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., 51 Franklin Street, Fifth Floor, Boston,
  19    MA 02110-1301, 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 /* This array manages threads spawned from the top level, which will
  36    return to the idle loop once the current PARALLEL construct ends.  */
  37 static struct gomp_thread **gomp_threads;
  38 static unsigned gomp_threads_size;
  39 static unsigned gomp_threads_used;
  40
  41 /* This attribute contains PTHREAD_CREATE_DETACHED.  */
  42 pthread_attr_t gomp_thread_attr;
  43
  44 /* This barrier holds and releases threads waiting in gomp_threads.  */
  45 static gomp_barrier_t gomp_threads_dock;
  46
  47 /* This is the libgomp per-thread data structure.  */
  48 #ifdef HAVE_TLS
  49 __thread struct gomp_thread gomp_tls_data;
  50 #else
  51 pthread_key_t gomp_tls_key;
  52 #endif
  53
  54
  55 /* This structure is used to communicate across pthread_create.  */
  56
  57 struct gomp_thread_start_data
  58 {
  59   struct gomp_team_state ts;
  60   void (*fn) (void *);
  61   void *fn_data;
  62   bool nested;
  63 };
  64
  65
  66 /* This function is a pthread_create entry point.  This contains the idle
  67    loop in which a thread waits to be called up to become part of a team.  */
  68
  69 static void *
  70 gomp_thread_start (void *xdata)
  71 {
  72   struct gomp_thread_start_data *data = xdata;
  73   struct gomp_thread *thr;
  74   void (*local_fn) (void *);
  75   void *local_data;
  76
  77 #ifdef HAVE_TLS
  78   thr = &gomp_tls_data;
  79 #else
  80   struct gomp_thread local_thr;
  81   thr = &local_thr;
  82   pthread_setspecific (gomp_tls_key, thr);
  83 #endif
  84   gomp_sem_init (&thr->release, 0);
  85
  86   /* Extract what we need from data.  */
  87   local_fn = data->fn;
  88   local_data = data->fn_data;
  89   thr->ts = data->ts;
  90
  91   thr->ts.team->ordered_release[thr->ts.team_id] = &thr->release;
  92
  93   if (data->nested)
  94     {
  95       gomp_barrier_wait (&thr->ts.team->barrier);
  96       local_fn (local_data);
  97       gomp_barrier_wait (&thr->ts.team->barrier);
  98     }
  99   else
 100     {
 101       gomp_threads[thr->ts.team_id] = thr;
 102
 103       gomp_barrier_wait (&gomp_threads_dock);
 104       do
 105         {
 106           struct gomp_team *team;
 107
 108           local_fn (local_data);
 109
 110           /* Clear out the team and function data.  This is a debugging
 111              signal that we're in fact back in the dock.  */
 112           team = thr->ts.team;
 113           thr->fn = NULL;
 114           thr->data = NULL;
 115           thr->ts.team = NULL;
 116           thr->ts.work_share = NULL;
 117           thr->ts.team_id = 0;
 118           thr->ts.work_share_generation = 0;
 119           thr->ts.static_trip = 0;
 120
 121           gomp_barrier_wait (&team->barrier);
 122           gomp_barrier_wait (&gomp_threads_dock);
 123
 124           local_fn = thr->fn;
 125           local_data = thr->data;
 126         }
 127       while (local_fn);
 128     }
 129
 130   return NULL;
 131 }
 132
 133
 134 /* Create a new team data structure.  */
 135
 136 static struct gomp_team *
 137 new_team (unsigned nthreads, struct gomp_work_share *work_share)
 138 {
 139   struct gomp_team *team;
 140   size_t size;
 141
 142   size = sizeof (*team) + nthreads * sizeof (team->ordered_release[0]);
 143   team = gomp_malloc (size);
 144   gomp_mutex_init (&team->work_share_lock);
 145
 146   team->work_shares = gomp_malloc (4 * sizeof (struct gomp_work_share *));
 147   team->generation_mask = 3;
 148   team->oldest_live_gen = work_share == NULL;
 149   team->num_live_gen = work_share != NULL;
 150   team->work_shares[0] = work_share;
 151
 152   team->nthreads = nthreads;
 153   gomp_barrier_init (&team->barrier, nthreads);
 154
 155   gomp_sem_init (&team->master_release, 0);
 156   team->ordered_release[0] = &team->master_release;
 157
 158   return team;
 159 }
 160
 161
 162 /* Free a team data structure.  */
 163
 164 static void
 165 free_team (struct gomp_team *team)
 166 {
 167   free (team->work_shares);
 168   gomp_mutex_destroy (&team->work_share_lock);
 169   gomp_barrier_destroy (&team->barrier);
 170   gomp_sem_destroy (&team->master_release);
 171   free (team);
 172 }
 173
 174
 175 /* Launch a team.  */
 176
 177 void
 178 gomp_team_start (void (*fn) (void *), void *data, unsigned nthreads,
 179                  struct gomp_work_share *work_share)
 180 {
 181   struct gomp_thread_start_data *start_data;
 182   struct gomp_thread *thr, *nthr;
 183   struct gomp_team *team;
 184   bool nested;
 185   unsigned i, n, old_threads_used = 0;
 186
 187   thr = gomp_thread ();
 188   nested = thr->ts.team != NULL;
 189
 190   team = new_team (nthreads, work_share);
 191
 192   /* Always save the previous state, even if this isn't a nested team.
