mono/metadata/sgen-workers.c

   1 /*
   2  * sgen-workers.c: Worker threads for parallel and concurrent GC.
   3  *
   4  * Copyright 2001-2003 Ximian, Inc
   5  * Copyright 2003-2010 Novell, Inc.
   6  * Copyright (C) 2012 Xamarin Inc
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Library General Public
  10  * License 2.0 as published by the Free Software Foundation;
  11  *
  12  * This library is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Library General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Library General Public
  18  * License 2.0 along with this library; if not, write to the Free
  19  * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20  */
  21
  22 #include "config.h"
  23 #ifdef HAVE_SGEN_GC
  24
  25 #include "metadata/sgen-gc.h"
  26 #include "metadata/sgen-workers.h"
  27 #include "metadata/sgen-thread-pool.h"
  28 #include "utils/mono-counters.h"
  29
  30 static int workers_num;
  31 static WorkerData *workers_data;
  32
  33 static SgenSectionGrayQueue workers_distribute_gray_queue;
  34 static gboolean workers_distribute_gray_queue_inited;
  35
  36 enum {
  37         STATE_NOT_WORKING,
  38         STATE_WORKING,
  39         STATE_NURSERY_COLLECTION
  40 } WorkersStateName;
  41
  42 typedef gint32 State;
  43
  44 static volatile State workers_state;
  45
  46 static guint64 stat_workers_num_finished;
  47
  48 static gboolean
  49 set_state (State old_state, State new_state)
  50 {
  51         if (old_state == STATE_NURSERY_COLLECTION)
  52                 SGEN_ASSERT (0, new_state != STATE_NOT_WORKING, "Can't go from nursery collection to not working");
  53
  54         return InterlockedCompareExchange (&workers_state, new_state, old_state) == old_state;
  55 }
  56
  57 static void
  58 assert_not_working (State state)
  59 {
  60         SGEN_ASSERT (0, state == STATE_NOT_WORKING, "Can only signal enqueue work when in no work state");
  61 }
  62
  63 static void
  64 assert_working (State state)
  65 {
  66         SGEN_ASSERT (0, state == STATE_WORKING, "A worker can't wait without being in working state");
  67 }
  68
  69 static void
  70 assert_nursery_collection (State state)
  71 {
  72         SGEN_ASSERT (0, state == STATE_NURSERY_COLLECTION, "Must be in the nursery collection state");
  73 }
  74
  75 static void
  76 assert_working_or_nursery_collection (State state)
  77 {
  78         if (state != STATE_WORKING)
  79                 assert_nursery_collection (state);
  80 }
  81
  82 static void
  83 workers_signal_enqueue_work (gboolean from_nursery_collection)
  84 {
  85         State old_state = workers_state;
  86         gboolean did_set_state;
  87
  88         if (from_nursery_collection)
  89                 assert_nursery_collection (old_state);
  90         else
  91                 assert_not_working (old_state);
  92
  93         did_set_state = set_state (old_state, STATE_WORKING);
  94         SGEN_ASSERT (0, did_set_state, "Nobody else should be mutating the state");
  95
  96         sgen_thread_pool_idle_signal ();
  97 }
  98
  99 static void
 100 workers_signal_enqueue_work_if_necessary (void)
 101 {
 102         if (workers_state == STATE_NOT_WORKING)
 103                 workers_signal_enqueue_work (FALSE);
 104 }
 105
 106 void
 107 sgen_workers_ensure_awake (void)
 108 {
 109         SGEN_ASSERT (0, workers_state != STATE_NURSERY_COLLECTION, "Can't wake workers during nursery collection");
 110         workers_signal_enqueue_work_if_necessary ();
 111 }
 112
 113 static void
 114 worker_finish (void)
 115 {
 116         State old_state;
 117
 118         ++stat_workers_num_finished;
 119
 120         do {
 121                 old_state = workers_state;
 122
 123                 assert_working_or_nursery_collection (old_state);
 124                 if (old_state == STATE_NURSERY_COLLECTION)
 125                         return;
 126
 127                 /* We are the last thread to go to sleep. */
 128         } while (!set_state (old_state, STATE_NOT_WORKING));
 129 }
 130
 131 static gboolean
 132 collection_needs_workers (void)
 133 {
 134         return sgen_collection_is_concurrent ();
