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 /*
  37  * Allowed transitions:
  38  *
  39  * | from \ to          | NOT WORKING | WORKING | WORK ENQUEUED | NURSERY COLLECTION |
  40  * |--------------------+-------------+---------+---------------+--------------------|
  41  * | NOT WORKING        | -           | -       | main          | main               |
  42  * | WORKING            | worker      | -       | main          | main               |
  43  * | WORK ENQUEUED      | -           | worker  | -             | main               |
  44  * | NURSERY COLLECTION | -           | -       | main          | -                  |
  45  *
  46  * The WORK ENQUEUED state guarantees that the worker thread will inspect the queue again at
  47  * least once.  Only after looking at the queue will it go back to WORKING, and then,
  48  * eventually, to NOT WORKING.  After enqueuing work the main thread transitions the state
  49  * to WORK ENQUEUED.  Signalling the worker thread to wake up is only necessary if the old
  50  * state was NOT WORKING.
  51  */
  52
  53 enum {
  54         STATE_NOT_WORKING,
  55         STATE_WORKING,
  56         STATE_WORK_ENQUEUED,
  57         STATE_NURSERY_COLLECTION
  58 } WorkersStateName;
  59
  60 typedef gint32 State;
  61
  62 static volatile State workers_state;
  63
  64 static SgenObjectOperations * volatile idle_func_object_ops;
  65
  66 static guint64 stat_workers_num_finished;
  67
  68 static gboolean
  69 set_state (State old_state, State new_state)
  70 {
  71         SGEN_ASSERT (0, old_state != new_state, "Why are we transitioning to the same state?");
  72         if (new_state == STATE_NOT_WORKING)
  73                 SGEN_ASSERT (0, old_state == STATE_WORKING, "We can only transition to NOT WORKING from WORKING");
  74         else if (new_state == STATE_WORKING)
  75                 SGEN_ASSERT (0, old_state == STATE_WORK_ENQUEUED, "We can only transition to WORKING from WORK ENQUEUED");
  76         if (new_state == STATE_NOT_WORKING || new_state == STATE_WORKING)
  77                 SGEN_ASSERT (6, sgen_thread_pool_is_thread_pool_thread (mono_native_thread_id_get ()), "Only the worker thread is allowed to transition to NOT_WORKING or WORKING");
  78
  79         return InterlockedCompareExchange (&workers_state, new_state, old_state) == old_state;
  80 }
  81
  82 static void
  83 assert_nursery_collection (State state)
  84 {
  85         SGEN_ASSERT (0, state == STATE_NURSERY_COLLECTION, "Must be in the nursery collection state");
  86 }
  87
  88 static gboolean
  89 state_is_working_or_enqueued (State state)
  90 {
  91         return state == STATE_WORKING || state == STATE_WORK_ENQUEUED;
  92 }
  93
  94 static void
  95 workers_signal_enqueue_work (gboolean from_nursery_collection)
  96 {
  97         State old_state;
  98         gboolean did_set_state;
  99
 100         do {
 101                 old_state = workers_state;
 102
 103                 if (from_nursery_collection)
 104                         assert_nursery_collection (old_state);
 105                 else
 106                         SGEN_ASSERT (0, old_state != STATE_NURSERY_COLLECTION, "If we're not in a nursery collection, how come the state is NURSERY COLLECTION?");
 107
 108                 if (old_state == STATE_WORK_ENQUEUED)
 109                         break;
 110
 111                 did_set_state = set_state (old_state, STATE_WORK_ENQUEUED);
 112                 if (from_nursery_collection)
 113                         SGEN_ASSERT (0, did_set_state, "Nobody else should be mutating the state");
 114         } while (!did_set_state);
 115
 116         if (!state_is_working_or_enqueued (old_state))
 117                 sgen_thread_pool_idle_signal ();
 118 }
 119
 120 void
 121 sgen_workers_ensure_awake (void)
 122 {
 123         SGEN_ASSERT (0, workers_state != STATE_NURSERY_COLLECTION, "Can't wake workers during nursery collection");
 124         workers_signal_enqueue_work (FALSE);
 125 }
 126
 127 static void
 128 worker_try_finish (void)
 129 {
 130         State old_state;
 131
 132         ++stat_workers_num_finished;
 133
 134         do {
 135                 old_state = workers_state;
 136
 137                 SGEN_ASSERT (0, old_state != STATE_NOT_WORKING, "How did we get from doing idle work to NOT WORKING without setting it ourselves?");
 138                 if (old_state == STATE_NURSERY_COLLECTION)
 139                         return;
 140                 if (old_state == STATE_WORK_ENQUEUED)
 141                         return;
 142                 SGEN_ASSERT (0, old_state == STATE_WORKING, "What other possibility is there?");
 143
 144                 /* We are the last thread to go to sleep. */
 145         } while (!set_state (old_state, STATE_NOT_WORKING));
 146 }
 147
 148 static gboolean
 149 collection_needs_workers (void)
 150 {
 151         return sgen_collection_is_concurrent ();
 152 }
 153
 154 void
 155 sgen_workers_enqueue_job (SgenThreadPoolJob *job)
 156 {
 157         if (!collection_needs_workers ()) {
 158                 job->func (NULL, job);
 159                 sgen_thread_pool_job_free (job);
 160                 return;
 161         }
 162
 163         sgen_thread_pool_job_enqueue (job);
 164 }
 165
 166 void
 167 sgen_workers_wait_for_jobs_finished (void)
 168 {
 169         sgen_thread_pool_wait_for_all_jobs ();
 170         /*
 171          * If the idle task was never triggered or it finished before the last job did and
 172          * then didn't get triggered again, we might end up in the situation of having
 173          * something in the gray queue yet the idle task not working.  The easiest way to
 174          * make sure this doesn't stay that way is to just trigger it again after all jobs
 175          * have finished.
