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  * Licensed under the MIT license. See LICENSE file in the project root for full license information.
   9  */
  10
  11 #include "config.h"
  12 #ifdef HAVE_SGEN_GC
  13
  14 #include <string.h>
  15
  16 #include "mono/sgen/sgen-gc.h"
  17 #include "mono/sgen/sgen-workers.h"
  18 #include "mono/sgen/sgen-thread-pool.h"
  19 #include "mono/utils/mono-membar.h"
  20 #include "mono/sgen/sgen-client.h"
  21
  22 static int workers_num;
  23 static volatile gboolean forced_stop;
  24 static WorkerData *workers_data;
  25
  26 static SgenSectionGrayQueue workers_distribute_gray_queue;
  27 static gboolean workers_distribute_gray_queue_inited;
  28
  29 /*
  30  * Allowed transitions:
  31  *
  32  * | from \ to          | NOT WORKING | WORKING | WORK ENQUEUED |
  33  * |--------------------+-------------+---------+---------------+
  34  * | NOT WORKING        | -           | -       | main          |
  35  * | WORKING            | worker      | -       | main          |
  36  * | WORK ENQUEUED      | -           | worker  | -             |
  37  *
  38  * The WORK ENQUEUED state guarantees that the worker thread will inspect the queue again at
  39  * least once.  Only after looking at the queue will it go back to WORKING, and then,
  40  * eventually, to NOT WORKING.  After enqueuing work the main thread transitions the state
  41  * to WORK ENQUEUED.  Signalling the worker thread to wake up is only necessary if the old
  42  * state was NOT WORKING.
  43  */
  44
  45 enum {
  46         STATE_NOT_WORKING,
  47         STATE_WORKING,
  48         STATE_WORK_ENQUEUED
  49 };
  50
  51 typedef gint32 State;
  52
  53 static volatile State workers_state;
  54
  55 static SgenObjectOperations * volatile idle_func_object_ops;
  56 static SgenThreadPoolJob * volatile preclean_job;
  57
  58 static guint64 stat_workers_num_finished;
  59
  60 static gboolean
  61 set_state (State old_state, State new_state)
  62 {
  63         SGEN_ASSERT (0, old_state != new_state, "Why are we transitioning to the same state?");
  64         if (new_state == STATE_NOT_WORKING)
  65                 SGEN_ASSERT (0, old_state == STATE_WORKING, "We can only transition to NOT WORKING from WORKING");
  66         else if (new_state == STATE_WORKING)
  67                 SGEN_ASSERT (0, old_state == STATE_WORK_ENQUEUED, "We can only transition to WORKING from WORK ENQUEUED");
  68         if (new_state == STATE_NOT_WORKING || new_state == STATE_WORKING)
  69                 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");
  70
  71         return InterlockedCompareExchange (&workers_state, new_state, old_state) == old_state;
  72 }
  73
  74 static gboolean
  75 state_is_working_or_enqueued (State state)
  76 {
  77         return state == STATE_WORKING || state == STATE_WORK_ENQUEUED;
  78 }
  79
  80 static void
  81 sgen_workers_ensure_awake (void)
  82 {
  83         State old_state;
  84         gboolean did_set_state;
  85
  86         do {
  87                 old_state = workers_state;
  88
  89                 if (old_state == STATE_WORK_ENQUEUED)
  90                         break;
  91
  92                 did_set_state = set_state (old_state, STATE_WORK_ENQUEUED);
  93         } while (!did_set_state);
  94
  95         if (!state_is_working_or_enqueued (old_state))
  96                 sgen_thread_pool_idle_signal ();
  97 }
  98
  99 static void
 100 worker_try_finish (WorkerData *data)
 101 {
 102         State old_state;
 103
 104         ++stat_workers_num_finished;
 105
 106         do {
 107                 old_state = workers_state;
 108
 109                 SGEN_ASSERT (0, old_state != STATE_NOT_WORKING, "How did we get from doing idle work to NOT WORKING without setting it ourselves?");
 110                 if (old_state == STATE_WORK_ENQUEUED)
 111                         return;
 112                 SGEN_ASSERT (0, old_state == STATE_WORKING, "What other possibility is there?");
 113
 114                 /* We are the last thread to go to sleep. */
 115         } while (!set_state (old_state, STATE_NOT_WORKING));
 116
 117         binary_protocol_worker_finish (sgen_timestamp (), forced_stop);
 118
 119         sgen_gray_object_queue_trim_free_list (&data->private_gray_queue);
 120 }
 121
 122 void
 123 sgen_workers_enqueue_job (SgenThreadPoolJob *job, gboolean enqueue)
 124 {
 125         if (!enqueue) {
 126                 job->func (NULL, job);
 127                 sgen_thread_pool_job_free (job);
 128                 return;
 129         }
 130
 131         sgen_thread_pool_job_enqueue (job);
 132 }
 133
 134 void
 135 sgen_workers_wait_for_jobs_finished (void)
 136 {
 137         sgen_thread_pool_wait_for_all_jobs ();
 138         /*
 139          * If the idle task was never triggered or it finished before the last job did and
 140          * then didn't get triggered again, we might end up in the situation of having
 141          * something in the gray queue yet the idle task not working.  The easiest way to
 142          * make sure this doesn't stay that way is to just trigger it again after all jobs
 143          * have finished.