 135 }
 136
 137 void
 138 sgen_workers_enqueue_job (SgenThreadPoolJob *job)
 139 {
 140         if (!collection_needs_workers ()) {
 141                 job->func (NULL, job);
 142                 sgen_thread_pool_job_free (job);
 143                 return;
 144         }
 145
 146         sgen_thread_pool_job_enqueue (job);
 147 }
 148
 149 void
 150 sgen_workers_wait_for_jobs_finished (void)
 151 {
 152         sgen_thread_pool_wait_for_all_jobs ();
 153 }
 154
 155 void
 156 sgen_workers_signal_start_nursery_collection_and_wait (void)
 157 {
 158         State old_state;
 159
 160         do {
 161                 old_state = workers_state;
 162
 163                 if (old_state != STATE_NOT_WORKING)
 164                         assert_working (old_state);
 165         } while (!set_state (old_state, STATE_NURSERY_COLLECTION));
 166
 167         sgen_thread_pool_idle_wait ();
 168
 169         assert_nursery_collection (workers_state);
 170 }
 171
 172 void
 173 sgen_workers_signal_finish_nursery_collection (void)
 174 {
 175         assert_nursery_collection (workers_state);
 176         workers_signal_enqueue_work (TRUE);
 177 }
 178
 179 static gboolean
 180 workers_get_work (WorkerData *data)
 181 {
 182         SgenMajorCollector *major;
 183
 184         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 185
 186         /* If we're concurrent, steal from the workers distribute gray queue. */
 187         major = sgen_get_major_collector ();
 188         if (major->is_concurrent) {
 189                 GrayQueueSection *section = sgen_section_gray_queue_dequeue (&workers_distribute_gray_queue);
 190                 if (section) {
 191                         sgen_gray_object_enqueue_section (&data->private_gray_queue, section);
 192                         return TRUE;
 193                 }
 194         }
 195
 196         /* Nobody to steal from */
 197         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 198         return FALSE;
 199 }
 200
 201 static void
 202 concurrent_enqueue_check (char *obj)
 203 {
 204         g_assert (sgen_concurrent_collection_in_progress ());
 205         g_assert (!sgen_ptr_in_nursery (obj));
 206         g_assert (SGEN_LOAD_VTABLE (obj));
 207 }
 208
 209 static void
 210 init_private_gray_queue (WorkerData *data)
 211 {
 212         sgen_gray_object_queue_init (&data->private_gray_queue,
 213                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 214 }
 215
 216 static void
 217 thread_pool_init_func (void *data_untyped)
 218 {
 219         WorkerData *data = data_untyped;
 220         SgenMajorCollector *major = sgen_get_major_collector ();
 221
 222         mono_thread_info_register_small_id ();
 223
 224         if (!major->is_concurrent)
 225                 return;
 226
 227         init_private_gray_queue (data);
 228 }
 229
 230 static gboolean
 231 marker_idle_func (void *data_untyped)
 232 {
 233         WorkerData *data = data_untyped;
 234         SgenMajorCollector *major = sgen_get_major_collector ();
 235
 236         if (workers_state != STATE_WORKING)
 237                 return FALSE;
 238
 239         SGEN_ASSERT (0, sgen_get_current_collection_generation () != GENERATION_NURSERY, "Why are we doing work while there's a nursery collection happening?");
 240
 241         if (!sgen_gray_object_queue_is_empty (&data->private_gray_queue) || workers_get_work (data)) {
 242                 SgenObjectOperations *ops = sgen_concurrent_collection_in_progress ()
 243                         ? &major->major_concurrent_ops
 244                         : &major->major_ops;
 245                 ScanCopyContext ctx = { ops->scan_object, NULL, &data->private_gray_queue };
 246
 247                 SGEN_ASSERT (0, !sgen_gray_object_queue_is_empty (&data->private_gray_queue), "How is our gray queue empty if we just got work?");
 248
 249                 sgen_drain_gray_stack (32, ctx);
 250
 251                 return TRUE;
 252         }
 253
 254         worker_finish ();
 255
 256         return FALSE;
 257 }
 258
 259 static void
 260 init_distribute_gray_queue (void)
