libgomp/team.c

   1 /* Copyright (C) 2005 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 Lesser General Public License as published by
   8    the Free Software Foundation; either version 2.1 of the License, or
   9    (at your option) 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 Lesser General Public License for
  14    more details.
  15
  16    You should have received a copy of the GNU Lesser General Public License
  17    along with libgomp; see the file COPYING.LIB.  If not, write to the
  18    Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  19    MA 02111-1307, USA.  */
  20
  21 /* As a special exception, if you link this library with other files, some
  22    of which are compiled with GCC, to produce an executable, this library
  23    does not by itself cause the resulting executable to be covered by the
  24    GNU General Public License.  This exception does not however invalidate
  25    any other reasons why the executable file might be covered by the GNU
  26    General Public License.  */
  27
  28 /* This file handles the maintainence of threads in response to team
  29    creation and termination.  */
  30
  31 #include "libgomp.h"
  32 #include <stdlib.h>
  33 #include <string.h>
  34
  35
  36 /* This array manages threads spawned from the top level, which will
  37    return to the idle loop once the current PARALLEL construct ends.  */
  38 static struct gomp_thread **gomp_threads;
  39 static unsigned gomp_threads_size;
  40 static unsigned gomp_threads_used;
  41
  42 /* This attribute contains PTHREAD_CREATE_DETACHED.  */
  43 static pthread_attr_t gomp_thread_attr;
  44
  45 /* This barrier holds and releases threads waiting in gomp_threads.  */
  46 static gomp_barrier_t gomp_threads_dock;
  47
  48 /* This is the libgomp per-thread data structure.  */
  49 #ifdef HAVE_TLS
  50 __thread struct gomp_thread gomp_tls_data;
  51 #else
  52 pthread_key_t gomp_tls_key;
  53 #endif
  54
  55
  56 /* This structure is used to communicate across pthread_create.  */
  57
  58 struct gomp_thread_start_data
  59 {
  60   struct gomp_team_state ts;
  61   void (*fn) (void *);
  62   void *fn_data;
  63   bool nested;
  64 };
  65
  66
  67 /* This function is a pthread_create entry point.  This contains the idle
  68    loop in which a thread waits to be called up to become part of a team.  */
  69
  70 static void *
  71 gomp_thread_start (void *xdata)
  72 {
  73   struct gomp_thread_start_data *data = xdata;
  74   struct gomp_thread *thr;
  75   void (*local_fn) (void *);
  76   void *local_data;
  77
  78 #ifdef HAVE_TLS
  79   thr = &gomp_tls_data;
  80 #else
  81   struct gomp_thread local_thr;
  82   thr = &local_thr;
  83   pthread_setspecific (gomp_tls_key, thr);
  84 #endif
  85   gomp_sem_init (&thr->release, 0);
  86
  87   /* Extract what we need from data.  */
  88   local_fn = data->fn;
  89   local_data = data->fn_data;
  90   thr->ts = data->ts;
  91
  92   thr->ts.team->ordered_release[thr->ts.team_id] = &thr->release;
  93
  94   if (data->nested)
  95     {
  96       gomp_barrier_wait (&thr->ts.team->barrier);
  97       local_fn (local_data);
  98       gomp_barrier_wait (&thr->ts.team->barrier);
  99     }
 100   else
 101     {
 102       gomp_threads[thr->ts.team_id] = thr;
 103
 104       gomp_barrier_wait (&gomp_threads_dock);
 105       do
 106         {
 107           struct gomp_team *team;
 108
 109           local_fn (local_data);
 110
 111           /* Clear out the team and function data.  This is a debugging
 112              signal that we're in fact back in the dock.  */
 113           team = thr->ts.team;
 114           thr->fn = NULL;
 115           thr->data = NULL;
 116           thr->ts.team = NULL;
 117           thr->ts.work_share = NULL;
 118           thr->ts.team_id = 0;
 119           thr->ts.work_share_generation = 0;
 120           thr->ts.static_trip = 0;
 121
 122           gomp_barrier_wait (&team->barrier);
 123           gomp_barrier_wait (&gomp_threads_dock);
 124
 125           local_fn = thr->fn;
 126           local_data = thr->data;
 127         }
 128       while (local_fn);
 129     }
 130
 131   return NULL;
 132 }
 133
 134
 135 /* Create a new team data structure.  */
 136
 137 static struct gomp_team *
 138 new_team (unsigned nthreads, struct gomp_work_share *work_share)
 139 {
 140   struct gomp_team *team;
 141   size_t size;
 142
 143   size = sizeof (*team) + nthreads * sizeof (team->ordered_release[0]);
 144   team = gomp_malloc (size);
 145   gomp_mutex_init (&team->work_share_lock);
 146
 147   team->work_shares = gomp_malloc (4 * sizeof (struct gomp_work_share *));
 148   team->generation_mask = 3;
 149   team->oldest_live_gen = work_share == NULL;
 150   team->num_live_gen = work_share != NULL;
 151   team->work_shares[0] = work_share;
 152
 153   team->nthreads = nthreads;
 154   gomp_barrier_init (&team->barrier, nthreads);
 155
 156   gomp_sem_init (&team->master_release, 0);
 157   team->ordered_release[0] = &team->master_release;
 158
 159   return team;
 160 }
 161
 162
 163 /* Free a team data structure.  */
 164
 165 static void
 166 free_team (struct gomp_team *team)
 167 {
 168   free (team->work_shares);
 169   gomp_mutex_destroy (&team->work_share_lock);
 170   gomp_barrier_destroy (&team->barrier);
 171   gomp_sem_destroy (&team->master_release);
 172   free (team);
 173 }
 174
 175
 176 /* Launch a team.  */
 177
 178 void
 179 gomp_team_start (void (*fn) (void *), void *data, unsigned nthreads,
 180                  struct gomp_work_share *work_share)
 181 {
 182   struct gomp_thread_start_data *start_data;
 183   struct gomp_thread *thr, *nthr;
 184   struct gomp_team *team;
 185   bool nested;
 186   unsigned i, n, old_threads_used = 0;
 187
 188   thr = gomp_thread ();
 189   nested = thr->ts.team != NULL;
 190
 191   team = new_team (nthreads, work_share);
 192
 193   /* Always save the previous state, even if this isn't a nested team.