 144          */
 145         sgen_workers_ensure_awake ();
 146 }
 147
 148 static gboolean
 149 workers_get_work (WorkerData *data)
 150 {
 151         SgenMajorCollector *major;
 152
 153         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 154
 155         /* If we're concurrent, steal from the workers distribute gray queue. */
 156         major = sgen_get_major_collector ();
 157         if (major->is_concurrent) {
 158                 GrayQueueSection *section = sgen_section_gray_queue_dequeue (&workers_distribute_gray_queue);
 159                 if (section) {
 160                         sgen_gray_object_enqueue_section (&data->private_gray_queue, section);
 161                         return TRUE;
 162                 }
 163         }
 164
 165         /* Nobody to steal from */
 166         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 167         return FALSE;
 168 }
 169
 170 static void
 171 concurrent_enqueue_check (GCObject *obj)
 172 {
 173         g_assert (sgen_concurrent_collection_in_progress ());
 174         g_assert (!sgen_ptr_in_nursery (obj));
 175         g_assert (SGEN_LOAD_VTABLE (obj));
 176 }
 177
 178 static void
 179 init_private_gray_queue (WorkerData *data)
 180 {
 181         sgen_gray_object_queue_init (&data->private_gray_queue,
 182                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL,
 183                         FALSE);
 184 }
 185
 186 static void
 187 thread_pool_init_func (void *data_untyped)
 188 {
 189         WorkerData *data = (WorkerData *)data_untyped;
 190         SgenMajorCollector *major = sgen_get_major_collector ();
 191
 192         sgen_client_thread_register_worker ();
 193
 194         if (!major->is_concurrent)
 195                 return;
 196
 197         init_private_gray_queue (data);
 198 }
 199
 200 static gboolean
 201 continue_idle_func (void)
 202 {
 203         return state_is_working_or_enqueued (workers_state);
 204 }
 205
 206 static void
 207 marker_idle_func (void *data_untyped)
 208 {
 209         WorkerData *data = (WorkerData *)data_untyped;
 210
 211         SGEN_ASSERT (0, continue_idle_func (), "Why are we called when we're not supposed to work?");
 212         SGEN_ASSERT (0, sgen_concurrent_collection_in_progress (), "The worker should only mark in concurrent collections.");
 213
 214         if (workers_state == STATE_WORK_ENQUEUED) {
 215                 set_state (STATE_WORK_ENQUEUED, STATE_WORKING);
 216                 SGEN_ASSERT (0, workers_state != STATE_NOT_WORKING, "How did we get from WORK ENQUEUED to NOT WORKING?");
 217         }
 218
 219         if (!forced_stop && (!sgen_gray_object_queue_is_empty (&data->private_gray_queue) || workers_get_work (data))) {
 220                 ScanCopyContext ctx = CONTEXT_FROM_OBJECT_OPERATIONS (idle_func_object_ops, &data->private_gray_queue);
 221
 222                 SGEN_ASSERT (0, !sgen_gray_object_queue_is_empty (&data->private_gray_queue), "How is our gray queue empty if we just got work?");
 223
 224                 sgen_drain_gray_stack (ctx);
 225         } else {
 226                 SgenThreadPoolJob *job = preclean_job;
 227                 if (job) {
 228                         sgen_thread_pool_job_enqueue (job);
 229                         preclean_job = NULL;
 230                 } else {
 231                         worker_try_finish (data);
 232                 }
 233         }
 234 }
 235
 236 static void
 237 init_distribute_gray_queue (void)
 238 {
 239         if (workers_distribute_gray_queue_inited) {
 240                 g_assert (sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue));
 241                 g_assert (workers_distribute_gray_queue.locked);
 242                 return;
 243         }
 244
 245         sgen_section_gray_queue_init (&workers_distribute_gray_queue, TRUE,
 246                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 247         workers_distribute_gray_queue_inited = TRUE;
 248 }
 249
 250 void
 251 sgen_workers_init_distribute_gray_queue (void)
 252 {
 253         SGEN_ASSERT (0, sgen_get_major_collector ()->is_concurrent,
 254                         "Why should we init the distribute gray queue if we don't need it?");
 255         init_distribute_gray_queue ();
 256 }
 257
 258 void
 259 sgen_workers_init (int num_workers)
 260 {
 261         int i;
