mono/sgen/sgen-workers.c

   1 /**
   2  * \file
   3  * Worker threads for parallel and concurrent GC.
   4  *
   5  * Copyright 2001-2003 Ximian, Inc
   6  * Copyright 2003-2010 Novell, Inc.
   7  * Copyright (C) 2012 Xamarin Inc
   8  *
   9  * Licensed under the MIT license. See LICENSE file in the project root for full license information.
  10  */
  11
  12 #include "config.h"
  13 #ifdef HAVE_SGEN_GC
  14
  15 #include <string.h>
  16
  17 #include "mono/sgen/sgen-gc.h"
  18 #include "mono/sgen/sgen-workers.h"
  19 #include "mono/sgen/sgen-thread-pool.h"
  20 #include "mono/utils/mono-membar.h"
  21 #include "mono/sgen/sgen-client.h"
  22
  23 static int workers_num;
  24 static int active_workers_num;
  25 static volatile gboolean started;
  26 static volatile gboolean forced_stop;
  27 static WorkerData *workers_data;
  28 static SgenWorkerCallback worker_init_cb;
  29
  30 static SgenThreadPool pool_inst;
  31 static SgenThreadPool *pool; /* null if we're not using workers */
  32
  33 /*
  34  * When using multiple workers, we need to have the last worker
  35  * enqueue the preclean jobs (if there are any). This lock ensures
  36  * that when the last worker takes it, all the other workers have
  37  * gracefully finished, so it can restart them.
  38  */
  39 static mono_mutex_t finished_lock;
  40 static volatile gboolean workers_finished;
  41 static int worker_awakenings;
  42
  43 static SgenSectionGrayQueue workers_distribute_gray_queue;
  44 static gboolean workers_distribute_gray_queue_inited;
  45
  46 /*
  47  * Allowed transitions:
  48  *
  49  * | from \ to          | NOT WORKING | WORKING | WORK ENQUEUED |
  50  * |--------------------+-------------+---------+---------------+
  51  * | NOT WORKING        | -           | -       | main / worker |
  52  * | WORKING            | worker      | -       | main / worker |
  53  * | WORK ENQUEUED      | -           | worker  | -             |
  54  *
  55  * The WORK ENQUEUED state guarantees that the worker thread will inspect the queue again at
  56  * least once.  Only after looking at the queue will it go back to WORKING, and then,
  57  * eventually, to NOT WORKING.  After enqueuing work the main thread transitions the state
  58  * to WORK ENQUEUED.  Signalling the worker thread to wake up is only necessary if the old
  59  * state was NOT WORKING.
  60  */
  61
  62 enum {
  63         STATE_NOT_WORKING,
  64         STATE_WORKING,
  65         STATE_WORK_ENQUEUED
  66 };
  67
  68 #define SGEN_WORKER_MIN_SECTIONS_SIGNAL 4
  69
  70 typedef gint32 State;
  71
  72 static SgenObjectOperations * volatile idle_func_object_ops;
  73 static SgenObjectOperations *idle_func_object_ops_par, *idle_func_object_ops_nopar;
  74 /*
  75  * finished_callback is called only when the workers finish work normally (when they
  76  * are not forced to finish). The callback is used to enqueue preclean jobs.
  77  */
  78 static volatile SgenWorkersFinishCallback finish_callback;
  79
  80 static guint64 stat_workers_num_finished;
  81
  82 static gboolean
  83 set_state (WorkerData *data, State old_state, State new_state)
  84 {
  85         SGEN_ASSERT (0, old_state != new_state, "Why are we transitioning to the same state?");
  86         if (new_state == STATE_NOT_WORKING)
  87                 SGEN_ASSERT (0, old_state == STATE_WORKING, "We can only transition to NOT WORKING from WORKING");
  88         else if (new_state == STATE_WORKING)
  89                 SGEN_ASSERT (0, old_state == STATE_WORK_ENQUEUED, "We can only transition to WORKING from WORK ENQUEUED");
  90         if (new_state == STATE_NOT_WORKING || new_state == STATE_WORKING)
  91                 SGEN_ASSERT (6, sgen_thread_pool_is_thread_pool_thread (pool, mono_native_thread_id_get ()), "Only the worker thread is allowed to transition to NOT_WORKING or WORKING");
  92
  93         return InterlockedCompareExchange (&data->state, new_state, old_state) == old_state;
  94 }
  95
  96 static gboolean
  97 state_is_working_or_enqueued (State state)
  98 {
  99         return state == STATE_WORKING || state == STATE_WORK_ENQUEUED;
 100 }
 101
 102 static void
 103 sgen_workers_ensure_awake (void)
 104 {
 105         int i;
 106         gboolean need_signal = FALSE;
 107
 108         /*
 109          * All workers are awaken, make sure we reset the parallel context.
