mono/sgen/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 <string.h>
  26
  27 #include "mono/sgen/sgen-gc.h"
  28 #include "mono/sgen/sgen-workers.h"
  29 #include "mono/sgen/sgen-thread-pool.h"
  30 #include "mono/utils/mono-membar.h"
  31 #include "mono/sgen/sgen-client.h"
  32
  33 static int workers_num;
  34 static WorkerData *workers_data;
  35
  36 static SgenSectionGrayQueue workers_distribute_gray_queue;
  37 static gboolean workers_distribute_gray_queue_inited;
  38
  39 /*
  40  * Allowed transitions:
  41  *
  42  * | from \ to          | NOT WORKING | WORKING | WORK ENQUEUED | NURSERY COLLECTION |
  43  * |--------------------+-------------+---------+---------------+--------------------|
  44  * | NOT WORKING        | -           | -       | main          | main               |
  45  * | WORKING            | worker      | -       | main          | main               |
  46  * | WORK ENQUEUED      | -           | worker  | -             | main               |
  47  * | NURSERY COLLECTION | -           | -       | main          | -                  |
  48  *
  49  * The WORK ENQUEUED state guarantees that the worker thread will inspect the queue again at
  50  * least once.  Only after looking at the queue will it go back to WORKING, and then,
  51  * eventually, to NOT WORKING.  After enqueuing work the main thread transitions the state
  52  * to WORK ENQUEUED.  Signalling the worker thread to wake up is only necessary if the old
  53  * state was NOT WORKING.
  54  */
  55
  56 enum {
  57         STATE_NOT_WORKING,
  58         STATE_WORKING,
  59         STATE_WORK_ENQUEUED,
  60         STATE_NURSERY_COLLECTION
  61 };
  62
  63 typedef gint32 State;
  64
  65 static volatile State workers_state;
  66
  67 static SgenObjectOperations * volatile idle_func_object_ops;
  68
  69 static guint64 stat_workers_num_finished;
  70
  71 static gboolean
  72 set_state (State old_state, State new_state)
  73 {
  74         SGEN_ASSERT (0, old_state != new_state, "Why are we transitioning to the same state?");
  75         if (new_state == STATE_NOT_WORKING)
  76                 SGEN_ASSERT (0, old_state == STATE_WORKING, "We can only transition to NOT WORKING from WORKING");
  77         else if (new_state == STATE_WORKING)
  78                 SGEN_ASSERT (0, old_state == STATE_WORK_ENQUEUED, "We can only transition to WORKING from WORK ENQUEUED");
  79         if (new_state == STATE_NOT_WORKING || new_state == STATE_WORKING)
  80                 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");
  81
  82         return InterlockedCompareExchange (&workers_state, new_state, old_state) == old_state;
  83 }
  84
  85 static void
  86 assert_nursery_collection (State state)
  87 {
  88         SGEN_ASSERT (0, state == STATE_NURSERY_COLLECTION, "Must be in the nursery collection state");
  89 }
  90
  91 static gboolean
  92 state_is_working_or_enqueued (State state)
  93 {
  94         return state == STATE_WORKING || state == STATE_WORK_ENQUEUED;
  95 }
  96
  97 static void
  98 workers_signal_enqueue_work (gboolean from_nursery_collection)
  99 {
 100         State old_state;
 101         gboolean did_set_state;
 102
 103         do {
 104                 old_state = workers_state;
 105
 106                 if (from_nursery_collection)
 107                         assert_nursery_collection (old_state);
 108                 else
 109                         SGEN_ASSERT (0, old_state != STATE_NURSERY_COLLECTION, "If we're not in a nursery collection, how come the state is NURSERY COLLECTION?");
 110
 111                 if (old_state == STATE_WORK_ENQUEUED)
 112                         break;
 113
 114                 did_set_state = set_state (old_state, STATE_WORK_ENQUEUED);
 115                 if (from_nursery_collection)
 116                         SGEN_ASSERT (0, did_set_state, "Nobody else should be mutating the state");
 117         } while (!did_set_state);
 118
 119         if (!state_is_working_or_enqueued (old_state))
 120                 sgen_thread_pool_idle_signal ();
 121 }
 122
 123 void
 124 sgen_workers_ensure_awake (void)
 125 {
 126         SGEN_ASSERT (0, workers_state != STATE_NURSERY_COLLECTION, "Can't wake workers during nursery collection");
 127         workers_signal_enqueue_work (FALSE);
 128 }
 129
 130 static void
 131 worker_try_finish (void)
 132 {
 133         State old_state;
 134
 135         ++stat_workers_num_finished;
 136
 137         do {
 138                 old_state = workers_state;
 139
 140                 SGEN_ASSERT (0, old_state != STATE_NOT_WORKING, "How did we get from doing idle work to NOT WORKING without setting it ourselves?");