 262         void **workers_data_ptrs = (void **)alloca(num_workers * sizeof(void *));
 263
 264         if (!sgen_get_major_collector ()->is_concurrent) {
 265                 sgen_thread_pool_init (num_workers, thread_pool_init_func, NULL, NULL, NULL);
 266                 return;
 267         }
 268
 269         //g_print ("initing %d workers\n", num_workers);
 270
 271         workers_num = num_workers;
 272
 273         workers_data = (WorkerData *)sgen_alloc_internal_dynamic (sizeof (WorkerData) * num_workers, INTERNAL_MEM_WORKER_DATA, TRUE);
 274         memset (workers_data, 0, sizeof (WorkerData) * num_workers);
 275
 276         init_distribute_gray_queue ();
 277
 278         for (i = 0; i < workers_num; ++i)
 279                 workers_data_ptrs [i] = (void *) &workers_data [i];
 280
 281         sgen_thread_pool_init (num_workers, thread_pool_init_func, marker_idle_func, continue_idle_func, workers_data_ptrs);
 282
 283         mono_counters_register ("# workers finished", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_workers_num_finished);
 284 }
 285
 286 void
 287 sgen_workers_stop_all_workers (void)
 288 {
 289         preclean_job = NULL;
 290         mono_memory_write_barrier ();
 291         forced_stop = TRUE;
 292
 293         sgen_thread_pool_wait_for_all_jobs ();
 294         sgen_thread_pool_idle_wait ();
 295         SGEN_ASSERT (0, workers_state == STATE_NOT_WORKING, "Can only signal enqueue work when in no work state");
 296 }
 297
 298 void
 299 sgen_workers_start_all_workers (SgenObjectOperations *object_ops, SgenThreadPoolJob *job)
 300 {
 301         forced_stop = FALSE;
 302         idle_func_object_ops = object_ops;
 303         preclean_job = job;
 304         mono_memory_write_barrier ();
 305
 306         sgen_workers_ensure_awake ();
 307 }
 308
 309 void
 310 sgen_workers_join (void)
 311 {
 312         int i;
 313
 314         sgen_thread_pool_wait_for_all_jobs ();
 315         sgen_thread_pool_idle_wait ();
 316         SGEN_ASSERT (0, workers_state == STATE_NOT_WORKING, "Can only signal enqueue work when in no work state");
 317
 318         /* At this point all the workers have stopped. */
 319
 320         SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue), "Why is there still work left to do?");
 321         for (i = 0; i < workers_num; ++i)
 322                 SGEN_ASSERT (0, sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue), "Why is there still work left to do?");
 323 }
 324
 325 /*
 326  * Can only be called if the workers are stopped.
 327  * If we're stopped, there are also no pending jobs.
 328  */
 329 gboolean
 330 sgen_workers_have_idle_work (void)
 331 {
 332         int i;
 333
 334         SGEN_ASSERT (0, forced_stop && sgen_workers_all_done (), "Checking for idle work should only happen if the workers are stopped.");
 335
 336         if (!sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue))
 337                 return TRUE;
 338
 339         for (i = 0; i < workers_num; ++i) {
 340                 if (!sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue))
 341                         return TRUE;
 342         }
 343
 344         return FALSE;
 345 }
 346
 347 gboolean
 348 sgen_workers_all_done (void)
 349 {
 350         return workers_state == STATE_NOT_WORKING;
 351 }
 352
 353 /* Must only be used for debugging */
 354 gboolean
 355 sgen_workers_are_working (void)
 356 {
 357         return state_is_working_or_enqueued (workers_state);
 358 }
 359
 360 void
 361 sgen_workers_assert_gray_queue_is_empty (void)
 362 {
 363         SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue), "Why is the workers gray queue not empty?");
 364 }
 365
 366 void
 367 sgen_workers_take_from_queue_and_awake (SgenGrayQueue *queue)
 368 {
 369         gboolean wake = FALSE;
 370
 371         for (;;) {
 372                 GrayQueueSection *section = sgen_gray_object_dequeue_section (queue);
 373                 if (!section)
 374                         break;
 375                 sgen_section_gray_queue_enqueue (&workers_distribute_gray_queue, section);
 376                 wake = TRUE;
 377         }
 378
 379         if (wake) {
 380                 SGEN_ASSERT (0, sgen_concurrent_collection_in_progress (), "Why is there work to take when there's no concurrent collection in progress?");
 381                 sgen_workers_ensure_awake ();
 382         }
 383 }
 384
 385 #endif