 110          * We call this function only when starting the workers so nobody is running,
 111          * or when the last worker is enqueuing preclean work. In both cases we can't
 112          * have a worker working using a nopar context, which means it is safe.
 113          */
 114         idle_func_object_ops = (active_workers_num > 1) ? idle_func_object_ops_par : idle_func_object_ops_nopar;
 115         workers_finished = FALSE;
 116
 117         for (i = 0; i < active_workers_num; i++) {
 118                 State old_state;
 119                 gboolean did_set_state;
 120
 121                 do {
 122                         old_state = workers_data [i].state;
 123
 124                         if (old_state == STATE_WORK_ENQUEUED)
 125                                 break;
 126
 127                         did_set_state = set_state (&workers_data [i], old_state, STATE_WORK_ENQUEUED);
 128                 } while (!did_set_state);
 129
 130                 if (!state_is_working_or_enqueued (old_state))
 131                         need_signal = TRUE;
 132         }
 133
 134         if (need_signal)
 135                 sgen_thread_pool_idle_signal (pool);
 136 }
 137
 138 static void
 139 worker_try_finish (WorkerData *data)
 140 {
 141         State old_state;
 142         int i, working = 0;
 143
 144         ++stat_workers_num_finished;
 145
 146         mono_os_mutex_lock (&finished_lock);
 147
 148         for (i = 0; i < active_workers_num; i++) {
 149                 if (state_is_working_or_enqueued (workers_data [i].state))
 150                         working++;
 151         }
 152
 153         if (working == 1) {
 154                 SgenWorkersFinishCallback callback = finish_callback;
 155                 SGEN_ASSERT (0, idle_func_object_ops == idle_func_object_ops_nopar, "Why are we finishing with parallel context");
 156                 /* We are the last one left. Enqueue preclean job if we have one and awake everybody */
 157                 SGEN_ASSERT (0, data->state != STATE_NOT_WORKING, "How did we get from doing idle work to NOT WORKING without setting it ourselves?");
 158                 if (callback) {
 159                         finish_callback = NULL;
 160                         callback ();
 161                         worker_awakenings = 0;
 162                         /* Make sure each worker has a chance of seeing the enqueued jobs */
 163                         sgen_workers_ensure_awake ();
 164                         SGEN_ASSERT (0, data->state == STATE_WORK_ENQUEUED, "Why did we fail to set our own state to ENQUEUED");
 165                         goto work_available;
 166                 }
 167         }
 168
 169         do {
 170                 old_state = data->state;
 171
 172                 SGEN_ASSERT (0, old_state != STATE_NOT_WORKING, "How did we get from doing idle work to NOT WORKING without setting it ourselves?");
 173                 if (old_state == STATE_WORK_ENQUEUED)
 174                         goto work_available;
 175                 SGEN_ASSERT (0, old_state == STATE_WORKING, "What other possibility is there?");
 176         } while (!set_state (data, old_state, STATE_NOT_WORKING));
 177
 178         /*
 179          * If we are second to last to finish, we set the scan context to the non-parallel
 180          * version so we can speed up the last worker. This helps us maintain same level
 181          * of performance as non-parallel mode even if we fail to distribute work properly.