 176          */
 177         sgen_workers_ensure_awake ();
 178 }
 179
 180 void
 181 sgen_workers_signal_start_nursery_collection_and_wait (void)
 182 {
 183         State old_state;
 184
 185         do {
 186                 old_state = workers_state;
 187
 188                 if (old_state != STATE_NOT_WORKING)
 189                         SGEN_ASSERT (0, old_state != STATE_NURSERY_COLLECTION, "Why are we transitioning to NURSERY COLLECTION when we're already there?");
 190         } while (!set_state (old_state, STATE_NURSERY_COLLECTION));
 191
 192         sgen_thread_pool_idle_wait ();
 193
 194         assert_nursery_collection (workers_state);
 195 }
 196
 197 void
 198 sgen_workers_signal_finish_nursery_collection (void)
 199 {
 200         assert_nursery_collection (workers_state);
 201         workers_signal_enqueue_work (TRUE);
 202 }
 203
 204 static gboolean
 205 workers_get_work (WorkerData *data)
 206 {
 207         SgenMajorCollector *major;
 208
 209         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 210
 211         /* If we're concurrent, steal from the workers distribute gray queue. */
 212         major = sgen_get_major_collector ();
 213         if (major->is_concurrent) {
 214                 GrayQueueSection *section = sgen_section_gray_queue_dequeue (&workers_distribute_gray_queue);
 215                 if (section) {
 216                         sgen_gray_object_enqueue_section (&data->private_gray_queue, section);
 217                         return TRUE;
 218                 }
 219         }
 220
 221         /* Nobody to steal from */
 222         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 223         return FALSE;
 224 }
 225
 226 static void
 227 concurrent_enqueue_check (char *obj)
 228 {
 229         g_assert (sgen_concurrent_collection_in_progress ());
 230         g_assert (!sgen_ptr_in_nursery (obj));
 231         g_assert (SGEN_LOAD_VTABLE (obj));
 232 }
 233
 234 static void
 235 init_private_gray_queue (WorkerData *data)
 236 {
 237         sgen_gray_object_queue_init (&data->private_gray_queue,
 238                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 239 }
 240
 241 static void
 242 thread_pool_init_func (void *data_untyped)
 243 {
 244         WorkerData *data = data_untyped;
 245         SgenMajorCollector *major = sgen_get_major_collector ();
 246
 247         mono_thread_info_register_small_id ();
 248
 249         if (!major->is_concurrent)
 250                 return;
 251
 252         init_private_gray_queue (data);
 253 }
 254
 255 static gboolean
 256 continue_idle_func (void)
 257 {
 258         return state_is_working_or_enqueued (workers_state);
 259 }
 260
 261 static void
 262 marker_idle_func (void *data_untyped)
 263 {
 264         WorkerData *data = data_untyped;
 265
 266         if (!continue_idle_func ())
 267                 return;
 268
 269         SGEN_ASSERT (0, sgen_concurrent_collection_in_progress (), "The worker should only mark in concurrent collections.");
 270         SGEN_ASSERT (0, sgen_get_current_collection_generation () != GENERATION_NURSERY, "Why are we doing work while there's a nursery collection happening?");
 271
 272         if (workers_state == STATE_WORK_ENQUEUED) {
 273                 set_state (STATE_WORK_ENQUEUED, STATE_WORKING);
 274                 SGEN_ASSERT (0, workers_state != STATE_NOT_WORKING, "How did we get from WORK ENQUEUED to NOT WORKING?");
 275         }
 276
 277         if (!sgen_gray_object_queue_is_empty (&data->private_gray_queue) || workers_get_work (data)) {
 278                 ScanCopyContext ctx = CONTEXT_FROM_OBJECT_OPERATIONS (idle_func_object_ops, &data->private_gray_queue);
 279
 280                 SGEN_ASSERT (0, !sgen_gray_object_queue_is_empty (&data->private_gray_queue), "How is our gray queue empty if we just got work?");
 281
 282                 sgen_drain_gray_stack (32, ctx);
 283         } else {