 141                 if (old_state == STATE_NURSERY_COLLECTION)
 142                         return;
 143                 if (old_state == STATE_WORK_ENQUEUED)
 144                         return;
 145                 SGEN_ASSERT (0, old_state == STATE_WORKING, "What other possibility is there?");
 146
 147                 /* We are the last thread to go to sleep. */
 148         } while (!set_state (old_state, STATE_NOT_WORKING));
 149 }
 150
 151 static gboolean
 152 collection_needs_workers (void)
 153 {
 154         return sgen_collection_is_concurrent ();
 155 }
 156
 157 void
 158 sgen_workers_enqueue_job (SgenThreadPoolJob *job)
 159 {
 160         if (!collection_needs_workers ()) {
 161                 job->func (NULL, job);
 162                 sgen_thread_pool_job_free (job);
 163                 return;
 164         }
 165
 166         sgen_thread_pool_job_enqueue (job);
 167 }
 168
 169 void
 170 sgen_workers_wait_for_jobs_finished (void)
 171 {
 172         sgen_thread_pool_wait_for_all_jobs ();
 173         /*
 174          * If the idle task was never triggered or it finished before the last job did and
 175          * then didn't get triggered again, we might end up in the situation of having
 176          * something in the gray queue yet the idle task not working.  The easiest way to
 177          * make sure this doesn't stay that way is to just trigger it again after all jobs
 178          * have finished.
 179          */
 180         sgen_workers_ensure_awake ();
 181 }
 182
 183 void
 184 sgen_workers_signal_start_nursery_collection_and_wait (void)
 185 {
 186         State old_state;
 187
 188         do {
 189                 old_state = workers_state;
 190
 191                 if (old_state != STATE_NOT_WORKING)
 192                         SGEN_ASSERT (0, old_state != STATE_NURSERY_COLLECTION, "Why are we transitioning to NURSERY COLLECTION when we're already there?");
 193         } while (!set_state (old_state, STATE_NURSERY_COLLECTION));
 194
 195         sgen_thread_pool_idle_wait ();
 196
 197         assert_nursery_collection (workers_state);
 198 }
 199
 200 void
 201 sgen_workers_signal_finish_nursery_collection (void)
 202 {
 203         assert_nursery_collection (workers_state);
 204         workers_signal_enqueue_work (TRUE);
 205 }
 206
 207 static gboolean
 208 workers_get_work (WorkerData *data)
 209 {
 210         SgenMajorCollector *major;
 211
 212         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 213
 214         /* If we're concurrent, steal from the workers distribute gray queue. */
 215         major = sgen_get_major_collector ();
 216         if (major->is_concurrent) {
 217                 GrayQueueSection *section = sgen_section_gray_queue_dequeue (&workers_distribute_gray_queue);
 218                 if (section) {
 219                         sgen_gray_object_enqueue_section (&data->private_gray_queue, section);
 220                         return TRUE;
 221                 }
 222         }
 223
 224         /* Nobody to steal from */
 225         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 226         return FALSE;
 227 }
 228
 229 static void
 230 concurrent_enqueue_check (GCObject *obj)
 231 {
 232         g_assert (sgen_concurrent_collection_in_progress ());
 233         g_assert (!sgen_ptr_in_nursery (obj));
 234         g_assert (SGEN_LOAD_VTABLE (obj));
 235 }
 236
 237 static void
 238 init_private_gray_queue (WorkerData *data)
 239 {
 240         sgen_gray_object_queue_init (&data->private_gray_queue,
 241                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 242 }
 243
 244 static void
 245 thread_pool_init_func (void *data_untyped)
 246 {
 247         WorkerData *data = data_untyped;
 248         SgenMajorCollector *major = sgen_get_major_collector ();
 249
 250         sgen_client_thread_register_worker ();
 251
 252         if (!major->is_concurrent)
 253                 return;
 254
 255         init_private_gray_queue (data);
 256 }
 257
 258 static gboolean
 259 continue_idle_func (void)
 260 {
 261         return state_is_working_or_enqueued (workers_state);
 262 }
 263
 264 static void
 265 marker_idle_func (void *data_untyped)
 266 {
 267         WorkerData *data = data_untyped;
 268
 269         if (!continue_idle_func ())
 270                 return;
 271
 272         SGEN_ASSERT (0, sgen_concurrent_collection_in_progress (), "The worker should only mark in concurrent collections.");
 273         SGEN_ASSERT (0, sgen_get_current_collection_generation () != GENERATION_NURSERY, "Why are we doing work while there's a nursery collection happening?");
 274
 275         if (workers_state == STATE_WORK_ENQUEUED) {