 182          */
 183         if (working == 2)
 184                 idle_func_object_ops = idle_func_object_ops_nopar;
 185
 186         workers_finished = TRUE;
 187         mono_os_mutex_unlock (&finished_lock);
 188
 189         binary_protocol_worker_finish (sgen_timestamp (), forced_stop);
 190
 191         sgen_gray_object_queue_trim_free_list (&data->private_gray_queue);
 192         return;
 193
 194 work_available:
 195         mono_os_mutex_unlock (&finished_lock);
 196 }
 197
 198 void
 199 sgen_workers_enqueue_job (SgenThreadPoolJob *job, gboolean enqueue)
 200 {
 201         if (!enqueue) {
 202                 job->func (NULL, job);
 203                 sgen_thread_pool_job_free (job);
 204                 return;
 205         }
 206
 207         sgen_thread_pool_job_enqueue (pool, job);
 208 }
 209
 210 static gboolean
 211 workers_get_work (WorkerData *data)
 212 {
 213         SgenMajorCollector *major = sgen_get_major_collector ();
 214         SgenMinorCollector *minor = sgen_get_minor_collector ();
 215         GrayQueueSection *section;
 216
 217         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 218         g_assert (major->is_concurrent || minor->is_parallel);
 219
 220         section = sgen_section_gray_queue_dequeue (&workers_distribute_gray_queue);
 221         if (section) {
 222                 sgen_gray_object_enqueue_section (&data->private_gray_queue, section, major->is_parallel);
 223                 return TRUE;
 224         }
 225
 226         /* Nobody to steal from */
 227         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 228         return FALSE;
 229 }
 230
 231 static gboolean
 232 workers_steal_work (WorkerData *data)
 233 {
 234         SgenMajorCollector *major = sgen_get_major_collector ();
 235         SgenMinorCollector *minor = sgen_get_minor_collector ();
 236         int generation = sgen_get_current_collection_generation ();
 237         GrayQueueSection *section = NULL;
 238         int i, current_worker;
 239
 240         if ((generation == GENERATION_OLD && !major->is_parallel) ||
 241                         (generation == GENERATION_NURSERY && !minor->is_parallel))
 242                 return FALSE;
 243
 244         /* If we're parallel, steal from other workers' private gray queues  */
 245         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 246
 247         current_worker = (int) (data - workers_data);
 248
 249         for (i = 1; i < active_workers_num && !section; i++) {
 250                 int steal_worker = (current_worker + i) % active_workers_num;
 251                 if (state_is_working_or_enqueued (workers_data [steal_worker].state))
 252                         section = sgen_gray_object_steal_section (&workers_data [steal_worker].private_gray_queue);
 253         }
 254
 255         if (section) {
 256                 sgen_gray_object_enqueue_section (&data->private_gray_queue, section, TRUE);
 257                 return TRUE;
 258         }
 259
 260         /* Nobody to steal from */
 261         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 262         return FALSE;
 263 }
 264
 265 static void
 266 concurrent_enqueue_check (GCObject *obj)
 267 {
 268         g_assert (sgen_concurrent_collection_in_progress ());
 269         g_assert (!sgen_ptr_in_nursery (obj));
 270         g_assert (SGEN_LOAD_VTABLE (obj));
 271 }
 272
 273 static void
 274 init_private_gray_queue (WorkerData *data)
 275 {
 276         sgen_gray_object_queue_init (&data->private_gray_queue,
 277                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL,
 278                         FALSE);
 279 }
 280
 281 static void
 282 thread_pool_init_func (void *data_untyped)
 283 {
 284         WorkerData *data = (WorkerData *)data_untyped;
 285         SgenMajorCollector *major = sgen_get_major_collector ();
 286         SgenMinorCollector *minor = sgen_get_minor_collector ();
 287
 288         sgen_client_thread_register_worker ();
 289
 290         if (!major->is_concurrent && !minor->is_parallel)
 291                 return;
 292
 293         init_private_gray_queue (data);
 294
 295         if (worker_init_cb)
 296                 worker_init_cb (data);
 297 }
 298
 299 static gboolean
 300 continue_idle_func (void *data_untyped)
 301 {
 302         if (data_untyped) {
 303                 WorkerData *data = (WorkerData *)data_untyped;
 304                 return state_is_working_or_enqueued (data->state);
 305         } else {
 306                 /* Return if any of the threads is working */
 307                 return !sgen_workers_all_done ();
 308         }
 309 }
 310
 311 static gboolean
 312 should_work_func (void *data_untyped)
 313 {
 314         WorkerData *data = (WorkerData*)data_untyped;
 315         int current_worker = (int) (data - workers_data);
 316
 317         return started && current_worker < active_workers_num;
 318 }
 319
 320 static void
 321 marker_idle_func (void *data_untyped)
 322 {
 323         WorkerData *data = (WorkerData *)data_untyped;
 324
 325         SGEN_ASSERT (0, continue_idle_func (data_untyped), "Why are we called when we're not supposed to work?");
 326