 194      In particular, we should save any work share state from an outer
 195      orphaned work share construct.  */
 196   team->prev_ts = thr->ts;
 197
 198   thr->ts.team = team;
 199   thr->ts.work_share = work_share;
 200   thr->ts.team_id = 0;
 201   thr->ts.work_share_generation = 0;
 202   thr->ts.static_trip = 0;
 203
 204   if (nthreads == 1)
 205     return;
 206
 207   i = 1;
 208
 209   /* We only allow the reuse of idle threads for non-nested PARALLEL
 210      regions.  This appears to be implied by the semantics of
 211      threadprivate variables, but perhaps that's reading too much into
 212      things.  Certainly it does prevent any locking problems, since
 213      only the initial program thread will modify gomp_threads.  */
 214   if (!nested)
 215     {
 216       old_threads_used = gomp_threads_used;
 217
 218       if (nthreads <= old_threads_used)
 219         n = nthreads;
 220       else if (old_threads_used == 0)
 221         {
 222           n = 0;
 223           gomp_barrier_init (&gomp_threads_dock, nthreads);
 224         }
 225       else
 226         {
 227           n = old_threads_used;
 228
 229           /* Increase the barrier threshold to make sure all new
 230              threads arrive before the team is released.  */
 231           gomp_barrier_reinit (&gomp_threads_dock, nthreads);
 232         }
 233
 234       /* Not true yet, but soon will be.  We're going to release all
 235          threads from the dock, and those that aren't part of the
 236          team will exit.  */
 237       gomp_threads_used = nthreads;
 238
 239       /* Release existing idle threads.  */
 240       for (; i < n; ++i)
 241         {
 242           nthr = gomp_threads[i];
 243           nthr->ts.team = team;
 244           nthr->ts.work_share = work_share;
 245           nthr->ts.team_id = i;
 246           nthr->ts.work_share_generation = 0;
 247           nthr->ts.static_trip = 0;
 248           nthr->fn = fn;
 249           nthr->data = data;
 250           team->ordered_release[i] = &nthr->release;
 251         }
 252
 253       if (i == nthreads)
 254         goto do_release;
 255
 256       /* If necessary, expand the size of the gomp_threads array.  It is
 257          expected that changes in the number of threads is rare, thus we
 258          make no effort to expand gomp_threads_size geometrically.  */
 259       if (nthreads >= gomp_threads_size)
 260         {
 261           gomp_threads_size = nthreads + 1;
 262           gomp_threads
 263             = gomp_realloc (gomp_threads,
 264                             gomp_threads_size
 265                             * sizeof (struct gomp_thread_data *));
 266         }
 267     }
 268
 269   start_data = alloca (sizeof (struct gomp_thread_start_data) * (nthreads-i));
 270
 271   /* Launch new threads.  */
 272   for (; i < nthreads; ++i, ++start_data)
 273     {
 274       pthread_t pt;
 275       int err;
 276
 277       start_data->ts.team = team;
 278       start_data->ts.work_share = work_share;
 279       start_data->ts.team_id = i;
 280       start_data->ts.work_share_generation = 0;
 281       start_data->ts.static_trip = 0;
 282       start_data->fn = fn;
 283       start_data->fn_data = data;
 284       start_data->nested = nested;
 285
 286       err = pthread_create (&pt, &gomp_thread_attr,
 287                             gomp_thread_start, start_data);
 288       if (err != 0)
 289         gomp_fatal ("Thread creation failed: %s", strerror (err));
 290     }
 291
 292  do_release:
 293   gomp_barrier_wait (nested ? &team->barrier : &gomp_threads_dock);
 294
 295   /* Decrease the barrier threshold to match the number of threads
 296      that should arrive back at the end of this team.  The extra
 297      threads should be exiting.  Note that we arrange for this test
 298      to never be true for nested teams.  */
 299   if (nthreads < old_threads_used)
 300     gomp_barrier_reinit (&gomp_threads_dock, nthreads);
 301 }
 302
 303
 304 /* Terminate the current team.  This is only to be called by the master
 305    thread.  We assume that we must wait for the other threads.  */
 306
 307 void
 308 gomp_team_end (void)
 309 {
 310   struct gomp_thread *thr = gomp_thread ();
 311   struct gomp_team *team = thr->ts.team;
 312
 313   gomp_barrier_wait (&team->barrier);
 314
 315   thr->ts = team->prev_ts;
 316
 317   free_team (team);
 318 }
 319
 320
 321 /* Constructors for this file.  */
 322
 323 static void __attribute__((constructor))
 324 initialize_team (void)
 325 {
 326   struct gomp_thread *thr;
 327
 328 #ifndef HAVE_TLS
 329   pthread_key_create (&gomp_tls_key, free);
 330 #endif
 331
 332 #ifdef HAVE_TLS
 333   thr = &gomp_tls_data;
 334 #else
 335   thr = gomp_malloc_cleared (sizeof (*thr));
 336   pthread_setspecific (gomp_tls_key, thr);
 337 #endif
 338   gomp_sem_init (&thr->release, 0);
 339
 340   pthread_attr_init (&gomp_thread_attr);
 341   pthread_attr_setdetachstate (&gomp_thread_attr, PTHREAD_CREATE_DETACHED);
 342 }