 261 {
 262         if (workers_distribute_gray_queue_inited) {
 263                 g_assert (sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue));
 264                 g_assert (workers_distribute_gray_queue.locked);
 265                 return;
 266         }
 267
 268         sgen_section_gray_queue_init (&workers_distribute_gray_queue, TRUE,
 269                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 270         workers_distribute_gray_queue_inited = TRUE;
 271 }
 272
 273 void
 274 sgen_workers_init_distribute_gray_queue (void)
 275 {
 276         SGEN_ASSERT (0, sgen_get_major_collector ()->is_concurrent && collection_needs_workers (),
 277                         "Why should we init the distribute gray queue if we don't need it?");
 278         init_distribute_gray_queue ();
 279 }
 280
 281 void
 282 sgen_workers_init (int num_workers)
 283 {
 284         int i;
 285         void *workers_data_ptrs [num_workers];
 286
 287         if (!sgen_get_major_collector ()->is_concurrent) {
 288                 sgen_thread_pool_init (num_workers, thread_pool_init_func, NULL, NULL);
 289                 return;
 290         }
 291
 292         //g_print ("initing %d workers\n", num_workers);
 293
 294         workers_num = num_workers;
 295
 296         workers_data = sgen_alloc_internal_dynamic (sizeof (WorkerData) * num_workers, INTERNAL_MEM_WORKER_DATA, TRUE);
 297         memset (workers_data, 0, sizeof (WorkerData) * num_workers);
 298
 299         init_distribute_gray_queue ();
 300
 301         for (i = 0; i < workers_num; ++i)
 302                 workers_data_ptrs [i] = &workers_data [i];
 303
 304         sgen_thread_pool_init (num_workers, thread_pool_init_func, marker_idle_func, workers_data_ptrs);
 305
 306         mono_counters_register ("# workers finished", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_workers_num_finished);
 307 }
 308
 309 void
 310 sgen_workers_start_all_workers (void)
 311 {
 312         if (!collection_needs_workers ())
 313                 return;
 314
 315         workers_signal_enqueue_work (FALSE);
 316 }
 317
 318 void
 319 sgen_workers_join (void)
 320 {
 321         int i;
 322
 323         if (!collection_needs_workers ())
 324                 return;
 325
 326         sgen_thread_pool_wait_for_all_jobs ();
 327
 328         for (;;) {
 329                 SGEN_ASSERT (0, workers_state != STATE_NURSERY_COLLECTION, "Can't be in nursery collection when joining");
 330                 sgen_thread_pool_idle_wait ();
 331                 assert_not_working (workers_state);
 332
 333                 /*
 334                  * Checking whether there is still work left and, if not, going to sleep,
 335                  * are two separate actions that are not performed atomically by the
 336                  * workers.  Therefore there's a race condition where work can be added
 337                  * after they've checked for work, and before they've gone to sleep.
 338                  */
 339                 if (sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue))
 340                         break;
 341
 342                 workers_signal_enqueue_work (FALSE);
 343         }
 344
 345         /* At this point all the workers have stopped. */
 346
 347         g_assert (sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue));
 348         for (i = 0; i < workers_num; ++i)
 349                 g_assert (sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue));
 350 }
 351
 352 gboolean
 353 sgen_workers_all_done (void)
 354 {
 355         return workers_state == STATE_NOT_WORKING;
 356 }
 357
 358 gboolean
 359 sgen_workers_are_working (void)
 360 {
 361         return workers_state == STATE_WORKING;
 362 }
 363
 364 void
 365 sgen_workers_wait (void)
 366 {
 367         sgen_thread_pool_idle_wait ();
 368         SGEN_ASSERT (0, sgen_workers_all_done (), "Why are the workers not done after we wait for them?");
 369 }
 370
 371 SgenSectionGrayQueue*
 372 sgen_workers_get_distribute_section_gray_queue (void)
 373 {
 374         return &workers_distribute_gray_queue;
 375 }
 376
 377 #endif