 327         if (data->state == STATE_WORK_ENQUEUED) {
 328                 set_state (data, STATE_WORK_ENQUEUED, STATE_WORKING);
 329                 SGEN_ASSERT (0, data->state != STATE_NOT_WORKING, "How did we get from WORK ENQUEUED to NOT WORKING?");
 330         }
 331
 332         if (!forced_stop && (!sgen_gray_object_queue_is_empty (&data->private_gray_queue) || workers_get_work (data) || workers_steal_work (data))) {
 333                 ScanCopyContext ctx = CONTEXT_FROM_OBJECT_OPERATIONS (idle_func_object_ops, &data->private_gray_queue);
 334
 335                 SGEN_ASSERT (0, !sgen_gray_object_queue_is_empty (&data->private_gray_queue), "How is our gray queue empty if we just got work?");
 336
 337                 sgen_drain_gray_stack (ctx);
 338
 339                 if (data->private_gray_queue.num_sections >= SGEN_WORKER_MIN_SECTIONS_SIGNAL
 340                                 && workers_finished && worker_awakenings < active_workers_num) {
 341                         /* We bound the number of worker awakenings just to be sure */
 342                         worker_awakenings++;
 343                         mono_os_mutex_lock (&finished_lock);
 344                         sgen_workers_ensure_awake ();
 345                         mono_os_mutex_unlock (&finished_lock);
 346                 }
 347         } else {
 348                 worker_try_finish (data);
 349         }
 350 }
 351
 352 static void
 353 init_distribute_gray_queue (void)
 354 {
 355         if (workers_distribute_gray_queue_inited) {
 356                 g_assert (sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue));
 357                 g_assert (workers_distribute_gray_queue.locked);
 358                 return;
 359         }
 360
 361         sgen_section_gray_queue_init (&workers_distribute_gray_queue, TRUE,
 362                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 363         workers_distribute_gray_queue_inited = TRUE;
 364 }
 365
 366 void
 367 sgen_workers_init_distribute_gray_queue (void)
 368 {
 369         SGEN_ASSERT (0, sgen_get_major_collector ()->is_concurrent || sgen_get_minor_collector ()->is_parallel,
 370                         "Why should we init the distribute gray queue if we don't need it?");
 371         init_distribute_gray_queue ();
 372 }
 373
 374 void
 375 sgen_workers_init (int num_workers, SgenWorkerCallback callback)
 376 {
 377         int i;
 378         WorkerData **workers_data_ptrs = (WorkerData**)alloca(num_workers * sizeof(WorkerData*));
 379
 380         mono_os_mutex_init (&finished_lock);
 381         //g_print ("initing %d workers\n", num_workers);
 382
 383         workers_num = num_workers;
 384         active_workers_num = num_workers;
 385
 386         workers_data = (WorkerData *)sgen_alloc_internal_dynamic (sizeof (WorkerData) * num_workers, INTERNAL_MEM_WORKER_DATA, TRUE);
 387         memset (workers_data, 0, sizeof (WorkerData) * num_workers);
 388
 389         init_distribute_gray_queue ();
 390
 391         for (i = 0; i < num_workers; ++i)
 392                 workers_data_ptrs [i] = &workers_data [i];
 393
 394         worker_init_cb = callback;
 395
 396         pool = &pool_inst;
 397         sgen_thread_pool_init (pool, num_workers, thread_pool_init_func, marker_idle_func, continue_idle_func, should_work_func, (SgenThreadPoolData**)workers_data_ptrs);
 398
 399         mono_counters_register ("# workers finished", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_workers_num_finished);
 400 }
 401
 402 void
 403 sgen_workers_shutdown (void)
 404 {
 405         if (pool)
 406                 sgen_thread_pool_shutdown (pool);
 407 }
 408
 409 void
 410 sgen_workers_stop_all_workers (void)
 411 {
 412         finish_callback = NULL;
 413         mono_memory_write_barrier ();
 414         forced_stop = TRUE;
 415
 416         sgen_thread_pool_wait_for_all_jobs (pool);
 417         sgen_thread_pool_idle_wait (pool);
 418         SGEN_ASSERT (0, sgen_workers_all_done (), "Can only signal enqueue work when in no work state");
 419
 420         started = FALSE;
 421 }
 422
 423 void
 424 sgen_workers_set_num_active_workers (int num_workers)
 425 {
 426         if (num_workers) {
 427                 SGEN_ASSERT (0, active_workers_num <= workers_num, "We can't start more workers than we initialized");
 428                 active_workers_num = num_workers;
 429         } else {
 430                 active_workers_num = workers_num;
 431         }
 432 }
 433
 434 void
 435 sgen_workers_start_all_workers (SgenObjectOperations *object_ops_nopar, SgenObjectOperations *object_ops_par, SgenWorkersFinishCallback callback)
 436 {
 437         SGEN_ASSERT (0, !started, "Why are we starting to work without finishing previous cycle");
 438
 439         idle_func_object_ops_par = object_ops_par;
 440         idle_func_object_ops_nopar = object_ops_nopar;
 441         forced_stop = FALSE;
 442         finish_callback = callback;
 443         worker_awakenings = 0;
 444         started = TRUE;
 445         mono_memory_write_barrier ();
 446
 447         /*
 448          * We expect workers to start finishing only after all of them were awaken.