 193      In particular, we should save any work share state from an outer
 194      orphaned work share construct.  */
 195   team->prev_ts = thr->ts;
 196
 197   thr->ts.team = team;
 198   thr->ts.work_share = work_share;
 199   thr->ts.team_id = 0;
 200   thr->ts.work_share_generation = 0;
 201   thr->ts.static_trip = 0;
 202
 203   if (nthreads == 1)
 204     return;
 205
 206   i = 1;
 207
 208   /* We only allow the reuse of idle threads for non-nested PARALLEL
 209      regions.  This appears to be implied by the semantics of
 210      threadprivate variables, but perhaps that's reading too much into
 211      things.  Certainly it does prevent any locking problems, since
 212      only the initial program thread will modify gomp_threads.  */
 213   if (!nested)
 214     {
 215       old_threads_used = gomp_threads_used;
 216
 217       if (nthreads <= old_threads_used)
 218         n = nthreads;
 219       else if (old_threads_used == 0)
 220         {
 221           n = 0;
 222           gomp_barrier_init (&gomp_threads_dock, nthreads);
 223         }
 224       else
 225         {
 226           n = old_threads_used;
 227
 228           /* Increase the barrier threshold to make sure all new
 229              threads arrive before the team is released.  */
 230           gomp_barrier_reinit (&gomp_threads_dock, nthreads);
 231         }
 232
 233       /* Not true yet, but soon will be.  We're going to release all
 234          threads from the dock, and those that aren't part of the
 235          team will exit.  */
 236       gomp_threads_used = nthreads;
 237
 238       /* Release existing idle threads.  */
 239       for (; i < n; ++i)
 240         {
 241           nthr = gomp_threads[i];
 242           nthr->ts.team = team;
 243           nthr->ts.work_share = work_share;
 244           nthr->ts.team_id = i;
 245           nthr->ts.work_share_generation = 0;
 246           nthr->ts.static_trip = 0;
 247           nthr->fn = fn;
 248           nthr->data = data;
 249           team->ordered_release[i] = &nthr->release;
 250         }
 251
 252       if (i == nthreads)
 253         goto do_release;
 254
 255       /* If necessary, expand the size of the gomp_threads array.  It is
 256          expected that changes in the number of threads is rare, thus we
 257          make no effort to expand gomp_threads_size geometrically.  */
 258       if (nthreads >= gomp_threads_size)
 259         {
 260           gomp_threads_size = nthreads + 1;
 261           gomp_threads
 262             = gomp_realloc (gomp_threads,
 263                             gomp_threads_size
 264                             * sizeof (struct gomp_thread_data *));
 265         }
 266     }
 267
 268   start_data = gomp_alloca (sizeof (struct gomp_thread_start_data)
 269                             * (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   static struct gomp_thread initial_thread_tls_data;
 330
 331   pthread_key_create (&gomp_tls_key, NULL);
 332   pthread_setspecific (gomp_tls_key, &initial_thread_tls_data);
 333 #endif
 334
 335 #ifdef HAVE_TLS
 336   thr = &gomp_tls_data;
 337 #else
 338   thr = &initial_thread_tls_data;
 339 #endif
 340   gomp_sem_init (&thr->release, 0);
 341 }