libgomp/parallel.c

   1 /* Copyright (C) 2005, 2007, 2008, 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 (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 *thread = gomp_thread();
  41   struct gomp_task_icv *icv;
  42   unsigned threads_requested, max_num_threads, num_threads;
  43   unsigned long remaining;
  44
  45   icv = gomp_icv (false);
  46
  47   if (specified == 1)
  48     return 1;
  49   else if (thread->ts.active_level >= 1 && !icv->nest_var)
  50     return 1;
  51   else if (thread->ts.active_level >= gomp_max_active_levels_var)
  52     return 1;
  53
  54   /* If NUM_THREADS not specified, use nthreads_var.  */
  55   if (specified == 0)
  56     threads_requested = icv->nthreads_var;
  57   else
  58     threads_requested = specified;
  59
  60   max_num_threads = threads_requested;
  61
  62   /* If dynamic threads are enabled, bound the number of threads
  63      that we launch.  */
  64   if (icv->dyn_var)
  65     {
  66       unsigned dyn = gomp_dynamic_max_threads ();
  67       if (dyn < max_num_threads)
  68         max_num_threads = dyn;
  69
  70       /* Optimization for parallel sections.  */
  71       if (count && count < max_num_threads)
  72         max_num_threads = count;
  73     }
  74
  75   /* ULONG_MAX stands for infinity.  */
  76   if (__builtin_expect (gomp_thread_limit_var == ULONG_MAX, 1)
  77       || max_num_threads == 1)
  78     return max_num_threads;
  79
  80 #ifdef HAVE_SYNC_BUILTINS
  81   do
  82     {
  83       remaining = gomp_remaining_threads_count;
  84       num_threads = max_num_threads;
  85       if (num_threads > remaining)
  86         num_threads = remaining + 1;
  87     }
  88   while (__sync_val_compare_and_swap (&gomp_remaining_threads_count,
  89                                       remaining, remaining - num_threads + 1)
  90          != remaining);
  91 #else
  92   gomp_mutex_lock (&gomp_remaining_threads_lock);
  93   num_threads = max_num_threads;
  94   remaining = gomp_remaining_threads_count;
  95   if (num_threads > remaining)
  96     num_threads = remaining + 1;
  97   gomp_remaining_threads_count -= num_threads - 1;
  98   gomp_mutex_unlock (&gomp_remaining_threads_lock);
  99 #endif
 100
 101   return num_threads;
 102 }
 103
 104 void
 105 GOMP_parallel_start (void (*fn) (void *), void *data, unsigned num_threads)
 106 {
 107   num_threads = gomp_resolve_num_threads (num_threads, 0);
 108   gomp_team_start (fn, data, num_threads, gomp_new_team (num_threads));
 109 }
 110
 111 void
 112 GOMP_parallel_end (void)
 113 {
 114   if (__builtin_expect (gomp_thread_limit_var != ULONG_MAX, 0))
 115     {
 116       struct gomp_thread *thr = gomp_thread ();
 117       struct gomp_team *team = thr->ts.team;
 118       if (team && team->nthreads > 1)
 119         {
 120 #ifdef HAVE_SYNC_BUILTINS
 121           __sync_fetch_and_add (&gomp_remaining_threads_count,
 122                                 1UL - team->nthreads);
 123 #else
 124           gomp_mutex_lock (&gomp_remaining_threads_lock);
 125           gomp_remaining_threads_count -= team->nthreads - 1;
 126 #endif
 127         }
 128     }
 129   gomp_team_end ();
 130 }
 131
 132 \f
 133 /* The public OpenMP API for thread and team related inquiries.  */
 134
 135 int
 136 omp_get_num_threads (void)
 137 {
 138   struct gomp_team *team = gomp_thread ()->ts.team;
 139   return team ? team->nthreads : 1;
 140 }
 141
 142 int
 143 omp_get_thread_num (void)
 144 {
 145   return gomp_thread ()->ts.team_id;
 146 }
 147
 148 /* This wasn't right for OpenMP 2.5.  Active region used to be non-zero
 149    when the IF clause doesn't evaluate to false, starting with OpenMP 3.0
 150    it is non-zero with more than one thread in the team.  */
 151
 152 int
 153 omp_in_parallel (void)
 154 {
 155   return gomp_thread ()->ts.active_level > 0;
 156 }
 157
 158 int
 159 omp_get_level (void)
 160 {
 161   return gomp_thread ()->ts.level;
 162 }
 163
 164 int
 165 omp_get_ancestor_thread_num (int level)
 166 {
 167   struct gomp_team_state *ts = &gomp_thread ()->ts;
 168   if (level < 0 || level > ts->level)
 169     return -1;
 170   for (level = ts->level - level; level > 0; --level)
 171     ts = &ts->team->prev_ts;
 172   return ts->team_id;
 173 }
 174
 175 int
 176 omp_get_team_size (int level)
 177 {
 178   struct gomp_team_state *ts = &gomp_thread ()->ts;
 179   if (level < 0 || level > ts->level)
 180     return -1;
 181   for (level = ts->level - level; level > 0; --level)
 182     ts = &ts->team->prev_ts;
 183   if (ts->team == NULL)
 184     return 1;
 185   else
 186     return ts->team->nthreads;
 187 }
 188
 189 int
 190 omp_get_active_level (void)
 191 {
 192   return gomp_thread ()->ts.active_level;
 193 }
 194
 195 ialias (omp_get_num_threads)
 196 ialias (omp_get_thread_num)
 197 ialias (omp_in_parallel)
 198 ialias (omp_get_level)
 199 ialias (omp_get_ancestor_thread_num)
 200 ialias (omp_get_team_size)
 201 ialias (omp_get_active_level)