 449          * Otherwise we might think that we have fewer workers and use wrong context.
 450          */
 451         mono_os_mutex_lock (&finished_lock);
 452         sgen_workers_ensure_awake ();
 453         mono_os_mutex_unlock (&finished_lock);
 454 }
 455
 456 void
 457 sgen_workers_join (void)
 458 {
 459         int i;
 460
 461         sgen_thread_pool_wait_for_all_jobs (pool);
 462         sgen_thread_pool_idle_wait (pool);
 463         SGEN_ASSERT (0, sgen_workers_all_done (), "Can only signal enqueue work when in no work state");
 464
 465         /* At this point all the workers have stopped. */
 466
 467         SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue), "Why is there still work left to do?");
 468         for (i = 0; i < active_workers_num; ++i)
 469                 SGEN_ASSERT (0, sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue), "Why is there still work left to do?");
 470
 471         started = FALSE;
 472 }
 473
 474 /*
 475  * Can only be called if the workers are stopped.
 476  * If we're stopped, there are also no pending jobs.
 477  */
 478 gboolean
 479 sgen_workers_have_idle_work (void)
 480 {
 481         int i;
 482
 483         SGEN_ASSERT (0, forced_stop && sgen_workers_all_done (), "Checking for idle work should only happen if the workers are stopped.");
 484
 485         if (!sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue))
 486                 return TRUE;
 487
 488         for (i = 0; i < active_workers_num; ++i) {
 489                 if (!sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue))
 490                         return TRUE;
 491         }
 492
 493         return FALSE;
 494 }
 495
 496 gboolean
 497 sgen_workers_all_done (void)
 498 {
 499         int i;
 500
 501         for (i = 0; i < active_workers_num; i++) {
 502                 if (state_is_working_or_enqueued (workers_data [i].state))
 503                         return FALSE;
 504         }
 505         return TRUE;
 506 }
 507
 508 /* Must only be used for debugging */
 509 gboolean
 510 sgen_workers_are_working (void)
 511 {
 512         return !sgen_workers_all_done ();
 513 }
 514
 515 void
 516 sgen_workers_assert_gray_queue_is_empty (void)
 517 {
 518         SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue), "Why is the workers gray queue not empty?");
 519 }
 520
 521 void
 522 sgen_workers_take_from_queue (SgenGrayQueue *queue)
 523 {
 524         sgen_gray_object_spread (queue, sgen_workers_get_job_split_count ());
 525
 526         for (;;) {
 527                 GrayQueueSection *section = sgen_gray_object_dequeue_section (queue);
 528                 if (!section)
 529                         break;
 530                 sgen_section_gray_queue_enqueue (&workers_distribute_gray_queue, section);
 531         }
 532
 533         SGEN_ASSERT (0, !sgen_workers_are_working (), "We should fully populate the distribute gray queue before we start the workers");
 534 }
 535
 536 SgenObjectOperations*
 537 sgen_workers_get_idle_func_object_ops (void)
 538 {
 539         return (idle_func_object_ops_par) ? idle_func_object_ops_par : idle_func_object_ops_nopar;
 540 }
 541
 542 /*
 543  * If we have a single worker, splitting into multiple jobs makes no sense. With
 544  * more than one worker, we split into a larger number of jobs so that, in case
 545  * the work load is uneven, a worker that finished quickly can take up more jobs
 546  * than another one.
 547  */
 548 int
 549 sgen_workers_get_job_split_count (void)
 550 {
 551         return (active_workers_num > 1) ? active_workers_num * 4 : 1;
 552 }
 553
 554 void
 555 sgen_workers_foreach (SgenWorkerCallback callback)
 556 {
 557         int i;
 558
 559         for (i = 0; i < workers_num; i++)
 560                 callback (&workers_data [i]);
 561 }
 562
 563 gboolean
 564 sgen_workers_is_worker_thread (MonoNativeThreadId id)
 565 {
 566         if (!pool)
 567                 return FALSE;
 568         return sgen_thread_pool_is_thread_pool_thread (pool, id);
 569 }
 570
 571 #endif