 284                 worker_try_finish ();
 285         }
 286 }
 287
 288 static void
 289 init_distribute_gray_queue (void)
 290 {
 291         if (workers_distribute_gray_queue_inited) {
 292                 g_assert (sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue));
 293                 g_assert (workers_distribute_gray_queue.locked);
 294                 return;
 295         }
 296
 297         sgen_section_gray_queue_init (&workers_distribute_gray_queue, TRUE,
 298                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 299         workers_distribute_gray_queue_inited = TRUE;
 300 }
 301
 302 void
 303 sgen_workers_init_distribute_gray_queue (void)
 304 {
 305         SGEN_ASSERT (0, sgen_get_major_collector ()->is_concurrent && collection_needs_workers (),
 306                         "Why should we init the distribute gray queue if we don't need it?");
 307         init_distribute_gray_queue ();
 308 }
 309
 310 void
 311 sgen_workers_init (int num_workers)
 312 {
 313         int i;
 314         void *workers_data_ptrs [num_workers];
 315
 316         if (!sgen_get_major_collector ()->is_concurrent) {
 317                 sgen_thread_pool_init (num_workers, thread_pool_init_func, NULL, NULL, NULL);
 318                 return;
 319         }
 320
 321         //g_print ("initing %d workers\n", num_workers);
 322
 323         workers_num = num_workers;
 324
 325         workers_data = sgen_alloc_internal_dynamic (sizeof (WorkerData) * num_workers, INTERNAL_MEM_WORKER_DATA, TRUE);
 326         memset (workers_data, 0, sizeof (WorkerData) * num_workers);
 327
 328         init_distribute_gray_queue ();
 329
 330         for (i = 0; i < workers_num; ++i)
 331                 workers_data_ptrs [i] = &workers_data [i];
 332
 333         sgen_thread_pool_init (num_workers, thread_pool_init_func, marker_idle_func, continue_idle_func, workers_data_ptrs);
 334
 335         mono_counters_register ("# workers finished", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_workers_num_finished);
 336 }
 337
 338 void
 339 sgen_workers_start_all_workers (SgenObjectOperations *object_ops)
 340 {
 341         if (!collection_needs_workers ())
 342                 return;
 343
 344         idle_func_object_ops = object_ops;
 345         mono_memory_write_barrier ();
 346
 347         workers_signal_enqueue_work (FALSE);
 348 }
 349
 350 void
 351 sgen_workers_join (void)
 352 {
 353         int i;
 354
 355         SGEN_ASSERT (0, workers_state != STATE_NURSERY_COLLECTION, "Can't be in nursery collection when joining");
 356
 357         if (!collection_needs_workers ())
 358                 return;
 359
 360         sgen_thread_pool_wait_for_all_jobs ();
 361         sgen_thread_pool_idle_wait ();
 362         SGEN_ASSERT (0, workers_state == STATE_NOT_WORKING, "Can only signal enqueue work when in no work state");
 363
 364         /* At this point all the workers have stopped. */
 365
 366         SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue), "Why is there still work left to do?");
 367         for (i = 0; i < workers_num; ++i)
 368                 SGEN_ASSERT (0, sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue), "Why is there still work left to do?");
 369 }
 370
 371 gboolean
 372 sgen_workers_all_done (void)
 373 {
 374         return workers_state == STATE_NOT_WORKING;
 375 }
 376
 377 /* Must only be used for debugging */
 378 gboolean
 379 sgen_workers_are_working (void)
 380 {
 381         return state_is_working_or_enqueued (workers_state);
 382 }
 383
 384 void
 385 sgen_workers_wait (void)
 386 {
 387         sgen_thread_pool_idle_wait ();
 388         SGEN_ASSERT (0, sgen_workers_all_done (), "Why are the workers not done after we wait for them?");
 389 }
 390
 391 SgenSectionGrayQueue*
 392 sgen_workers_get_distribute_section_gray_queue (void)
 393 {
 394         return &workers_distribute_gray_queue;
 395 }
 396
 397 #endif