 276                 set_state (STATE_WORK_ENQUEUED, STATE_WORKING);
 277                 SGEN_ASSERT (0, workers_state != STATE_NOT_WORKING, "How did we get from WORK ENQUEUED to NOT WORKING?");
 278         }
 279
 280         if (!sgen_gray_object_queue_is_empty (&data->private_gray_queue) || workers_get_work (data)) {
 281                 ScanCopyContext ctx = CONTEXT_FROM_OBJECT_OPERATIONS (idle_func_object_ops, &data->private_gray_queue);
 282
 283                 SGEN_ASSERT (0, !sgen_gray_object_queue_is_empty (&data->private_gray_queue), "How is our gray queue empty if we just got work?");
 284
 285                 sgen_drain_gray_stack (32, ctx);
 286         } else {
 287                 worker_try_finish ();
 288         }
 289 }
 290
 291 static void
 292 init_distribute_gray_queue (void)
 293 {
 294         if (workers_distribute_gray_queue_inited) {
 295                 g_assert (sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue));
 296                 g_assert (workers_distribute_gray_queue.locked);
 297                 return;
 298         }
 299
 300         sgen_section_gray_queue_init (&workers_distribute_gray_queue, TRUE,
 301                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 302         workers_distribute_gray_queue_inited = TRUE;
 303 }
 304
 305 void
 306 sgen_workers_init_distribute_gray_queue (void)
 307 {
 308         SGEN_ASSERT (0, sgen_get_major_collector ()->is_concurrent && collection_needs_workers (),
 309                         "Why should we init the distribute gray queue if we don't need it?");
 310         init_distribute_gray_queue ();
 311 }
 312
 313 void
 314 sgen_workers_init (int num_workers)
 315 {
 316         int i;
 317         void **workers_data_ptrs = alloca(num_workers * sizeof(void *));
 318
 319         if (!sgen_get_major_collector ()->is_concurrent) {
 320                 sgen_thread_pool_init (num_workers, thread_pool_init_func, NULL, NULL, NULL);
 321                 return;
 322         }
 323
 324         //g_print ("initing %d workers\n", num_workers);
 325
 326         workers_num = num_workers;
 327
 328         workers_data = sgen_alloc_internal_dynamic (sizeof (WorkerData) * num_workers, INTERNAL_MEM_WORKER_DATA, TRUE);
 329         memset (workers_data, 0, sizeof (WorkerData) * num_workers);
 330
 331         init_distribute_gray_queue ();
 332
 333         for (i = 0; i < workers_num; ++i)
 334                 workers_data_ptrs [i] = (void *) &workers_data [i];
 335
 336         sgen_thread_pool_init (num_workers, thread_pool_init_func, marker_idle_func, continue_idle_func, workers_data_ptrs);
 337
 338         mono_counters_register ("# workers finished", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_workers_num_finished);
 339 }
 340
 341 void
 342 sgen_workers_start_all_workers (SgenObjectOperations *object_ops)
 343 {
 344         if (!collection_needs_workers ())
 345                 return;
 346
 347         idle_func_object_ops = object_ops;
 348         mono_memory_write_barrier ();
 349
 350         workers_signal_enqueue_work (FALSE);
 351 }
 352
 353 void
 354 sgen_workers_join (void)
 355 {
 356         int i;
 357
 358         SGEN_ASSERT (0, workers_state != STATE_NURSERY_COLLECTION, "Can't be in nursery collection when joining");
 359
 360         if (!collection_needs_workers ())
 361                 return;
 362
 363         sgen_thread_pool_wait_for_all_jobs ();
 364         sgen_thread_pool_idle_wait ();
 365         SGEN_ASSERT (0, workers_state == STATE_NOT_WORKING, "Can only signal enqueue work when in no work state");
 366
 367         /* At this point all the workers have stopped. */
 368
 369         SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue), "Why is there still work left to do?");
 370         for (i = 0; i < workers_num; ++i)
 371                 SGEN_ASSERT (0, sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue), "Why is there still work left to do?");
 372 }
 373
 374 gboolean
 375 sgen_workers_all_done (void)
 376 {
 377         return workers_state == STATE_NOT_WORKING;
 378 }
 379
 380 /* Must only be used for debugging */
 381 gboolean
 382 sgen_workers_are_working (void)
 383 {
 384         return state_is_working_or_enqueued (workers_state);
 385 }
 386
 387 void
 388 sgen_workers_wait (void)
 389 {
 390         sgen_thread_pool_idle_wait ();
 391         SGEN_ASSERT (0, sgen_workers_all_done (), "Why are the workers not done after we wait for them?");
 392 }
 393
 394 SgenSectionGrayQueue*
 395 sgen_workers_get_distribute_section_gray_queue (void)
 396 {
 397         return &workers_distribute_gray_queue;
 398 }
 399
 400 #endif