 1)
 107          != busy);
 108 #else
 109   gomp_mutex_lock (&gomp_managed_threads_lock);
 110   num_threads = max_num_threads;
 111   busy = pool->threads_busy;
 112   if (icv->thread_limit_var - busy + 1 < num_threads)
 113     num_threads = icv->thread_limit_var - busy + 1;
 114   pool->threads_busy += num_threads - 1;
 115   gomp_mutex_unlock (&gomp_managed_threads_lock);
 116 #endif
 117
 118   return num_threads;
 119 }
 120
 121 void
 122 GOMP_parallel_start (void (*fn) (void *), void *data, unsigned num_threads)
 123 {
 124   num_threads = gomp_resolve_num_threads (num_threads, 0);
 125   gomp_team_start (fn, data, num_threads, 0, gomp_new_team (num_threads));
 126 }
 127
 128 void
 129 GOMP_parallel_end (void)
 130 {
 131   struct gomp_task_icv *icv = gomp_icv (false);
 132   if (__builtin_expect (icv->thread_limit_var != UINT_MAX, 0))
 133     {
 134       struct gomp_thread *thr = gomp_thread ();
 135       struct gomp_team *team = thr->ts.team;
 136       unsigned int nthreads = team ? team->nthreads : 1;
 137       gomp_team_end ();
 138       if (nthreads > 1)
 139         {
 140           /* If not nested, there is just one thread in the
 141              contention group left, no need for atomicity.  */
 142           if (thr->ts.team == NULL)
 143             thr->thread_pool->threads_busy = 1;
 144           else
 145             {
 146 #ifdef HAVE_SYNC_BUILTINS
 147               __sync_fetch_and_add (&thr->thread_pool->threads_busy,
 148                                     1UL - nthreads);
 149 #else
 150               gomp_mutex_lock (&gomp_managed_threads_lock);
 151               thr->thread_pool->threads_busy -= nthreads - 1;
 152               gomp_mutex_unlock (&gomp_managed_threads_lock);
 153 #endif
 154             }
 155         }
 156     }
 157   else
 158     gomp_team_end ();
 159 }
 160 ialias (GOMP_parallel_end)
 161
 162 void
 163 GOMP_parallel (void (*fn) (void *), void *data, unsigned num_threads, unsigned int flags)
 164 {
 165   num_threads = gomp_resolve_num_threads (num_threads, 0);
 166   gomp_team_start (fn, data, num_threads, flags, gomp_new_team (num_threads));
 167   fn (data);
 168   ialias_call (GOMP_parallel_end) ();
 169 }
 170
 171 bool
 172 GOMP_cancellation_point (int which)
 173 {
 174   if (!gomp_cancel_var)
 175     return false;
 176
 177   struct gomp_thread *thr = gomp_thread ();
 178   struct gomp_team *team = thr->ts.team;
 179   if (which & (GOMP_CANCEL_LOOP | GOMP_CANCEL_SECTIONS))
 180     {
 181       if (team == NULL)
 182         return false;
 183       return team->work_share_cancelled != 0;
 184     }
 185   else if (which & GOMP_CANCEL_TASKGROUP)
 186     {
 187       if (thr->task->taskgroup && thr->task->taskgroup->cancelled)
 188         return true;
 189       /* FALLTHRU into the GOMP_CANCEL_PARALLEL case,
 190          as #pragma omp cancel parallel also cancels all explicit
 191          tasks.  */
 192     }
 193   if (team)
 194     return gomp_team_barrier_cancelled (&team->barrier);
 195   return false;
 196 }
 197 ialias (GOMP_cancellation_point)
 198
 199 bool
 200 GOMP_cancel (int which, bool do_cancel)
 201 {
 202   if (!gomp_cancel_var)
 203     return false;
 204
 205   if (!do_cancel)
 206     return ialias_call (GOMP_cancellation_point) (which);
 207
 208   struct gomp_thread *thr = gomp_thread ();
 209   struct gomp_team *team = thr->ts.team;
 210   if (which & (GOMP_CANCEL_LOOP | GOMP_CANCEL_SECTIONS))
 211     {
 212       /* In orphaned worksharing region, all we want to cancel
 213          is current thread.  */
 214       if (team != NULL)
 215         team->work_share_cancelled = 1;
 216       return true;
 217     }
 218   else if (which & GOMP_CANCEL_TASKGROUP)
 219     {
 220       if (thr->task->taskgroup && !thr->task->taskgroup->cancelled)
 221         {
 222           gomp_mutex_lock (&team->task_lock);
 223           thr->task->taskgroup->cancelled = true;
 224           gomp_mutex_unlock (&team->task_lock);
 225         }
 226       return true;
 227     }
 228   team->team_cancelled = 1;
 229   gomp_team_barrier_cancel (team);
 230   return true;
 231 }
 232 \f
 233 /* The public OpenMP API for thread and team related inquiries.  */
 234
 235 int
 236 omp_get_num_threads (void)
 237 {
 238   struct gomp_team *team = gomp_thread ()->ts.team;
 239   return team ? team->nthreads : 1;
 240 }
 241
 242 int
 243 omp_get_thread_num (void)
 244 {
 245   return gomp_thread ()->ts.team_id;
 246 }
 247
 248 /* This wasn't right for OpenMP 2.5.  Active region used to be non-zero
 249    when the IF clause doesn't evaluate to false, starting with OpenMP 3.0
 250    it is non-zero with more than one thread in the team.  */
 251
 252 int
 253 omp_in_parallel (void)
 254 {
 255   return gomp_thread ()->ts.active_level > 0;
 256 }
 257
 258 int
 259 omp_get_level (void)
 260 {
 261   return gomp_thread ()->ts.level;
 262 }
 263
 264 int
 265 omp_get_ancestor_thread_num (int level)
 266 {
 267   struct gomp_team_state *ts = &gomp_thread ()->ts;
 268   if (level < 0 || level > ts->level)
 269     return -1;
 270   for (level = ts->level - level; level > 0; --level)
 271     ts = &ts->team->prev_ts;
 272   return ts->team_id;
 273 }
 274
 275 int
 276 omp_get_team_size (int level)
 277 {
 278   struct gomp_team_state *ts = &gomp_thread ()->ts;
 279   if (level < 0 || level > ts->level)
 280     return -1;
 281   for (level = ts->level - level; level > 0; --level)
 282     ts = &ts->team->prev_ts;
 283   if (ts->team == NULL)
 284     return 1;
 285   else
 286     return ts->team->nthreads;
 287 }
 288
 289 int
 290 omp_get_active_level (void)
 291 {
 292   return gomp_thread ()->ts.active_level;
 293 }
 294
 295 ialias (omp_get_num_threads)
 296 ialias (omp_get_thread_num)
 297 ialias (omp_in_parallel)
 298 ialias (omp_get_level)
 299 ialias (omp_get_ancestor_thread_num)
 300 ialias (omp_get_team_size)
 301 ialias (omp_get_active_level)